Polyanhydrides cross-linked

Similar to polyorthoesters, polyanhydrides have been investigated primarily for orthopaedic applications. FFowever, the modest Young s Modulus for entangled polyanhydride networks has limited their application in weight-bearing environments [47]. This limitation resulted in further studies involving the formation of cross-linked polyanhydrides networks with incorporated imides [53,77]. Scaffolds formed... 

A considerable number of non-cross-linked aromatic and heterocyclic polymers has been produced. These include polyaromatic ketones, aromatic and heterocyclic polyanhydrides, polythiazoles, polypyrazoles, polytriazoles, poly-quinoxalines, polyketoquinolines, polybenzimidazoles, polyhydantoins, and polyimides. Of these the last two have achieved some technical significance, and have already been considered in Chapters 21 and 18 respectively. The most important polyimides are obtained by reacting pyromellitic dianhydride with an aromatic diamine to give a product of general structure (Figure 29.17). 

As pointed out by Heller (2), polymer erosion can be controlled by the following three types of mechanisms (1) water-soluble polymers insolubilized by hydrolytically unstable cross-links (2) water-insoluble polymers solubilized by hydrolysis, ionization, or protonation of pendant groups (3) hydrophobic polymers solubilized by backbone cleavage to small water soluble molecules. These mechanisms represent extreme cases the actual erosion may occur by a combination of mechanisms. In addition to poly (lactic acid), poly (glycolic acid), and lactic/glycolic acid copolymers, other commonly used bioerodible/biodegradable polymers include polyorthoesters, polycaprolactone, polyaminoacids, polyanhydrides, and half esters of methyl vinyl ether-maleic anhydride copolymers (3). 

Many cyclic acid anhydrides are used industrially for cross-linking epoxy resins. These are mono and polyanhydrides. Following are some typical commercially used anhydrides ... 

Unsaturated homopolymers are crystalline and insoluble in common organic solvents, whereas copolymers with aliphatic diacids are less crystalline and soluble in chlorinated hydrocarbons. The unsaturated polyanhydrides also provide a means for cross-linking through the double bonds that remain intact during the polymerisation process, and thus their mechanical properties can be improved (Domb et al., 1991). 

Domb, A.J., Mathiowitz, E., Ron E, Giannos, S. and hanger, R. (1991) Polyanhydrides IV. Unsaturated and cross-linked poly(anhydrides)./. Polyrn. Sci. Part A Polymer Chemistry, 29, 571. 

Bhardwaj and Mohanty [8] proposed and demonstrated a new industrially relevant methodology to develop a polylactide (PLA)-based nano blend having outstanding stiffness-toughness balance. In this approach, a hydroxyl functional hyper branched polymer (HBP) was in situ cross-linked with a polyanhydride (PA) in the PLA matrix during melt processing. There was formation of new HBP-based cross-linked particles in the PLA matrix. TEM and AFM revealed the sea-island morphology of... 

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