General properties of polymer networks - Physical Gels from Biological and Synthetic Polymers - page 122

G ) spectra of telechelic ionomers also show the presence of double peaks (Agarwal

and Lundberg, 1984 ). For poly(isoprene) ionomers with carboxylate, amine and zwit-
terion end groups, the shift factors for the frequency dependence of the G 0 (

″ ( ω

ω ) spectrum

could reach very high values (10 5 10 7 ) at room temperature, before the network even- -

tually relaxed (Fetters et al., 1988 ).

4.5 Conclusions

For permanent rubber-like polymer networks, the science and the development of theory
can be said to be quite mature. The essential assumption of classical rubber elasticity, that
the retractive forces are entropic, is well accepted, and development of the theory is
essentially now concerned with second-order effects. There still remain some controver-
sies, but they are well discussed in texts such as the monograph by Erman and Mark
( 1997 ), and we do not consider them further in this volume.
By contrast, for temporary networks

it appears from
both the models and the experiments that the rheological response of linear polymers melts
and concentrated solutions can be considerably modi

- the topic of major interest to us -

ed by the introduction of associating
groups which can be either end-capped or randomly distributed along the chains. The
viscoelasticity of such systems depends on the structure of the network (for example, low
functionality junctions, micelles and entanglements) and on the lifetime of the clusters
formed by the associating groups. Most studies have been devoted to telechelic materials,
some on polymers with only one functionalized chain end. More detailed results and
comparisons with theory will be discussed in Chapter 6 for triblock copolymers.

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