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Homogeneous tandem catalysis involving a highly selective, aluminoxane-activated bis(2-decylthioethyl)amine·CrCl3 complex for the synthesis of 1-hexene in tandem with a number of metallocene catalysts is discussed. Analysis by means of DSC, CRYSTAF, HT-GPC, ¹³C NMR, and FTIR suggests that copolymers of 1-hexene and ethylene are produced with significant selectivity toward 1-hexene as comonomer. The selectivity of 1-hexene incorporation by the metallocene catalysts follows the trend in the order [Me2Si(2-Me-Ind)2]ZrCl2 > [Me2Si(2,3,4,5-Me-Cp)(t-Bu-N)]TiCl2 > Cp2ZrCl2. The highly selective nature of the ethylene trimerization catalyst employed in this study means that the industrial application of tandem catalysis is becoming increasingly viable since it approaches conventional 1-hexene LLDPE in terms of polymer microstructure control.

The ability to synthesize core/shell particles with distinct geometries is becoming increasingly important due to their potential applications. In this study structured particles with liquid cores and polymeric shells were synthesized by an in situ miniemulsion polymerization reaction. The resulting materials were used to evaluate morphology prediction models based on thermodynamic considerations. Results showed that thermodynamic models are inadequate for the morphology prediction of in situ polymerized species. For particles prepared in this way, kinetic influences, e.g. anchoring effects, chain mobility, and viscosity, play a significant role in defining the end morphology of the particles.

Model alkali-soluble rheology modifiers of different molar masses were synthesized by the reversible addition–fragmentation chain-transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well-controlled molar mass, molar mass linearly increasing with conversion, and the ability to chain-extend by forming an AB block copolymer. The steady-shear and dynamic properties of a core-shell emulsion, thickened with the different model alkali-soluble rheology modifiers, were measured at constant pH and temperature. The steady-shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid-like (dominant G') behavior as compared with the associative rheology modifiers that give the latex solution a liquid-like (dominant G") character. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 223–235, 2003

A novel approach to conducting controlled free radical polymerization in water-borne organic dispersions using reversible addition−fragmentation chain transfer (RAFT) has been studied. The novel approach in this study focused on eliminating monomer and oligomer transport and comprised two fundamental steps:  the synthesis of dithiobenzoate-end-capped styrene oligomers in bulk followed by emulsification of these oligomers to yield a polymerizable water-borne dispersion. Dithioesters that act as chain transfer agents in the RAFT process were synthesized in situ. The free radical polymerization of the dithiobenzoate-end-capped styrene oligomers in the water-borne organic dispersion proceeded in a controlled manner; molar mass increased in a linear fashion with increasing conversion, while polydispersities remained low. The familiar red layer formation associated with RAFT polymerization in conventional emulsions was not observed under these conditions. The effects of changing the costabilizer (hydrophobe) and the degree of polymerization of the emulsified oligomers were investigated. Better control was achieved with a less hydrophilic costabilizer and for the shorter of the oligomers tested.

Epoxy–acrylate composite emulsions such as the one in this study can be used as metal coatings, etc. Many factors can influence the final quality of the product, and it is the aim of this study to highlight some of these factors. Statistically designed experiments were performed to investigate the influence of monomer level, the polymeric dispersant level, epoxy level, and the initiator level on particle size (light scattering), particle size distribution, and fractional conversion. It was found that the monomer level significantly influenced particle size and particle size distribution. The epoxy level and the monomer level influenced fractional conversion significantly. A qualitative model based on these observations is put forward to describe the mechanism of particle formation and polymerization. This model states that the high internal viscosity of the initial dispersed epoxy phase inhibits the formation of smaller particles and accelerates the polymerization rate during the first few minutes of polymerization by inducing a gel effect that inhibits termination and chain transfers of radical species. The addition of a monomer lowers the internal viscosity of the particles and causes them to break up into droplets containing dissolved epoxy, polyacrylate, and monomer. At the same time, radical species inside the smaller droplets can now undergo termination and chain transfer reactions. To confirm this model, polyacrylates of varying molecular masses were synthesized. Variation of the molecular masses of these polyacrylates resulted in variation in the viscosity of the dispersed phase. Polymerizations conducted with the polyacrylates confirmed the model observations. A dispersed phase with a high viscosity results in an increased polymerization rate, larger overall particle size, and a higher mass average molecular mass copolymer compared to lower molecular mass polyacrylates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 368–381, 2000

The past decade has seen the development of high-performance epoxy-acrylate coatings. Some of these coatings are used exclusively as can coatings. To improve chemical resistance, emulsion polymerization in the presence of the dispersed epoxy resin can be conducted. Replicated factorial designs were designed to investigate some of the factors that contribute to the performance and stability of the epoxy-acrylate coating. The factors investigated in this study were: the type and amount of neutralizing amine, the type of initiator, the presence or absence of salt, and the stirring speed of the impeller. The measured responses for the experimental design were particle size, particle size distribution, and conversion. It has been shown in this study that the type of amine used to neutralize the polyacrylic stabilizer significantly influenced the observed responses probably by acting as chain transfer agent during polymerization. The addition of salt significantly affected the observed responses by shielding the surface charges on the particle surface that impart stability to the latex through electrostatic repulsion. Stirring speed of the impeller and the type of initiator as factors in the range investigated do not influence the kinetics or the particle size and polydispersity to any great extent either on their own or in combination with other factors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1347–1360, 1999