Thermoplastic film adhesives based on phenol-functional acrylic copolymers: synthesis, mechanical and adhesion properties

Acrylic polymers possessing varying proportions of pendant phenol groups we re synthesized by the free radical copolymerization of N-(4-hydroxyphenyl) maleimide (HPM) with butyl acrylate (BuA) and acrylonitrile (AN) and charac terized. These thermoplastics form excellent films and their mechanical and adhesion properties were evaluated as a function of the phenol content. En hancing the HPM content increased both the tensile strength and the modulus but decreased the elongation. A nominal increase in the phenol content was found to be conducive for improving the adhesion properties of the films. At higher concentrations, the adhesion properties showed a decreasing trend due to the embrittlement caused by the rigid maleimide groups. The adhesio n property at 50 degreesC increased linearly with the HPM content due to an increased T-g, whereas a reverse trend was observed for the adhesion prope rty measured at -196 degreesC, due to the dominance of the embrittlement ef fect. The reduced flow characteristics of the high HPM-loaded systems led t o a diminished honeycomb flat-wise tensile strength. Enhancing the HPM conc entration in the chain promoted the adhesion properties for the vulcanizati on bonding of nitrile rubber to aluminium. Addition of silica filler margin ally improved the lap shear strength (LSS) for the metal-metal system, but was detrimental for rubber-metal bonding; a reverse trend was observed for the carbon-filled system. The diminished performance for metal-metal bondin g by carbon could be attributed to the weakening of the interphase, whereas the enhanced rubber-metal bonding could be due to possible reinforcement o f the rubber phase by carbon. The fillers generally improved the high tempe rature adhesion. However, they impaired the flow properties of the resin an d, thereby, adversely affected the flat-wise tensile strength in both cases .