Role of the Soft and Hard Segments Structure in Modifying the Performance of Acrylic Adhesives Modified by Polyurethane Macromonomers

Acrylic pressure sensitive adhesives, modified by polyurethane (PU), achieve selective optimization through the designability of polyurethanes. In this paper, PU macromonomers were prepared by a two-step synthesis method, using polypropylene glycol or polyethylene glycol with different molecular weights as soft segments and different types of diisocyanates: isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethylmethane diisocyanate (HMDI), 2,4-toluene diisocyanate (TDI), and 4,4′-diphenylmethane diisocyanate (MDI) and chain extenders as hard segments. After being terminated by capping agents, a series of PU macromonomers of different molecular weights and structures were obtained and used to modify the acrylic base adhesives. Compared to unmodified adhesives, acrylic adhesives modified by PU macromonomers have improved adhesion performances and heat resistance and show an increasing trend with the increase of molecular weight of diols. Diols with a molecular weight of 600 have the best effect. Diisocyanates containing benzene rings can better improve the thermal performance of adhesives, where PMDI containing a biphenyl ring is the best, while aliphatic isocyanate groups have a greater improvement in adhesion performance, and the adhesion performance of PHDI with a long carbon chain is the best.