Manipulating Latex Polymer Microstructure Using Chain Transfer Agent and Cross‐Linker to Modify PSA Performance and Viscoelasticity

Two series of butyl acrylate (BA)/acrylic acid (AA)/2‐hydroxy ethyl methacrylate latexes were produced via starved seeded semi‐batch emulsion polymerization. The first series, five latexes with gel contents ranging from 0 to 75 wt.‐%, were generated by varying the amount of chain transfer agent (CTA, n‐dodecyl mercaptan) in the absence of cross‐linker. The second series, two latexes with gel contents of 49 and 74 wt.‐%, were obtained by manipulating the amount of CTA in the presence of a constant cross‐linker (allyl methacrylate) concentration. Latexes with similar gel contents, one from each series, were compared with respect to their microstructure, viscoelastic properties and pressure‐sensitive adhesive performance. At similar gel contents, latexes obtained in the absence of cross‐linker had larger sol polymer molecular weight (M̄ _ w ) and molecular weight between cross‐linking points (Mc), compared to the latexes generated using both CTA and cross‐linker. The different microstructures of latexes with similar gel contents resulted in significantly different viscoelastic properties and shear strength of the pressure‐sensitive adhesive films cast from the latexes. magnified image