Graft Copolymers of N-Isopropylacrylamide with Poly(d, l -lactide) or Poly(ϵ-caprolactone) Macromonomers: A Promising Class of Thermoresponsive Polymers with a Tunable LCST

A series of well-defined poly(d,l-lactide) and poly(ϵ-caprolactone) macromonomers (M_nof ∼600 and 1200 Da) bearing a (meth)acrylate group at one side of the chain and either a hydrophobic nonpolar butyl group or a hydrophilic polar hydroxyl group at the other side of the chain were synthesized via 1,8-diazabicyclo[5.4.0]undec-7-ene-catalyzed ring-opening polymerization (ROP) of d,l-lactide and methanesulfonic acid-catalyzed ROP of ϵ-caprolactone, respectively. Then, a series of well-defined random copolymers (M_nof ∼30-000 Da,< 1.25) were prepared via reversible addition-fragmentation chain transfer (RAFT)-mediated copolymerization of N-isopropylacrylamide with these macromonomers. It was found that the cloud point temperature of the graft copolymers almost linearly decreased from 32.1 to 14 °C, with increasing the content of the polyester macromonomer with a hydrophobic butyl end group in a copolymer chain from 0 to 17 wt %. A much smaller shift in the transition temperature (from 32.1 to ∼23 °C) was observed for the graft copolymers of N-isopropylacrylamide with polyesters bearing a polar hydroxyl group at the chain end. The thermoresponsive behavior dependence on the copolymer composition of the synthesized graft copolymers or their binary mixtures with poly(N-isopropylacrylamide) (PNIPAM) was also demonstrated in this study. Finally, it was proved that the obtained graft copolymers showed no cytotoxicity, and films prepared from these copolymers displayed better cell adhesion as compared to those prepared from neat PNIPAM.