Polymer association. VI. Reversible gelation of polystyrene carrying a small number of short polycaprolactam side chains

A styrene copolymer with 2.3 mole % of methacrylic acid was modified by grafting short polycaprolactam side chains to the carboxyl residues. The creep and creep recovery was studied over a range of temperatures on graft polymers containing 20% dioctyl phthalate plasticizer. A sample in which the side chains contained on the average 5 caprolactam units was a rubber-like elastomer at 125°C., showing no evidence of an irreversible creep. This behavior was interpreted as due to the formation of a gel network by hydrogen-bonding between the polycaprolactam side chains. Covalent cross-linking could be excluded since the graft polymer was soluble in various solvent media. At higher temperatures the interpretation of the data was uncertain because of slow plasticizer loss and chemical degradation, but the molding behavior of the sample at 205°C. indicated that the gel structure had disappeared at that temperature.