Simultaneous Free‐Radical and Addition Miniemulsion Polymerization: Effect of the Chain Transfer Agent on the Microstructure of Polyurethane‐Acrylic Pressure‐Sensitive Adhesives

Abstract

The effects of the CTA concentration on polymerization kinetics, polymer microstructure, particle morphology, and adhesive performance of waterborne hybrid PSAs prepared by simultaneous free‐radical and addition miniemulsion polymerizations are studied. The development of the microstructure is shown to differ from waterborne acrylic PSAs obtained by free‐radical polymerization because of the contribution of the addition reaction, which in turn causes marked differences in the adhesive performance of the final films. A computer simulation is developed to obtain detailed information about the microstructure of PU/acrylic hybrids and to correlate the microstructure with the final adhesive properties.magnified image

Influence of Polyol Molecular Weight and Type on the Tack and Peel Properties of Waterborne Polyurethane Pressure‐Sensitive Adhesives

“…Polymers made using bisphenol A as the chain extender led to adhesives with greater shear resistance, probably because of the resulting higher crosslinking density and acceptable viscoelasticity. In later work, the same group found that increasing the chain transfer agent (CTA) concentration increased the tack adhesion because of a lower gel content and greater chain mobility . However, there was an upper acceptable limit for the CTA concentration before there was lower cohesion.…”

Role of Grafting on Particle and Film Morphology and Film Properties of Zero VOC Polyurethane/Poly(meth)acrylate Hybrid Dispersions

“…The use of a functional monomer that can introduce double bonds in the PU chains that subsequently can participate in the free‐radical polymerization of (meth)acrylics offers a way to produce grafted hybrids and improve the compatibility between PU and (meth)acrylics . Functional monomers containing both hydroxyl and (meth)acrylic groups are interesting because this dual functionality allows the monomers to react with the isocyanate groups during the formation of the polyurethane and with radicals during the formation of the poly(meth)acrylic chains.…”

Challenges and Opportunities in Continuous Production of Emulsion Polymers: a Review

“…[47] The results reported in terms of adhesive properties (tack measured as work of adhesion, peel resistance, and shear resistance measured as shear adhesion failure temperature, SAFT) showed that the incorporation of PU allowed obtaining a very high shear resistance (equivalent to solvent PSAs) with quite good values of peel resistance and work of adhesion ( Figure 12). Trying to further improve these PSAs, we realized that in the experiments carried out by Lopez et al, [44][45][46][47] the branching of acrylates was not controlled. In the polymerization of acrylic monomers, temperature plays a critical role because the activation energies of the transfer to polymer reactions are higher than that of propagation.…”