On the origin and consequences of high DMAEMA reactivity ratio in ATRP copolymerization with MMA: An experimental and theoretical study(#)

Designing and tuning a copolymerization process to obtain specific material properties is still fundamentally empirical and requires the determination of apparent reactivity ratios r(s). To this end, PEG-(MMA-DMAEMA)(n) copolymers obtained via ATRP of MMA and DMAEMA using a PEG-based initiator in toluene were analyzed to extract monomer relative reactivities; the impact of changing solvent on the latter was also tested. Differing from previous free radical and controlled radical copolymerizations (CRcoP), we found that DMAEMA is preferentially included (MMA=0.36(+/- 10%) and DMAEMA=2.76(+/- 15%)) in toluene; increasing the solvent polarity decreased the gap between r(s). With these data, kMC simulations based on the copolymerization terminal model were used to investigate copolymer microstructure, which is not amenable to NMR investigation. kMC simulations evidenced both a gradient-like nature of the copolymers and a somewhat unexpected qualitative change in the probability of finding MMA-rich triads along the chain depending on initial feed composition. An additional DFT analysis suggested the likely formation of a DMAEMA:CuBr:2-2-bipyridine complex, which being involved in the regeneration of reactive radicals from dormant species, is expected to locally increase DMAEMA concentration favoring its addition to the growing chains. The formation of such complex is also supported by H-1-NMR experiments. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1366-1382