Calorimetric study of block-copolymers of poly(n-butyl acrylate) and gradient poly(n-butyl acrylate-co-methyl methacrylate)

The nanophase separation in diblock and triblock copolymers consisting of immiscible poly(n-butyl acrylate) (block A) and gradient copolymers of methyl methacrylate (MMA) and n-butyl acrylate (n BA) (block M/A) were investigated by means of their heat capacity, C-p, as a function of the composition of the blocks M/A and temperature. In all copolymers studied, both blocks are represented by their C-p and glass transition temperature, T-g, as well as the broadening of the transition-temperature range. The low-temperature transition of the blocks A is always close to that of the pure poly(n-butyl acrylate) and is independent of the analyzed compositions of the block copolymer, but broadened asymmetrically relative to the homopolymer due to the small phase size. The higher transition is related to the glass transition of the copolymer block of composition M/A. Besides the asymmetric broadening of the transition due to the phase separation, it decreases in T-g and broadens, in addition, symmetrically with increasing acrylate content. The concentration gradient is not able to introduce a further phase separation with a third glass transition inside the M/A block. (C) 2002 Elsevier Science Ltd. All rights reserved.