Noncorrosive Pressure-Sensitive Adhesives of Acryl Polymers by Sulfur-Free Addition–Fragmentation Chain Transfer Agents

A series of sulfur-free chain transfer agents (CTAs) for radical polymerization were synthesized to control the molecular weight of acrylic polymers for pressure-sensitive adhesion (PSA). PSAs are commonly used in daily life and industrial manufacturing, and their mechanical properties can be tuned by balancing adhesion and cohesion depending on the molecular weight of the polymer. The molecular weight is typically controlled by adding CTAs, such as n-dodecyl mercaptan (NDM), to the radical polymerization system, although sulfur compounds often cause problems, such as bad smell and metal corrosion. Therefore, sulfur-free CTAs were designed by substituting methacrylates and methacrylonitrile with phenyl groups and malonate skeletons. Among them, CTA containing a methacrylonitrile skeleton functioned efficiently in the solution and suspension polymerizations of (meth)acrylates, although it exhibited lower reinitiation efficiency than NDM. Nevertheless, the extension of the reaction time to 6 h resulted in monomer conversion and number-average molar mass (Mn) comparable to the polymerization in the presence of NDM. The resulting polymers did not lead to copper corrosion, while the PSAs prepared with these polymers exhibited mechanical properties comparable to those of conventional PSA in peel, creep, and probe-tack tests. PSAs that realize sufficient strength and no metal corrosion are particularly effective in applications involving LED elements and electronic circuit boards, where silver electrodes and wires are in direct contact with PSAs.