Amorphous polymers folded chain model

If the ordered, crystalline regions are cross sections of bundles of chains and the chains go from one bundle to the next (although not necessarily in the same plane), this is the older fringe-micelle model. If the emerging chains repeatedly fold buck and reenter the same bundle in this or a different plane, this is the folded-chain model. In either case the mechanical deformation behavior of such complex structures is varied and difficult to unravel unambiguously on a molecular or microscopic scale. In many respects the behavior of crystalline polymers is like that of two-ph ise systems as predicted by the fringed-micelle- model illustrated in Figure 7, in which there is a distinct crystalline phase embedded in an amorphous phase (134). 

Numerous studies of the structure and properties of drawn crystalline polymers have led to the microfibrillar model of fibrous morphology177 179 180. According to Peterlin 179) and Prevorsek et al. 180), the long and thin microfibrils are the basic elements of the fibrous structure. The microfibrils consist of alternating folded chain crystallites and amorphous regions. The axial connection between the crystallites is accomplished by intrafibrillar tie-molecules inside each microfibril and by inter-fibrillar tie-molecules between adjacent microfibrils. 

Fig. 1.2 Model of a semic stalline polymer showing chain-folded c stallites embedded in an amorphous matrix (Reproduced from [37a]).

We reconsidered the folded-chain fringed-micelle model, proposed nearly forty years ago, and found it to be appropriate to explain mesophase ordering and crystallisation in the polymer melt and amorphous state. Putting together the evidence provided by Strobl for crystallisation as a multi-stage process [13], the folded-chain fringed-micellar grain model [202-206], the smectic phase of iPP [6,152,153], density fluctuation before crystalliza-... 

Figure 5.5 Models of the amorphous state in pictorial form, (a) Flory s random coil model the (b) Privalko and Lipatov randomly folded chain conformations (c) Yeh s folded-chain fringed-micellar model and (d) Pechhold s meander model. Models increase in degree of order from (a) to (d). References, (a) P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY, 1953. (b) V. P. Privalko and Y. S. Lipatov, Makromol. Chem., 175, 641 (1972). (c) G. S. Y. Yeh, J. Makoromol. Scl. Phys., 6, 451 (1972). (cf) W. Pechhold, M. E. T. Hauber, and E. Liska, KolloIdZ. Z. Polym., 251, 818 (1973). W. Pechhold, lUPAC Preprints, 789 (1971).

Hence, the results of the present section demonstrate that local order domains (clusters) in the cluster model of the amorphous state structure of polymers by both physical significance (let us be reminded that clusters have thermofluctuational origin [7, 8]) and their critical sizes correspond to heterophase fluctuations, which become nucleus crystallites. Let us note that dynamic local order domains in the devitrificated state can consist partly of folded chains unlike those in a glassy state. Results obtained for... 

Not only did it substantiate the Robertson prediction of djd. 0.65 for a random coil but it adopted Robertson s idea of chain folding in amorphous polymers as a viable model for the amorphous state. 

Fig. 15. Hie "random-coil" folded-chain fringed micelle grain model based on Fig. 6 of ref. 103, but first proposed by Yeh in 1972 in refs. 101 and 102. See Fig. 4 of ref. 102 for amorphous and crystalline polymers, and Fig. 6 of ref. 102 for PE.

As discussed earlier, solid polymers can be distinguished into amorphous and the semicrystalline categories. Amorphous solid polymers are either in the glassy state, or - with chain cross linking - in the rubbery state. The usual model of the macromolecule in the amorphous state is the "random coil". Also in polymer melts the "random coil" is the usual model. The fact, however, that melts of semi-crystalline molecules, although very viscous, show rapid crystallisation when cooled, might be an indication that the conformation of a polymer molecule in such a melt is more nearly an irregularly folded molecule than it is a completely random coil. 

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