Aramids direct polymerization

Reichert and Mathias prepared related branched aramids, to those of Kim,t5-34] from 3,5-dibromoaniline (23) under Pd-catalyzed carbonylation conditions (Scheme 6.7). These brominated hyperbranched materials (24) were insoluble in solvents such as DMF, DMAc, and NMP, in contrast to the polyamine and polycarboxylic acid terminated polymers that Kim synthesized, which were soluble. This supports the observation that surface functionality plays a major role in determining the physical properties of hyperbranched and dendritic macromolecules J4,36 A high degree of cross-linking could also significantly effect solubility. When a four-directional core was incorporated into the polymerization via tetrakis(4-iodophenyl)adamantanc,1371 the resultant hyperbranched polybromide (e.g., 25) possessed enhanced solubility in the above solvents, possibly as a result of the disruption of crystallinity and increased porosity. 

DuPont s w-aramid polymer, MPDI, is polymerized using essentially a 1 1 molar ratio of w-phenylenediamine and isophthaloyl chloride [85]. Patent literature indicates that the fiber, Nomex, is spun directly from the polymerization solution in DMAc, which contains caldum chloride. MPDI polymer solutions containing >3% by weight calcium chloride are quite stable [2]. 

In principle, all fibres available for FRP can also be used as reinforcement in prepregs, the most common ones being carbon and glass fibres. Polymeric fibres made from aramid or polyethylene are also quite coimnon, as are inorganic basalt fibres, or natural fibres like hemp or flax. Often, the fibres are directly impregnated to make unidirectional (UD) tapes. Alternatively, they can first be transformed into fabric products, such as woven fabrics or non-crimp fabrics (NCF), and then impregnated to create multi-directional prepregs. 

Commercially available pultruded bars are made of glass, carbon or aramid fibres, oriented in the axial direction and embedded in a polymeric matrix, usually made of vinylester or epoxy resin. The FRP bars most often used in civil engineering applications combine vinylester and glass fibres. 

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... 

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