Living radical polymerization immobilized on wang resins: Synthesis and harvest of narrow polydispersity poly(methacrylate)s

Wang resin has been transformed into an initiator for copper(I)-mediated li ving radical polymerization of methacrylates at initiator loading of 0.9 an d 3.5 mmol g(-1). The immobilized initiator was characterized by ATR FTIR, gel phase C-13 NMR, and solid-state CP/MAS C-13 NMR using two different spi nning frequencies as well as a TOSS pulse sequence. The immobilized initiat or has been used to prepare poly(methyl methacrylate), PMMA, homopolymer, a nd poly(methyl methacrylate)-block-poly(benzyl methacrylate-co-methyl metha crylate), P(MMA)-block-P(BzMA-co-MMA), block copolymers. The poly(methacryl ate)s have been harvested from the insoluble resin by a simple trifluoroace tic acid, TFA, wash which selectively cleaved the activated benzyl ester li nkage, so as to facilitate analysis. At an initiator loading of 0.9 mmol g( -1) the M-n increases linearly with conversion with kinetics following firs t-order behavior in monomer as would be expected for living polymerization. After 3 h a 61.9% conversion of MMA is reached, with the isolated polymer chains having an average number molar mass, M-n, of 8200 and a polydispersi ty, PDI, of 1.18. High conversions, >90%, lead to considerable increases in M-n and PDI. Moreover, small amounts of "free" chains present in the super natant, ca. 5-8% after 4 h of reaction time, were found. The morphology of the beads was monitored by SEM with the integrity being maintained througho ut the transformations. Attempts to prepare true block copolymers via a two -stage process involving isolation of the Wang resins with the first block and subsequent reuse to attach the second block were not satisfactory. Howe ver, a one-shot addition of BzMA at high conversion of MMA allowed the synt hesis of P(MMA)-block-P(BzMA-co-MMA) with a narrow molar mass distribution, as confirmed with SEC, DSC, and NMR. The paper demonstrates that Wang immo bilized chemistry can be used to prepare excellent polymers maintaining the characteristics of analogous homogeneous living radical polymerizations wh ile allowing for catalyst removal by simple washing procedures. The potenti al for automation of this chemistry for high throughput synthesis has been demonstrated.