RAFT synthesis of polystyrene-block-poly(polyethylene glycol monomethyl ether acrylate) for zinc phthalocyanine-loaded polymeric micelles as photodynamic therapy photosensitizers

A series of polystyrene-block-poly(polyethylene glycol monomethyl ether acrylate) (PSt(m)-b-PPEGA(n)) polymers were systematically synthesized as carriers for zinc phthalocyanine (ZnPc) for photodynamic therapy via reversible addition and fragmentation chain transfer polymerization. The degree of polymerization of the styrene (m) and PEGA units (n) of the resulting block copolymers were characterized to be n=174, 40, and 18 for m=52; and n=200, 84, and 31 for m=30. All the block copolymers formed micelles in water. The critical micelle concentration (CMC) of the PSt(m)-b-PPEGA(n) was determined by fluorometry using pyrene as a hydrophobic probe. The CMC value increased from 4.5 to 20 mgL(-1) with an increase in the mole fraction of PEGA units. The median diameters of the micelles increased from 19 to 31 nm for PSt(52)-b-PPEGA(n) and from 15 to 23 nm for PSt(30)-b-PPEGA(n) with increasing n value. ZnPc-loaded micelles were prepared by dialysis of the block copolymer in the presence of ZnPc followed by removal of large aggregates by filtration. The encapsulation efficiency was dramatically changed in the range of 0-68%. The light-dose-dependent cytotoxicity of the ZnPc-loaded PSt(30)-b-PPEGA(200) was clearly established in HeLa cell lines; while no cytotoxicity was confirmed under the dark. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 560-570