利用动态光散射、透射电镜研究了嵌段共聚物聚苯乙烯 b 聚丙烯酸(PS b PAA)与均聚物聚苯乙烯(PS)在选择性溶剂水中的自组装行为.由于均聚物PS与PS嵌段具有相同的结构单元,均聚物PS参与胶束的形成,和嵌段共聚物的PS链段一同组成胶束的核...利用动态光散射、透射电镜研究了嵌段共聚物聚苯乙烯 b 聚丙烯酸(PS b PAA)与均聚物聚苯乙烯(PS)在选择性溶剂水中的自组装行为.由于均聚物PS与PS嵌段具有相同的结构单元,均聚物PS参与胶束的形成,和嵌段共聚物的PS链段一同组成胶束的核;在适当的均聚物分子量和含量条件下,PS b PAA PS可以自组装形成单分散的纳米胶束;通过改变体系中均聚物PS的分子量和含量可在较大范围内调变胶束的尺寸.展开更多
The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections （regu- lar triangles, squares, and ellipses） is investigated using a simulated annealing technique. In th...The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections （regu- lar triangles, squares, and ellipses） is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel＇s cross section. In the case of triangle-shaped cross sections, stacked parallel lamel- lae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end- to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels.展开更多
Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles ...Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.展开更多
Morphological transformations of amphiphilic AB diblock copolymers in mixtures of a common solvent （S1） and a selective solvent （S2） for the B block are studied using the simulated annealing method. We focus on th...Morphological transformations of amphiphilic AB diblock copolymers in mixtures of a common solvent （S1） and a selective solvent （S2） for the B block are studied using the simulated annealing method. We focus on the morphological transformation depending on the fraction of the selective solvent Cs2, the concentration of the polymer Cp, and the polymers-solvent interactions εij （i = A, B; j = S1, S2）. Morphology diagrams are constructed as functions of Cp, Cs2, and/or εAs2. The copolymer morpho- logical sequence from dissolved → sphere → rod → ring/cage → vesicle is obtained upon increasing Cs2 at a fixed Cv. This morphology sequence is consistent with previous experimental observations. It is found that the selectivity of the selective solvent affects the self-assembled microstructure signifi- cantly. In particular, when tile interaction εBS2 is negative, aggregates of stacked lamellae dominate the diagram. The mechanisms of aggregate transformation and the formation of stacked lamellar ag- gregates are discussed by analyzing variations of the average contact numbers of the A or B monomers with monomers and with molecules of the two types of solvent, as well as the mean square end-to-end distances of chains. It is found that the basic morphological sequence of spheres to rods to vesicles and the stacked lamellar aggregates result from competition between the interfacial energy and the chain conformational entropy. Analysis of the vesicle structure reveals that the vesicle size increases with increasing Cp or with decreasing Cs2, but remains almost unchanged with variations in εAS2.展开更多
Self assembly of an amphiphilic diblock copolymer polysyrene b polyvinylbenzoic acid in ethanol,which is a selective solvent for the polybenzoic acid segment was studied by means of transmission electron microscopy.Th...Self assembly of an amphiphilic diblock copolymer polysyrene b polyvinylbenzoic acid in ethanol,which is a selective solvent for the polybenzoic acid segment was studied by means of transmission electron microscopy.The diblock copolymers can self assemble into nano scale aggregates with polystyrene segment as the core and polyvinylbenzoic acid segment as the corona.The morphology of the aggregates is mainly controlled by the ratio of the two segment of the diblock copolymer.As the content of the ethanol insoluble polystyrene segment increased,the morphology can be changed from spheres to rods.The diameter of the aggregates increases slightly with concentration and decreases with the addition of CoCl 2 salt.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
文摘利用动态光散射、透射电镜研究了嵌段共聚物聚苯乙烯 b 聚丙烯酸(PS b PAA)与均聚物聚苯乙烯(PS)在选择性溶剂水中的自组装行为.由于均聚物PS与PS嵌段具有相同的结构单元,均聚物PS参与胶束的形成,和嵌段共聚物的PS链段一同组成胶束的核;在适当的均聚物分子量和含量条件下,PS b PAA PS可以自组装形成单分散的纳米胶束;通过改变体系中均聚物PS的分子量和含量可在较大范围内调变胶束的尺寸.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11204215,51302187,20990234,20925414,21204040,and 91227121)the Natural Science Foundation of Tianjin City,China(Grant Nos.12JCYBJC32500 and 14JCZDJC32100)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT)(Grant No.IRT1257)the 111 Project.A.C.Shi gratefully acknowledges the supports from the Natural Sciences and Engineering Research Council(NSERC)of Canada
文摘The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections （regu- lar triangles, squares, and ellipses） is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel＇s cross section. In the case of triangle-shaped cross sections, stacked parallel lamel- lae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end- to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels.
文摘Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 21204040, 20904027, 21574071, 21528401, 20925414, and 91227121）, the Pro- gram for Changjiang Scholars and Innovative Research Team in University of China （PCSIRT） （Grant No. IRT1257）, and the 111 Project （Grant No. B16027）.
文摘Morphological transformations of amphiphilic AB diblock copolymers in mixtures of a common solvent （S1） and a selective solvent （S2） for the B block are studied using the simulated annealing method. We focus on the morphological transformation depending on the fraction of the selective solvent Cs2, the concentration of the polymer Cp, and the polymers-solvent interactions εij （i = A, B; j = S1, S2）. Morphology diagrams are constructed as functions of Cp, Cs2, and/or εAs2. The copolymer morpho- logical sequence from dissolved → sphere → rod → ring/cage → vesicle is obtained upon increasing Cs2 at a fixed Cv. This morphology sequence is consistent with previous experimental observations. It is found that the selectivity of the selective solvent affects the self-assembled microstructure signifi- cantly. In particular, when tile interaction εBS2 is negative, aggregates of stacked lamellae dominate the diagram. The mechanisms of aggregate transformation and the formation of stacked lamellar ag- gregates are discussed by analyzing variations of the average contact numbers of the A or B monomers with monomers and with molecules of the two types of solvent, as well as the mean square end-to-end distances of chains. It is found that the basic morphological sequence of spheres to rods to vesicles and the stacked lamellar aggregates result from competition between the interfacial energy and the chain conformational entropy. Analysis of the vesicle structure reveals that the vesicle size increases with increasing Cp or with decreasing Cs2, but remains almost unchanged with variations in εAS2.
文摘Self assembly of an amphiphilic diblock copolymer polysyrene b polyvinylbenzoic acid in ethanol,which is a selective solvent for the polybenzoic acid segment was studied by means of transmission electron microscopy.The diblock copolymers can self assemble into nano scale aggregates with polystyrene segment as the core and polyvinylbenzoic acid segment as the corona.The morphology of the aggregates is mainly controlled by the ratio of the two segment of the diblock copolymer.As the content of the ethanol insoluble polystyrene segment increased,the morphology can be changed from spheres to rods.The diameter of the aggregates increases slightly with concentration and decreases with the addition of CoCl 2 salt.
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.
