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2019 Volume 50 Issue 11
2019, 50(11):
Abstract:
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2019, 50(11): 1133-1145
doi: 10.11777/j.issn1000-3304.2019.19150
Abstract:
Janus polymerization combines cationic and anionic polymerizations at two ends of a single propagating chain involving a living/controlled chain-growth polymerization and a self-triggered stepwise polycondensation, which provides a facile way to synthesize novel polymers with sophisticated topologies in one step directly from monomers. Di-/Multi-block copolymers, branch polymers, mikto-arm star copolymers and cylindrical polymer brushes are synthesized using rare earth triflates catalysts assisted by various epoxy initiators owing to their specific position at the middle of the chain. This work reviews recent progress on Janus polymerization in our group. Specifically, the characteristic of rare earth metal catalysts and mechanism of Janus polymerization are discussed in detail where tripedal crows are employed to illustrate the mechanism. New methodologies for the construction of topological polymers are introduced, together with the unique and prominent properties, such as thermoplastic properties, self-assembly and self-healing behaviors and the corresponding applications in self-sealing films for plants and electrostatic spinning. A new Janus system is put forward which affords a facile synthetic method for functional polyesters by incorporating a modifiable monomer 3,3-bis(chloromethyl)oxacyclobutane. Finally, the development of Janus polymerization including new catalytic systems and monomers is also prospected. The concept of Janus polymerization makes significant breakthroughs into traditional cognitions about incompatible cationic and anionic polymerization mechanisms in one system which motivates the power in the catalysis and synthesis of polymer chemistry.
Janus polymerization combines cationic and anionic polymerizations at two ends of a single propagating chain involving a living/controlled chain-growth polymerization and a self-triggered stepwise polycondensation, which provides a facile way to synthesize novel polymers with sophisticated topologies in one step directly from monomers. Di-/Multi-block copolymers, branch polymers, mikto-arm star copolymers and cylindrical polymer brushes are synthesized using rare earth triflates catalysts assisted by various epoxy initiators owing to their specific position at the middle of the chain. This work reviews recent progress on Janus polymerization in our group. Specifically, the characteristic of rare earth metal catalysts and mechanism of Janus polymerization are discussed in detail where tripedal crows are employed to illustrate the mechanism. New methodologies for the construction of topological polymers are introduced, together with the unique and prominent properties, such as thermoplastic properties, self-assembly and self-healing behaviors and the corresponding applications in self-sealing films for plants and electrostatic spinning. A new Janus system is put forward which affords a facile synthetic method for functional polyesters by incorporating a modifiable monomer 3,3-bis(chloromethyl)oxacyclobutane. Finally, the development of Janus polymerization including new catalytic systems and monomers is also prospected. The concept of Janus polymerization makes significant breakthroughs into traditional cognitions about incompatible cationic and anionic polymerization mechanisms in one system which motivates the power in the catalysis and synthesis of polymer chemistry.
2019, 50(11): 1146-1155
doi: 10.11777/j.issn1000-3304.2019.19094
Abstract:
Cascade polymerization, or domino polymerization, is a polymerization process involving two or more consecutive polymerizations under the same reaction condition, in which the subsequent polymerizations result as a consequence of the functional polymer intermediates formed in the previous polymerization step, i.e., two or more polymerizations proceed cascade in an in situ one feeding step, one pot system. As the separation and purification of intermediate polymers are not needed, cascade polymerization has the characteristics of " green” and high efficiency, which is especially important in the synthesis of block copolymers. This review introduces the concept of cascade polymerization, with the focus on the cascade polycondensation-coupling ring-opening polymerization (PROP) method developed by our research group, as well as the kinetics, thermodynamics and the application of PROP in the synthesis of polyesters and copolyesters. By the combination of chain-growth and step-growth polymerization together in one system, PROP has the merits of fast polymerization speed, easy to handle with mild polymerization conditions, controlled rigid to soft segments weight ratio, and can be used for the synthesis of multiblock copolymers which are hard to be synthesized by traditional polymerization techniques. These multiblock copolyesters have potential applications in elastomers and energy storage materials.
Cascade polymerization, or domino polymerization, is a polymerization process involving two or more consecutive polymerizations under the same reaction condition, in which the subsequent polymerizations result as a consequence of the functional polymer intermediates formed in the previous polymerization step, i.e., two or more polymerizations proceed cascade in an in situ one feeding step, one pot system. As the separation and purification of intermediate polymers are not needed, cascade polymerization has the characteristics of " green” and high efficiency, which is especially important in the synthesis of block copolymers. This review introduces the concept of cascade polymerization, with the focus on the cascade polycondensation-coupling ring-opening polymerization (PROP) method developed by our research group, as well as the kinetics, thermodynamics and the application of PROP in the synthesis of polyesters and copolyesters. By the combination of chain-growth and step-growth polymerization together in one system, PROP has the merits of fast polymerization speed, easy to handle with mild polymerization conditions, controlled rigid to soft segments weight ratio, and can be used for the synthesis of multiblock copolymers which are hard to be synthesized by traditional polymerization techniques. These multiblock copolyesters have potential applications in elastomers and energy storage materials.
2019, 50(11): 1156-1166
doi: 10.11777/j.issn1000-3304.2019.19133
Abstract:
The polymeric drug delivery systems (DDS) have showed promising potential for improving cancer therapy, which can lengthen the blood circulation and minimize the adverse effect of chemotherapeutics. Despite promising, the therapeutic performance of polymeric-based DDS is affected by a series of physiological barriers, including limited tumor accumulation, restricted tumor penetration, insufficient cellular uptake, and slow drug release inside the tumor cells. It has been well-investigated that there is an acidic microenvironment inside the solid tumors due to the abnormal glucose metabolism of tumor cells. Moreover, the subcellular organelles including endosome and lysosome display much lower acidic pH than that of cytosol. The extracellular and intracellular acidic microenvironments have thus been exploited as both a trigger and target for tumor-targeted drug delivery. In this review article, we summarized our recent advances in developing acid-responsive polymeric DDS by taking the advantage of the acidic microenvironment of tumor tissue and tumor cells. We particularly highlighted the acid-responsive chemical bonds and components employed for constructing the acid-activatable DDS. These acid-activatable nanovectors have been exploited for combating the physiological barriers by surface charge conversion, nanostructure dissociation, and ligand presentation. We also provided a perspective regarding of the challenges and opportunities about clinical translation of the stimuli-activatable DDS.
The polymeric drug delivery systems (DDS) have showed promising potential for improving cancer therapy, which can lengthen the blood circulation and minimize the adverse effect of chemotherapeutics. Despite promising, the therapeutic performance of polymeric-based DDS is affected by a series of physiological barriers, including limited tumor accumulation, restricted tumor penetration, insufficient cellular uptake, and slow drug release inside the tumor cells. It has been well-investigated that there is an acidic microenvironment inside the solid tumors due to the abnormal glucose metabolism of tumor cells. Moreover, the subcellular organelles including endosome and lysosome display much lower acidic pH than that of cytosol. The extracellular and intracellular acidic microenvironments have thus been exploited as both a trigger and target for tumor-targeted drug delivery. In this review article, we summarized our recent advances in developing acid-responsive polymeric DDS by taking the advantage of the acidic microenvironment of tumor tissue and tumor cells. We particularly highlighted the acid-responsive chemical bonds and components employed for constructing the acid-activatable DDS. These acid-activatable nanovectors have been exploited for combating the physiological barriers by surface charge conversion, nanostructure dissociation, and ligand presentation. We also provided a perspective regarding of the challenges and opportunities about clinical translation of the stimuli-activatable DDS.
2019, 50(11): 1167-1176
doi: 10.11777/j.issn1000-3304.2019.19070
Abstract:
Block copolymer (BCP) nanoparticles with three different block sequences, PDMA-PNAT-PDAAM (M-N-D), PDMA-PDAAM-PNAT (M-D-N) and PDMA-P(NAT-co-DAAM) (M-[N-co-D]), are prepared via polymerization-induced self-assembly (PISA). Soluble N-acryloyloxy thiomorpholine (NAT) and diacetone acrylamide (DAAM) are used as monomers to form insoluble core blocks in water, while PDMA35 bearing a trithiocarbonate is utilized as stabilizer and macromolecular chain transfer agent (macro-CTA) to render a RAFT control. Specifically, M-[N-co-D] nano-objects are synthesized via direct RAFT dispersion copolymerization of NAT and DAAM at 70 °C employing PDMA35 macro-CTA. To produce M-N-D and M-D-N triblock copolymers, PDMA-PNAT (M-N) and PDMA-PDAAM (M-D) nano-objects are prepared via RAFT dispersion PISA syntheses of NAT and DAAM respectively utilizing PDMA35 macro-CTA and then used for seeded dispersion polymerization of DAAM and NAT respectively without intermediate postpolymerization purification. The thioether moiety in NAT can be oxidized by reactive oxygen species (ROS) into a hydrophilic sulfoxide. Therefore, in the precense of hydrogen peroxide (H2O2), oxidation-responsive morphological degradation of these nano-objects occurs due to the increasing hydrophilicity of NAT units. Given the poor control over polymerization of NAT in pure water, 1,4-dioxane is used as a cosolvent to the PNAT block. So the PISA syntheses are conducted in water/1,4-dioxane (9/1, V/V) mixture to achieve a good control over the molecular weight and narrow distribution. 1H-NMR spectra indicate that quantitative monomer conversions (> 99%) are achieved within 5 h. Differential scanning calorimeter (DLS) and transmission electron microscopy (TEM) are used to characterize final morphologies of PISA-generated nano-objects and morphological evolution of nano-objects in the presence of H2O2 (10 mol/L). These aqueous sequence-controlled PISA formulations are expected to provide responsive nanoparticles with tunable kinetics due to the response-dependent morphological transitions, which may be potentially used as carriers for drug delivery and controlled release.
Block copolymer (BCP) nanoparticles with three different block sequences, PDMA-PNAT-PDAAM (M-N-D), PDMA-PDAAM-PNAT (M-D-N) and PDMA-P(NAT-co-DAAM) (M-[N-co-D]), are prepared via polymerization-induced self-assembly (PISA). Soluble N-acryloyloxy thiomorpholine (NAT) and diacetone acrylamide (DAAM) are used as monomers to form insoluble core blocks in water, while PDMA35 bearing a trithiocarbonate is utilized as stabilizer and macromolecular chain transfer agent (macro-CTA) to render a RAFT control. Specifically, M-[N-co-D] nano-objects are synthesized via direct RAFT dispersion copolymerization of NAT and DAAM at 70 °C employing PDMA35 macro-CTA. To produce M-N-D and M-D-N triblock copolymers, PDMA-PNAT (M-N) and PDMA-PDAAM (M-D) nano-objects are prepared via RAFT dispersion PISA syntheses of NAT and DAAM respectively utilizing PDMA35 macro-CTA and then used for seeded dispersion polymerization of DAAM and NAT respectively without intermediate postpolymerization purification. The thioether moiety in NAT can be oxidized by reactive oxygen species (ROS) into a hydrophilic sulfoxide. Therefore, in the precense of hydrogen peroxide (H2O2), oxidation-responsive morphological degradation of these nano-objects occurs due to the increasing hydrophilicity of NAT units. Given the poor control over polymerization of NAT in pure water, 1,4-dioxane is used as a cosolvent to the PNAT block. So the PISA syntheses are conducted in water/1,4-dioxane (9/1, V/V) mixture to achieve a good control over the molecular weight and narrow distribution. 1H-NMR spectra indicate that quantitative monomer conversions (> 99%) are achieved within 5 h. Differential scanning calorimeter (DLS) and transmission electron microscopy (TEM) are used to characterize final morphologies of PISA-generated nano-objects and morphological evolution of nano-objects in the presence of H2O2 (10 mol/L). These aqueous sequence-controlled PISA formulations are expected to provide responsive nanoparticles with tunable kinetics due to the response-dependent morphological transitions, which may be potentially used as carriers for drug delivery and controlled release.
2019, 50(11): 1177-1186
doi: 10.11777/j.issn1000-3304.2019.19078
Abstract:
This study discusses a new strategy for synthesis of long chain-branched polypropylene (LCB-PP) with Ziegler-Natta catalysts, which, on the basis of conventional nonconjugated α,ω-diolefin/propylene copolymerization incapable of affording LCB, utilizes a dichlorosilane-functionalized α,ω-diolefin instead to carry out the copolymerization. Such a copolymerization with Ziegler-Natta catalysts will give PP bearing pending dichlorosilane functional groups, and it will undergo facile interchain condensations, leading to long chain-branched formation under methanol treatment and water vapor treatment. A MgCl2/TiCl4 catalyst containing a diether-type internal electron donor, 9,9-bis(methoxymethyl)fluorine (BMMF), was employed to catalyze di(5-hexenyl)dichlorosilane/propylene copolymerization in slurry conditions. It was found that di(5-hexenyl)dichlorosilane neither did harm to catalyst activity, nor changed the chain transfer/chain termination reaction of the original propylene polymerization. Incorporations of the mono-polymerized di(5-hexenyl)dichlorosilane were found to be between 0.02 mol% and 0.1 mol%. After the copolymerization completed, the obtained copolymers were treated with methanol or water vapor, respectively. Both the treatments could effectively transform the polymer chains-pending dichlorosilane groups into siloxane groups. The condensation degrees were distributed, which were centralized between 2 and 3 with methanol treatment. Water vapor treatment showed higher efficiency for dichlorosilane condensation than methanol treatment did. It could be found that water-treated samples exhibited systematically higher degrees of long chain-branched than their methanol-treated counterparts did with multiple evidences. Gel permeation chromatography measurement showed that the molecular weights of the copolymerized samples treated by both water vapor and methanol were improved, and the copolymers treated by water vapor in the Mark-Houwink equation curve were more deviated from the linear polypropylene than those of methanol treatment. The linear viscoelasticity of copolymers with different di(5-hexenyl)dichlorosilane concentrations after water vapor treatment and methanol treatment was investigated by means of small amplitude oscillatory shear (SAOS) to verify the existence of long chain-branched structure. According to extensional rheometry measurement, the strain hardening phenomena of the copolymers treated with water vapor were more obvious than those treated with methanol.
This study discusses a new strategy for synthesis of long chain-branched polypropylene (LCB-PP) with Ziegler-Natta catalysts, which, on the basis of conventional nonconjugated α,ω-diolefin/propylene copolymerization incapable of affording LCB, utilizes a dichlorosilane-functionalized α,ω-diolefin instead to carry out the copolymerization. Such a copolymerization with Ziegler-Natta catalysts will give PP bearing pending dichlorosilane functional groups, and it will undergo facile interchain condensations, leading to long chain-branched formation under methanol treatment and water vapor treatment. A MgCl2/TiCl4 catalyst containing a diether-type internal electron donor, 9,9-bis(methoxymethyl)fluorine (BMMF), was employed to catalyze di(5-hexenyl)dichlorosilane/propylene copolymerization in slurry conditions. It was found that di(5-hexenyl)dichlorosilane neither did harm to catalyst activity, nor changed the chain transfer/chain termination reaction of the original propylene polymerization. Incorporations of the mono-polymerized di(5-hexenyl)dichlorosilane were found to be between 0.02 mol% and 0.1 mol%. After the copolymerization completed, the obtained copolymers were treated with methanol or water vapor, respectively. Both the treatments could effectively transform the polymer chains-pending dichlorosilane groups into siloxane groups. The condensation degrees were distributed, which were centralized between 2 and 3 with methanol treatment. Water vapor treatment showed higher efficiency for dichlorosilane condensation than methanol treatment did. It could be found that water-treated samples exhibited systematically higher degrees of long chain-branched than their methanol-treated counterparts did with multiple evidences. Gel permeation chromatography measurement showed that the molecular weights of the copolymerized samples treated by both water vapor and methanol were improved, and the copolymers treated by water vapor in the Mark-Houwink equation curve were more deviated from the linear polypropylene than those of methanol treatment. The linear viscoelasticity of copolymers with different di(5-hexenyl)dichlorosilane concentrations after water vapor treatment and methanol treatment was investigated by means of small amplitude oscillatory shear (SAOS) to verify the existence of long chain-branched structure. According to extensional rheometry measurement, the strain hardening phenomena of the copolymers treated with water vapor were more obvious than those treated with methanol.
2019, 50(11): 1187-1195
doi: 10.11777/j.issn1000-3304.2019.19081
Abstract:
A series of novel amino-functionalized isotactic polypropylenes with high molecular weight and satisfying functional comonomer incorporation were prepared by direct copolymerization of propylene and α-olefins carrying carbazole functional groups. The homogeneous non-metallocene catalyst system consisting of dimethyl(pyridylamido)Hf(IV) complex, [Ph3C][B(C6F5)4], and AliBu3 showed good tolerance to carbazole groups and promoted the copolymerization of propylene with 11-carbazole-1-undecene effectively under mild reaction conditions, in which very high catalytic activity (up to 4.08 × 106 gpolymer molCat.−1 h−1) was achieved. The functional copolymers obtained possessed high molecular weight (up to 7.02 × 105) and tacticity ([mmmm] > 99%), as well as decent incorporation of carbazole functional groups (up to 13.5 mol%). Besides, DSC and TGA results verified the excellent thermostability of most copolymer products by giving decomposition temperatures around 450 °C as well as high melting points. Representative physical properties such as hydrophilicity, mechanical performance, and fluorescent characteristics of these iPPs functionalized by carbazole groups have also been explored. The increased incorporation of 11-carbazole-1-undecene monomer could reduce the water contact angle gradually and thus make significant improvement in surface properties; the copolymers became hydrophilic when comonomer incorporation exceeded 4.1 mol%. In terms of the mechanical properties, elongation at break of the copolymer barely increased at low incorporation (1.2 mol%), and the material still showed typical attributes of rigidity and brittleness. As more 11-carbazole-1-undecene monomer was incorporated (> 6.2 mol%), toughness of the materials was dramatically enhanced yet their stiffness was inevitably sacrificed. In addition, the introduction of carbazole group endowed the copolymers with unique fluorescent characteristics—they could emit purple fluorescence under 365 nm UV light in both solution and film states, thereby making this kind of functional polypropylene materials valuable and promising for the extensive applications in optoelectronic devices.
A series of novel amino-functionalized isotactic polypropylenes with high molecular weight and satisfying functional comonomer incorporation were prepared by direct copolymerization of propylene and α-olefins carrying carbazole functional groups. The homogeneous non-metallocene catalyst system consisting of dimethyl(pyridylamido)Hf(IV) complex, [Ph3C][B(C6F5)4], and AliBu3 showed good tolerance to carbazole groups and promoted the copolymerization of propylene with 11-carbazole-1-undecene effectively under mild reaction conditions, in which very high catalytic activity (up to 4.08 × 106 gpolymer molCat.−1 h−1) was achieved. The functional copolymers obtained possessed high molecular weight (up to 7.02 × 105) and tacticity ([mmmm] > 99%), as well as decent incorporation of carbazole functional groups (up to 13.5 mol%). Besides, DSC and TGA results verified the excellent thermostability of most copolymer products by giving decomposition temperatures around 450 °C as well as high melting points. Representative physical properties such as hydrophilicity, mechanical performance, and fluorescent characteristics of these iPPs functionalized by carbazole groups have also been explored. The increased incorporation of 11-carbazole-1-undecene monomer could reduce the water contact angle gradually and thus make significant improvement in surface properties; the copolymers became hydrophilic when comonomer incorporation exceeded 4.1 mol%. In terms of the mechanical properties, elongation at break of the copolymer barely increased at low incorporation (1.2 mol%), and the material still showed typical attributes of rigidity and brittleness. As more 11-carbazole-1-undecene monomer was incorporated (> 6.2 mol%), toughness of the materials was dramatically enhanced yet their stiffness was inevitably sacrificed. In addition, the introduction of carbazole group endowed the copolymers with unique fluorescent characteristics—they could emit purple fluorescence under 365 nm UV light in both solution and film states, thereby making this kind of functional polypropylene materials valuable and promising for the extensive applications in optoelectronic devices.
2019, 50(11): 1196-1201
doi: 10.11777/j.issn1000-3304.2019.19053
Abstract:
To improve the hydrophilic properties of poly(propylene carbonate) (PPC), hydroxyl-functionalized PPC (PPC-OH) were prepared by two steps. First, PPC containing o-nitrobenzyl (ONB) protecting groups (PPC-ONB) were synthesized by terpolymerization reactions of 2-{[(2-nitrophenyl)methoxy]-methyl}oxirane (monomer a ), propylene oxide (PO), and CO2 over SalenCo(III)Cl/bis(triphenylphosphine)iminium chloride (PPNCl) catalyst system. 1H-NMR result showed that the PPC-ONB was a random copolymer with monomer a randomly inserted. Then PPC-OH were obtained with the removal of o-nitrobenzyl (ONB) protecting groups under ultraviolet (UV) irradiation. PPC-ONB were synthesized with various feed ratios of the monomer a and different reaction time. Based on the analysis of 1H-NMR, 13C-NMR, gel permeation chromatography (GPC), and differential scanning calorimeter (DSC), SalenCo(III)Cl catalyst performed high reactivity and high selectivity (> 94%). The polycarbonate exhibited excellent regioselectivity and perfect alternating copolymerization of CO2 and PO with the carbonate linkages up to 98%, and the head-to-tail linkage (HT) up to 99%. With the increase of the feed ratios of the monomer a , the polymer ratio of the monomer a increased to 19.4% without sacrificing the reactive activity, while the molecular weight (Mn) decreased slightly owing to the better reactivity of monomer a . The glass transition temperatures (Tg) were in the range of 35.7 − 38.9 °C. The kinetics of deprotection by UV irradiation proved that the ONB protecting groups could be carried out efficiently within minutes. And the characterization of polymer by 1H-NMR, Fourier transform infrared spectrometer (FTIR) and GPC showed that the ONB protecting groups were removed and the ―OH was observed. Meanwhile, no degradation of polymer backbone occurred. The contact angle (CA) measurement of PPC-ONB and PPC-OH displayed a difference in hydrophilia. The hydrophilia of PPC-OH has been greatly improved compared with PPC-ONB due to the increase in polarity, and the CA of PPC-OH decreased from 78.3° to 58.6° when the molar ratio of ―OH increased to 19.4%.
To improve the hydrophilic properties of poly(propylene carbonate) (PPC), hydroxyl-functionalized PPC (PPC-OH) were prepared by two steps. First, PPC containing o-nitrobenzyl (ONB) protecting groups (PPC-ONB) were synthesized by terpolymerization reactions of 2-{[(2-nitrophenyl)methoxy]-methyl}oxirane (monomer a ), propylene oxide (PO), and CO2 over SalenCo(III)Cl/bis(triphenylphosphine)iminium chloride (PPNCl) catalyst system. 1H-NMR result showed that the PPC-ONB was a random copolymer with monomer a randomly inserted. Then PPC-OH were obtained with the removal of o-nitrobenzyl (ONB) protecting groups under ultraviolet (UV) irradiation. PPC-ONB were synthesized with various feed ratios of the monomer a and different reaction time. Based on the analysis of 1H-NMR, 13C-NMR, gel permeation chromatography (GPC), and differential scanning calorimeter (DSC), SalenCo(III)Cl catalyst performed high reactivity and high selectivity (> 94%). The polycarbonate exhibited excellent regioselectivity and perfect alternating copolymerization of CO2 and PO with the carbonate linkages up to 98%, and the head-to-tail linkage (HT) up to 99%. With the increase of the feed ratios of the monomer a , the polymer ratio of the monomer a increased to 19.4% without sacrificing the reactive activity, while the molecular weight (Mn) decreased slightly owing to the better reactivity of monomer a . The glass transition temperatures (Tg) were in the range of 35.7 − 38.9 °C. The kinetics of deprotection by UV irradiation proved that the ONB protecting groups could be carried out efficiently within minutes. And the characterization of polymer by 1H-NMR, Fourier transform infrared spectrometer (FTIR) and GPC showed that the ONB protecting groups were removed and the ―OH was observed. Meanwhile, no degradation of polymer backbone occurred. The contact angle (CA) measurement of PPC-ONB and PPC-OH displayed a difference in hydrophilia. The hydrophilia of PPC-OH has been greatly improved compared with PPC-ONB due to the increase in polarity, and the CA of PPC-OH decreased from 78.3° to 58.6° when the molar ratio of ―OH increased to 19.4%.
2019, 50(11): 1202-1210
doi: 10.11777/j.issn1000-3304.2019.19064
Abstract:
It is a traditional method to improve the thermal conductivity of matrix by adding fillers. However, it is a great challenge to construct a dense heat conduction network in composite material. The current researches on building thermal conductive network is to combine different fillers through structure design for achieving high thermal conductivity with the lowest possible filler content. Due to the electrical insulation requirements of electronic equipment, hexagonal boron nitride (h-BN) has been extensively studied as an inorganic thermal conductive filler. It has a layer structure that shows a relatively high TC of 300 W·m–1·K–1 in the h-BN planar direction. In this study, the foam was introduced into the epoxy resin as a skeleton, and thermal conductive network was constructed by immersing the BN/E51 mixture into the foam. By comparing the hot deformation behavior of two kinds of foams with different structures and compositions: polyurethane foam (PF) and nano-melamine (melamine) foam (MF), epoxy resin-based composites with high thermal conductivity were obtained by hot press curing under the right compression ratio. PF has a large single arm size and good elastic deformation ability, but it is easy to become a barrier between BN, which is bad for forming thermal conductive path after compression. However, MF has a small single arm size and can be broken into four needle-like scaffold structures after compression. The needle-like scaffold structure promotes the good dispersion of BN, and finally forms a thermal path of BN throughout the material, which plays a key role in improving the thermal conductivity of the composite. As a result, MF-BN/E51 showed an excellent thermal conductivity of 3.88 W·m–1·K–1 at 41 wt% BN load when the degree of hot pressing was 90%. It provides a new way for the composites to achieve a higher thermal conductivity with a less filler load.
It is a traditional method to improve the thermal conductivity of matrix by adding fillers. However, it is a great challenge to construct a dense heat conduction network in composite material. The current researches on building thermal conductive network is to combine different fillers through structure design for achieving high thermal conductivity with the lowest possible filler content. Due to the electrical insulation requirements of electronic equipment, hexagonal boron nitride (h-BN) has been extensively studied as an inorganic thermal conductive filler. It has a layer structure that shows a relatively high TC of 300 W·m–1·K–1 in the h-BN planar direction. In this study, the foam was introduced into the epoxy resin as a skeleton, and thermal conductive network was constructed by immersing the BN/E51 mixture into the foam. By comparing the hot deformation behavior of two kinds of foams with different structures and compositions: polyurethane foam (PF) and nano-melamine (melamine) foam (MF), epoxy resin-based composites with high thermal conductivity were obtained by hot press curing under the right compression ratio. PF has a large single arm size and good elastic deformation ability, but it is easy to become a barrier between BN, which is bad for forming thermal conductive path after compression. However, MF has a small single arm size and can be broken into four needle-like scaffold structures after compression. The needle-like scaffold structure promotes the good dispersion of BN, and finally forms a thermal path of BN throughout the material, which plays a key role in improving the thermal conductivity of the composite. As a result, MF-BN/E51 showed an excellent thermal conductivity of 3.88 W·m–1·K–1 at 41 wt% BN load when the degree of hot pressing was 90%. It provides a new way for the composites to achieve a higher thermal conductivity with a less filler load.
2019, 50(11): 1211-1219
doi: 10.11777/j.issn1000-3304.2019.19076
Abstract:
We developped a material genome approach to accelerate the design and synthesis of novel heat-resistant silicon-containing arylacetylene resins. The material genome approach is based on the consideration that silicon-containing arylacetylene resins can be regard as a combination of silane and diyne units which can be defined as genes used for combination screening. The approach presented here contains two steps. In the first step, various kinds of diynes were collected from the chemical database as candidate structures; the bond dissociation energy (BDE) reflecting heat resistance of resins was calculated; the candidate structures were preliminarily screened with the criteria of BDE; and finally 16 diynes with high BDE were obtained. In the second step, LUMO-HOMO and 50% decomposition temperature (Td50) were calculated by density functional theory and molecular connection index method, respectively; and the optimized gene was obtained out of 16 candidate structures. The screened resin is poly(diphenylsilylene-ethynylene-naphthalene-ethynylene) (abbreviated as PSNP) containing the gene of 2,7-diethynylnaphthalene. To verify the screened results, we first synthsized the PSNP by Sonogashira coupling of dichlorodiphenylsilane and 2,7-diethynylnaphthalene. The molecular structure of PSNP resin was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR). The curing process of PSNP resin was studied by differential scanning calorimetry (DSC). The results show that the curing peak temperature (Tpeak) of PSNP and the enthalpy of exothermic reaction are 212 °C and 173.8 J/g, respectively, which are lower than those of traditional poly(silylene-acetylenearyleneacetylene) resin (PSA). The cured PSNP resin exhibits excellent heat-resistance, where the 5% decomposition temperature (Td5) of the cured PSNP resin is 561 °C. The properties of the resin are consistent with the theoretical design results, which confirms the validity of material genome method for structural screening of new silicon-containing arylacetylene resins.
We developped a material genome approach to accelerate the design and synthesis of novel heat-resistant silicon-containing arylacetylene resins. The material genome approach is based on the consideration that silicon-containing arylacetylene resins can be regard as a combination of silane and diyne units which can be defined as genes used for combination screening. The approach presented here contains two steps. In the first step, various kinds of diynes were collected from the chemical database as candidate structures; the bond dissociation energy (BDE) reflecting heat resistance of resins was calculated; the candidate structures were preliminarily screened with the criteria of BDE; and finally 16 diynes with high BDE were obtained. In the second step, LUMO-HOMO and 50% decomposition temperature (Td50) were calculated by density functional theory and molecular connection index method, respectively; and the optimized gene was obtained out of 16 candidate structures. The screened resin is poly(diphenylsilylene-ethynylene-naphthalene-ethynylene) (abbreviated as PSNP) containing the gene of 2,7-diethynylnaphthalene. To verify the screened results, we first synthsized the PSNP by Sonogashira coupling of dichlorodiphenylsilane and 2,7-diethynylnaphthalene. The molecular structure of PSNP resin was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR). The curing process of PSNP resin was studied by differential scanning calorimetry (DSC). The results show that the curing peak temperature (Tpeak) of PSNP and the enthalpy of exothermic reaction are 212 °C and 173.8 J/g, respectively, which are lower than those of traditional poly(silylene-acetylenearyleneacetylene) resin (PSA). The cured PSNP resin exhibits excellent heat-resistance, where the 5% decomposition temperature (Td5) of the cured PSNP resin is 561 °C. The properties of the resin are consistent with the theoretical design results, which confirms the validity of material genome method for structural screening of new silicon-containing arylacetylene resins.
2019, 50(11): 1220-1228
doi: 10.11777/j.issn1000-3304.2019.19072
Abstract:
The phase behavior of diblock copolymer AB/homopolymer C blends in solution was studied by simulated annealing method. The study was focused on the compatibilization between the homopolymer and the copolymer with repulsive interactions due to the addition of solvent. We investigated the amount of solvent (characterized by the concentration of the polymer segments Φ), the volume fraction fc of the homopolymer C, the ratio of homopolymer chain length to the copolymer chain length X, the repulsion between C and A or B segments, εAC and εBC, and the attraction between solvent and C on the phase behavior of the blending system. We built phase diagrams in the space of Φ and fc at different X. Studies have shown that when X is less than 0.5, and the values of εAC and εBC are not very large, the addition of solvent strongly selective to A and C segments can improve the compatibility of the system. In solution, lamellae, gyroids, cylinders in layers, core-shell cylinders and cylindrical structures are formed. Moreover, the structure of cylinders in layers has not been observed in the neat diblock copolymer system. C-segments are distributed at the interfaces between A/B domains at high Φ region, while they are inside the A domain at low Φ region. Short homopolymer chains are easily compatible with diblock copolymers. Macroscopic phase separation has taken place in long homopolymer chains even with a small amount of homopolymer added. Moreover, increasing the values of εAC and εBC will reduce the compatibility of the system. The transformation between different phases and that from microphase separation to macrophase separation are the results of the competition between the energy and entropy of the system. The macrophase separation in the solution system is different from that in the melt system. Some C-segments are at the interface of AB domains to reduce the contact between A and B segments in the solution system, while all C-segments are separated from the AB domains in the melts.
The phase behavior of diblock copolymer AB/homopolymer C blends in solution was studied by simulated annealing method. The study was focused on the compatibilization between the homopolymer and the copolymer with repulsive interactions due to the addition of solvent. We investigated the amount of solvent (characterized by the concentration of the polymer segments Φ), the volume fraction fc of the homopolymer C, the ratio of homopolymer chain length to the copolymer chain length X, the repulsion between C and A or B segments, εAC and εBC, and the attraction between solvent and C on the phase behavior of the blending system. We built phase diagrams in the space of Φ and fc at different X. Studies have shown that when X is less than 0.5, and the values of εAC and εBC are not very large, the addition of solvent strongly selective to A and C segments can improve the compatibility of the system. In solution, lamellae, gyroids, cylinders in layers, core-shell cylinders and cylindrical structures are formed. Moreover, the structure of cylinders in layers has not been observed in the neat diblock copolymer system. C-segments are distributed at the interfaces between A/B domains at high Φ region, while they are inside the A domain at low Φ region. Short homopolymer chains are easily compatible with diblock copolymers. Macroscopic phase separation has taken place in long homopolymer chains even with a small amount of homopolymer added. Moreover, increasing the values of εAC and εBC will reduce the compatibility of the system. The transformation between different phases and that from microphase separation to macrophase separation are the results of the competition between the energy and entropy of the system. The macrophase separation in the solution system is different from that in the melt system. Some C-segments are at the interface of AB domains to reduce the contact between A and B segments in the solution system, while all C-segments are separated from the AB domains in the melts.
2019, 50(11): 1229-1238
doi: 10.11777/j.issn1000-3304.2019.19074
Abstract:
The dynamical and conformational properties of individual ring polymers with different chain lengths are investigated in Poiseuille flow through a tube using a hybrid mesoscale hydrodynamic simulation method, and migration behaviors are compared with those of linear chains. As the flow strength is increased, the ring chains migrate towards the centerline of the tube when the hydrodynamic interactions are included, but towards the tube wall when the hydrodynamic interactions are switched off. By analyzing the radial center-of-mass distribution function and the width of the distribution function of the ring chains, our studies reveal that the migration towards the centerline of the tube should be attributed to the hydrodynamic interactions rather than to the shear gradient in the Poiseuille flow. With the increase of flow intensity, the ring chains stretched more along the flow direction and shrunk smaller along the radial direction, independent of the location of their center-of-mass across the tube. When the hydrodynamic interactions are switched off, the extension along the flow direction and the shrinkage along the radial direction of the ring polymers are more pronounced than those with the hydrodynamic interactions. For a given flow strength, the longer the ring chain is, the eaiser it is to concentrate around the center of the tube due to the stronger hydrodynamic interactions between the chain and the tube wall, and the resulting distribution structure transits from the platform to the bimodal, and finally to the single-peaked with increasing chain length. By comparing the center-of-mass distributions and the structural properties between the ring and linear chains with the same chain length or the equilibrium radius of gyration, our simulation results show that the linear chains exhibit a more stretched conformation along the flow direction than the ring polymer chains, leading to the outward migration with a lower number density in the tube center.
The dynamical and conformational properties of individual ring polymers with different chain lengths are investigated in Poiseuille flow through a tube using a hybrid mesoscale hydrodynamic simulation method, and migration behaviors are compared with those of linear chains. As the flow strength is increased, the ring chains migrate towards the centerline of the tube when the hydrodynamic interactions are included, but towards the tube wall when the hydrodynamic interactions are switched off. By analyzing the radial center-of-mass distribution function and the width of the distribution function of the ring chains, our studies reveal that the migration towards the centerline of the tube should be attributed to the hydrodynamic interactions rather than to the shear gradient in the Poiseuille flow. With the increase of flow intensity, the ring chains stretched more along the flow direction and shrunk smaller along the radial direction, independent of the location of their center-of-mass across the tube. When the hydrodynamic interactions are switched off, the extension along the flow direction and the shrinkage along the radial direction of the ring polymers are more pronounced than those with the hydrodynamic interactions. For a given flow strength, the longer the ring chain is, the eaiser it is to concentrate around the center of the tube due to the stronger hydrodynamic interactions between the chain and the tube wall, and the resulting distribution structure transits from the platform to the bimodal, and finally to the single-peaked with increasing chain length. By comparing the center-of-mass distributions and the structural properties between the ring and linear chains with the same chain length or the equilibrium radius of gyration, our simulation results show that the linear chains exhibit a more stretched conformation along the flow direction than the ring polymer chains, leading to the outward migration with a lower number density in the tube center.
