Polyanhydride

Biodegradable polymers, such as polyanhydrides, are capable of releasing physically entrapped or encapsulated drugs by well-defined kinetics and are a growing area of medical research.

The rapid degradation and limited mechanical properties of polyanhydrides render them ideal as controlled drug delivery devices.

Aliphatic polyanhydrides consist of R groups containing carbon atoms bonded in straight or branched chains.

This class of polymers is characterized by a crystalline structure, melting temperature range of 50–90 °C, and solubility in chlorinated hydrocarbons.

Properties of this class include a crystalline structure, insolubility in common organic solvents, and melting points greater than 100 °C.

Characterization of polyanhydrides determines the structure, composition, molecular weight, and thermal properties of the molecule.

Traditionally, polyanhydrides have been prepared by melt condensation polymerization, which results in high molecular weight polymers.

Melt condensation polymerization involves reacting dicarboxylic acid monomers with excess acetic anhydride at a high temperature and under a vacuum to form the polymers.

Some of the other methods include: microwave heating, high-throughput synthesis (synthesis of polymers in parallel), ring opening polymerization (removal of cyclic monomers), interfacial condensation (high temperature reaction of two monomers), dehydrative coupling agents (removing the water group from two carboxyl groups), and solution polymerization (reacting in a solution).

The chemical structure and composition of polyanhydrides can be determined using nuclear magnetic resonance (NMR) spectroscopy.

Aside from using NMR to determine a polyanhydride’s molecular weight, gel permeation chromatography (GPC), and viscosity measurements may also be used.