Flexibility linkage between monomers

Such monomers with separated bifunctional sides for polymer formation diow better flexibility of the polymer by the linkage between Pc-units. The heating of (97) produces a prepolymer gel it can be processed into any desired form by additional heating. In air such polymers are stable over several thousand hours at 523-573 K. 

All polymers are formed by the creation of chemical linkages between relatively small molecules, or monomers, to form very large molecules, or polymers. As mentioned, if the chemical linkages form a rigid, cross-linked molecular structure, a thermosetting plastic results. If a somewhat flexible molecular structure is formed, either linear or branched, a thermoplastic results. Illustrations of these molecular structures are presented in Fig. IN.2. 

Poly(a-ester)s, the most expansively studied class of biodegradable polymer, contain aliphatic ester linkages in their backbone which can be cleaved hydrolytically. It is reported that mere aliphatic polyesters with practically small aliphatic chains between ester bonds can decompose over the time needed for the majority of the biomedical applications. Poly(a-ester)s demonstrate enormous diversity and synthetic flexibility and, depending on the monomeric units, can be synthesized from a variety of monomers via condensation polymerization and ring-opening routes [19]. Poly(glycolic acid) and the stereoisomers of poly(lactic acid) are the most expansively investigated poly(a-ester)s polymers. 

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