The Reinforcement Effect in Well-Defined Segmented Copolymers: Counting the Topological Constraints at the Mesoscopic Scale

Abstract

Well-defined linear segmented block copolymers made of a sequence of hard (T4T diamides) and soft (polytetrahydrofuran) units were melt-processed and characterized rheologically by using small-amplitude oscillation shear measurements. Increasing the hard-segment (HS) content within the chains from 0 to 5, 10, 15, and 20 wt %HS was found to strongly enhance their plateau modulus, passing respectively from 1.7 to 3.2, 8.5, 13, and 30 MPa. After a brief review of the main models predicting such reinforcement in both homogeneous melts (rubber elasticity) and biphasic materials (hydrodynamics), we propose an alternative view based on a recent work describing the mesoscale structure of our materials. Starting from basic topological arguments, our approach lies on evaluating the volume occupied by a single chain entanglement in the soft phase (Ve) and using it as a reference for counting the number of “stickers” (i.e., HSs) that an equivalent volume in the hard phase would have contained. In this way, the crysta...