Listed below are some aspects of rubberlike elasticity which are clearly in need of additional research (Mark, 2004a, b). Most have already been mentioned or will be obvious from the discussions in the preceding chapters.

• Improved understanding of dependence of the transition temperatures Tg and Tm on polymer structure

• Preparation and characterization of “high-performance” elastomers

• New cross-linking techniques

• Improved understanding of network topology

• Generalization of phenomenological theory

• More experimental results for deformations other than elongation and swelling

• Better characterization of segmental orientation, and its effects on strain-induced crystallization

• More detailed understanding of critical phenomena and gel collapse

• Additional molecular characterizations using NMR spectroscopy and various scattering techniques

• Study of possibly unique properties of bioelastomers

• Improved understanding of reinforcing effects of filler particles in a network

• Quantitative interpretation of the toughening effects of elastomers in blends and in composites, particularly the polymer-modified ceramics

• Environmental concerns ranging from elastomer synthesis to recycling

There is a real need for more high-performance elastomers, which are materials that remain elastomeric to very low temperatures and are relatively stable at very high temperatures. Some phosphazene polymers (Mark et al., 1992a, 2005b) are in this category. These polymers have rather low glass transition temperatures in spite of the fact that the skeletal bonds of the chains are thought to have some double-bond character. There are thus a number of interesting problems related to the elastomeric behavior of these unusual semi-inorganic polymers. There is also increasing interest in the study of elastomers that also exhibit the type of mesomorphic behavior described in Chapter 16.