Radical capture efficiencies in emulsion polymerization

A theoretical procedure is developed that allows the importance of bimolecular termination in the aqueous phase of an emulsion polymerization to be determined. This shows that with sparingly-soluble and slowly propagating monomers like styrene, significant termination occurs in the aqueous phase at high initiator concentrations, as found experimentally. With more water soluble monomers, aqueous phase termination is likely to be small

Emulsion polymerization kinetics. General solutions for Smith-Ewart cases I and II

Matrix methods are used to obtain general solutions for the Smith-Ewart case II mechanism for emulsion polymerizations; this relates to systems for which bimolecular termination is considered to be more important than free radical exit from the particles. These solutions are compared with simplified forms of the general solutions derived from case I, wherein exit is assumed to be more significant than termination. In neither case is resort made to the steady state approximation. There appears to be general agreement between theory and the results for the seeded emulsion polymerization of vinyl acetate, although discrepancies were apparent when very stringent comparisons were made

Thermoresponsive behavior of amphiphilic diblock co-oligomers of ethylene glycol and styrene in aqueous solution

We report the thermoresponsive behavior in aqueous solution of amphiphilic diblock co-oligomers of ethylene glycol (EG) and styrene (S) obtained by reversible addition fragmentation chain transfer (RAFT) polymerization (mPEG16-b-PS2, mPEG16-b-PS4 and mPEG16-b-PS6). The block co-oligomers were obtained from the polymerization of styrene mediated by a PEG macro-RAFT agent, mPEG-PBTC. The precise control offered by RAFT polymerization over the length of the short hydrophobic chain permits tuning of the thermoresponsive behavior for all the studied methoxy poly(ethylene glycol)-block-polystyrene copolymers. mPEG 16-b-PS2 was shown to self-assemble into micelles at temperatures below the lower critical solution temperature (LCST) of the block co-oligomer, whilst no such critical temperature was observed for solutions of self-assembled mPEG16-b-PS4 and mPEG16-b- PS6. mPEG16-b-PS4 self-assembles into relatively mobile spherical particles which evolve into prolate spheroids with increasing temperature, whilst mPEG16-b-PS6 forms particle clusters, which have lower mobility than the mPEG16-b-PS4 particles. This work is the first study on the aggregation behavior of such short chain lengths of mPEG-b-PS as a function of temperature, and shows how tuning the PS oligomer length permits control of the thermoresponsive behavior of mPEG-b-PS assemblies in water

Characterization of an ionic liquid ferrofluid electrospray emission pattern

© 2014 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 2014 by Brandon Jackson, Lyon B. King

Water-binding and oxygen permeability in poly(vinyl alcohol) films

The measurement and interpretation of isotherms for sorption of water onto, and oxygen permeability of, polymer substrates are important for designing polymers in applications such as agricultural seed coatings. In a preliminary study of water sorption in the commonly used copolymer poly(vinyl alcohol-'co'-vinyl acetate), moisture sorption isotherms were measured for a series of substrates of different comonomer composition at 25°C. The data were fitted to the D'Arcy-Watt model, which gave physically reasonable values for parameters related to the strength of monolayer adsorption to high affinity sites on the substrate and the number of sites for secondary water adsorption per unit mass. The oxygen permeability of poly(vinyl alcohol) films was found to be a function only of the water content of the films, with no other obvious contributing factors. Marked differences were seen in the populations of 'bound' and 'unbound' water characterized by ¹H nuclear magnetic resonance (NMR) spectroscopy and moisture sorption isotherm fitting. There was no correlation of oxygen permeability with 'bound' or 'unbound' water measured by any means, a fact suggesting that there is a continuum of water environments within the materials