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2019 Volume 50 Issue 4
2019, 50(4):
Abstract:
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2019, 50(4): 327-337
doi: 10.11777/j.issn1000-3304.2018.18232
Abstract:
Aliphatic polyesters are a class of technologically important biodegradable and/or biocompatible polymers and have realized wide applications in biological medicine, temporary implants for tissue engineering, and packaging. Ring-opening polymerization (ROP) has proven to be a powerful methodology to prepare large-scale polyesters with different structures and properties. However, up to date, the monomers suitable for ROP are only restricted to the cyclic esters or lactones with a relatively high strain energy, which greatly limits the development and application of this methodology. Biomass-derived γ-butyrolactone (γ-BL), commercially available at a low price, would be a desirable monomer for ROP, but it is commonly referred as "non-polymerizable" in textbooks and the literature due to low strain energy of its five-membered ring. In 2016, Hong and Chen et al. established the first efficient ROP of γ-BL under mild conditions by controlling thermodynamics and kinetic conditions, which also provided a new approach for recyclable polymers. This breakthrough work attracted the attention of the scientific researchers in a short time, and a series of new catalysts have been developed for the ROP of γ-BL and its derivatives. In this context, this review article systematically summarizes the progress of the emerging area in the past three years by focusing on the discussion of the relationship between the catalyst structure and polymerization behavior, the structure-dependent polymer properties, as well as the recyclability of the resultant polymers. The currently unmet challenges in this field, and thus the suggested corresponding future research directions, are also presented.
Aliphatic polyesters are a class of technologically important biodegradable and/or biocompatible polymers and have realized wide applications in biological medicine, temporary implants for tissue engineering, and packaging. Ring-opening polymerization (ROP) has proven to be a powerful methodology to prepare large-scale polyesters with different structures and properties. However, up to date, the monomers suitable for ROP are only restricted to the cyclic esters or lactones with a relatively high strain energy, which greatly limits the development and application of this methodology. Biomass-derived γ-butyrolactone (γ-BL), commercially available at a low price, would be a desirable monomer for ROP, but it is commonly referred as "non-polymerizable" in textbooks and the literature due to low strain energy of its five-membered ring. In 2016, Hong and Chen et al. established the first efficient ROP of γ-BL under mild conditions by controlling thermodynamics and kinetic conditions, which also provided a new approach for recyclable polymers. This breakthrough work attracted the attention of the scientific researchers in a short time, and a series of new catalysts have been developed for the ROP of γ-BL and its derivatives. In this context, this review article systematically summarizes the progress of the emerging area in the past three years by focusing on the discussion of the relationship between the catalyst structure and polymerization behavior, the structure-dependent polymer properties, as well as the recyclability of the resultant polymers. The currently unmet challenges in this field, and thus the suggested corresponding future research directions, are also presented.
2019, 50(4): 338-343
doi: 10.11777/j.issn1000-3304.2018.18274
Abstract:
During the past decade, poly(carbonate-ether) polyols, also known as CO2-polyols, have been synthesized by the copolymerization of CO2 and propylene oxide (PO) with double metal cyanide (DMC) catalyst in the presence of various chain transfer agents. CO2-polyols show great potential as substitutes for polyols derived from fossil feedstock in the polyurethane industry. However, the ring opening reaction of PO generally occurs at the methylene carbon-oxygen bond due to less steric hindrance producing CO2-polyol mainly with the second hydroxyl (2° OH) as terminal group, therefore, the terminal primary hydroxyl (1° OH) content is usually lower than 20%, which leads to their much lower reactivity with isocyanate. Three methods were chosen for increasing the primary hydroxyl content of CO2-polyols, including ethylene oxide (EO) end-capping, copolymerization end-capping of EO and CO2, and one-pot ternary polymerization (PO, EO and CO2) end-capping. The primary hydroxyl content of the polyols was analysed based on the difference in 19F-NMR chemical shifts between the primary and secondary trifluoroacetyl esters of the polyols. 19F-NMR and 1H-NMR spectroscopy indicated that EO end-capping could improve the 1° OH content of CO2 polyols in some extent, while accompanied with obvious loss of the carbonate unit content. Therefore, the EO end-capping method can only provide polyols with low carbonate unit content. Yet CO2-polyols with 72% of 1° OH content have been synthesized by copolymerization end-capping of EO and CO2, and the content of carbonate unit decreases little. Finally, taking advantage of the different reactivity of PO and EO with double metal cyanide catalysts (DMC), we synthesized CO2-polyols with 62% of 1° OH content by one-pot ternary polymerization of PO, EO and CO2, and the carbonate unit content was almost unaffected. This strategy provides a safe and efficient possibility to synthesize high 1° OH content CO2-polyols.
During the past decade, poly(carbonate-ether) polyols, also known as CO2-polyols, have been synthesized by the copolymerization of CO2 and propylene oxide (PO) with double metal cyanide (DMC) catalyst in the presence of various chain transfer agents. CO2-polyols show great potential as substitutes for polyols derived from fossil feedstock in the polyurethane industry. However, the ring opening reaction of PO generally occurs at the methylene carbon-oxygen bond due to less steric hindrance producing CO2-polyol mainly with the second hydroxyl (2° OH) as terminal group, therefore, the terminal primary hydroxyl (1° OH) content is usually lower than 20%, which leads to their much lower reactivity with isocyanate. Three methods were chosen for increasing the primary hydroxyl content of CO2-polyols, including ethylene oxide (EO) end-capping, copolymerization end-capping of EO and CO2, and one-pot ternary polymerization (PO, EO and CO2) end-capping. The primary hydroxyl content of the polyols was analysed based on the difference in 19F-NMR chemical shifts between the primary and secondary trifluoroacetyl esters of the polyols. 19F-NMR and 1H-NMR spectroscopy indicated that EO end-capping could improve the 1° OH content of CO2 polyols in some extent, while accompanied with obvious loss of the carbonate unit content. Therefore, the EO end-capping method can only provide polyols with low carbonate unit content. Yet CO2-polyols with 72% of 1° OH content have been synthesized by copolymerization end-capping of EO and CO2, and the content of carbonate unit decreases little. Finally, taking advantage of the different reactivity of PO and EO with double metal cyanide catalysts (DMC), we synthesized CO2-polyols with 62% of 1° OH content by one-pot ternary polymerization of PO, EO and CO2, and the carbonate unit content was almost unaffected. This strategy provides a safe and efficient possibility to synthesize high 1° OH content CO2-polyols.
2019, 50(4): 344-351
doi: 10.11777/j.issn1000-3304.2018.18256
Abstract:
A series of spiropyrane-containing copolymer assemblies— poly(N,N-dimethylaminoethyl methacrylate)-b-poly{(benzyl methacrylate)-co-[1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2'-indoline)]} (PDMA-b-P(BzMA-co-SPMA)) were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA), where SPMA units act as the photo-responsive moieties, P(BzMA-co-SPMA) chains as the core-forming blocks, and PDMA chains as shell-forming blocks. First, PDMA was prepared by RAFT polymerization in ethanol at 80 °C. With PDMA as macro chain transfer agent, the RAFT PISA of BzMA and SPMA in ethanol at 70 °C were completed. By changing the feed ratios of BzMA, SPMA, and PDMA, diverse morphologies, such as spheres, worms, " octopus”-like structures, vesicles, and solid particles, were readily prepared. During UV irradiation, the absorbance maximum at 585 nm increased successively, suggesting the spiropyrane structure gradually isomerized into merocyanine structure. As a result, copolymer assembly dispersion underwent a colorless-to-colorful transformation. Subsequently, the colorful copolymer assembly dispersion was exposed to visible light. The results suggested that the absorbance maximum at 585 nm gradually decreased and the colorful copolymer assembly dispersion transformed into colorless. Using the copolymer assembly dispersion as ink, the characters and patterns were drawn on papers. Since the copolymer assembly dispersion was colorless, the characters and patterns were invisible. Upon UV irradiation, with spiropyrane isomerized into merocyanine, the characters and patterns changed to blue and visible, while upon visible light irradiation or heating, merocyanine structure isomerized into spiropyrane, which induced the characters and patterns to become colorless and invisible. Taking advantage of ink-jet printing, fine-patterned patterns and two-dimensional materials could be rapidly and massively produced, which also underwent reversible invisible-to-visible transformation, upon alternative UV irradiation and visible light irradiation/heating.
A series of spiropyrane-containing copolymer assemblies— poly(N,N-dimethylaminoethyl methacrylate)-b-poly{(benzyl methacrylate)-co-[1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2'-indoline)]} (PDMA-b-P(BzMA-co-SPMA)) were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA), where SPMA units act as the photo-responsive moieties, P(BzMA-co-SPMA) chains as the core-forming blocks, and PDMA chains as shell-forming blocks. First, PDMA was prepared by RAFT polymerization in ethanol at 80 °C. With PDMA as macro chain transfer agent, the RAFT PISA of BzMA and SPMA in ethanol at 70 °C were completed. By changing the feed ratios of BzMA, SPMA, and PDMA, diverse morphologies, such as spheres, worms, " octopus”-like structures, vesicles, and solid particles, were readily prepared. During UV irradiation, the absorbance maximum at 585 nm increased successively, suggesting the spiropyrane structure gradually isomerized into merocyanine structure. As a result, copolymer assembly dispersion underwent a colorless-to-colorful transformation. Subsequently, the colorful copolymer assembly dispersion was exposed to visible light. The results suggested that the absorbance maximum at 585 nm gradually decreased and the colorful copolymer assembly dispersion transformed into colorless. Using the copolymer assembly dispersion as ink, the characters and patterns were drawn on papers. Since the copolymer assembly dispersion was colorless, the characters and patterns were invisible. Upon UV irradiation, with spiropyrane isomerized into merocyanine, the characters and patterns changed to blue and visible, while upon visible light irradiation or heating, merocyanine structure isomerized into spiropyrane, which induced the characters and patterns to become colorless and invisible. Taking advantage of ink-jet printing, fine-patterned patterns and two-dimensional materials could be rapidly and massively produced, which also underwent reversible invisible-to-visible transformation, upon alternative UV irradiation and visible light irradiation/heating.
2019, 50(4): 352-358
doi: 10.11777/j.issn1000-3304.2019.19010
Abstract:
The drying process of organic films directly affects final morphology of blends and through in situ scattering technique, the details of morphology inside thin films can be monitored. By designing and running in situ detection system, the crystallization behaviour of polymer molecules in PTB7-th:PC71BM blend, which shows a high efficiency, and the effect of additive (DIO) on the morphology evolution during the process of drying can be investigated. It was observed that the packing style of polymer molecules inside the blend was similar to that of spin-coated samples, indicating that the change of coating mode would not affect the orientation of crystallization. From 2D GIXD profile, it was found that at the beginning of film-forming process, aggregates were formed in the solution, ordered but highly swollen by solvent. With the evaporation of the solvent, the degree of order increased and the solvent was expelled, causing a tighter arrangement of chains and a smaller spacing. With the removal of solvent, the effective size and ordered length scale of the aggregates decreased. The interaction between PTB7-th and DIO was different from that with solvent. As a poor solvent, DIO can slow down the drying process of thin films. Thus the addition of DIO led to the increase of crystal coherence length of PTB7-th. The crystallization of polymer molecule was completed at the beginning of film forming process, which was prolonged by the addition of DIO, but the final crystallinity of the blend was not affected. At the same time, through the printing equipment integrated in the system, the power conversion efficiency (PCE) of our printed devices reached nearly 9%, very close to the efficiency of spin-coated devices. This work strengthened the understanding of morphology inside organic photovoltaic thin films, promoted the progress of industrial production technology of organic photovoltaic devices and had great scientific and commercial value.
The drying process of organic films directly affects final morphology of blends and through in situ scattering technique, the details of morphology inside thin films can be monitored. By designing and running in situ detection system, the crystallization behaviour of polymer molecules in PTB7-th:PC71BM blend, which shows a high efficiency, and the effect of additive (DIO) on the morphology evolution during the process of drying can be investigated. It was observed that the packing style of polymer molecules inside the blend was similar to that of spin-coated samples, indicating that the change of coating mode would not affect the orientation of crystallization. From 2D GIXD profile, it was found that at the beginning of film-forming process, aggregates were formed in the solution, ordered but highly swollen by solvent. With the evaporation of the solvent, the degree of order increased and the solvent was expelled, causing a tighter arrangement of chains and a smaller spacing. With the removal of solvent, the effective size and ordered length scale of the aggregates decreased. The interaction between PTB7-th and DIO was different from that with solvent. As a poor solvent, DIO can slow down the drying process of thin films. Thus the addition of DIO led to the increase of crystal coherence length of PTB7-th. The crystallization of polymer molecule was completed at the beginning of film forming process, which was prolonged by the addition of DIO, but the final crystallinity of the blend was not affected. At the same time, through the printing equipment integrated in the system, the power conversion efficiency (PCE) of our printed devices reached nearly 9%, very close to the efficiency of spin-coated devices. This work strengthened the understanding of morphology inside organic photovoltaic thin films, promoted the progress of industrial production technology of organic photovoltaic devices and had great scientific and commercial value.
2019, 50(4): 359-365
doi: 10.11777/j.issn1000-3304.2018.18251
Abstract:
Functional supramolecular complexes co-assembled with multiple proteins and nucleic acids are ubiquitous in nature, such as ribosome and viruses. It is fundamentally important to understand and utilize these heterogeneous structures. Here, we reported a protein-DNA submicrometre superstructure fabricated from the self-assembly of protein CsgA and DNA nanostructures. By inspecting the physiological conditions of protein-DNA co-assembly, we found that the originally soluble CsgA could polymerize into insoluble fibers in a particular buffer (30 mmol/L Tris-HCl, 450 mmol/L NaCl, pH = 7.2), and such fibers benefited the storage of tetrahedron DNA nanostructure (TDN). Concentration and fibrillation time were optimized for the aggregation-free conversion of CsgA into amyloid fibers. Specifically, the optimum conversion of monomeric CsgA into micrometer-scale fibers could be realized at a concentration of 5 μmol/L. Meanwhile, atomic force microscopy (AFM) suggested that CsgA assembled into mature fibers in 5 days and formed larger aggregates after 7 days. The height of mature fibers and aggregates was about 3.9 and 6.1 nm, respectively. Afterwards, TDN was modified with NTA molecule and conjugated to CsgA through the chelation of Ni2+, His-tag, and NTA. A submicrometre complex CsgA fiber-dTDN was further generated by hybridizing two copies of TDN in dimeric structure (dTDN) through β-sheet interactions and Watson-Crick hybridization. This approach could fabricate a series of dTDN structures precisely without inducing the random aggregation of molecules. The yield of up to 44% was higher than that obtained from the direct connection of DNA modules via DNA technology. In summary, our findings demonstrated that CsgA fibers could act as a sort of novel scaffold for the assembly of protein-templated DNA nanostructure. Particularly, this model provides a deep insight into the generation of functional superstructures through self-assembly of protein and DNA-based building blocks.
Functional supramolecular complexes co-assembled with multiple proteins and nucleic acids are ubiquitous in nature, such as ribosome and viruses. It is fundamentally important to understand and utilize these heterogeneous structures. Here, we reported a protein-DNA submicrometre superstructure fabricated from the self-assembly of protein CsgA and DNA nanostructures. By inspecting the physiological conditions of protein-DNA co-assembly, we found that the originally soluble CsgA could polymerize into insoluble fibers in a particular buffer (30 mmol/L Tris-HCl, 450 mmol/L NaCl, pH = 7.2), and such fibers benefited the storage of tetrahedron DNA nanostructure (TDN). Concentration and fibrillation time were optimized for the aggregation-free conversion of CsgA into amyloid fibers. Specifically, the optimum conversion of monomeric CsgA into micrometer-scale fibers could be realized at a concentration of 5 μmol/L. Meanwhile, atomic force microscopy (AFM) suggested that CsgA assembled into mature fibers in 5 days and formed larger aggregates after 7 days. The height of mature fibers and aggregates was about 3.9 and 6.1 nm, respectively. Afterwards, TDN was modified with NTA molecule and conjugated to CsgA through the chelation of Ni2+, His-tag, and NTA. A submicrometre complex CsgA fiber-dTDN was further generated by hybridizing two copies of TDN in dimeric structure (dTDN) through β-sheet interactions and Watson-Crick hybridization. This approach could fabricate a series of dTDN structures precisely without inducing the random aggregation of molecules. The yield of up to 44% was higher than that obtained from the direct connection of DNA modules via DNA technology. In summary, our findings demonstrated that CsgA fibers could act as a sort of novel scaffold for the assembly of protein-templated DNA nanostructure. Particularly, this model provides a deep insight into the generation of functional superstructures through self-assembly of protein and DNA-based building blocks.
2019, 50(4): 366-374
doi: 10.11777/j.issn1000-3304.2018.18242
Abstract:
As the multidrug-resistant (MDR) microorganism caused by antibiotics abuse has posed a serious threat to human health and even life security, it is of great significance to study and develop new antibacterial materials for the treatment of MDR microbial infection. Silver nanoparticles (AgNPs) are prevalent choices for biomedical applications due to their robust antimicrobial activity against bacteria and fungus, especially the MDR microorganism, while their synthesis via environmentally friendly approaches remains challengeable. On the other hand, it has been increasingly valued to investigate the incorporation of AgNPs into collagen, for as-fabricated nanocomposite wound dressing can be tailored with unique biological functions, excellent biocompatibility, weak antigenicity, favorable biodegradability, and effective antibacterial activity. Herein, dialdehyde amylose (DA) with different aldehyde contents was firstly prepared by controlling the amount of sodium periodate added, and AgNPs were subsequently synthesized using the DA obtained as both eco-friendly reducing agent and stabilizer. With collagen dressing swollen directly into the DA-AgNPs aqueous solution, the final product of collagen-based antibacterial dressing (AgNPs-Col) could be afforded after freeze-drying. It is worth noting that collagen could be crosslinked by DA via Schiff’s base reaction in the process of AgNPs incorporation. In-depth exploration revealed that partially oxidized DA functioned as both a reducing agent and a stabilizer to transform AgNO3 into AgNPs after heating for 150 min, and the participation of AgNPs into DA crosslinking process endowed AgNPs-Col dressing with a dense microstructure. In addition to the desirable decrease in porosity, water absorption rate, and vapor transmission rate, as-fabricated composite dressing also demonstrated a shape memory behavior as well as repeatability between swelling and physical pressing. More importantly, AgNPs-Col dressing exhibited a strong antibacterial activity against both Gram-positive and Gram-negative bacteria while serving as a robust barrier to bacterial infiltration in the meantime. Together with an excellent performance in blood compatibility, the AgNPs-Col antibacterial dressing developed in this work has promising application prospects in the field of biomedical applications.
As the multidrug-resistant (MDR) microorganism caused by antibiotics abuse has posed a serious threat to human health and even life security, it is of great significance to study and develop new antibacterial materials for the treatment of MDR microbial infection. Silver nanoparticles (AgNPs) are prevalent choices for biomedical applications due to their robust antimicrobial activity against bacteria and fungus, especially the MDR microorganism, while their synthesis via environmentally friendly approaches remains challengeable. On the other hand, it has been increasingly valued to investigate the incorporation of AgNPs into collagen, for as-fabricated nanocomposite wound dressing can be tailored with unique biological functions, excellent biocompatibility, weak antigenicity, favorable biodegradability, and effective antibacterial activity. Herein, dialdehyde amylose (DA) with different aldehyde contents was firstly prepared by controlling the amount of sodium periodate added, and AgNPs were subsequently synthesized using the DA obtained as both eco-friendly reducing agent and stabilizer. With collagen dressing swollen directly into the DA-AgNPs aqueous solution, the final product of collagen-based antibacterial dressing (AgNPs-Col) could be afforded after freeze-drying. It is worth noting that collagen could be crosslinked by DA via Schiff’s base reaction in the process of AgNPs incorporation. In-depth exploration revealed that partially oxidized DA functioned as both a reducing agent and a stabilizer to transform AgNO3 into AgNPs after heating for 150 min, and the participation of AgNPs into DA crosslinking process endowed AgNPs-Col dressing with a dense microstructure. In addition to the desirable decrease in porosity, water absorption rate, and vapor transmission rate, as-fabricated composite dressing also demonstrated a shape memory behavior as well as repeatability between swelling and physical pressing. More importantly, AgNPs-Col dressing exhibited a strong antibacterial activity against both Gram-positive and Gram-negative bacteria while serving as a robust barrier to bacterial infiltration in the meantime. Together with an excellent performance in blood compatibility, the AgNPs-Col antibacterial dressing developed in this work has promising application prospects in the field of biomedical applications.
2019, 50(4): 375-383
doi: 10.11777/j.issn1000-3304.2018.18239
Abstract:
In this study, cationic polymerization of p-methylstyrene (p-MeSt) was studied in ionic liquid (IL) reaction media. The effects of ILs on p-MeSt cationic polymerization were analyzed through density functional theory (DFT) and experimental method. The influences of various initiating systems on p-MeSt cationic polymerization were investigated, and the efficiencies of various ILs as reaction solvents were discussed. The structure of the polymerization product was characterized through 1H-NMR and FTIR characterization analyses; number-average molecular weight (Mn) and molecular weight distribution were measured through gel permeation chromatography (GPC); a temperature recorder tracked the relationship between polymerization system temperature variation and reaction time. The results showed that a CumOH(2-phenyl-2-propanol)/BF3·OEt2 initiating system is relatively effective in IL media over those frequently used in cationic polymerization reactions. The products polymerized in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2]) IL media have higher molecular weight and yield (up to 99%) and narrower molecular weight distribution (Mw/Mn is ~ 2.0) than those in traditional molecular solvents (such as CH2Cl2). An analysis of the effects of ILs on polymerization indicated that ILs act as inert solvents in p-MeSt cationic polymerization and do not directly participate in the polymerization reaction. The ionic environment of IL cannot inhibit a chain transfer reaction completely, but can stabilize active species and disperse positive charges. Thus, the polymerization reaction is milder in IL media than that in traditional molecular solvents. The results of IL recovery and reuse showed that these solvents can be used as reaction medium over a number of cycles without remarkable influence on the products. Finally, the corresponding elementary reaction mechanism of the cationic polymerization of p-MeSt initiated by the CumOH/BF3·OEt2 system in [Bmim][NTf2] IL media was proposed in this study. As is known, ILs are recyclable and environmentally friendly green solvents. This study expands the reaction solvent of cationic polymerization and promotes the development of green chemistry.
In this study, cationic polymerization of p-methylstyrene (p-MeSt) was studied in ionic liquid (IL) reaction media. The effects of ILs on p-MeSt cationic polymerization were analyzed through density functional theory (DFT) and experimental method. The influences of various initiating systems on p-MeSt cationic polymerization were investigated, and the efficiencies of various ILs as reaction solvents were discussed. The structure of the polymerization product was characterized through 1H-NMR and FTIR characterization analyses; number-average molecular weight (Mn) and molecular weight distribution were measured through gel permeation chromatography (GPC); a temperature recorder tracked the relationship between polymerization system temperature variation and reaction time. The results showed that a CumOH(2-phenyl-2-propanol)/BF3·OEt2 initiating system is relatively effective in IL media over those frequently used in cationic polymerization reactions. The products polymerized in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2]) IL media have higher molecular weight and yield (up to 99%) and narrower molecular weight distribution (Mw/Mn is ~ 2.0) than those in traditional molecular solvents (such as CH2Cl2). An analysis of the effects of ILs on polymerization indicated that ILs act as inert solvents in p-MeSt cationic polymerization and do not directly participate in the polymerization reaction. The ionic environment of IL cannot inhibit a chain transfer reaction completely, but can stabilize active species and disperse positive charges. Thus, the polymerization reaction is milder in IL media than that in traditional molecular solvents. The results of IL recovery and reuse showed that these solvents can be used as reaction medium over a number of cycles without remarkable influence on the products. Finally, the corresponding elementary reaction mechanism of the cationic polymerization of p-MeSt initiated by the CumOH/BF3·OEt2 system in [Bmim][NTf2] IL media was proposed in this study. As is known, ILs are recyclable and environmentally friendly green solvents. This study expands the reaction solvent of cationic polymerization and promotes the development of green chemistry.
2019, 50(4): 384-392
doi: 10.11777/j.issn1000-3304.2018.18240
Abstract:
The thermoresponsive property of poly(N,N-diethylacrylamide) (PDEAAm) and its copolymer with N,N-dimethylacrylamide (DMAAm) has been studied using various types of the copolymers. The group transfer polymerization (GTP) of N,N-diethylacrylamide (DEAAm) and N,N-dimethylacrylamide (DMAAm) was carried out using tris(pentafluorophenyl borane (B(C6F5)3) as the organocatalyst and triethyl((1-methoxy-2-methylprop-1-en-1-yl)o-xy)silane (SKAEt) as the initiator to produce the random, di-, tri-, and penta-block copolymers along with the homopolymers of PDEAAm and PDMAAm. The polymerization degrees (PDs) of homopolymers were 25, 50, 100, 200, 300, and 500 for PDEAAm, 25, 50, and 100 for PDMAAm and those of all copolymers was 100, and their dispersity was in the range of 1.05–1.26. The monomer compositions (m/n) in the copolymers were 90/10, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 25/75, and 10/90 for the random copolymer of PDEAAmm-r-PDMAAmn and 90/10, 75/25, 50/50, 25/75, and 10/90 for the di-block copolymer of PDEAAmm-b-PDMAAmn. The monomer compositions in the tri-block copolymer were PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDMAAm25-b-PDEAAm50-b-PDMAAm25, and those in the penta-block copolymer were PDEAAm20-b-PDMAAm25-b-PDEAAm50-b-PDMAAm25-b-PDEAAm20 and PDMAAm20-b-PDEAAm20-b-PDMAAm20-b-PDEAAm20-b-PDMAAm20. The thermoresponsive property concerning with a coil-globule phase transition was estimated using the temperature of cloud point (Tcp) of aqueous polymer solutions, i.e., the lower critical solution temperature (LCST). The Tcp of PDEAAm increased with the increasing PD from 36.5 °C to 29.5 °C. For PDEAAmm-r-PDMAAmn, the Tcp increased with the increasing DMAAm unit from 38.5 °C to 68.0 °C and none of the Tcps was observed for the copolymers with the m/n ratios of 25/75 and 10/90. For PDEAAmm-b-PDMAAmn, the Tcp increased with the increasing segment length of PDMAAm from 34.5 °C to 44.5 °C and no phase transition was observed for PDEAAm10-b-PDMAAm90. For the tri- and penta-block copolymers, which consist of the PDMAAm segment at both copolymer ends, PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDEAAm20-b-PDMAAm25-b-PDEAAm50-b-PDMAAm25-b-PDEAAm20 only exhibited the phase transition, such as the Tcps of 51.5 and 55.0 °C, respectively. These phase transition behaviors were confirmed by nuclear magnetic resonance spectroscopy (NMR) and dynamic light scattering (DLS) measurements. The hydrodynamic radius (Rh) of PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDEAAm20-b-PDMAAm20-b-PDEAAm20-b-PDMAAm20-b-PDEAAm20 surged from lower temperature of 45 °C to higher temperature of 75 °C.
The thermoresponsive property of poly(N,N-diethylacrylamide) (PDEAAm) and its copolymer with N,N-dimethylacrylamide (DMAAm) has been studied using various types of the copolymers. The group transfer polymerization (GTP) of N,N-diethylacrylamide (DEAAm) and N,N-dimethylacrylamide (DMAAm) was carried out using tris(pentafluorophenyl borane (B(C6F5)3) as the organocatalyst and triethyl((1-methoxy-2-methylprop-1-en-1-yl)o-xy)silane (SKAEt) as the initiator to produce the random, di-, tri-, and penta-block copolymers along with the homopolymers of PDEAAm and PDMAAm. The polymerization degrees (PDs) of homopolymers were 25, 50, 100, 200, 300, and 500 for PDEAAm, 25, 50, and 100 for PDMAAm and those of all copolymers was 100, and their dispersity was in the range of 1.05–1.26. The monomer compositions (m/n) in the copolymers were 90/10, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 25/75, and 10/90 for the random copolymer of PDEAAmm-r-PDMAAmn and 90/10, 75/25, 50/50, 25/75, and 10/90 for the di-block copolymer of PDEAAmm-b-PDMAAmn. The monomer compositions in the tri-block copolymer were PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDMAAm25-b-PDEAAm50-b-PDMAAm25, and those in the penta-block copolymer were PDEAAm20-b-PDMAAm25-b-PDEAAm50-b-PDMAAm25-b-PDEAAm20 and PDMAAm20-b-PDEAAm20-b-PDMAAm20-b-PDEAAm20-b-PDMAAm20. The thermoresponsive property concerning with a coil-globule phase transition was estimated using the temperature of cloud point (Tcp) of aqueous polymer solutions, i.e., the lower critical solution temperature (LCST). The Tcp of PDEAAm increased with the increasing PD from 36.5 °C to 29.5 °C. For PDEAAmm-r-PDMAAmn, the Tcp increased with the increasing DMAAm unit from 38.5 °C to 68.0 °C and none of the Tcps was observed for the copolymers with the m/n ratios of 25/75 and 10/90. For PDEAAmm-b-PDMAAmn, the Tcp increased with the increasing segment length of PDMAAm from 34.5 °C to 44.5 °C and no phase transition was observed for PDEAAm10-b-PDMAAm90. For the tri- and penta-block copolymers, which consist of the PDMAAm segment at both copolymer ends, PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDEAAm20-b-PDMAAm25-b-PDEAAm50-b-PDMAAm25-b-PDEAAm20 only exhibited the phase transition, such as the Tcps of 51.5 and 55.0 °C, respectively. These phase transition behaviors were confirmed by nuclear magnetic resonance spectroscopy (NMR) and dynamic light scattering (DLS) measurements. The hydrodynamic radius (Rh) of PDEAAm25-b-PDMAAm50-b-PDEAAm25 and PDEAAm20-b-PDMAAm20-b-PDEAAm20-b-PDMAAm20-b-PDEAAm20 surged from lower temperature of 45 °C to higher temperature of 75 °C.
2019, 50(4): 393-401
doi: 10.11777/j.issn1000-3304.2018.18226
Abstract:
Traditional breath figure method was improved via the introduction of polymer pre-phase separation. The morphology and size distribution of microsturctures prepared could be finely tuned by pre-phase separation time, PEG molecular weight, the ratio between different PEG molecules, and blending with small PS molecules. Specifically, compared with 20 and 30 min, the pre-phase separation time of 10 min could yield the most uniform structures; PEG2000 stood out from all PEG molecules tested with molecular weight from 2000 to 10000 and afforded microstructures of the highest compactness and homogeneity; introducing PEG200 the even smaller molecule would enhance the phase separation degree between PS and PEG. Furthermore, ratio variation between PEG200 and PEG2000 suggested that the maximal micro-convexes could be obtained at ratio of 2:8, while a honeycomb morphology was observed at 3:7. Among all the factors investigated, PS molecular weight played a dominant role on topography regulation. PS with lower molecular weight could reduce the molecular chain twisting for all polymer components, which conduced to the polymer phase separation. Addition of PS18000 rather than PS260000 could increase micro-convex amount as well as improve the uniformity of as-prepared structures dramatically. The honeycomb micro-hemisphere arrays were ultimately achieved through one-step breath figure method under the optimized conditions of pre-phase separation time as 10 min, PEG200:PEG2000 ratio as 3:7, and PS18000 participation; in the meantime, three structures including holes, half-holes, and convexes appeared on the substrate. Scrutinize of the underlying mechanism indicated that distribution and assembly of PEG molecules inside or on the surface of water droplets functioned decisively towards the topography of structures formed. This study provides novel insight into highly efficent fabrication of micro-hemispheres arrays.
Traditional breath figure method was improved via the introduction of polymer pre-phase separation. The morphology and size distribution of microsturctures prepared could be finely tuned by pre-phase separation time, PEG molecular weight, the ratio between different PEG molecules, and blending with small PS molecules. Specifically, compared with 20 and 30 min, the pre-phase separation time of 10 min could yield the most uniform structures; PEG2000 stood out from all PEG molecules tested with molecular weight from 2000 to 10000 and afforded microstructures of the highest compactness and homogeneity; introducing PEG200 the even smaller molecule would enhance the phase separation degree between PS and PEG. Furthermore, ratio variation between PEG200 and PEG2000 suggested that the maximal micro-convexes could be obtained at ratio of 2:8, while a honeycomb morphology was observed at 3:7. Among all the factors investigated, PS molecular weight played a dominant role on topography regulation. PS with lower molecular weight could reduce the molecular chain twisting for all polymer components, which conduced to the polymer phase separation. Addition of PS18000 rather than PS260000 could increase micro-convex amount as well as improve the uniformity of as-prepared structures dramatically. The honeycomb micro-hemisphere arrays were ultimately achieved through one-step breath figure method under the optimized conditions of pre-phase separation time as 10 min, PEG200:PEG2000 ratio as 3:7, and PS18000 participation; in the meantime, three structures including holes, half-holes, and convexes appeared on the substrate. Scrutinize of the underlying mechanism indicated that distribution and assembly of PEG molecules inside or on the surface of water droplets functioned decisively towards the topography of structures formed. This study provides novel insight into highly efficent fabrication of micro-hemispheres arrays.
2019, 50(4): 402-409
doi: 10.11777/j.issn1000-3304.2018.18253
Abstract:
In this work, high thermal conductive polyimide (PI) composites with reduced graphene oxide (rGO) as filler were prepared. In order to improve the thermal conductivity of rGO in the PI composites, rGO should form heat conductive paths in PI matrix, and the in-plane direction of rGO should be consistent with the heat dissipation direction of composite materials. Therefore, three-dimensional rGO networks (3DrGO) were prepared by freeze-drying technology to construct an effective thermal conductive path in PI matrix. In order to stabilize 3DrGO networks during the preparation process of PI composites, the 3DrGO networks were adhered and reinforced by PI. The process includes: (1) the rGO dispersion containing 3 wt% polyamide acid (PAA) was freeze-dried to prepare the PAA-reinforced 3DrGO network (3DrGO-PAA); (2) the 3DrGO-PAA was treated by thermal imidization to obtain the PI-reinforced 3DrGO network (3DrGO-PI); (3) 10 wt% PAA was cast onto the 3DrGO-PI template and imidized at 100, 200, and 350 °C for 1 h, respectively, at each temperature to obtain the 3DrGO-PI/PI composite films. The 3DrGO-PI/PI composite film exhibits the thermal conductivity of 1.57 W·m−1·K−1 with 8 wt% rGO (772% enhancement compared to that of neat PI film). Whereas the PI composite films with random distributed rGO (rGO/PI composite film) or unreinforced 3DrGO (3DrGO-water/PI composite film) only exhibit the thermal conductivity of 0.51 W·m−1·K−1 (183% enhancement compared to that of neat PI film) or 1.02 W·m−1·K−1 (467% enhancement compared to that of neat PI film), respectively. All the composite films maintain very good thermal stabilities. The Td5% (thermal decomposition temperature at 5 wt% weight loss) values of the composite films are higher than that at 540 °C. Compared with that of neat PI, the Tgs of the composite films are slightly enhanced and relatively higher (higher than 390 °C). The coefficient of thermal expansion (CTE) of the composite films can be greatly decreased by the addition of 3DrGO. The CTE of 3DrGO-PI/PI composite film is as low as 2.16 × 10–5/°C when loading 8 wt% 3DrGO.
In this work, high thermal conductive polyimide (PI) composites with reduced graphene oxide (rGO) as filler were prepared. In order to improve the thermal conductivity of rGO in the PI composites, rGO should form heat conductive paths in PI matrix, and the in-plane direction of rGO should be consistent with the heat dissipation direction of composite materials. Therefore, three-dimensional rGO networks (3DrGO) were prepared by freeze-drying technology to construct an effective thermal conductive path in PI matrix. In order to stabilize 3DrGO networks during the preparation process of PI composites, the 3DrGO networks were adhered and reinforced by PI. The process includes: (1) the rGO dispersion containing 3 wt% polyamide acid (PAA) was freeze-dried to prepare the PAA-reinforced 3DrGO network (3DrGO-PAA); (2) the 3DrGO-PAA was treated by thermal imidization to obtain the PI-reinforced 3DrGO network (3DrGO-PI); (3) 10 wt% PAA was cast onto the 3DrGO-PI template and imidized at 100, 200, and 350 °C for 1 h, respectively, at each temperature to obtain the 3DrGO-PI/PI composite films. The 3DrGO-PI/PI composite film exhibits the thermal conductivity of 1.57 W·m−1·K−1 with 8 wt% rGO (772% enhancement compared to that of neat PI film). Whereas the PI composite films with random distributed rGO (rGO/PI composite film) or unreinforced 3DrGO (3DrGO-water/PI composite film) only exhibit the thermal conductivity of 0.51 W·m−1·K−1 (183% enhancement compared to that of neat PI film) or 1.02 W·m−1·K−1 (467% enhancement compared to that of neat PI film), respectively. All the composite films maintain very good thermal stabilities. The Td5% (thermal decomposition temperature at 5 wt% weight loss) values of the composite films are higher than that at 540 °C. Compared with that of neat PI, the Tgs of the composite films are slightly enhanced and relatively higher (higher than 390 °C). The coefficient of thermal expansion (CTE) of the composite films can be greatly decreased by the addition of 3DrGO. The CTE of 3DrGO-PI/PI composite film is as low as 2.16 × 10–5/°C when loading 8 wt% 3DrGO.
2019, 50(4): 410-418
doi: 10.11777/j.issn1000-3304.2018.18241
Abstract:
Amphiphilic copolymers, poly(styrene)-block-poly(hydroxyethyl methacrylate)/Eu complex (PS-b-PHEMA/Eu complex) were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The structure and composition of the amphiphilic copolymers, PS-b-PHEMA/Eu complex, were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance spectroscopy (1H-NMR) and solid-state fluorescence spectrum. The honeycomb structured porous films were fabricated by dropping the PS-b-PHEMA/Eu complex copolymer solutions onto glass substrates via the breath figure method. The effects of solvent, copolymer concentration, and copolymers’ molecular weight on the formation of porous films were investigated. The surface morphology and elemental mapping of the highly ordered porous films were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and laser scanning confocal microscopy (LSCM). The results indicated that the solvent type, copolymer concentration, and copolymers’ molecular weight can affect the surface morphology of the honeycomb structured porous films. Organic solvents with low boiling point, high volatility, and insolubility in water are conducive to the formation of porous films with high regularity and uniform pore size. The average diameter of the pores in the porous films decreased with the increasing polymer concentration and the molecular weight of the copolymers. The FESEM-EDX analysis further verified that the hydrophilic groups (Eu complex groups) were mainly distributed at the sidewall of the pore, which was consistent with the LSCM results. It is worth mentioning that after the porous films were placed in the air for half a year, most of the Eu elements originally concentrated in the inner wall of the pore migrated to the surface of the films. This might be due to the migration of hydrophilic groups attached on the polymer chains with free rotation of the chains.
Amphiphilic copolymers, poly(styrene)-block-poly(hydroxyethyl methacrylate)/Eu complex (PS-b-PHEMA/Eu complex) were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The structure and composition of the amphiphilic copolymers, PS-b-PHEMA/Eu complex, were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance spectroscopy (1H-NMR) and solid-state fluorescence spectrum. The honeycomb structured porous films were fabricated by dropping the PS-b-PHEMA/Eu complex copolymer solutions onto glass substrates via the breath figure method. The effects of solvent, copolymer concentration, and copolymers’ molecular weight on the formation of porous films were investigated. The surface morphology and elemental mapping of the highly ordered porous films were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and laser scanning confocal microscopy (LSCM). The results indicated that the solvent type, copolymer concentration, and copolymers’ molecular weight can affect the surface morphology of the honeycomb structured porous films. Organic solvents with low boiling point, high volatility, and insolubility in water are conducive to the formation of porous films with high regularity and uniform pore size. The average diameter of the pores in the porous films decreased with the increasing polymer concentration and the molecular weight of the copolymers. The FESEM-EDX analysis further verified that the hydrophilic groups (Eu complex groups) were mainly distributed at the sidewall of the pore, which was consistent with the LSCM results. It is worth mentioning that after the porous films were placed in the air for half a year, most of the Eu elements originally concentrated in the inner wall of the pore migrated to the surface of the films. This might be due to the migration of hydrophilic groups attached on the polymer chains with free rotation of the chains.
2019, 50(4): 419-428
doi: 10.11777/j.issn1000-3304.2018.18230
Abstract:
A novel DOPO derivative (DIDOPO) is incorporated together with amine-based multi-walled carbon nanotubes (MWCNTs) into PA6 by melt blending. Mechanical properties, thermal stability, crystallinity, and combustion properties are measured using universal testing machine, thermogravimetric analyzer, differential scanning calorimeter, and cone calorimeter, respectively. After combustion, the morphology of char layer is further observed by a scanning electron microscope. The results show that MWCNTs-incorporated flame-retardant nanocomposites exhibit a tensile strength that is 55% higher than that of the PA6/DIDOPO composites. From the TG and DTG curves, it can be seen that the T5wt% of PA6 composites increased slightly and the maximum weight loss rate temperature (Tmax) gradually improved after adding MWCNTs, indicating that the addition of MWCNTs delays the process of thermal degradation of the PA6 composites. With the incorporation of MWCNTs, the amount of residual carbon is also increased. From the non-isothermal crystallization curve, it can be seen that the crystallization initial temperature (Tonset) and crystallization peak temperature (Tc) of the PA6 composites are significantly improved with the addition of MWCNTs. However, the crystallinity is lower due to the heterogeneous nucleation of the MWCNTs. From UL-94 datas, the combustion time (t1 + t2) is increased with the incorporation of MWCNTs into PA6/DIDOPO composites, which results in a V-1 level in the UL-94 test and a slightly increased LOI value. This phenomenon can be attributed to an increment in melt viscosity and a decrement in flow properties. Combined with the curves of effective combustion heat, total smoke release and CO release rate, it can be concluded that the synergistic effect between MWCNTs and DIDOPO weakens the thermal degradation process of the PA6 composites, thus increasing the incomplete combustion and reducing the complete combustion of the PA6 composites, which is beneficial to the flame retardance of the materials. Addition of 2 wt% MWCNTs results in a peak heat release rate (PHRR) of 367.28 kW/m2, which corresponds to a 58.9% lower rate than that of pure PA6, as revealed by cone calorimetry. Based on SEM and Raman, a continuous and compact char layer is observed upon addition of MWCNTs, which is ascribed to a synergistic effect between MWCNTs and DIDOPO.
A novel DOPO derivative (DIDOPO) is incorporated together with amine-based multi-walled carbon nanotubes (MWCNTs) into PA6 by melt blending. Mechanical properties, thermal stability, crystallinity, and combustion properties are measured using universal testing machine, thermogravimetric analyzer, differential scanning calorimeter, and cone calorimeter, respectively. After combustion, the morphology of char layer is further observed by a scanning electron microscope. The results show that MWCNTs-incorporated flame-retardant nanocomposites exhibit a tensile strength that is 55% higher than that of the PA6/DIDOPO composites. From the TG and DTG curves, it can be seen that the T5wt% of PA6 composites increased slightly and the maximum weight loss rate temperature (Tmax) gradually improved after adding MWCNTs, indicating that the addition of MWCNTs delays the process of thermal degradation of the PA6 composites. With the incorporation of MWCNTs, the amount of residual carbon is also increased. From the non-isothermal crystallization curve, it can be seen that the crystallization initial temperature (Tonset) and crystallization peak temperature (Tc) of the PA6 composites are significantly improved with the addition of MWCNTs. However, the crystallinity is lower due to the heterogeneous nucleation of the MWCNTs. From UL-94 datas, the combustion time (t1 + t2) is increased with the incorporation of MWCNTs into PA6/DIDOPO composites, which results in a V-1 level in the UL-94 test and a slightly increased LOI value. This phenomenon can be attributed to an increment in melt viscosity and a decrement in flow properties. Combined with the curves of effective combustion heat, total smoke release and CO release rate, it can be concluded that the synergistic effect between MWCNTs and DIDOPO weakens the thermal degradation process of the PA6 composites, thus increasing the incomplete combustion and reducing the complete combustion of the PA6 composites, which is beneficial to the flame retardance of the materials. Addition of 2 wt% MWCNTs results in a peak heat release rate (PHRR) of 367.28 kW/m2, which corresponds to a 58.9% lower rate than that of pure PA6, as revealed by cone calorimetry. Based on SEM and Raman, a continuous and compact char layer is observed upon addition of MWCNTs, which is ascribed to a synergistic effect between MWCNTs and DIDOPO.
