Entanglement model glassy polymers

Free volume is an intrinsic property of the polymer matrix and is created by the gaps left between entangled polymer chains. Under the free volume model the absorption and diffusion of molecules in polymers depend greatly on the available free volume. For instance, many polymers show a sorption increase as the amount of free volume increases. One of the earliest models describing this behavior was developed by Fujita et al. [32]. Since then many researchers have worked with different models based on the free volume concept to describe sorption and diffusion in the glassy state [33-36]. 

Within this section of the chapter we concentrate on the success of the tube model of viscoelastic behaviour in uncrosslinked material. In uncrosslinked material entanglements are supposed to form a tube around every polymer it they can reptate out of the tube creating a new tube. There is considerable experimental support for this picture (see ref. 14 for a general reference) which should still be valid when reptation is stopped by permanent crosslinks. Once the tube concept is accepted a rich theory of rubbery, perhaps even glassy, material can be developed. 

---