Thermoplastic polyurethane elastomers (TPUs) of constant composition were prepared by using the prepolymer method and by changing the reaction conditions (prepolymerization and chain-extension time) to study the influence of these conditions on the final TPU properties. The TPUs were characterized by gel permeation chromatography, differential scanning calorimetry, strain-stress measurements, and contactangle measurements. To test the adhesion properties of the TPUs, poly(vinyl chloride) strips were bonded to each other by using TPU solutions and the T-peel strength of the adhesive joints was measured. It was found that provided a threshold is crossed, the prepolymerization time markedly influences the final properties of the TPUs (viscosity of solutions, molecular weight, mechanical and adhesive behavior), whereas the chain extension time does not. Therefore, it is possible to prepare TPUs with specific properties by playing with the prepolymerization conditions.

No abstract

Pressure-sensitive adhesives must develop simultaneously two conflicting properties:  adhesion and cohesion. To fulfill these requirements, it is imaginable to synthesize suitable materials by free-radical emulsion copolymerization of complementary monomers:  methyl methacrylate (MMA) and 2-ethylhexyl acrylate (EHA). The copolymerization kinetics of various MMA/EHA mixtures is studied using a “batch” process. In all cases, the reaction proceeds at a steady-state rate and the copolymer composition (evaluated by 1H NMR analysis) is quite proportional to the conversion degree. The tack properties of films obtained by coalescence of the latexes are evaluated using a “mechano-optical tack tester”, which allows one to determine the tack strength (F tack), the tack energy (G tack), and the actual contact area (A) as functions of time. These tack properties are correlated with the copolymers and adhesive film structures.