Properties of waterborne pressure-sensitive adhesives with a poly(acrylic acid)-block-poly(butyl acrylate) diblock copolymer additive

A common issue when designing polymers for pressure sensitive adhesive (PSA) applications is an inverse relationship between shear strength (cohesion) and both peel and tack (adhesion) properties. A high shear resistance can be obtained by increasing the stiffness of an adhesive. However, an increase in modulus can lead to poor wetting and limited fibrillation during debonding. High tack and peel strength require an increase in viscous properties that negatively effects shear strength.
Acrylic acid (AA) is often polymerized as a comonomer in waterborne pressure sensitive adhesives (PSA)s to aid in latex stability by electrostatic repulsion at neutral pH and improve adhesive performance. The adhesive strength is greatly affected by the location of the acrylic acid moieties on the latex particle. Introduction of AA to a polymer particle also allows for a strategy to adjust PSA performance by adjusting pH.
In the present study, a commercial PSA with 0% or 1% acid in its backbone was formulated with an amphiphilic diblock copolymer, poly(acrylic acid)-block-(butyl acrylate) (pAA-b-pBA), synthesized by reversible-addition fragmentation chain-transfer (RAFT) polymerization. It was hypothesized that the diblock copolymer would adsorb onto the soft acrylic latex particles in the emulsion state. Formation of a thin hard layer in the film state can produce a percolated network, increasing PSA cohesion without decreasing adhesion. Film drying conditions can also alter the morphology of the final film. The pH of the nanocomposites was also varied to evaluate changes in PSA properties with respect to the ionization of the AA portion of the diblock copolymer.