Aramids solution polymerization

The term aramid is used to describe aromatic polyamides, which were developed to improve the heat and flammability resistance of nylon. Nomex is a highly heat-resistance nylon introduced in 1961 by DuPont. It is produced by the solution or interfacial polymerization of isophthaloyl chloride and 7M-phe-nylenediamine ... 

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]. 

Liquid Crystal Polymers (LCP) This novel polymeric family excels in thermal and mechanical performance. The uniqueness of these polymers stems from the extraordinary crystalline stmcture, exhibiting ordered domains even in the liquid state. These are chainlike macromolecules of rigid structure, mainly because of the existence of aromatic rings such as aromatic polyamides and polyesters. There are two major groups—lyotropic and thermotropic. In the former group, the liquid crystals are formed in an appropriate solution, usually forming fibers (like Kevlar , that appeared in 1965 as an aramide). 

Specific inter- and intramolecular bonding are not necessary for ordered structures to persist in dilute solution. Ordered structures, that lead to highly asymmetric molecules, can be perpetuated by severe steric repulsions of substituents or an inherent restraint to rotations about single bonds. Such structures are known, even among synthetic macromolecules, and they form liquid-crystal systems. Some examples are polymeric aramides, poly(N-alkyl isocyanates) and some cellulose derivatives. 

Another test of the theory is to compare the experimentally determined dependence of Up, the volume fraction at which the nematic phase separates, on the axial ratio." The agreement between theory and experiment is particularly good with the alpha-helical polypeptide poly(y-benzyl-L-glutamate).(94-96) Studies of solutions ofthe polymeric aramides, such as poly(p-benzamide) and poly(/ -phenylene tereph-thalamide) indicate a qualitative accord between theory and experiment. Studies... 

Aramid yarns (Kevlar of DuPont, Twaron of Teijin-Twaron) are produced from poly(p-phenylene terephthalamide), PPTA (2), which is specially developed for fiber spinning and not used in any other application. DuPont had experience with poly(m-phenylene isophthalamide) in a fiber product called Nomex for high-temperature applications. The polymer is produced in dimethylacetamide and the solution is dry-spun. This cannot be done with the stiff-chain para-para analogue PPTA. The polymer does not dissolve in organic solvents. A special polymerization route had to be developed, and the discovery of lyotropic behavior of concentrated solutions in sulfuric acid then led the way to the production of a magnificent new fiber material. 

Conventional air gap wet spinning of the as-polymerized solutions of polymers with Mw 60,000-150,000 (Twaron aramid calibration SEC in methane sulfonic acid) at 180°C into a water or dilute phosphoric acid bath, proceeded readily spindraw ratios attainable depend on spinning orifice diameter and the result normally delivers filaments with a diameter of about 10 mm, which are further washed to a low phosphorus content and drawn (by a few percent at most) at high temperature (>400°C) to produce the final, high modulus product. It is unclear whether the crystal solvate can form... 

Poly(l,4-benzamide) (I, PBA) is most commonly prepared by low-temperature solution polycondensation of 4-aminobenzoyl chloride hydrochloride. Poly(l,4-phenylene terephthalamide) (II, PPTA), which is the aramid that has become of prime commercial importance, t5 ically is s)mthesized by solution polycondensation of terephthaloyl chloride and 1,4-phenylene diamine (1-3 see also references 4 and 5 for excellent reviews of the polymerization and processing of aramids). 

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. ... 

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