Increasing Branching and Functionalization Decreases Crystallinity and Crystallization Rate in Linear EVOH

We report the crystallization behavior of linear poly(ethylene-co-vinyl alcohol) (LEVOH) under isothermal crystallization as a function of both OH incorporation and undercooling and compare the results to conventional branched EVOH. This LEVOH is synthesized by postpolymerization functionalization of polycyclooctene, and it exhibits a half-crystallization time and primary crystallization rate nearly an order of magnitude faster than branched EVOH at ∼6 mol % OH incorporation. While LEVOH obtains approximately twice the extent of crystallization compared to the branched equivalent, as OH incorporation increases, the crystallization kinetics and crystallinity of LEVOH decrease. The crystal structure of LEVOH is orthorhombic at low functionalization (≤11 mol % OH), a mixture of orthorhombic and hexagonal at moderate functionalization (17–21 mol %), and hexagonal at high functionalization (23%). LEVOH crystallizes into plates, with crystallite widths ∼20–60 times the crystallite thickness. Ultimately, we show LEVOH crystallizes faster and to a greater extent than commercial branched EVOH, a potential advantage of postpolymerization functionalization as part of polymer-to-polymer upcycling.