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A block copolymer of N‐isopropylacrylamide (NIPAAm) and LA may combine the thermosensitive property of poly(NIPAAm) and the degradation of PLA. Micelles from such copolymers can improve protein release properties. Temperature change can alter the hydrophilicity and conformation of PNIPAAm, which may affect the physicochemical properties of micelles of the polymer. Amphiphilic block copolymers of NIPAAm and LA were prepared by first synthesizing hydroxy‐terminated PNIPAAm followed by ROP of LA in toluene using Sn(Oct)₂ as a catalyst (Figure 4.10) [73].

Similar copolymers have recently been synthesized by ROP of LA using the two hydroxyl groups of S,S′‐bis(2‐hydroxyethyl‐2′‐butyrate)trithiocarbonate (BHBT). The triblock copolymers PLA‐b‐PNIPAAm‐b‐PLA were synthesized by ROP of LA initiated by BHBT followed by reversible addition–fragmentation chain transfer (RAFT) polymerization of NIPAAm with a centered trithiocarbonate unit as a RAFT agent [74]. Self‐organization of such amphiphilic block copolymers in aqueous solutions indicated the formation of vesicles. Stabilization of vesicles was attained by cross‐linking chain extension of the NIPAAm block using hexamethylene diacrylate [73]. Multifunctional micelles for cancer cell targeting, distribution, and anticancer drug delivery were prepared using poly(NIPAAm‐co‐methacrylic acid‐g‐DLA) and diblock copolymers [41].

FIGURE 4.10 Reaction sequence for preparation of PNIPAAm‐b‐PLA [72].