Polymers with molecular weight dependent LCSTs are essential for cooperative behaviour

The potential to fine-tune the transition temperatures of polymers displaying lower-critical solution temperatures (LCST) by a simple mixing strategy is investigated. Using a panel of four distinct polymer classes (poly[oligo(ethyleneglycol) methacrylate], poly(N-vinylpiperidone), poly(N-vinylcaprolactam) poly(N-isopropylacrylamide)) it was shown that only those with strong molecular weight dependent LCSTs produced a single, cooperative, transition when blended together. Furthermore, the actual transition temperature was linked to the weight average not the number average molecular weight. The only polymer which did not show strong molecular-weight-LCST correlation was poly(oligo(ethyleneglycol) methacrylate), which showed two independent transitions, one for each polymer.