Polymorphism and side group location of ethylene copolymers characterized by FTIR and NMR spectroscopy

Fourier transform infrared spectroscopy (FTIR) was used to characterize the polymorphism, crystalline phase transformation, and side group location of ethylene copolymers (poly(ethylene-co-vinyl acetate), ab. EVA and poly(ethylene-co-vinyl alcohol), ab. EVOH). Sample films were prepared through a melt-pressing method, and submitted to cryogenic FTIR spectra measurement. Besides the occurrence of a normally orthorhombic crystalline phase (OCP), a monoclinic crystalline phase (MCP) was also detected for EVA copolymers with a relatively higher comonomer content (>14 wt%). The annealing temperatures greatly influence the transformation from MCP to OCP. As for EVOH copolymers, only thermodynamically stable OCP was found to exist in the crystalline region, and the hydroxyl groups were proved to enter the crystalline region of ethylene segments, while the side groups of EVA exist predominantly in the amorphous region.