In polyester anhydrides the inclusion of a proportion of anhydride linkages in a polymer in which the remaining linkages are either coaxial, that is are positioned 1,4- to each other if attached to the same ring, or if in different rings are in positions parallel and oppositely directed, results in improvements in processability of the polymer.  For example, a polymer of p-hydroxybenzoic acid or polymers of unsubstituted dihydric phenols and unsubstituted dicarboxylic acids are polymers which are intractable or processable only with difficult because they tend to decompose before melting.  The inclusion of at least 5% of anhydride linkages in such polymers introduces a degree of flexibility into the otherwise rigid chain which enables the melting point of the polymer to be reduced to an extent that a substantially non-melt-processable polymer is then capable of being melt processed.  In addition to converting non-melt-processable polymers into melt-processable polymers the inclusion of a proportion of anhydride linkages can improve the processability of a polymer which is already melt processable.  The physical properties of the polymer, such as toughness, melt strength, extensibility may also be improved.

Surprisingly, a considerable range of the polymers according to the invention exhibit liquid crystal behaviour in the melt (thermotropic behaviour).  Useful advantages may be obtained by incorporation of the anhydride linkages even though the resulting polymer is not thermotropic.

The mixed anhydrides may be prepared by the known processes, such as by heating an appropriate dicarboxylic acid in the presence of an excess of an anhydride of a monofunctional carboxylic acid, such as acetic anhydride.  Alternatively free acids or their alkali metal salts may be reacted with acyl chlorides.

(Griffin and MacDonald, US Patent 4,414,381, 11/8/1983)

Polyester Anhydride Drug Delivery    
Polyesters  
Polymers /Resins  

Comments