Influence of Molecular Weight on Physical and Mechanical Properties of Linear Symmetric S-(S/B)-S Triblock Copolymers

摘要

Symmetric linear S-(S/B)-S triblock copolymers with 80 wt.-% of PS having a block composition of 20-60-20 and a S/B ratio of 70:30 in the middle block are studied with varying molecular weights ((M) over bar (w)). Increase in the ((M) over bar (w)) leads to a change in the morphology from disordered to ordered microphase separated structure, as characterised by TEM and SAXS. Two distinct glass transitions for PS- and PB-rich phases are observed from DMA measurements, which are due to phase separation at high ((M) over bar (w)). Rheological studies (master curves) reveal an extended rubbery plateau and a delay in the terminal response with an increase in (M) over bar (w), whereas a terminal flow behaviour is observed for materials having a disordered nature at low (M) over bar (w). A brittle-to-tough transition is observed from tenile tests with the increase in (M) over bar (w).