Independent control of sol molar mass and gel content in acrylate polymer/latexes

Poly n-butylacrylate latexes are commonly used as the base ingredient in the formulation of pressure sensitive adhesives, PSA. In the typical starved semi-batch process carried out to produce this latex and due to the non-linear nature of the kinetics, chain transfer to polymer plus bimolecular termination by combination, polymer networks are produced. The molar mass distribution of these polymer latexes is characterized by a soluble and an insoluble fraction, so-called gel. Both fractions strongly affect the adhesion properties, but unfortunately the independent control of these properties is a difficult task, that has not been solved yet. In this work, the concentrations of chain transfer agent and cross-linker were used in an attempt to exercise control over the molar mass of the soluble part and the amount of gel polymer. It was found that by simultaneously manipulating both variables it was possible to modify the gel content of the polymer without completely sacrificing the sol molar mass. The adhesion properties, tack and resistance to shear, measured on films cast from the latex demonstrated that a good PSA can be obtained by properly balancing the amount of CTA and cross-linker in the formulation.