Adjacent-reentry model

Fig. 11-4. Possible conformations of poly inerchains al the surfaces of chain-folded single crystals, (a) Adjacent reentry model with smooth, regular chain folds, (b) adjacent reentry model with rough fold surface, and (c) random reentry (switchboard) model.

From all these data analyses, we can definitely say that the D and H chain stems are distributed statistically randomly in the crystalline lamellae of the D/H cocrystallized blend. This conclusion is quite important in relation with the chain-folding problem, a controversial research theme that had been discussed for a long time (30). The random distribution of the D and H chain stems naturally supports the idea that the D and H chains reenter randomly into and out of the crystalline lamellae as shown in Fig. 5.7. The regular adjacent reentry model is impossible to apply at all as for as the melt-crystallized sample is concerned. 

Figure 5.7 Illustration of the chain-folding models, (a) A regular adjacent reentry model, (b) a random reentry model, and (c) a cluster model consisting of the mixed structures of (a) and (b). (From Reference 46 with permission from the Society of Polymer Science, Japan).

A final difficulty with the adjacent-reentry model was thought to be of a kinetic nature in that the reeling-in of long-chain molecules from the melt onto a growth face of a lamella was considered to be far too slow to account for the observed growth rates (Flory and Yoon 1978). 

FIGURE 1.5. Models of chain folding, (a) Adjacent reentry model, and (b) nonadjacent reentry model. 

What is the folded chain lamella An adjacent-reentry model A switchboard or a nonad-jacent-reentiy model ... 

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