Control of the confined and unconfined crystallization in glassy-crystalline poly(vinylcyclohexane)-b-poly(ethylene)-b-poly-(vinylcyclohexane) triblock copolymer in solution

摘要

The influence of the solvent evaporation rate on the crystallization of the poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane) (PVCH-PE-PVCH) triblock copolymer with the high T_g of PVCH segment in chloroform was investigated.The competition between the crystallization of PE block and the vitrification of PVCH in the triblock copolymer was controlled through changing the solvent evaporation rate in the solution system at different temperatures (T_e).It was found that the melting temperature (Tm) of PVCH-PE-PVCH samples increased with increasing the T_e when the T_e was lower than the solvent boiling point (bp),depending on the crystalline temperatures.However,when T_e was just a little above the solvent bp,two melting peaks,which corresponding to the fusion of the confined and unconfined crystals,respectively,were observed on the DSC curves of the samples.As T_e increased to be higher temperature,only one lower melting peak,which corresponding to the fusion of the confined crystals,existed for each samples.It was also found that the crystallinity (X_c) of the samples decreased gradually when T_e was lower than the solvent bp,and then decreased suddenly when T_e was just a little above the solvent bp,finally reached a plateau (about 13.5%) at higher T_e.The changes in X_c of the samples depend on the evaporating time in the solution.The results should be related to the competition between the crystallization of PE block in solvent and the vitrification of PVCH block with the solvent evaporation.Furthermore,the competition was controlled through changing the solvent evaporation rate.The confined and unconfined crystallization of the samples could be freely adjusted.