Macromolecules, 2018, vol 51, 1, pp. 128-136
DOI:10.1021/acs.macromol.7b02188
Abstract
Multi-nanolayered polystyrene/poly(l,l-lactide) (PS/PLLA) films were obtained by the layer-multiplying coextrusion process, with an individual PLLA layer thickness as thin as 20 nm. The confinement of the amorphous PLLA induced a change in the molecular mobility, evidenced by a drop of the cooperative rearranging region (CRR) size at the glass transition. The annealing of confined PLLA layers revealed slower crystallization kinetics and two-dimensional crystalline growth geometry. Furthermore, the annealing of PLLA in confined layers allowed a decoupling between the amorphous and crystalline phase, evidenced by the absence of a rigid amorphous fraction (RAF). As a consequence, the dynamic heterogeneity at the glass transition remained unaffected by the annealing procedure. In bulk polymers, where the level of coupling between amorphous and crystals is high, the glass transition temperature increased significantly whereas the CRR size fell. It is deduced that the glass transition dynamics in semicrystalline polymers is strongly related to the mobility landscape at the interface with crystals.
