End‐group controlling aqueous solution properties in star‐shaped poly(2‐hydroxyethyl acrylate) and poly(2‐hydroxyethyl acrylate)‐b‐poly(N‐isopropylacrylamide) polymers

Abstract

AbstractStar‐shaped poly(2‐hydroxyethyl acrylate) (PHEA)6 polymers were synthesized using hexafunctional chain transfer agent (CTA) trithiocarbonate type via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The (PHEA)6 polymers with dodecyl chain‐end were non‐water soluble. As the molecular weight increased, the polymers could disperse in water, forming large aggregates with a DH of 1027 to 525 nm. On the contrary, the (PHEA)6 polymers with the carboxylic acid group at the chain‐end were completely soluble in water. Then, (PHEA)6 polymers were chain extended with N‐isopropylacrylamide (NIPAM) to obtain poly(2‐hydroxyethyl acrylate)‐b‐poly(N‐isopropylacrylamide) (PHEA‐b‐PNIPAM) block copolymers. The dodecyl group strongly affects the aqueous solution properties of the copolymers even with a high PNIPAM content. Copolymers with dodecyl chain‐end were insoluble or partially soluble in water, forming large aggregates (0.5 mg/ml in distilled water). The copolymers with carboxylic acid end‐group were totally water soluble. The thermo‐responsive phase behavior of the star‐shaped block copolymers was studied, and for this purpose, it was necessary to remove the RAFT group containing the dodecyl tail. The intense turbidity observed in the aqueous dispersions of the corresponding copolymers made it challenging to determine the LCST accurately. The copolymers with a carboxylic end group were evaluated as is.