Grafting Polyisobutylene from Nanoparticle Surfaces: Concentration and Surface Effects on Livingness
journal contributionposted on 13.10.2009 by Wolfgang H. Binder, Ronald Zirbs, Doris Machl, Markus Gahleitner
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We report on the grafting-from living cationic polymerization of isobutylene from SiO2-nanoparticles surfaces. After modification of the NP-surfaces (SiO2; 6 nm) initiators (I) for the cationic polymerization of isobutylene (IB) were grafted onto the NP surface in variable densities (0.1−0.85 molecules initiator/nm2). With densely packed initiators (0.85 molecules initiator/nm2) PIB-brushes with controlled molecular weights (5000−50 000 g mol−1) could be obtained. Various concentration-ranges of initiator-moieties in solution as well as isobutylene were studied, revealing a controlled polymerization process only in the range between [I] = 0.4−30 mM and [IB] = ∼0.04−3.3 M without the use of sacrificial soluble initiating systems, thus enabling a high-volume density polymerization of grafted nanoparticles without homopolymer formation. At high grafting densities (0.6−0.8 initiator molecules/nm2), the polymerization proceeded with three different rate-constants, with a slower polymerization at the beginning and increasing rates of polymerization after ∼300 and 600 s, respectively. With reduced initiators densities (below 0.4 molecules initiator/nm2) loss of control over the polymerization process and a significant change of the polymerization kinetics was observed.