In situ synthesis of thermo-responsive ABC triblock terpolymer nano-objects by seeded RAFT polymerization

RAFT polymerization of N -isopropylacrylamide under heterogeneous conditions in the presence of diblock copolymer nano-objects of polystyrene- block -poly( N , N -dimethylacrylamide) trithiocarbonate (PS- b -PDMA-TTC) with the Z -group RAFT terminal on the outer side of the solvophilic poly( N , N -dimethylacrylamide) (PDMA) block is performed. This heterogeneous RAFT polymerization, which is named seeded RAFT polymerization, affords the in situ synthesis of the polystyrene- block -poly( N , N -dimethylacrylamide)- block -poly( N -isopropylacrylamide) (PS- b -PDMA- b -PNIPAM) triblock terpolymer nano-objects. The molecular weight of the triblock terpolymer linearly increases with the monomer conversion during the seeded RAFT polymerization. The morphology of the PS- b -PDMA- b -PNIPAM triblock terpolymer nano-objects is merely duplicated from the seed of the PS- b -PDMA-TTC diblock copolymer, which is the binary mixture of nanospheres and nanorods, when the polymerization degree (DP) of the poly( N -isopropylacrylamide) (PNIPAM) block is low or moderately large. When the DP of the PNIPAM block is relatively large, the triblock terpolymer nanospheres are formed. The size of the PS- b -PDMA- b -PNIPAM triblock terpolymer nano-objects slightly increases initially and subsequently decreases with the monomer conversion during the seeded RAFT polymerization. In water at temperature above the phase-transition temperature (PTT) of the PNIPAM block, the PNIPAM chains deposit onto the polystyrene (PS) core to form the triblock terpolymer multicompartment nano-objects containing a microphase separated solvophobic core of PS/PNIPAM and a solvophilic PDMA corona. Our findings are anticipated to be useful in preparation of concentrated ABC triblock terpolymer nano-objects.