Amorphous polymer networks

As mentioned above (Section 4.2), infra-red absorption bands of amor- 

Here A and t are the extension ratio and tensile stress respectively, V is the volume of the strained specimen and a reference volume which may usually be taken as the unstrained volume. p,R,T, and A/ , are, respectively, density, gas constant, absolute temperature and repeat unit molecular weight. The parameter G, defined by Flory and Abe, provides a measure of the average correlation of local transition moment directions with respect to the chain end-to-end vector. Positive values of denote a tendency for the transition moments to orient in line with the end-to-end vector and negative G values are characteristic of 

Local orthogonal axes defined by Flory and Abe for the conformations 

Values of GJ (or f%) were evaluated for various conformational sequences and transition moment directions in polyethylene. Table 1 lists some selected values which are considered, on the basis of Snyder s assignments, to be appropriate to the major amorphous infra-red absorptions. Values taken from Flory and Abe s work correspond to transition moment directions along local axes chosen to conform with symmetry features for the various conformations, as illustrated in Fig. 10 (a), (b) and (c). The values obtained from Nagai each refer to the axes specified in Fig. 10(c). All values correspond to a temperature of 140°C and to conformational energies Eg = 500 cal/mol and Egg- = 2500 cal/mol, Eg and gg being the energies of g and gg states, respectively, relative to reference trans states of zero energy. 

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General quantitative relations between observed dichroic ratios and structural orientation functions have been considered by several authors. These include Fraser,Beer, Patterson and Ward, Stein, Chappel, Kawai and Stein, and Nomura et al More recently, Flory and Abe, and also Nagai, have carried out statistical calculations relating specifically to the stress-dichroism coefficients of amorphous polymer networks. Some results of these calculations will be summarised below. First, however, it is informative to derive some general relationships between the dichroic ratio and appropriate orientation functions. 

Fig. 1 Four types of SMPs (dual-shape effect) depicted as a function of their dynamic thermomechanical behavior. Plotted is the tensile storage modulus vs temperature as measured using a smtdl oscillatory deformation at 1 Hz for (a) Cat. A-I, chemically crosslinked amorphous polymer network (7, = Tg) (b) Cat. A-II, chemically crosslinked semicrystalline polymer networks (Ttrans = 7m) (c) Cat. B-I, physically crosslinked thermoplastic with r,ra,K = 7g and (d) Cat. B-II, physically crosslinked thermoplastic (Tlrans = Tm). Taken from ref [5], Copyright 2007. Reproduced by permission of the Roytd Society of Chemistry, http //dx.doi.org/10.1039/b615954k...

Fig. 14 Results of a strain-controlled cyclic, thermomechanical test. Results of strain-controlled cyclic, thermomechanical test of amorphous polymer network LGF2 synthesized from (ohgo[(l-lactide)-ran-glycolide]dimethaycrylates (M = 2,800gmop and Tg = 53 °C) for different Tiow (a) Tiow = 10°C and (b) Flow = 50°C n cycle number, a stress elongation. Taken and modified from ref. [13], Copyright 2007. Reproduced by permission of The Royal Society of Chemistry (RSC). http //dx.doi.oig/10.1039/b702515g...

THEORY OF SEGMENTAL ORIENTATION IN AMORPHOUS POLYMER NETWORKS AND COMPARISON WITH EXPERIMENTAL DETERMINATION OF ORIENTATION IN POLYISOPRENE NETWORKS BY FLUORESCENCE POLARIZATION... 

Kloczkowski, A., Mark, J.E. and Erman, B. (1995) A diffused-constraint theory for the elasticity of amorphous polymer networks. 1. Fundamentals and stress-strain isotherms in elongation. Macromolecules, 28,5089. 

Kausch, H.H. (1971) Elastic and ultimate behavior of amorphous polymer networks. 

As an alternative to dilute solution techniques, thermoelastic measurements on strained, amorphous polymer networks can also yield k. Mark [211,212] has reviewed this technique, which is based on the equation... 

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