Aramids polymerization methods

The most common method for obtaining aramids is the reaction of diamines with dicarboxylic add chlorides in a dipolar aprotic solvent at low temperature. N/f-Dimethylacetamide (DMAc), N-methylpyrrolidinone (NMP) and tetramethylurea (TMU) are the preferred solvents for such polymerizations, giving good polymer solubility and acting as add acceptors. However, as the molecular weight builds up, organic solvents alone are not sufficient to keep aramids in solution. However, addition of lithium chloride and/or caldum chloride to DMAc has been shown to greatly increase polymer solubility. ... 

More recendy, aramids have been obtained by direct polycondensation of aromatic dicarboxylic adds and aromatic diamines in amide solvents using triphenyl phosphite and pyridine as condensing agents. This method uses dicarboxylic acids which are easier to handle than acid chlorides and eliminates the additional step of converting the dicarboxylic adds into add chlorides. Lithium chloride and calcium chloride have also been added to these polymerization mixtures to increase polymer solubility. This method has been used to synthesize both flexible and rodlike polyamides with high inherent viscosity values (ie, up to 6.2 dL/g). It has also been shown that additional triphenyl phosphite ensures complete polymerization with... 

The preparation of aramids by direct polycondensation of aromatic diamines with aromatic dicarboxylic acids using triphenyl phosphite and pyridine as condensing agents has been well documented. This method was used here to polymerize the commercially available diamines, 4,4 -oxydianiline (ODA) and 1,4-phenylenediamine (PDA), with 10,11,15, and 16. Polymers obtained with this method formed fibrous precipitates on pouring the reaction mixtures into stirring methanol. Essentially quantitative yields were obtained for all systems evaluated. High molecular weight... 

---