Polyanhydrides

Polyanhydride Chemistry

“…(2) Involving polymerization of prepolymer units at elevated temperature under high vacuum conditions to get a PA with a degree of polymerization of 100 to over 1000. This method is successful in the synthesis of a variety of aliphatic, aromatic, aliphatic-aromatic, and fatty acid-based Pas. − ,− ,− A variety of coordination metal catalysts has been used for the synthesis of high molecular weight PAs with shorter reaction time. Some of these catalysts include calcium oxide, barium oxide, cadmium acetate, diethyl zinc, and calcium carbonate.…”

“…PAs are classified into aromatic, aliphatic, and unsaturated PAs. − ,− ,− However, owing to the use of PAs for biomedical applications, other subclasses such as aromatic–aliphatic, cross-linked, and fatty-acid based PAs have also been developed. The classification of PAs is mainly based on the type of monomer unit connected through an anhydride bond.…”

“…For example, the synthesis of poly­(isophthalic anhydride) and poly­(terephthalic anhydride) has been provided in Scheme . A gamut of aliphatic, aromatic, unsaturated PAs, and combinations thereof have been developed by several research groups employing the method depicted below. − ,− ,− This is currently the most widely employed method for the synthesis of PAs …”

“…Moreover, the rate hydrolysis of PAs is much higher due to shorter average half-lives than other classes of biodegradable polymers such as polyesters, polycarbonates, and amides . These characteristics allowed PAs as surface-eroding drug delivery carriers in various forms such as biomedical implantable devices, microparticles, nanoparticles, microspheres, pasty formulations, etc. − ,− By altering the type and ratio of the monomer microstructure, a variety of biocompatible PAs were developed with controlled drug release characteristics and predictable hydrolytic degradation rates. − ,− …”

“…Considering rapid hydrolytic degradation of the PAs as an important characteristic for drug delivery applications, in 1983 Langer et al exploited the use of these materials for the first time as biodegradable drug delivery carriers . Following this outstanding invention, exhaustive research has been conducted over the years by several research groups and industries, resulting in numerous research articles and patents. − ,− ,− The majority of these studies focus on the development of new PA structures, scalable synthetic schemes, physical and chemical characterization, toxicity studies, degradation kinetics, and their applications in the controlled and localized delivery of low/high-molecular-weight therapeutic agents and bioactive compounds. In biomedical applications, a “Gliadel wafer” using poly­(sebacic acid- co -1,3-bis­(p-carboxyphenoxy)­propane) (P­(CPP-SA)), has been approved by the FDA to deliver the chemotherapeutic agent 1,3-bis­(2-chloroethyl)-N-nitrosourea (BCNU) for the treatment of brain cancer. ,− However, this is the only PA-based product available commercially in the market.…”