Poly(n-butyl acrylate)/Poly(vinyl acetate-co-methyl methacrylate) Structural Rubber Latex Particles as Impact Modifier for Unsaturated Polyester Resin: Preparation and Characterization

Structural composite latex particles were prepared via a two-stage emulsion polymerization. In the first stage, partially cross-linked poly(n-butyl acrylate) (PBA) cores were prepared, and in the second stage, a poly(vinyl acetate-co-methyl methacrylate) abbreviated as P(VAc-co-MMA), shell was grafted onto the rubber cores. In this case, a starved feed of shell monomer(s) was applied to avoid further formation of secondary particles in the aqueous phase. The effects of shell chemical composition and MMA/VAc ratio, on the characteristics and morphology of the resulting emulsion particles have been investigated. The resultant particles were characterized by dynamic laser light scattering (DLLS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). TEM Micrographs showed that, the increase of methyl methacrylate (MMA) content level in the shell structure of above 50% (by weight) led to composite latex particles with more separated core and shell regions. In addition, the structural rubber particles with various shell structures were used to toughen the cured styrene/unsaturated polyester alkyd (ST/UPA: 75/25) resin. The results showed that the incorporation of rubber core-shell structured particles with VAc/MMA (50/50 wt/wt) copolymer shell improved the impact fracture energy of the ST/UPA resin (UP) considerably. Scanning electron microscopy (SEM) and TEM micrographs revealed dispersed particles as singlet inside the above blend sample, which showed the highest impact fracture energy. Further increase of MMA units of above 50% (by weight) in the shell composition resulted in significant increase in rubber particles agglomeration as big clusters within the UP matrix. However, the particle shell composition and subsequently the particle/resin interfacial adhesion seem to have a crucial role on the dispersion state and toughening efficiency of the rubbery particles inside the UP matrix.