The Effect of Polymer Microstructure and Thermal Post-Treatment on Latex-Based Pressure Sensitive Adhesive Performance

Summary: Butyl acrylate/acrylic acid/2-hydroxyl methacrylate (BA/AA/HEMA, weight ratio: 96/2/2) latexes were produced via starved seeded semi-batch emulsion polymerization. The microstructure of the latex polymers was controlled by varying the amount of chain transfer agent (1-dodecanethiol). The latexes were characterized for gel content, M_c (molecular weight between two adjacent cross-linking points), M_w (molecular weight of sol polymers) and M_e (molecular weight between entanglements). From these latexes, PSA films were cast, dried, conditioned and then thermally post-treated at 120 °C to react the carboxyl and hydroxyl groups from the AA and HEMA units. Tack, peel strength and shear strength of the PSA films were then measured. The thermal post-treatment was shown to be an effective way to improve latex-based PSA performance. The effectiveness of the post-treatment was observed to depend on the polymer microstructure (M_c relative to M_e relative to M_w) of the untreated latex-based PSAs and on the gel content.