Macromolecular Reaction Engineering

Cover: Uniform micron-sized particles are formed by dispersion copolymerization of methyl methacrylate with the bio-renewable monomer γ-methyl-α-methylene-γ-butyrolactone. A distinct population of 50 nm precursor particles are continually formed and swept up by the larger particles during polymerization. Further details can be found in the article by R. A. Cockburn, T. F. L. McKenna, and R. A. Hutchinson^*on page 404.

The effects of varying polymerization conditions and chromium nuclearity were investigated. Branch density was highly dependent on the polyethylene yield, which proved that the branching through copolymerization with in-situ-produced α-olefins. Comparison of the ability among the model catalysts with controlled nuclearity proved an enhancement in methyl branching on dinuclear chromium species relative to the mononuclear chromium species.

An accurate prediction of the phase inversion process is vital to control a heterogeneous polymerization. Significant attention has been paid to the conditions that ensure the particle stability during a dispersion polymerization, but those where such stability is lost are poorly understood. In this work, the phase inversion in a dispersion polymerization is investigated. The proposed approach can be extended to other heterogeneous polymerizations.

The experimental characterization of crosslinked polymers is limited. A computer simulation approach able to give detailed information of the microstructure of crosslinked acrylic-polyurethane hybrid polymers synthesized by miniemulsion polymerization is presented. The analysis of these complex materials by computer simulation opens the possibility of fine-tuning the polymer performance by controlling its structure.

The effect of carboxylic monomers and its type, the concentration and type of surfactants and the pH during the synthesis of high solids content MMA/BA latexes with average particle sizes around 300nm was addressed. Stable unimodal latexes with solids content up to 61wt% and small amount of surfactant (0.40wt%) were obtained at basic pH.

Although the method of moments has been used to determine the properties of copolymerizations, the accounting for branching in simulation has either required the use of multiple dimensions or been ignored. By combining a simplified segment model with branch trackers, we have developed a model to account for branching, even hyperbranching without resorting to multiple dimensions. This model is especially useful for simulating hyperbranched polymers used as targeted drug delivery vehicles.

There are several practical and numerical deficiencies in estimating copolymerization reactivity ratios using instantaneous composition data. This paper demonstrates that implementing cumulative models on composition data at any conversion level (i.e., low, moderate, and high) increases the accuracy of the reactivity ratio estimates. Using the numerically integrated cumulative model is a direct and reliable approach, avoiding difficulties associated with common practice so far.

The effects of continuous phase composition and comonomer content on reaction rate and particle size are analysed. The relative importance of solution polymerization is also studied by adding cobalt(II) catalytic chain transfer to the system. A distinct population of 50–100nm particles is observed throughout the course of polymerization, in addition to the micron-sized dispersion product formed.

The effect of different cocatalysts (methylaluminoxane and tetrakis(pentafluorophenyl) borate dimethylanilinium salt) on the polymerization kinetics of ethylene and ethylene/1-octene using rac-dimethylsilyl-bis(indenyl)hafnium dimethyl catalyst are investigated in a solution polymerization reactor. Kinetic parameters are estimated systematically using monomer uptake curves and polymer molecular weight averages. The figure shows point estimates and confidence intervals for some lumped kinetic polymerization parameters for these two systems.

Pulse tracer studies were done to determine differences in flow characteristics between a homogeneous aqueous salt mixture versus a heterogeneous miniemulsion mixture in a continuous tubular reactor. Two heterogeneous systems were studied: a monomer-in-water droplet dispersion and one with fully formed polymer particles dispersed in water. There were differences observed between all of the systems tested, none of them matched an ideal plug flow condition, and the dispersion model was found to model the system quite well in most cases.

Surfadditives having a “head-neck-body” chain microstructure are designed to modify plastic surfaces in molding. The “head” or “neck” provides required surface functionalities and enables migration of surfadditives to the surface, while the “body” offers interactions with the part matrix. As an example, tri-block methacrylates containing triethoxysilylpropyl, perfluorodecyl, and methacrylate backbones are synthesized using ATRP and are applied in PMMA molding.

A comprehensive model is presented to describe thermally-initiated polymerization of styrene over the temperature range of 100–170°C. Parameter ranking and selection algorithms are employed, along with hand-tuning of autoacceleration parameters, to refine model predictions by adjusting key model parameters.

An ideal kinetic model has been developed and applied for solution ARGET ATRP of styrene, methyl methacrylate, and butyl acrylate. A highly active initiation/catalyst system with a large ATRP equilibrium constant results in a poor control of the polymerization. Reducing agent with a moderate rate coefficient gives good control over ARGET ATRP.

The removal of residual monomers from polymer latexes via post-polymerization with redox initiators and nitrogen stripping is experimentally investigated. It is demonstrated that residual MMA and BuA monomers and VOCs can be successfully removed from polymer latexes by these methods, whereas the combined application of post-polymerization and nitrogen stripping aids the overall reduction of VOCs generated during the monomer removal process.

Heterogeneous precipitation copolymerization of water-soluble monomers in organic solvent is investigated experimentally. The effects of different operating parameters on reaction rate, copolymer composition and final molecular weights are considered. Since the final product is in particulate form, the evolutions of particle size distribution and structure of the final aggregates is also analyzed.

A comprehensive kinetic model is developed to simulate the precipitation copolymerization of water soluble monomers in organic solvent. Such model represents an effective tool to elucidate major reaction mechanisms such as reaction locus, active chain interphase transport, and buildup of the molecular weight distribution.

Morphology and specific areas of core–shell particles produced by combined semibatch emulsion/suspension polymerizations depend on the glass transition temperature of emulsified particles and vary considerably, depending on reaction conditions and used monomers. Based on observed data, a physical model is proposed to explain the formation of the shell of core–shell particles produced through combined suspension/emulsion polymerizations.