Dendritic polyesters bearing COOH groups at the focal points were grafted onto nanometer silica premodified with 3-aminopropyltriethoxysilane by N,N′-dicyclohexylcarbodiimide mediated amidation. The products were cha...Dendritic polyesters bearing COOH groups at the focal points were grafted onto nanometer silica premodified with 3-aminopropyltriethoxysilane by N,N′-dicyclohexylcarbodiimide mediated amidation. The products were characterized qualitatively by FTIR, TGA and elemental analysis. It was shown that a significant grafting （10%15% net grafting for this reaction） was obtained despite the steric hindrance of the dendrons.展开更多
The crystallization of poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane)(PVCH-PE-PVCH) triblock copolymer/chloroform solution was investigated. The solvent of the solution system was evaporated at vario...The crystallization of poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane)(PVCH-PE-PVCH) triblock copolymer/chloroform solution was investigated. The solvent of the solution system was evaporated at various temperatures. It was found that the crystallinity was decreased with increasing the solvent evaporating temperature. This indicated that the crystallinity depends on the crystallization time because the higher the evaporating temperature, the faster the speed of the solvent evaporating is. However, the melting temperature(T_m) of the block copolymer was found to depend on the competition between the crystallization and the microphase separation. When the evaporating temperature is lower(below 333 K), i.e. the speed of the solvent-evaporating is slow, the PE block crystallized freely and the T_m increased with increasing the solvent evaporating temperature, implying that the T_m only depends on the crystalline temperature. On the other hand, with the increasing temperature up to above 343 K for solvent evaporating, two melting peaks at 356 and 377 K were observed for the crystallization of PVCH-PE-PVCH in the solution. It resulted in that the crystallization and the microphase separation of the block copolymer occurred simultaneously. And the confined and unconfined crystallization coexisted for the samples. The competition of the crystallization and the microphase separation can be controlled through changing the solvent evaporating speed.展开更多
文摘Dendritic polyesters bearing COOH groups at the focal points were grafted onto nanometer silica premodified with 3-aminopropyltriethoxysilane by N,N′-dicyclohexylcarbodiimide mediated amidation. The products were characterized qualitatively by FTIR, TGA and elemental analysis. It was shown that a significant grafting （10%15% net grafting for this reaction） was obtained despite the steric hindrance of the dendrons.
文摘The crystallization of poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane)(PVCH-PE-PVCH) triblock copolymer/chloroform solution was investigated. The solvent of the solution system was evaporated at various temperatures. It was found that the crystallinity was decreased with increasing the solvent evaporating temperature. This indicated that the crystallinity depends on the crystallization time because the higher the evaporating temperature, the faster the speed of the solvent evaporating is. However, the melting temperature(T_m) of the block copolymer was found to depend on the competition between the crystallization and the microphase separation. When the evaporating temperature is lower(below 333 K), i.e. the speed of the solvent-evaporating is slow, the PE block crystallized freely and the T_m increased with increasing the solvent evaporating temperature, implying that the T_m only depends on the crystalline temperature. On the other hand, with the increasing temperature up to above 343 K for solvent evaporating, two melting peaks at 356 and 377 K were observed for the crystallization of PVCH-PE-PVCH in the solution. It resulted in that the crystallization and the microphase separation of the block copolymer occurred simultaneously. And the confined and unconfined crystallization coexisted for the samples. The competition of the crystallization and the microphase separation can be controlled through changing the solvent evaporating speed.
