Homo- and block copolymers coalesced from their cyclodextrin-inclusion compounds

Homo- and block copolymers coalesced from their cyclodextrin-inclusion compounds 

Each of the behaviors unique to coalesced PET can be attributed to the g tg + kink conformations assumed by its ethylene glycol fragments when included in the narrow channels of its y-CD-IC, which are compared schematically in Fig. 11.3 (bottom) to the dll-trans crystalline conformation (top) of PET. The kink conformations are nearly as extended as the crystalline, ll-trans conformation, but they have a smaller cross-section, which explains their preferential inclusion in the narrow channels of its y-CD-lC (see Fig. 11.1). When coalesced from its y-CD-IC the PET chains can readily and rapidly convert to the all-trans conformation through simple counter rotations about the —CH2—O— bonds and therefore crystallize. Normal melts of PET consist of chains with predominantly g —CH2—CH2— bonds, which must be rotated to the trans conformation during crystallization. This conformational transition is difficult to accomplish without long-range movements of chain segments, consistent with the normally slow crystallization rate of PET. Furthermore, both solid-state FTIR and C-NMR observations 

3 Schematic of the crystalline aW-trans (top) and y-CD-included g tg + gauche trans-gauche kink +) (bottom) conformations of PET. 

The nanostructuring of PET by processing with y-CD has important consequences for other macroscopic properties. For example, con5)ared with PET annealed at high temperature to achieve the same level of crystallinity as coalesced PET, the coalesced sample has a higher density and exhibits a 

When coalesced from its a-CD-lC, the structure and properties of the biodegradable-bioabsorbable di-block copolymer (PCL-b-PLLA) are found to be significantly different from the as-synthesized sample, as can be seen in Table 11.1. Note, for example, that both the levels of block phase segregation and crystallinity are substantially reduced in the coalesced di-block. This results in a much more rapid biodegradation of the coalesced di-block, compared with the as-synthesized sample, which is critical to several of its potential applications. 

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