Studies on micellization behavior of thermosensitive PNIPAAm-b-PLA amphiphilic block copolymers

Thermo-sensitive amphiphilic block copolymers, poly(N-isopropylacrylamide)-block- poly(D,L-lactide) (PNIPAAm-b-PLA), were synthesized through a simple free radical copolymerization route based on a bifunctional initiator, 2,2'-azobis(2-methylpropion amidine) dihydrochloride (AMAD), followed by the ring-opening polymerization of D,L-lactide in the presence of Sn(Oct)2 catalyst. The Chemical structure characterization were conducted by means of 1H NMR, FT-IR, GPC. The amphiphilic PNIPAAm-b-PLA block copolymers could self-assemble into micelles with regularly spherical shape in an aqueous solution, with a TEM diameter range of 46-56 nm, DLS hydrodynamic diameter of 158-199 nm. This behavior depends on the environmental temperature, the hydrophobic interactions among PNIPAAm molecular chains, intermolecular hydrogen bonding between the PNIPAAm chains and water molecules as well as intramolecular hydrogen bonding between -CONH2 groups. The copolymers held a CMC from 5.50 to 6.17 mg L(-1) and LCST from 31.41-32.03 degrees C, being more or less affected by their compositions, PLA or PNIPAAm block length. The as-prepared PNIPAAm-b-PLA block polymers are anticipated to be applied as a potential candidate of drug release carriers.