press release

What happens to particle size distributions when making reactive surfactants and polymer colloids by emulsion polymerization?

What happens to particle size distributions when making reactive surfactants and polymer colloids by emulsion polymerization?

When we synthesize polymer colloids by emulsion polymerization, molecular surfactants are often employed. These are required to keep the polymer latex particles dispersed in the water phase, so that they do not clump together, a phenomenon known as coagulation. Keeping polymer dispersions stable is especially important in end applications, such as waterborne coatings and adhesives.

A downside of the use of surfactant molecules is that they can desorb from the surface of the latex particles. This makes the particles colloidally unstable, and they coagulate. This can be disastrous in product formulations, such as water-based paints which have many components. Another downside of this mobility of the surfactant molecules is that they can migrate in the final coating, once applied on a substrate. This leads to deterioration of the properties of the coated film.

BonLab collaborates to produce bacteria containing biocoatings

BonLab collaborates to produce bacteria containing biocoatings

We have a long history of making polymer dispersions to be used in waterborne coatings. The polymer colloids, or latex particles, are made by emulsion polymerization. Prof. Joe Keddie from the Physics Department at Surrey University contacted us if we were interested to help out on a bio-coatings project that needed some bespoke polymer latexes and colloidal formulations. With the term bio-coatings we mean here the coating formulation has the ability to entrap metabolically-active bacteria within the dried polymer film.

We loved the concept. In BonLab, PhD student Josh Booth optimized the synthesis of acrylic polymer latexes at approximately 40wt% solids with a monomodal particle size distributions. Important was to use bacteria-friendly surfactants in the semi-batch emulsion polymerization processes. Important was also to have a dry glass transition temperature of the polymer latex binder around 34 ℃, so that film formation could occur at temperatures which preserved viability of the bacteria.

The latexes were formulated as mixtures with halloysite nanoclay (hollow tubes) and E coli bacteria back at Surrey. The tubular clay was introduced to create porosity inside the polymer nanocomposite films. The overall composition of the waterborne formulation was optimized for mechanical and bacterial performance.

New method to study chain transfer in radical polymerizations

New method to study chain transfer in radical polymerizations

Synthetic polymers in most cases do not have one bespoke molecular weight. A sample typically consists of a large number of individual polymer chains, each having a different molecular weight. The average molecular weights and the shape of the molecular weight distribution are a kinetic fingerprint of how to polymer material was made. The resulting molecular weight distribution dictates physical and mechanical properties.

In free radical polymerizations, four key mechanistic events need to be considered. These are initiation, propagation, termination, and chain transfer. The latter often gets brushed under the carpet in introductory textbooks, but is pivotal.

When one targets polymers of low molecular weight, chain transfer agents are often used. One prominent class of chain transfer agents are thiol compounds, for example n-dodecanethiol. To understand how the molecular weight distribution develops throughout the polymerization process, the ability to determine the reactivity of the chain transfer agent is crucial. This reactivity is often expressed in the form of a chain transfer constant, Ctr, which is the ratio of the rate coefficients of chain transfer and propagation.