Crystalline structure, addition polymers polyesters

In the early distinction by Carrothers (1) between condensation and addition polymers, polyesters were uniformly considered as examples of the former. However it was soon appreciated that a large family of polymers could be made which were functionally "polyesters" but did not fall into the synthesis based definition of condensation polymers. This family of polymers are usually prepared by ionic routes, generally a ring opening polymerization, and are structurally different from the condensation polyesters by having a chain sense i.e. the crystalline chain conformation possesses an intrinsic dipole moment. Accordingly, a structurally based definition of polyesters in terms of "polar and non-polar" crystalline conformations will be used in this report. The non-polar molecules considered will be aromatic polyesters and the polar molecules will be polyalkanoates. 

As crystalline materials melt, their appearance transforms from opaque to transparent because the ordered structure is lost Highly amorphous polymers, including acryhcs, polycarbonate, and polystyrene do not form crystals, so are transparent (Figure 4.6). An exception is crystalline polyester poly (ethylene terephthalate) used in fizzy drinks botdes, which is transparent because its crystals are too small to interfere with hght waves. Fillers and additives usually decrease the light transmission of a plastic by scattering incident light. 

One purpose of the present investigation was to obtain some additional information on structure-crystallinity relationships in this family of polymers by the preparation of stereoregular isotactic polyesters from a single asymmetric isomer of the chiral monomer that is, from an optically-active a,a-disubstituted-s-propiolactone. Because the polymerization reaction mechanism operates through scission of the alkyl-oxygen bond and does not involve bond reorganizations at the asymmetric center, it was fully expected that polymerization of the optically-active monomer... 

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