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2016 Volume 34 Issue 8
2016, 34(8): 919-932
doi: 10.1007/s10118-016-1810-8
Abstract:
A series of mono-functional benzoxazine monomers with different N-substituents were synthesized from phenol, formaldehyde, and various amines (ammonia, methylamine, n-butylamine, dodecylamine), named P-am, P-m, P-b, and P-da, respectively. The surface properties of these polybenzoxazine films were proven by contact angle measurements. The hydrogen bond network of the polybenzoxazine systems was studied using the FTIR spectra. And the results showed that the surface free energy increased with increasing the fraction of intermolecular hydrogen bonding when the N-substituent was an alkyl chain. However, the rule was not suitable when the N-substituent was H. That was because there was one more kind of intramolecular hydrogen bond in the poly(P-am). Based on these findings, we proposed that both the N-substituent alkyl group and the fraction of intermolecular hydrogen bonding had effects on the surface free energy.
A series of mono-functional benzoxazine monomers with different N-substituents were synthesized from phenol, formaldehyde, and various amines (ammonia, methylamine, n-butylamine, dodecylamine), named P-am, P-m, P-b, and P-da, respectively. The surface properties of these polybenzoxazine films were proven by contact angle measurements. The hydrogen bond network of the polybenzoxazine systems was studied using the FTIR spectra. And the results showed that the surface free energy increased with increasing the fraction of intermolecular hydrogen bonding when the N-substituent was an alkyl chain. However, the rule was not suitable when the N-substituent was H. That was because there was one more kind of intramolecular hydrogen bond in the poly(P-am). Based on these findings, we proposed that both the N-substituent alkyl group and the fraction of intermolecular hydrogen bonding had effects on the surface free energy.
2016, 34(8): 933-948
doi: 10.1007/s10118-016-1813-5
Abstract:
To improve the processability and thermal stability of polyimide, a series of novel phenylethynyl-endcapped oligoimides (PEPA-oligoimides) with calculated molecular weights (MnC) were successfully prepared from thermal imidization of 4, 4'-(9-fluorenylidene) dianiline (BAFL) as fluorenyl diamine, 4, 4'-oxy-diphthalic anhydride (ODPA) as aromatic dianhydride and 4-phenylethynylphthalic anhydride (4-PEPA) acted as reactive end-capping reagent at elevated temperatures. Experiment results indicated that the oligoimides were the mixtures of PEPA-endcapped oligomers with different degrees of polymerization characterized by MALDI-TOF mass spectra. The influence of chemical structures on the melt processabilities of the oligoimides, the thermal, dielectric and mechanical properties of the thermoset resins was studied. The typical oligoimide resin owned minimum melt viscosity of 0.2 Pa·s at around 310℃ and wide melting processing window, suitable for resin transfer molding (RTM). Besides, its corresponding thermal-cured polyimide resin possessed glass transition temperature (Tg) as high as 514℃. The dielectric constants of polyimide resins decreased from 3.15 to 2.80 by reducing the MnC. The mechanical properties of the polyimide neat resins were improved gradually with increasing MnC. Finally, the carbon fiber/polyimide (Cf/PI) composite laminates showed excellent mechanical strength retention rate at 350℃, might be long-term served at extremely high temperature in aerospace and aviation field.
To improve the processability and thermal stability of polyimide, a series of novel phenylethynyl-endcapped oligoimides (PEPA-oligoimides) with calculated molecular weights (MnC) were successfully prepared from thermal imidization of 4, 4'-(9-fluorenylidene) dianiline (BAFL) as fluorenyl diamine, 4, 4'-oxy-diphthalic anhydride (ODPA) as aromatic dianhydride and 4-phenylethynylphthalic anhydride (4-PEPA) acted as reactive end-capping reagent at elevated temperatures. Experiment results indicated that the oligoimides were the mixtures of PEPA-endcapped oligomers with different degrees of polymerization characterized by MALDI-TOF mass spectra. The influence of chemical structures on the melt processabilities of the oligoimides, the thermal, dielectric and mechanical properties of the thermoset resins was studied. The typical oligoimide resin owned minimum melt viscosity of 0.2 Pa·s at around 310℃ and wide melting processing window, suitable for resin transfer molding (RTM). Besides, its corresponding thermal-cured polyimide resin possessed glass transition temperature (Tg) as high as 514℃. The dielectric constants of polyimide resins decreased from 3.15 to 2.80 by reducing the MnC. The mechanical properties of the polyimide neat resins were improved gradually with increasing MnC. Finally, the carbon fiber/polyimide (Cf/PI) composite laminates showed excellent mechanical strength retention rate at 350℃, might be long-term served at extremely high temperature in aerospace and aviation field.
2016, 34(8): 949-964
doi: 10.1007/s10118-016-1807-3
Abstract:
Full polysaccharide crosslinked-chitosan membranes were prepared by crosslinking of chitosan with chitosan dialdehyde followed by reduction with sodium borohydride. Partially oxidized chitosan, generated from periodate oxidation of chitosan, was used as a crosslinker. The modulus values and elongation at break were increased with increasing the crosslinker weight ratio. The rheological measurements showed that depolymerization of chitosan can take place rapidly in the presence of the oxidizing agent. The weight reduction of crosslinked-chitosan membrane after 12 h, at pH=4 and pH=2 was found to be 85.0% and 90.0%, respectively. The structure of the crosslinked-chitosan and the silver nanocomposite were confirmed by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) reveals the presence of well-separated Ag nanoparticles with diameters in the range of 4-10 nm. The silver ion loading increases with increasing the silver ion concentration, and decreasing the crosslink density. The MBC/MIC ratio of 2.0, 2.0, and 1.0 was achieved for E. coli, S. aureus, and P. aeruginosa, respectively.
Full polysaccharide crosslinked-chitosan membranes were prepared by crosslinking of chitosan with chitosan dialdehyde followed by reduction with sodium borohydride. Partially oxidized chitosan, generated from periodate oxidation of chitosan, was used as a crosslinker. The modulus values and elongation at break were increased with increasing the crosslinker weight ratio. The rheological measurements showed that depolymerization of chitosan can take place rapidly in the presence of the oxidizing agent. The weight reduction of crosslinked-chitosan membrane after 12 h, at pH=4 and pH=2 was found to be 85.0% and 90.0%, respectively. The structure of the crosslinked-chitosan and the silver nanocomposite were confirmed by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) reveals the presence of well-separated Ag nanoparticles with diameters in the range of 4-10 nm. The silver ion loading increases with increasing the silver ion concentration, and decreasing the crosslink density. The MBC/MIC ratio of 2.0, 2.0, and 1.0 was achieved for E. coli, S. aureus, and P. aeruginosa, respectively.
2016, 34(8): 965-980
doi: 10.1007/s10118-016-1817-1
Abstract:
A double thermoresponsive ABC-type triblock copolymer (poly(ethyleneglycol)-block-poly(2-(2-methoxyethoxy) ethyl methacrylate)-block-poly(2-(2-methoxy ethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate, PEG-b-PMEO2MA-b-P(MEO2MA-co-OEGMA)) was designed and synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer endowed a thermal-induced two-step phase transition at 29 and 39℃, corresponding to the thermosensitive properties of PMEO2MA and P(MEO2MA-co-OEGMA) segments, respectively. The two-step self-assembly of copolymer solutions was studied by UV transmittance measurement, dynamic light scattering (DLS), transmission electron microscopy (TEM) and so on. The triblock copolymers showed the distinct thermosensitive behavior with respect to transition temperatures, aggregate type and size, which was correlated to the degree of polymerization of thermosensitive blocks and the molar fraction of OEGMA in the P(MEO2MA-co-OEGMA) segments. In addition, micelles could further aggregate to form the hydrogel by the self-associate of PEG chains under the abduction of the concentration and temperature. The transition from sol to gel was investigated by a test tube inverting method and dynamic rheological measurement.
A double thermoresponsive ABC-type triblock copolymer (poly(ethyleneglycol)-block-poly(2-(2-methoxyethoxy) ethyl methacrylate)-block-poly(2-(2-methoxy ethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate, PEG-b-PMEO2MA-b-P(MEO2MA-co-OEGMA)) was designed and synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer endowed a thermal-induced two-step phase transition at 29 and 39℃, corresponding to the thermosensitive properties of PMEO2MA and P(MEO2MA-co-OEGMA) segments, respectively. The two-step self-assembly of copolymer solutions was studied by UV transmittance measurement, dynamic light scattering (DLS), transmission electron microscopy (TEM) and so on. The triblock copolymers showed the distinct thermosensitive behavior with respect to transition temperatures, aggregate type and size, which was correlated to the degree of polymerization of thermosensitive blocks and the molar fraction of OEGMA in the P(MEO2MA-co-OEGMA) segments. In addition, micelles could further aggregate to form the hydrogel by the self-associate of PEG chains under the abduction of the concentration and temperature. The transition from sol to gel was investigated by a test tube inverting method and dynamic rheological measurement.
2016, 34(8): 981-990
doi: 10.1007/s10118-016-1818-0
Abstract:
A benign approach for efficient preparation of poly(ether sulfone) (PES) (ηinh=0.10-0.31 dL·g-1) has been presented by using ionic liquid (IL)/zwitterion (ZI) as reaction medium. It has been found that the interaction between 4, 4'-dihydroxydiphenylsulfone (Bisphenol-S) and ZI at elevated temperatures results in efficient reduction of dehydration time, which is confirmed by TGA curves, melting point of the mixture and FTIR spectra. Furthermore, no agglomeration is observed at dehydration stage, which is attributed to the high solubility of Bisphenol-S dipotassium salt in IL/ZI. This also makes the polymerization temperature (150℃) much lower than a conventional method (220-300℃). In order to demonstrate the efficiency of IL/ZI as reaction medium, the polymerization was also performed in sulfolane under the same reaction condition as that in IL/ZI.
A benign approach for efficient preparation of poly(ether sulfone) (PES) (ηinh=0.10-0.31 dL·g-1) has been presented by using ionic liquid (IL)/zwitterion (ZI) as reaction medium. It has been found that the interaction between 4, 4'-dihydroxydiphenylsulfone (Bisphenol-S) and ZI at elevated temperatures results in efficient reduction of dehydration time, which is confirmed by TGA curves, melting point of the mixture and FTIR spectra. Furthermore, no agglomeration is observed at dehydration stage, which is attributed to the high solubility of Bisphenol-S dipotassium salt in IL/ZI. This also makes the polymerization temperature (150℃) much lower than a conventional method (220-300℃). In order to demonstrate the efficiency of IL/ZI as reaction medium, the polymerization was also performed in sulfolane under the same reaction condition as that in IL/ZI.
2016, 34(8): 991-1000
doi: 10.1007/s10118-016-1812-6
Abstract:
PA1012/calcium silicate whisker nanocomposites with contents of whisker ranging from 10 wt% to 40 wt%, are prepared by twin screw extruder without any additions of coupling agent. The effect of whisker on the matrix is analyzed by the studies of morphology, the mechanical properties, water absorption and thermal stabilities. SEM micrographs obviously demonstrate, even under the high filler content of 40 wt% and without surface treatment, calcium silicate whisker can be homogeneously dispersed in polyamide, directly leading to the enhanced mechanical properties. The mechanism of higher efficiency of reinforcement is needle-like shape whisker, having access to be intercalated, and mutual affinity caused by hydrogen bonding interaction between carbonyl group in polyamide chain and hydroxyl group in whisker surface. Both aspects attach matrix with excellent stress-transfer properties. In addition, with the assistance of whisker, the nanocomposite favors an improved water absorption as well as thermal stability, which is intimately associated with physical performance.
PA1012/calcium silicate whisker nanocomposites with contents of whisker ranging from 10 wt% to 40 wt%, are prepared by twin screw extruder without any additions of coupling agent. The effect of whisker on the matrix is analyzed by the studies of morphology, the mechanical properties, water absorption and thermal stabilities. SEM micrographs obviously demonstrate, even under the high filler content of 40 wt% and without surface treatment, calcium silicate whisker can be homogeneously dispersed in polyamide, directly leading to the enhanced mechanical properties. The mechanism of higher efficiency of reinforcement is needle-like shape whisker, having access to be intercalated, and mutual affinity caused by hydrogen bonding interaction between carbonyl group in polyamide chain and hydroxyl group in whisker surface. Both aspects attach matrix with excellent stress-transfer properties. In addition, with the assistance of whisker, the nanocomposite favors an improved water absorption as well as thermal stability, which is intimately associated with physical performance.
2016, 34(8): 1001-1013
doi: 10.1007/s10118-016-1814-4
Abstract:
In this article, crystalline morphology and molecular orientation of isotactic polypropylene (iPP), random copolymerized polypropylene (co-PP) and β-nucleating agent (β-NA) composites prepared by pressure vibration injection molding (PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and iPP molecular chains was beneficial for the mechanical improvement and the introduction of β-NA further improved the toughness of iPP. In addition, after applying the pressure vibration injection molding (PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of iPP/co-PP/β-NA composites prepared by PVIM were simultaneously improved compared to those of the pure iPP prepared by conventional injection molding (CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of iPP/co-PP composites through dynamic processing strategy.
In this article, crystalline morphology and molecular orientation of isotactic polypropylene (iPP), random copolymerized polypropylene (co-PP) and β-nucleating agent (β-NA) composites prepared by pressure vibration injection molding (PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and iPP molecular chains was beneficial for the mechanical improvement and the introduction of β-NA further improved the toughness of iPP. In addition, after applying the pressure vibration injection molding (PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of iPP/co-PP/β-NA composites prepared by PVIM were simultaneously improved compared to those of the pure iPP prepared by conventional injection molding (CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of iPP/co-PP composites through dynamic processing strategy.
2016, 34(8): 1014-1020
doi: 10.1007/s10118-016-1802-8
Abstract:
Starting from an initial sample of butene-1/ethylene copolymer with stable form Ⅰ', we examined the nucleation of different crystalline polymorphs (here metastable form Ⅱ and stable form Ⅰ') at different isothermal crystallization temperatures after being melted at different melt temperature (Tmelt). When Tmelt was just above the melting temperature (Tm) of the crystallites, self-seeding took place. There, residue crystallites served as nuclei leading to the crystallization of the same crystalline phase. When Tmelt was a few degrees above the Tm, self-seeding was disabled due to complete melting of the initial crystals. Upon crystallization, the selection of the different polymorphs in this random copolymer was found to depend on an interplay between the domain size of segregated long crystallizable sequences and the size and energy barrier of the critical nucleus of the respective crystalline forms. Our results provide a clear understanding of the polymorphs selection during crystallization of a random copolymer as well as homo-polymers under confinement.
Starting from an initial sample of butene-1/ethylene copolymer with stable form Ⅰ', we examined the nucleation of different crystalline polymorphs (here metastable form Ⅱ and stable form Ⅰ') at different isothermal crystallization temperatures after being melted at different melt temperature (Tmelt). When Tmelt was just above the melting temperature (Tm) of the crystallites, self-seeding took place. There, residue crystallites served as nuclei leading to the crystallization of the same crystalline phase. When Tmelt was a few degrees above the Tm, self-seeding was disabled due to complete melting of the initial crystals. Upon crystallization, the selection of the different polymorphs in this random copolymer was found to depend on an interplay between the domain size of segregated long crystallizable sequences and the size and energy barrier of the critical nucleus of the respective crystalline forms. Our results provide a clear understanding of the polymorphs selection during crystallization of a random copolymer as well as homo-polymers under confinement.
2016, 34(8): 1021-1031
doi: 10.1007/s10118-016-1816-2
Abstract:
Hexagonal boron nitride nanosheets (BNNSs) can work as a more efficient nucleating agent for two polyesters compared to graphene. Studies on the crystallization and dewetting processes of two polyesters, poly(butylene succinate) and poly(butylene adipate), on the two substrate surfaces prove that the interaction between BNNSs and the polyesters is stronger than that between graphene and the polyesters. This strong interaction induces the pre-ordered conformation of molten PBA which has been identified by the in situ FTIR spectra. Thus BNNSs possess higher nucleation property than graphene. Finally, a new polymer-substrate interaction induced nucleation mechanism was proposed to explain the nucleation efficiency difference between graphene and BNNSs.
Hexagonal boron nitride nanosheets (BNNSs) can work as a more efficient nucleating agent for two polyesters compared to graphene. Studies on the crystallization and dewetting processes of two polyesters, poly(butylene succinate) and poly(butylene adipate), on the two substrate surfaces prove that the interaction between BNNSs and the polyesters is stronger than that between graphene and the polyesters. This strong interaction induces the pre-ordered conformation of molten PBA which has been identified by the in situ FTIR spectra. Thus BNNSs possess higher nucleation property than graphene. Finally, a new polymer-substrate interaction induced nucleation mechanism was proposed to explain the nucleation efficiency difference between graphene and BNNSs.
2016, 34(8): 1032-1038
doi: 10.1007/s10118-016-1821-5
Abstract:
The effects of three types of electrically-inert fillers, calcium carbonate (CaCO3), talc and glass fiber (GF), on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly(m-xylene adipamide) (MXD6)/multiwalled carbon nanotube (MWCNT) composites are investigated. The electrical resistivity of MXD6/MWCNT composites is significantly reduced with the addition of inert fillers due to the volume-exclusion effect that leads to increased effective concentration of MWCNTs in MXD6 matrix and also due to improved MWCNT dispersion. The crystallization temperature of MXD6 increases with the addition of MWCNTs, indicating that MWCNTs can act as nucleating agent and induce crystallization of MXD6. The incorporation of inert fillers has no further effect on crystallization behavior of MXD6, but significantly improves the storage modulus of MXD6/MWCNT composite, demonstrating that CaCO3, talc and GF filled MXD6/MWCNT composites are very promising materials with not only improved electrical property but also excellent mechanical properties.
The effects of three types of electrically-inert fillers, calcium carbonate (CaCO3), talc and glass fiber (GF), on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly(m-xylene adipamide) (MXD6)/multiwalled carbon nanotube (MWCNT) composites are investigated. The electrical resistivity of MXD6/MWCNT composites is significantly reduced with the addition of inert fillers due to the volume-exclusion effect that leads to increased effective concentration of MWCNTs in MXD6 matrix and also due to improved MWCNT dispersion. The crystallization temperature of MXD6 increases with the addition of MWCNTs, indicating that MWCNTs can act as nucleating agent and induce crystallization of MXD6. The incorporation of inert fillers has no further effect on crystallization behavior of MXD6, but significantly improves the storage modulus of MXD6/MWCNT composite, demonstrating that CaCO3, talc and GF filled MXD6/MWCNT composites are very promising materials with not only improved electrical property but also excellent mechanical properties.
2016, 34(8): 1039-1046
doi: 10.1007/s10118-016-1815-3
Abstract:
Cross-linked PEG-based copolymers were obtained via synthesis of polyethylene glycol (PEG) and methoxy polyethylene glycol (MPEG) by the bridging and/or cross-linking agent of 2, 4-tolylene diisocyanate (TDI) and/or hexamethylene-1, 6-diisocyanate homopolymer (HDI trimer). The effects on the crystallization behaviors of the samples could be found with the changes in molecular weight of MC-PEG and molecular weight of SC-PEG in certain cross-linked density. It is revealed that the samples appear not to crystallize when the molecular weight of MC-PEG and SC-PEG are 1000 g/mol or less than that. The samples begin to crystallize when the molecular weight of either MC-PEG or SC-PEG reaches 2000 g/mol. The crystallinity of crystallized MC-PEG decreases with the increasing molecular weight of uncrystallized SC-PEG and the crystallinity of crystallized SC-PEG declines with the rise of molecular weight of uncrystallizable MC-PEG. The chains of SC-PEG (Mn=2000 g/mol) can fold and align easilier than those of MC-PEG (Mn=2000 g/mol), when the content of PEG is the same.
Cross-linked PEG-based copolymers were obtained via synthesis of polyethylene glycol (PEG) and methoxy polyethylene glycol (MPEG) by the bridging and/or cross-linking agent of 2, 4-tolylene diisocyanate (TDI) and/or hexamethylene-1, 6-diisocyanate homopolymer (HDI trimer). The effects on the crystallization behaviors of the samples could be found with the changes in molecular weight of MC-PEG and molecular weight of SC-PEG in certain cross-linked density. It is revealed that the samples appear not to crystallize when the molecular weight of MC-PEG and SC-PEG are 1000 g/mol or less than that. The samples begin to crystallize when the molecular weight of either MC-PEG or SC-PEG reaches 2000 g/mol. The crystallinity of crystallized MC-PEG decreases with the increasing molecular weight of uncrystallized SC-PEG and the crystallinity of crystallized SC-PEG declines with the rise of molecular weight of uncrystallizable MC-PEG. The chains of SC-PEG (Mn=2000 g/mol) can fold and align easilier than those of MC-PEG (Mn=2000 g/mol), when the content of PEG is the same.
