Poly imide typical structures

Some copolymers of poly(imides) found practical applications, typically due to their good thermal resilience. One such copolymer is poly(3,3, 4,4 -benzo-phenone-tetracarboxylic dianhydride-co-m-phenylene-4,4 -oxydianiline) with the structure indicated below ... 

Oligomers end-capped with maleimide rings, which are known as bismaleimide (BMI) resins, exhibit thermal stability intermediate between epoxies and poly-imides. BMI systems are mainly used to fabricate structural composites capable of sustaining temperatures up to 230°C. Specific versions, such as American Cyanamid FM 32 and Ciba-Geigy Kerimid 601 have been developed to prepare adhesive compositions. Fig. 17 displays a typical constitutive unit of various commercial BMI resins based on bismaleimide 38, prepared from maleic anhydride 37 and 4,4 -methylenebisbenzeneamine (MDA) 34. 

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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