Stretching-induced swelling is investigated for polyrotaxane (PR)-based slide-ring gels with movable cross-links. The osmotic Poisson’s ratio (μ os ), which is a measure of strain-induced swelling, is examined as a function of imposed stretching (α x ) for three types of PR gels with various degrees of the mobility of slide-rings. Classical gels with topologically fixed cross-links and PR gels with constrained slide-rings exhibit α x -independent μ os . In contrast, PR gels with highly mobile slide-rings exhibit α x -dependent μ os . The μ os increases with α x in the case of moderate stretching (α x < 1.5), whereas it levels off in the case of high stretching (α x > 1.5). An increase in μ os with elongation results from the molecular pulley effect of slide-rings that homogenizes the structure of deformed networks. The pulley effect suppresses the stretching-induced swelling that originates from an entropic force to reduce the configurational anisotropy of the deformed networks.
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Murata et al. (2009) studied this question.