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A new method to obtain enzymatic rate coefficients for synthesis of biological homopolymers is presented. The new method involves fitting molecular weight distributions (MWDs) obtained by taking samples at successive times from an in vitro enzyme-catalyzed system. Enzymatic rate coefficients can then be obtained by fitting the observed MWDs to an assumed model. These types of results are complementary...
The mechanism for the formation of amphiphilic core–shell particles in water is elucidated via a kinetic study of semi-batch polymerization of methyl methacrylate (MMA) grafted from polyethylenimine (PEI) initiated with tert-butyl hydroperoxide in an emulsion polymerization. The monomer conversion, the polymerization kinetics, the particle size, the particle number density, the poly(methyl methacrylate)...
Over decades of carefully designed kinetic experiments and the development of complementary theory, a more or less complete picture of the mechanisms that govern emulsion polymerization systems has been established. This required means of determining the rate coefficients for the individual processes as functions of controllable variables such as initiator concentration and particle size, means of...
The kinetics of the photo-initiated polymerization of acrylamide in water, at up to 10% w/w polymer and under ambient conditions, are studied using in situ Raman spectroscopy. Three photo-initiators were studied, UO 22+ , 2,2′-azobis(2-amidinopropane) (“V-50”) and persulfate, with photo-initiation by a low-pressure Hg lamp. The dependences of polymerization rate on time, initiator concentration...
A range of comb polymers of poly(n-butyl methacrylate), where the degree of polymerization (DP) of both the backbone and branches was controlled using RAFT-mediated free-radical polymerization, was synthesized using the method of Vosloo et al. [Macromolecules 2004;37: 2371]. Individual architectural parameters (branch length, branch number and DP of the comb backbone) of these relatively monodisperse...
A variety of nanocomposites were synthesised by bulk polymerisation of methyl methacrylate (MMA), and also by extrusion of poly(methyl methacrylate) (PMMA). These were characterised by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). We applied image analysis to the TEM images of these PMMA–clay nanocomposites to quantify their structures; an analysis was made of the...
The effects of various components in an emulsion polymerization system on the dissociation rate coefficient of persulfate at 50°C are examined using iodometry. Styrene monomer is found to enhance greatly the dissociation, while there is either no effect or possibly a slightly reduced rate of dissociation with methyl methacrylate monomer. The saturated analogues of these monomers (ethylbenzene and...
The effects of methacrylic acid (MAA) on the physical properties of polymer made by emulsion copolymerization of butyl acrylate (BA) and MAA were examined. Emulsion polymerizations were performed with and without MAA and at temperatures of 0.1 and 50°C, using redox initiation so that the radical flux was essentially independent of temperature. The presence of methacrylic acid had only a small effect...
The kinetics of acrylamide (AAm) free radical polymerization at low conversion of monomer to polymer in the aqueous phase was investigated at 50°C using γ-radiolysis relaxation, which is sensitive to radical-loss processes. The values of the termination rate coefficients for AAm ranged from 8×10 6 to 3×10 7 M −1 s −1 as the weight fraction of polymer ranged from 0.002...
The mechanisms and kinetics of radical entry in emulsion polymerizations utilizing redox initiation are investigated using polymerization rate data obtained by reaction calorimetry and electrospray mass spectroscopy analysis of initiator-derived aqueous-phase products. These data have been used to evaluate an initiation scheme for redox-initiated emulsion polymerizations of common monomers such as...
The mechanical properties, amino acid composition, internal morphology, and solvent-induced interaction of silk produced by the endemic Australian leafhopper, Kahaono montana Evans (Hemiptera: Cicadellidae) were studied. Ion plasma etching/scanning electron microscopy examination of the internal morphology revealed a skin–core structure, with bands in the core region aligned regularly in a transverse...
The grafting efficiency of dimethylaminoethylmethacrylate (DMAEMA) on to natural rubber (NR) has been studied. Grafting was by ‘topology-controlled’ emulsion polymerization, whereby polymerization is initiated by a redox couple where one component (tetraethylene pentamine) is hydrophilic and the other (cumene hydroperoxide) is hydrophobic. This should promote grafting at the interface between hydrophobic...
Protocols were examined for the measurement of rates and enthalpies of polymerization (ΔH p ) using reaction calorimetry. ΔH p was determined to be 70.2kJmol −1 for a series of seeded styrene emulsion polymerizations under typical emulsion conditions, in good agreement with literature values. However, there was a significant deviation from this value for small-particle systems,...
A means is developed for forming polysaccharide-based composites with useful material properties through use of unmodified and chemically modified natural rubber latex (NRL). Starch was used as a model for polysaccharides. The NRL was modified by grafting with dimethylaminoethyl methacrylate (DMAEMA) to form a latex with cationic water-soluble polymeric ‘hairs’ of polyDMAEMA, which should form hydrogen...
The free-radical polymerization propagation rate coefficient (k p ) of acrylic acid (AA) was calculated using transition state theory and ab initio quantum chemistry in order to shed light on the very strong solvent effects observed experimentally. Calculations were performed using a gas-phase reaction simulation, and the contribution of solvent then taken into account using the Polarizable...
The two-component redox-initiation system, cumene hydroperoxide (CHP) and tetraethylene pentamine (TEPA), was used to polymerize dimethylaminoethyl methacrylate (DMAEMA) in the presence of synthetic polyisoprene latexes. The modified latex particles are postulated to possess a ‘hairy layer’ of surface-grafted poly(DMAEMA) chains formed via an abstraction reaction between cumyloxy radicals and the...
Kinetic behavior in emulsion polymerization can be conveniently assigned as either 'zero-one' or 'pseudo-bulk'. Sufficiently small particles in emulsion polymerizations obey zero-one kinetics, where entry of a radical into a particle which contains a growing radical leads to instantaneous termination. Pseudo-bulk kinetics applies to particles in which more than one free radical can co-exist for a...
Seeded and ab initio emulsion polymerizations of isoprene using redox initiation systems were investigated and suitable reaction conditions determined to prepare polyisoprene latexes with minimal cross-linking. Polymerizations initiated with the potassium persulfate/sodium bisulfite (KPS/SBS) redox couple had a significant inhibition period and low yield. Polymerizations initiated with the tert-butyl...
Electrosterically stabilized polystyrene latexes with a poly(acrylic acid) hydrophilic layer with either perdeuterated core or perdeuterated hydrophilic layer were prepared in situ in a styrene/acrylic acid copolymerization, in a manner similar to that commonly employed industrially. Small angle neutron scattering (SANS) measurements were made over a range of contrasts for three latexes at high and...
A strategy is explored for synthesizing latex particles with polystyrene cores and poly(vinyl acetate) shells. The seed particles are poly(vinyl acetate), which theory indicates should be immune to secondary particle formation when a second-stage seeded emulsion polymerization with styrene is carried out. The objective is to form a single hydrophobic core by inversion of the second and first stages...
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