Porosity aliphatic polyesters

The hydrolytic degradation behaviour of aliphatic polyesters depends on many factors such as matrix morphology, stereocomplexation, PLA configuration, chemical composition, size and porosity, dmg loading, etc. (Li, 1999,2006 Li and Vert, 1999). The influence of the factors on the degradation is discussed in the following sections. 

Another unique approach toward low 6 is to disperse fine foams in PI films, since the e of air is unity. This technique developed by Hedrick et al. [208] typically involves the preparation of PS-PAA-PS (PS polystyrene) triblock copolymer, imidization, and finally higher temperature annealing where thermally labile PS block undergoes thermolysis (depolymerization) to form submicron pores. They utilized a variety of other thermally unstable block such as poly(a-methylstyrene), poly(propylene oxide), PMMA, poly(e-caprolactone), and aliphatic polyesters and examined the effects of chemical structure, fraction, and molecular weight of the block on the resultant morphology (pore size, shape, porosity) and dielectric and thermal, and mechanical properties. In this case, the resulting porous structure depends on the initial microphase separation domain structure of the thermally labile triblock. For example, nano-foamed PI (19% porosity) prepared from triblock consisting of PMDA-3F [3F = l,l-bis(4-amino-phenyl)-l-phenyl-2,2,2-trifluoroethane] (see Fig. 62 for its structure) and poly(propylene oxide) showed a considerably lower e = 2.3) than that of the non-porous homo PMDA-3F e = 2.9) [209]. 

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