Lamellar structures in blends of amorphous–block–main-chain liquid crystal–block–amorphous copolymers and amorphous homopolymers: Effects of the amorphous homopolymer molecular weight

Abstract

T(x-y-x) block copolymers comprising of a main-chain liquid crystal (LC) BB-5(3-Me) polyester with a number-average molecular weight (Mn) of y kDa connected to poly(ethyl methacrylate) (PEMA) with a Mn of x kDa at both ends form long-range lamellar microdomains with the blocks segregated from one another over a wide-range of compositions. In this study, the lamellar forming T(5.5-39-5.5) and T(11-39-11) copolymers were blended with homoPEMA (Hz) with Mn of z kDa at a concentration of 20 wt% to give the two series of blends T(5.5-39-5.5)/Hz and T(11-39-11)/Hz. These blends were examined for microdomain morphology as a function of the molecular weight ratio of z/x. T(5.5-39-5.5)/Hz formed lamellar microdomains over the investigated z/x range of 0.8–4.1, whereas T(11-39-11)/Hz formed lamellae over a narrower range of 0.9–2.3. The lamellar spacing and the PEMA and LC lamellar thicknesses (dam and dLC) were constant over z/x and dam was greater than dam of the neat copolymer. However, the values of dLC for these two blends were different; T(5.5-39-5.5)/Hz had the same dLC as T(5.5-39-5.5), whereas T(11-39-11)/Hz had a smaller dLC than T(11-39-11). These lamellar thicknesses variations in the blends are discussed in view of the conformations of the copolymer blocks and the accommodation fashion of the Hz additives.