The effect of molecular weight and temperature on tack properties of model polyisobutylenes

The effect of molecular weight and temperature on the tack of non-crosslinked soft polymers was investigated using blends of low and high molecular weight polyisobutylene as model systems. Molecular weight between entanglements Me was varied systematically by changing the mixing ratio. Video-optical imaging confirms that these model systems exhibit the characteristic debonding features of pressure-sensitive adhesives, including cavitation as well as formation and deformation of fibrils. The initial peak in the stress–strain diagram is a function of both the cohesive strength and ability to wet the probe. It contributes significantly to the work of adhesion at low molecular weight, low temperature and high contact force. Beyond a critical molecular weight, debonding is dominated by fibril deformation. In this regime, the work of adhesion is essentially independent of temperature, molecular weight and the details of the fibrillation pattern (more but thinner fibrils are observed as molecular weight increases). The minimum molecular weight needed for significant fibrillation is around 850 kg/mol (≈3 Me) both at −10°C and 25°C.