Rigid-rod polyamide

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

Stein et al. [1992] investigated the polymerization of a monomer containing a solution of rigid-rod polymers and found conditions whereby molecular composites could be formed. A specific example involved a rigid rod polyamide dissolved in 4-vinyl pyridine (or N-vinyl pyrrolidone) along... 

I.K. SpiUopoulos, J.A. Mikroyannidis, Soluble, rigid-rod polyamide, polyimides, and polyazomethine with phenyl pendent groups derived from 4,4 -diamino-3,5,3 , 5 -tetraphenyl-p-terphenyl. Macromolecules 29 (16) (1996)5313-5319. 

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Despite its oxygen content, polyester (i.e., the aromatic polyethylene terephthalate) is degradation-resistant probably because of its rigid, rod-like chains. The same is true for polyamides in spite of their nitrogen content. 

Liquid crystalline compounds are remarkable because of their ability to show spontaneous anisotropy and readily induced orientation in the liquid crystalline state. When polymers are processed in the liquid crystalline state, this anisotropy may be maintained in the solid state and can readily lead to the formation of materials of great strength in the direction of orientation. A particularly important example of the use of this property for polymers is in the formation of fibers from aromatic polyamides which are spun from shear oriented liquid crystalline solutions Solutions of poly(benzyl glutamate) also show characteristics of liquid crystalline mesophases, and both of these types of polymers are examples of the lyotropic solution behaviour of rigid rod polymers which was predicted by Flory... 

Recently, combinations of polymers meeting the basic concept of molecular composites have been reported. Poly-(p-phenylene terephthalamide) miscibility with PA-6 and PA-66 was reported [Kyu et al., 1989]. The blends were prepared by rapid coagulation of methane sulfonic acid solutions in water. Above 70% of the rigid rod polymer, polyamide crystallization disappears implying a level of intermixing of the blend constituents. However, thermal treatment results in phase separation thus indicating metastability for this combination. 

Ringsdorf s research group have prepared novel types of rigid-rod polyesters and polyamides 56 with a disc-like mesogen in tte mainchain [75]. Most polymers with six lateral substituents appear to be thermotropic liquid crystals. Polyamides with Z = H and having four substituents on the diamine component are not liquid crystalline. The two substituents on the diacid component seem to contribute to decrease further the intermolecular hydrogen bonding. 

Aromatic polyamides with terminal acetylenic groups were formed from 2,2 -diiodo-diphenyl-4,4 -dicarbonyl chloride reacted with aromatic diamines. The phenylethynyl groups were introduced by reacting the iodine moieties with copper phenyl acetylide. Thermal treatment converted the prepolymers to 9-phenyl dibenzanthracene based rigid-rod polymers that fail to melt below 500... 

These are macromolecules that can align into crystalline arrays while they are in solution lyotropic) or while in a molten state thermotropic). Such liquids exhibit anisotropic behavior [51,52]. The regions of orderliness in such liquids are called mesophases. Molecular rigidity found in rigid rod-shaped polymers, for instance, is the chief cause of their liquid crystalline behavior. It excludes more than one molecule occupying a specific volume and it is not a result of intermolecular attractive forces. Some aromatic polyesters or polyamides are good examples, like polyphenylene terephthalate ... 

Perfluorinated Polymers, Polytetrafluoroethylene Polyamides, Aromatic Polyamides, Plastics Polyarylates Poly(arylene sufide)s Polycarbonates Cyclohexanedimethanol Polyesters Polyesters, Main Chain Aromatic Polyesters, Thermoplastic Polyethers, Aromatic Poly(ethylene naph-thanoate) Polyimides Polyketones Poly(phenylene ether) Polysulfones Poly(trimethylene terephthalate) Rigid Rod Polymers Syndiotactic Polystyrene . 

Rigid-rod polymers are often liquid crystalline polymers classified as lyotropic, such as the aramid Kevlar (DuPont), or thermotropic liquid crystalline polymers, such as Vectran (Celanese) (see Polyamides, Aromatic Liquid Crystalline Polymers, Main-Chain Liquid Crystalline Thermosets). 

Chuah H H, Kyu T and Helminiak T E (1989) Scaling analysis in the phase separation of poly(j> phenylene benzobisthiazole)/Nylon-66 rigid-rod molecular composites, Polymer 30 1591-1595. Chang K Y, Chang H M and Lee Y D (1994) Molecular composites. 2. Novel block copolymer and semi-interpenetrating polymer network of rigid polyamide and flexible polyamide polyimide, J Polym Sci Part A Polym Chem 32 2629-2639. 

High modulus fibers from lyotropic aromatic polyamides, poly(p-phenylene terephthalamide) (PPTA), were first conunercialized imder the Kevlar trademark by DuPont [414]. The aromatic polyamides, or aramids, are produced by a dry jet-wet spinning process where the nematic structure in solution is responsible for the high modulus fiber performance [415-419]. Another class of lyotropic fibers, also produced by dry jet-wet spinning, are the rigid rod polymers developed as part of the U.S. Air Force Ordered Polymers Program [420-424]. The most conunon of these ordered polymers, poly(p-phenylene benzobisthiazole) (PBZT), is difficult to process, but it exhibits the highest tensile properties of all the LCP fibers produced to date. 

Typically rigid-rod systems such as the aromatic polyamides or the poly-heterocyclic polymers do not exhibit a glass transition, because their amorphous fraction is negligibly small, and they decompose before their melting temperature. By comparison, many of the crystalline random coil polymers, such as the aliphatic nylons, exhibit normal melting phenomena, as well as glass transitions. Thus the properties of the new rigid-rod polymers are quite different from those of random coil polymers. 

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