Synthesis of fully acrylic thermoplastic elastomers by atom transfer radical polymerization (ATRP), 2 - Effect of the catalyst on the molecular control and the rheological properties of the triblock copolymers

Full Paper: The ATRP of MMA was initiated by a,omega-dibromo poly(n-butyl a crylate) in the presence of NiBr2(PPh3)(2) leading to poly(MMA)-b-poly(nBuA )-b-poly(MMA) triblock copolymers (MnBM). The initiation of the MMA polymer ization is slow compared to the chain propagation, which results in PMMA bl ocks of broad molecular weight distribution (MWD). In order to improve this situation, several experimental parameters were varied. CuBr/dNBipy was fi rst substituted for NiBr2(PPh3)(2), the results being, however, even worse. Then, the halide exchange was considered by substituting CuCl for CuBr. Th e CuCl/dNBipy catalyst proved superiority over the originally used NiBr2(PP h3)(2) system. Finally, the addition of an excess of CuCl2 (deactivator) to the CuCl/dNBipy catalyst was very beneficial in decreasing the MWD of the PMMA blocks. Indeed, the SEC chromatograms are monomodal and narrow from th e very beginning of the polymerization. The rheological analysis of the MnB M triblocks synthesized in the presence of each of the aforementioned catal ytic systems confirmed differences in the molecular control of the copolyme rization reaction.