Mathew J. Ballard

Molecular weight distributions in emulsion polymerizations: Evidence for coagulative nucleation

An examination of the number molecular weight distribution from emulsion polymerizations, obtained by using gel permeation chromatography, shows that, at low conversion, a distinct maximum is present at low molecular weights, while at higher molecular weights the distribution is exponential with decay constant given by the ratio of the rate coefficients of propagation and transfer. The maximum is attributed to coagulation of precursor particles during particle formation.

Illuminating Flash Point: Comprehensive Prediction Models

Flash point is an important property of chemical compounds that is widely used to evaluate flammability hazard. However, there is often a significant gap between the demand for experimental flash point data and their availability. Furthermore, the determination of flash point is difficult and costly, particularly for some toxic, explosive, or radioactive compounds. The development of a reliable and widely applicable method to predict flash point is therefore essential. In this paper, the construction of a quantitative structure – property relationship model with excellent performance and domain of applicability is reported. It uses the largest data set to date of 9399 chemically diverse compounds, with flash point spanning from less than −130 °C to over 900 °C. The model employs only computed parameters, eliminating the need for experimental data that some earlier computational models required. The model allows accurate prediction of flash point for a broad range of compounds that are unavailable or not yet synthesized. This single model with a very broad range of chemical and flash point applicability will allow accurate predictions of this important property to be made for a broad range of new materials.

“EMULSION COPOLYMER THEORY: KINETICS AND SEQUENCE DISTRIBUTIONS”

An outline is presented a general theory which provides prescriptions for the time evolution of the copolymer composition and copolymer sequence distributions (CSD) in terms of rate coefficients for microscopic events such a homo- and cross-propagation, -termination and -transfer. Such an extension is clearly worthwhile if it enables one to quantitatively describe properties which would be expected to differ from those expected from a single average of emulsion homopolymerization properties, or from an equivalent bulk polymerization: nonsteady-state properties here are particularly important. Results indicate new methods whereby emulsion copolymerization systems can be used to create formed polymers with prescribed characteristics.