Aliphatic aromatic polyanhydrides

Aliphatic-aromatic polyanhydrides, which are synthesized starting from diacids, having aliphatic and aromatic moieties. 

Several new series of polyanhydrides with advantageous properties for a variety of applications were also synthesized (8). The first ai e aliphatic-aromatic homopolyanhydrides of the structure... 

The analysis of 1H NMR spectra of aliphatic and aromatic polyanhydrides has been reported by Ron et al. (1991), and McCann et al. (1999) and Shen et al. (2002), and 13C NMR has been reported by Heatley et al. (1998). In 1H NMR, the aliphatic protons have chemical shifts between 1 and 2 ppm, unless they are adjacent to electron withdrawing groups. Aliphatic protons appear at about 2.45 ppm when a to an anhydride bond and can be shifted even further when adjacent to ether oxygens. Aromatic protons typically appear with chemical shifts between 6.5 and 8.5 ppm and are also shifted up by association with anhydride bonds. The sequence distribution of copolymers can be assessed, for example in P(CPH-SA), by discerning the difference between protons adjacent to CPH-CPH bonds, CPH SA bonds, and SA-SA bonds (Shen et al., 2002). FTIR and 111 NMR spectra for many of the polymers mentioned in Section II can be found in their respective references. 

Domb, A., and Langer, R. Poly(anhydrides) III. (Polyanhydrides) based on aliphatic-aromatic diacids. Macromolecules 22 3200—3204, 1989. 

Several combinations of monomers used to prepare polyanhydrides are classified as aliphatic, aromatic, aliphatic-aromatic, amine-based, and fatty acid-based polyanhydrides. The structures of these monomers determine... 

Polyanhydrides Polyanhydrides have a hydrophobic backbone with a hydrolytically labile anhydride linkage. These polymers widely vary in chemical composition and include aliphatic, aromatic, and fatty acid-based polyanhydrides. The rate of degradation depends on the chemical composition of the polymer. In general, aliphatic polyanhydrides degrade more rapidly than the aromatic polymer. Hence, copolymer blends with varying ratios of aliphatic-to-aromatic polyanhydrides can be synthesized to suit specific applications. 

The stability of polyanhydrides in a solution was studied using chloroform under dry nitrogen atmosphere at 37°C.f The aromatic polyanhydrides remained stable under these conditions during a three-day period, while copolymers with aliphatic S A had a significant molecular weight loss during the same time period. Therefore, polyanhydrides can be processed in a solution environment as long as the time is not extended more than this period. 

The melting point, as determined by differential scanning calorimeter, of these aromatic polyanhydrides is mnch higher than aliphatic polyanhydrides. The melting point of aliphatic-aromatic copolyanhydrides is proportional to aromatic content. For this type of copolymers, there is characteristically a minimnm between 5 and 20mol% of lower-melting component. The introdnction of fatty acids in the copolymer chain lowers the melting point as compared to that of bulk polymer [14]. 

The majority of polyanhydrides dissolve in solvents such as dichloromethane and chloroform. However, the aromatic polyanhydrides exhibit much lower solubility than aliphatic polyanhydrides. But the copolymers of two different aromatic monomers showed increased solubility with a decrease in T [15]. 

Owing to their pronounced hydrolytic instability, polyanhydrides have therefore been explored as degradable implant materials. Aliphatic polyanhydrides degrade within days whereas some aromatic polyanhydrides degrade over several years. Thus, aliphatic-aromatic copolymers, having intermediate rates of degradation, are usually employed. 

R = aliphatic, aromatic and a heterocyclic organic residue Scheme 5.6 Synthesis of polyanhydrides by solution polymerisation technique. 

The melting points of a large number of polymers have been determined and are shown in Table 2. Aliphatic polyanhydrides generally melt at lower temperatures than do aromatic polyanhydrides. The melting point of aromatic-aliphatic copolymers is proportional to the aromatic content in the copolymer. Introduction of fatty acids in copolymers also lowers the melting point of the bulk polymer. 

Details first report on synthesis of aromatic polyanhydride (1909) aliphatic polyanhydrides were reported in 1930-1932 in 1983 polyanhydrides were studied for drug delivery ... 

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