Acrylic emulsion pressure-sensitive adhesives (PSAs) were synthesized by the copolymerization of n-butyl acrylate with various levels of 2-ethyl hexyl acrylate (2EHA) and a small constant amount of acrylic acid. The effect of varying the n-butyl acrylate/2EHA monomer composition on the kinetic behavior of the polymerization and the characteristics of the copolymers prepared in a batch process were investigated. The results showed that increasing the amount of 2EHA in the monomer caused the polymerization rate and the glass-transition temperature of the acrylic copolymers to decrease. Increasing the amount of 2EHA caused the gel content of the copolymers to decrease, reaching a minimum at 50 wt %; thereafter, the gel content increased at higher 2EHA levels. For the acrylic emulsion, the peel-fracture energy of the PSAs decreased as the amount of 2EHA in the monomer was increased up to 50 wt %. At higher 2EHA levels, the peel-fracture energy was relatively constant. Interestingly, a synergistic effect of increased shear resistance at 25 wt % 2EHA was observed without a significant trade-off in terms of the peel and tack properties. This behavior was attributed to a good interconnection between the microgels and the free polymer chains inside the contacting particles in the adhesive film. Cooperation between various levels of 2EHA in the copolymer structure simultaneously changed the crosslink molecular weight (M c ) of the microgels and the entanglement molecular weight (M e ) of the free chains in the adhesive network morphology. The adhesive performance of the PSAs was found to be correlated with their M c /M e values as the 2EHA proportion was varied.
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