Grafting Polyisobutylene from Nanoparticle Surfaces: Concentration and Surface Effects on Livingness

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 ...