Rigid rod heterocyclic polymers

The last two decades of research on high performance rigid-rod polymers and molecular composites have produced a wide variety of material systems for evaluation. The purpose here is not to present a comprehensive review but rather to describe these relatively recent research developments with regard to the synthetic methods and approaches that have been utilized. In doing this some properties of the polymers are discussed as well as some of the problems encountered in conjunction with their synthesis and evaluation. In an effort to limit the scope of the review, we will address only aromatic heterocyclic rigid-rod polymers, extended chain polymers and derived molecular composites. 

Aromatic heterocyclic rigid-rod polymers that have exceptional thermal oxidative stability have been prepared using 1,5-naphthylene dicarboxylic acid and 2,5-diamino-1, 4-benzenedithiol. These heterocyclic rigid-rod polymers materials are useful as protective garments in ballistic vests and abrasion- and flame-resistant fabrics. 

Aliphatic polybenzimidazoles were first synthesized by scientists in the 1950s. However, it was not until the 1960s that H. Vogel and C.S. Marvel first synthesized aromatic polybenzimidazoles and discovered that these unique, highly stable linear heterocyclic rigid-rod polymers exhibited exceptional thermal and oxidative stability [65]. Poly[2,2 -(m-phenylene)-5,5 -bibenzimidazole], PBI, was prepared by the condensation polymerization of... 

C.C. Wu, P.Y. Tsay, H.Y. Cheng, and S.J. Bai, Polarized luminescence and absorption of highly oriented, fully conjugated, heterocyclic aromatic rigid-rod polymer poly-p-phenylenebenzoxazole, J. Appl. Phys., 95 417 123, 2004. 

Table 2. Electrical conductivities of the l rypton-implanted aggregated films of the heterocyclic ladder and pseudo-ladder rigid-rod polymers.

PBO, PBZ, and PlPD. PBZ, a family ofp-phenylene-heterocyclic rigid-rod and extended chain polymers includes poly(p-phenylene-2,6-benzobisthiazole) [69794-31-6] (trares-PBZT), poly(p-phenylene-2,6-benzobisoxazole) [60871-72-9] (cis-PBO), and poly[2,6-diimadazo[4,5-b 4, 5 -e]pyridinylene-l,4(2,5-... 

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. 

Tan L, Arnold F, Dang T et al (1994) Pseudo-ladder rigid-rod polymers tfihydroxy pendant benzothiazole aromatic heterocyclic polymer and copolymers. Polymer 35 3091-3101... 

Polybenzobisazoles (70), as well as some other heterocyclic conjugated rigid-rod polymers, like polyquinolines, are weak electron acceptors. Binary mixtures of these conjugated polymers with suitable donor... 

Materials. On the basis of the observations made above, the choice of molecular design has centered on that of an extended chain, rigid-rod molecule for reasons of molecular ordering and an aromatic-heterocyclic structure for thermal and oxidative stability. Three such polymers have been synthesized, PDIAB,(5) PBO,(3,6,7) and PBT.(8)... 

Emphasis will continue to be placed on learning to process the extended chain, rigid-rod aronatic-heterocyclic polymers into useful forms for structural applications. 

Molecular composites development has been concentrated primarily in physical blend systems in which rigid-rod aromatic-heterocyclic polymers functioned as the... 

As illustrated in Figures 4(b) and 4(c), the thermotropic main-chain LC polymers can be obtained from polymers that contain only rigid-rod units or a combination of rigid-rod and flexible units. The main stmctural elements of such linear polymers are composed of benzene or naphthalene rings, or different heterocyclic fragments collmearly linked to one another by such groups as... 

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