Investigation of crystallization of PVCH-PE-PVCH triblock copolymer in supercritical carbon dioxide

Crystallization of glassy-crystalline-glassy poly(vinylcyclohexane)-b- polyethylene-b-poly(vinylcyclohexane) (PVCH-PE-PVCH) triblock copolymer treated in supercritical Carbon Dioxide (scCO ₂) was investigated by using differential scanning calorimetry (DSC) and atomic force microscope (AFM). It was found that the melting temperatures (T _m) and the crystallinity (X _c) of the PVCH-PE-PVCH samples treated in scCO ₂ at different annealing temperatures (T) were all much higher than those of the untreated PVCH-PE-PVCH, indicating that the scCO ₂ could effectively induce the samples to further crystallize. With increasing the T, the T _m of the samples linearly increased, even up to 108°C, close to the T _m (∼ 110°C) of the PE homopolymer hydrogenated from polybutadiene which is equal to the PE block in the triblock copolymer. The results could be ascribed to the released PE chain ends linked to the PVCH block due to the lowered T _g of the PVCH block swollen by scCO ₂. It suggested that the origin of the confined crystallization in PVCH-PE-PVCH was the fixed PE chain ends by the glassy PVCH. AFM images of the samples treated in scCO ₂ showed that the PVCH lamella phase tended to connect each other and led to the aggregated structures. The result indicated that the PVCH block could be availably swollen by scCO ₂. It supported the DSC experiment results of the samples treated in scCO ₂.