The conventional free radical polymerization(FRP) of multivinyl monomers(MVMs) inevitably leads to gelation even at low monomer conversion resulting in difficulties to control and monitor the reaction process. Flory a...The conventional free radical polymerization(FRP) of multivinyl monomers(MVMs) inevitably leads to gelation even at low monomer conversion resulting in difficulties to control and monitor the reaction process. Flory and Stockmayer(F-S theory)studied it based on two fundamental assumptions:(1) independent and equivalent vinyl groups;(2) no intramolecular cyclization.However, until now its applicability to FRP of MVMs(especially regarding the extent of intramolecular cyclization) is still controversial. In this paper, Monte Carlo simulations are used to study FRP of divinyl monomers by two kinetic models:with/without cyclization models. The results of the simulations are compared with the calculated gel points based on F-S theory and the experimental data. It is found that the intramolecular cyclization has a negligible impact on the polymerization process and the gel point before gelation, which are in agreement with the prediction by F-S theory, but the effect becomes significant above the gel points.展开更多
Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpenty...Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpentyloxy]phenyl}styrene （Ic）, （＋）-2,5-bis{4＇-[（S）-4＂- methylhexyloxy]phenyl}styrene （Id）, （-）-2,5-bis{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （le）, （＋）-2-/4＇-[（S）-l＂-methyl- propyloxy]phenyl}-5-{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （Ⅱa）, （-）-2-{4＇-[（R）-1＂-methylpropyloxy]phenyl}-5-{4＇- [（S）- 1 ＂-methylpropyloxy]phenyl } styrene （lib）, and （＋）-2- { 4＇-[（S）-2＂-methylbutyloxy]phenyl }-5- { 4＇-[（S）- 1＂-methylpropyl- oxy]phenyl}styrene （Ⅲ）, were synthesized and radically polymerized. These molecules were designed to further understand long-range chirality transfer in radical polymerization and to possibly tune the chiroptical properties of the polymers by varying the spatial configuration, position, and various combination of the stereogenic centers at the ends ofp-terphenyl pendants. The resultant polymers adopted helical conformations with a predominant screw sense. When the stereogenic centers ran away from the terphenyl group as in Ⅰb-d, the corresponding polymers changed the direction of optical rotation in an alternative way and showed no obvious stereomutation upon annealing in tetrahydrofuran. The two stereogenic centers of Ⅱa, Ⅱb, and Ⅲ acted concertedly in chiral induction, whereas those of la and Ie played a counteractive role. The five polymers derived from Ⅰa, Ⅰe, Ⅱa, Ⅱb, and Ⅲ underwent stereomutation when annealed in tetrahydrofuran. The polymers PIa-e had good thermal stability and high glass transition temperatures （Tgs）. They generated liquid crystalline phases at above Tgs that could be kept upon cooling, with the exception of Pie. This result was consistent with the extended helical structures.展开更多
基金supported by the National Natural Science Foundation of China(51573129)Science Foundation Ireland Principal Investigator Award(13/IA/1962)+1 种基金Investigator Award(12/IP/1688)Health Research Board(HRA-POR-2013-412)
文摘The conventional free radical polymerization(FRP) of multivinyl monomers(MVMs) inevitably leads to gelation even at low monomer conversion resulting in difficulties to control and monitor the reaction process. Flory and Stockmayer(F-S theory)studied it based on two fundamental assumptions:(1) independent and equivalent vinyl groups;(2) no intramolecular cyclization.However, until now its applicability to FRP of MVMs(especially regarding the extent of intramolecular cyclization) is still controversial. In this paper, Monte Carlo simulations are used to study FRP of divinyl monomers by two kinetic models:with/without cyclization models. The results of the simulations are compared with the calculated gel points based on F-S theory and the experimental data. It is found that the intramolecular cyclization has a negligible impact on the polymerization process and the gel point before gelation, which are in agreement with the prediction by F-S theory, but the effect becomes significant above the gel points.
基金supported by the National Natural Science Foundation of China(21274003)the Research Fund for Doctoral Program of Higher Education of Ministry of Education(20110001110084)
文摘Eight chiral vinylterphenyl monomers, （＋）-2,5-bis{4＇-[（S）-1＂-methylpropyloxy]phenyl}styrene （Ia）, （＋）-2,5-bis{4＇-[（S）-2＂- methylbutyloxy]phenyl}styrene （Ib）, （＋）-2,5-bis{4＇-[（S）-3＂-methylpentyloxy]phenyl}styrene （Ic）, （＋）-2,5-bis{4＇-[（S）-4＂- methylhexyloxy]phenyl}styrene （Id）, （-）-2,5-bis{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （le）, （＋）-2-/4＇-[（S）-l＂-methyl- propyloxy]phenyl}-5-{4＇-[（R）-1＂-methylpropyloxy]phenyl}styrene （Ⅱa）, （-）-2-{4＇-[（R）-1＂-methylpropyloxy]phenyl}-5-{4＇- [（S）- 1 ＂-methylpropyloxy]phenyl } styrene （lib）, and （＋）-2- { 4＇-[（S）-2＂-methylbutyloxy]phenyl }-5- { 4＇-[（S）- 1＂-methylpropyl- oxy]phenyl}styrene （Ⅲ）, were synthesized and radically polymerized. These molecules were designed to further understand long-range chirality transfer in radical polymerization and to possibly tune the chiroptical properties of the polymers by varying the spatial configuration, position, and various combination of the stereogenic centers at the ends ofp-terphenyl pendants. The resultant polymers adopted helical conformations with a predominant screw sense. When the stereogenic centers ran away from the terphenyl group as in Ⅰb-d, the corresponding polymers changed the direction of optical rotation in an alternative way and showed no obvious stereomutation upon annealing in tetrahydrofuran. The two stereogenic centers of Ⅱa, Ⅱb, and Ⅲ acted concertedly in chiral induction, whereas those of la and Ie played a counteractive role. The five polymers derived from Ⅰa, Ⅰe, Ⅱa, Ⅱb, and Ⅲ underwent stereomutation when annealed in tetrahydrofuran. The polymers PIa-e had good thermal stability and high glass transition temperatures （Tgs）. They generated liquid crystalline phases at above Tgs that could be kept upon cooling, with the exception of Pie. This result was consistent with the extended helical structures.
