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The semi-continuous heterophase polymerization (SHP) under monomer-starved conditions of methyl methacrylate and hexyl methacrylate is reported, at various monomer addition rates to elucidate the effect of monomer solubility on the mechanism of particle nucleation and growth. Polymer particles in the nanometer range from both monomers were obtained, which decreased in size as monomer addition rate was decreased. Molar masses of both polymers also diminished as monomer addition rate was slowed down. The propagation rate constant dictates how fast the starved condition is achieved rather than the monomer solubility in the aqueous phase. A slow particle rate of growth helps to obtain a narrower PSD. [ABSTRACT FROM AUTHOR]

The synthesis of poly(hexyl methacrylate) nanoparticles in nanoemulsions containing squalane as hydrophobe is reported here. A comparison of the polymerization kinetics of nanoemulsions prepared byPhase Inversion Temperature(low energy method) andmicrofluidization(high energy method), as well as polymer characteristics are presented. Nanoemulsion polymerizations carried out a 20°C were extremely fast using a par redox especially for the low-energy nanoemulsions. The particles obtained were only slightly larger than the original nanoemulsion droplets, indicating that the droplets acted as templates, and that squalane diminished substantially monomer diffusion between reacting and non-reacting monomer droplets. Molar masses and glass transition temperatures of the poly(hexyl methacrylate) obtained here were practically independent of conversion and surfactant concentration, as well as of the nanoemulsification method used. [ABSTRACT FROM AUTHOR]

Nanoemulsions of water, Brij 56 and hexyl methacrylate (with a small amount of squalene as hydrophobe or costabilizer) were made by the phase inversion temperature (PIT) method and then polymerized. In the absence of squalene, the nanoemulsions destabilized within minutes; however with squalene, the nanoemulsions were kinetically stable for at least several hours, which is long enough to carry out the reactions, with diameters of narrow size distribution in the range from 32 to 44 nm, depending on the surfactant concentration. Polymerizations, carried out a 20°C using a par redox, were extremely fast (ca. 100% conversion in less than 5 min) yielding polymer particles of ca. 40 nm, which were similar to the original nanoemulsion droplets (ca. 35 nm), indicating that the nanoemulsion droplets act as templates, and that squalene diminishes substantially monomer diffusion between reacting and non-reacting monomer droplets. Molar masses were high and alike to those produced by microemulsion polymerization of this monomer, suggesting that chain transfer to monomer is the main termination mechanism. [ABSTRACT FROM PUBLISHER]

The effect of monomer feeding rate on particle size, molar masses, glass transition and tacticity of poly(n-butyl methacrylate) (PBMA) nanoparticles synthesized by semi-continuous heterophase polymerization under monomer-starved conditions is reported. Three feed rates were examined. Highly monomer-starved conditions at the two slower addition rates were confirmed by the low amount of residual monomer throughout the reaction and by the fact that the instantaneous polymerization and feeding rates became similar at later stages of the reaction. Under these conditions, polymer particles in the nanometer range (30 to 35 nm) were obtained. Glass transition temperatures are substantially higher than those reported for commercial PBMA. Polymers tacticity was determined by 13C-NMR spectroscopy. NMR measurements confirm that the syndiotactic content of the PBMA synthesized here is larger than those of the commercial ones made by free-radical polymerization. Molar masses are much lower than those expected from termination by chain transfer to monomer, which is the typical termination mechanism in microemulsion polymerization. [ABSTRACT FROM PUBLISHER]