Synthesis and structure-property relations of latexes containing graft copolymers between telechelic polybutadiene and dodecyl methacrylate

Latexes comprising novel copolymers were formed by second-stage emulsion polymerization of dodecyl methacrylate (DMA) onto a hydroxylated polybutadiene-based polyurethane prepolymer (PUD) as seed latex, with persulfate initiator. Morphology data from TEM imaging (including chemical fixation ultra-microtoming), glass transition temperature, dynamic mechanical analysis, and other mechanical-property data were all consistent with a system showing extensive grafting and compatibilization between the different polymeric components. Water adsorption and AFM measurements showed that samples with poorer film-forming properties had higher water sensitivity, greater mixing of the polymer phases, and poorer mechanical properties. These properties were related to a phase-inversion phenomenon occurring above a critical dodecyl methacrylate/prepolymer ratio. The compatibilization of the PUD and poly(DMA) given by these modifications resulted in a product with increased tackiness, although with a higher water sensitivity

Ab initio emulsion polymerization by RAFT-controlled self-assembly

A method is developed to enable emulsion polymerization to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of molecular weight control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-soluble monomer, from which diblocks can be created by the subsequent polymerization of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymerization is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymerization is then continued at any desired feed rate and composition of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymerization; molecular weight polydispersities are generally low. The number of RAFT-ended chains within a particle is much larger than the aggregation number at which the original micelles would have self-assembled, implying that in the early stages of the polymerization, there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymerization of two hydrophobic monomers gives completely novel core-shell particles where most chains extend from the core of the particles through the shell layer to the surface