A block copolymer composed of poly(N-isopropylacrylamide) [poly-(NIPAAm)] and a hydrophilic polymer such as poly(ethylene glycol) was prepared. The aqueous solution of the block copolymer exhibited a calorimetric endothermic peak on heating, similar to a poly(NIPAAm) homopolymer, although in a random copolymer composed of NIPAAm and a hydrophilic monomer such as acrylamide, no endothermic peak was observed. This result suggests that it is the NIPAAm sequence length which dominantly affects the LCST phenomenon of the copolymer rather than the content of hydrophilic comonomers.
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Yoshioka et al. (1994) studied this question.