Number of folds per chain

The lamellar thickening proceeds through many metastable states, each metastable state corresponding to a particular number of folds per chain, as illustrated in Fig. 8. In the original simulations of [22], Kg was monitored. Rg is actually very close to the lamellar thickness due to the asymmetric shape of the lamella. The number of folds indicated in Fig. 8 were identified by inspection of the coordinates of the united atoms. This quantization of the number of folds has been observed in experiments [50], as already mentioned. The process by which a state with p folds changes into a state with p - 1 folds is highly cooperative. The precursor lives in a quiescent state for a substantial time and suddenly it converts into the next state. By a succession of such processes, crystals thicken. If the simulation is run for a reasonably long time, the lamella settles down to the equilibrium number of folds per chain. 

The average number of folds per chain may be dependent upon the degree of crystallinity, at least in the earlier stages of crystallization when lateral dimensions are relatively small. 

The lamellar thickening proceeds through many metastable states, each metastable state corresponding to a particular number of folds per chain, as illustrated in Figure 1.25. This quantization of number of folds has been observed in experiments [25], as already mentioned. The process by which a state with p folds changes into a state with p + I folds is highly cooperative. The... 

Investigation has shown that chain transfer to polymer occurs predominantly on the acetate methyl group in preference to the chain backbone one estimate of the magnitude of the predominance is 40-fold (92,93). The number of branches per molecule of poly(vinyl acetate) polymerised at 60°C is ca 3, at 80% conversion. It rises rapidly thereafter and is ca 15 at 95% conversion and 1-2 x lO" number-average degrees of polymerisation. 

The chain fold in PE must contain TG (trans-gauche) sequences, and probably six TG bond sequences are required per fold. Although the number of TG bond sequences in a solution-crystallized sample can be calculated directly, the number of folds is not available because the TG conformation can be found in cilia and other defects as well as in folds. Relative changes in the number of TG units can be observed in a sample that has been annealed because annealing reduces the number of folds and therefore increases the stem length [47,48]. 

V number of particles per unit volume I, 1, p. 36 j dispersion frequency, I, V, p 243 Vi— number of i-fold particles per unit volume, I, VII, p 280 number of monomeric groups in statistical chain element, II, IV, p 95 ... 

Figure 7 Chain folding in a polymer crystallite. The number of re-enttrant folds. per unit surface area would be much higher than sketched here,.

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