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Living Radical Polymerization Immobilized on Wang Resins: Synthesis and Harvest of Narrow Polydispersity Poly(methacrylate)s
journal contribution
posted on 2001-01-17, 00:00 authored by Stephanie Angot, Neil Ayres, Stefan A. F. Bon, David M. HaddletonWang resin has been transformed into an initiator for copper(I)-mediated living radical
polymerization of methacrylates at initiator loading of 0.9 and 3.5 mmol g-1. The immobilized initiator
was characterized by ATR FTIR, gel phase 13C NMR, and solid-state CP/MAS 13C NMR using two different
spinning frequencies as well as a TOSS pulse sequence. The immobilized initiator has been used to prepare
poly(methyl methacrylate), PMMA, homopolymer, and poly(methyl methacrylate)-block-poly(benzyl
methacrylate-co-methyl methacrylate), P(MMA)-block-P(BzMA-co-MMA), block copolymers. The poly(methacrylate)s have been harvested from the insoluble resin by a simple trifluoroacetic acid, TFA, wash
which selectively cleaved the activated benzyl ester linkage, so as to facilitate analysis. At an initiator
loading of 0.9 mmol g-1 the Mn increases linearly with conversion with kinetics following first-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, Mn, of 8200
and a polydispersity, PDI, of 1.18. High conversions, >90%, lead to considerable increases in Mn and
PDI. Moreover, small amounts of “free” chains present in the supernatant, 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
throughout 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. However, a one-shot addition of BzMA at high conversion of MMA allowed
the synthesis 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 immobilized chemistry can be used to
prepare excellent polymers maintaining the characteristics of analogous homogeneous living radical
polymerizations while allowing for catalyst removal by simple washing procedures. The potential for
automation of this chemistry for high throughput synthesis has been demonstrated.