A mesogen-jacketed liquid crystal polymer,poly{2,5 -bis［(4′-hexyloxyphenyl)oxycarbonyl］styrene}(PHPCS),with number-average d molecular weight of 1.28×１０5 and polydispersity of 1.48 was prepared vi a 2,2,6,6 ...A mesogen-jacketed liquid crystal polymer,poly{2,5 -bis［(4′-hexyloxyphenyl)oxycarbonyl］styrene}(PHPCS),with number-average d molecular weight of 1.28×１０5 and polydispersity of 1.48 was prepared vi a 2,2,6,6 -tetramethyl-piperidinyloxy mediated free radical polymerization.The thermotr opic behavior was studied by a combination of differential scanning calorimetry, thermogravimetry,polarized optical microscope and wide-angle X-ray diffracti on.PHPCS was not crystalline over the entire temperature region studied.On hea ting,PHPCS first became an isotropic melt at glass transition temperature (T g) and then a mesophase at temperatures much higher than T g.On subseq uent cooling,the formed ordered phase disappeared above T g.Contrary to t heoretical predictions and previous experimental observations,the transition fr om isotropic melt to liquid crystalline phase was an endothermic process and th e order-disorder transition took place with concurrence of heat release.展开更多
This paper describes the synthesis and free radical polymerization of 2,5 bis(4′ alkyloxyphenyl)styrene(M n ) for mesogen jacketed liquid crystal polymers(MJLCPs), where p terphenyl subsituted by alkoxy groups at bot...This paper describes the synthesis and free radical polymerization of 2,5 bis(4′ alkyloxyphenyl)styrene(M n ) for mesogen jacketed liquid crystal polymers(MJLCPs), where p terphenyl subsituted by alkoxy groups at both ends was used as mesogenic unit. Because of the absence of the polar linkage groups, such as —COO— or —CONH— as employed in the previous reported MJLCPs, M n is believed to be polymerized easily by both free radical polymerization and ionic polymerization. The chemical structure of M n was proved by 1H NMR, mass spectrometry and elementary analysis. Their phase transition and liquid crystallinity were characterized by DSC and POM. Although M 1, M 2, M 3 and M 4 exhibited monotropic nematic mesophase, M 5 displayed enantiotropic nematic mesophase presumably because of its decreased melting transition temperature. All monomers were easily polymerized to moderately high molecular weight polymers. At elevated temperature above T g, poly[2,5 bis(4′ alkoxyphenyl)styrene] showed a very stable mesophase. The formed birefrigence did not disappear until thermal decomposition started. Compared to other MJLCPs, the polymers reported here have much higher thermal stability. [WT5HZ]展开更多
Discrete nano-aggregates of a poly(ethylene oxide)-b-polybutadiene diblock copolymer (PEO-b-PB) were obtained by self-assembling of the copolymer in a selective solvent of PB followed by the shell cross-linking.The av...Discrete nano-aggregates of a poly(ethylene oxide)-b-polybutadiene diblock copolymer (PEO-b-PB) were obtained by self-assembling of the copolymer in a selective solvent of PB followed by the shell cross-linking.The average behaviors of the PEO crystallization and melting confined within the nano-structured aggregates were studied by differential scanning calorimetry experiments.The experiments demonstrated that the confinement effect arisen from the shells could be tuned by adjusting the degree of PB cross-linking.For the deeply cross-linked sample,the individual particles only crystallized at very low crystallization temperature (T c),wherein the homogenous primary nucleation determined the crystallization rate.For the lightly cross-linked sample,the confinement effect is T c dependent.When T c exceeded 42℃,the lightly cross-linked sample possessed a higher melting temperature and a lower crystallinity compared with the pure PEO-b-PB.展开更多
To avoid the damage to catalytic system in ATRP by the carboxyl groups in vinyl benzoic acid, a well defined poly( p vinyl benzoic acid) was synthesized via ATRP in the tertiary butyl ester form. The ATRP of t butyl p...To avoid the damage to catalytic system in ATRP by the carboxyl groups in vinyl benzoic acid, a well defined poly( p vinyl benzoic acid) was synthesized via ATRP in the tertiary butyl ester form. The ATRP of t butyl p vinyl benzoate ( t BVB) was studied kinetically. The results showed that t BVB can be polymerized in a controlled way by ATRP. It was found that the polymerization rate of t BVB is much faster than that of St, meaning that the electron withdrawing ester group affects the polymerization obviously. Well defined diblock copolymers of St and t BVB were prepared by using bromo terminated PBVBs as macroinitiators via ATRP. After removal of the t butyl group by hydrolysis, well defined amphiphilic diblock copolymers of styrene and p vinyl benzoic acid (PSt b PBVA) were obtained.展开更多
The melts of a series of low molecular weight poly（ethylene oxide）（PEO） fractions on mica surfaces were studied by atomic force microscopy（AFM） and X-ray reflectivity（XRR） measurement.The PEO ultrathin films w...The melts of a series of low molecular weight poly（ethylene oxide）（PEO） fractions on mica surfaces were studied by atomic force microscopy（AFM） and X-ray reflectivity（XRR） measurement.The PEO ultrathin films were obtained via static dilute solution casting.Different from the melts of the PEO with both methoxyl（（—OCH3）） end groups that are dewetted on the mica surface,a pseudo-dewetting phenomenon of the PEO melts was observed when either one end group of the PEOs becomes hydroxyl（—OH） or both are hydroxyl groups.The wetting layer thicknesses of the pseudo-dewetted melts were measured to be 4.5～4.7 nm,independent on the molecular weight and the end groups of PEOs.However,the PEO melt droplets on the wetting layer varied from spherical caps with relatively high contact angle to irregular shapes with relatively low contact angle when increasing the molecular weight and the hydrophobicity of end groups of PEOs.展开更多
文摘A mesogen-jacketed liquid crystal polymer,poly{2,5 -bis［(4′-hexyloxyphenyl)oxycarbonyl］styrene}(PHPCS),with number-average d molecular weight of 1.28×１０5 and polydispersity of 1.48 was prepared vi a 2,2,6,6 -tetramethyl-piperidinyloxy mediated free radical polymerization.The thermotr opic behavior was studied by a combination of differential scanning calorimetry, thermogravimetry,polarized optical microscope and wide-angle X-ray diffracti on.PHPCS was not crystalline over the entire temperature region studied.On hea ting,PHPCS first became an isotropic melt at glass transition temperature (T g) and then a mesophase at temperatures much higher than T g.On subseq uent cooling,the formed ordered phase disappeared above T g.Contrary to t heoretical predictions and previous experimental observations,the transition fr om isotropic melt to liquid crystalline phase was an endothermic process and th e order-disorder transition took place with concurrence of heat release.
文摘This paper describes the synthesis and free radical polymerization of 2,5 bis(4′ alkyloxyphenyl)styrene(M n ) for mesogen jacketed liquid crystal polymers(MJLCPs), where p terphenyl subsituted by alkoxy groups at both ends was used as mesogenic unit. Because of the absence of the polar linkage groups, such as —COO— or —CONH— as employed in the previous reported MJLCPs, M n is believed to be polymerized easily by both free radical polymerization and ionic polymerization. The chemical structure of M n was proved by 1H NMR, mass spectrometry and elementary analysis. Their phase transition and liquid crystallinity were characterized by DSC and POM. Although M 1, M 2, M 3 and M 4 exhibited monotropic nematic mesophase, M 5 displayed enantiotropic nematic mesophase presumably because of its decreased melting transition temperature. All monomers were easily polymerized to moderately high molecular weight polymers. At elevated temperature above T g, poly[2,5 bis(4′ alkoxyphenyl)styrene] showed a very stable mesophase. The formed birefrigence did not disappear until thermal decomposition started. Compared to other MJLCPs, the polymers reported here have much higher thermal stability. [WT5HZ]
文摘Discrete nano-aggregates of a poly(ethylene oxide)-b-polybutadiene diblock copolymer (PEO-b-PB) were obtained by self-assembling of the copolymer in a selective solvent of PB followed by the shell cross-linking.The average behaviors of the PEO crystallization and melting confined within the nano-structured aggregates were studied by differential scanning calorimetry experiments.The experiments demonstrated that the confinement effect arisen from the shells could be tuned by adjusting the degree of PB cross-linking.For the deeply cross-linked sample,the individual particles only crystallized at very low crystallization temperature (T c),wherein the homogenous primary nucleation determined the crystallization rate.For the lightly cross-linked sample,the confinement effect is T c dependent.When T c exceeded 42℃,the lightly cross-linked sample possessed a higher melting temperature and a lower crystallinity compared with the pure PEO-b-PB.
文摘To avoid the damage to catalytic system in ATRP by the carboxyl groups in vinyl benzoic acid, a well defined poly( p vinyl benzoic acid) was synthesized via ATRP in the tertiary butyl ester form. The ATRP of t butyl p vinyl benzoate ( t BVB) was studied kinetically. The results showed that t BVB can be polymerized in a controlled way by ATRP. It was found that the polymerization rate of t BVB is much faster than that of St, meaning that the electron withdrawing ester group affects the polymerization obviously. Well defined diblock copolymers of St and t BVB were prepared by using bromo terminated PBVBs as macroinitiators via ATRP. After removal of the t butyl group by hydrolysis, well defined amphiphilic diblock copolymers of styrene and p vinyl benzoic acid (PSt b PBVA) were obtained.
文摘The melts of a series of low molecular weight poly（ethylene oxide）（PEO） fractions on mica surfaces were studied by atomic force microscopy（AFM） and X-ray reflectivity（XRR） measurement.The PEO ultrathin films were obtained via static dilute solution casting.Different from the melts of the PEO with both methoxyl（（—OCH3）） end groups that are dewetted on the mica surface,a pseudo-dewetting phenomenon of the PEO melts was observed when either one end group of the PEOs becomes hydroxyl（—OH） or both are hydroxyl groups.The wetting layer thicknesses of the pseudo-dewetted melts were measured to be 4.5～4.7 nm,independent on the molecular weight and the end groups of PEOs.However,the PEO melt droplets on the wetting layer varied from spherical caps with relatively high contact angle to irregular shapes with relatively low contact angle when increasing the molecular weight and the hydrophobicity of end groups of PEOs.
