Manipulation of chain transfer agent and cross-linker concentration to modify latex micro-structure for pressure-sensitive adhesives

Abstract

Abstract N -Dodecyl mercaptan (NDM) chain transfer agent and allyl methacrylate (AMA) cross-linker were used to manipulate latex properties in a starved seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA) or with a third monomer, acrylic acid (AA). Latexes with higher gel content and lower sol polymer molecular weight ( M w ) were produced by adding only AMA. On the other hand, latexes with lower gel content and M w were produced by adding only NDM. In addition, at a constant AMA concentration (0.2 phm), the addition of NDM (0.2 phm) decreased gel content, increased molecular weight between cross-linking points ( M c ), and decreased M w . Adding more NDM (to a total of 0.4 phm) further decreased the gel content, while decreasing the tested M c and increasing M w . It was also found that using higher concentrations of both AMA and NDM could produce latex with similar gel content, but smaller M c and M w , compared to the latex produced at lower concentrations of both NDM and AMA. Regarding the influence of AA, gel content was increased and M w was significantly decreased with an increase in AA concentration and a decrease in MMA concentration. The performance of the latexes was evaluated for application as a pressure-sensitive adhesive (PSA).