Rigid‐Rod Polymers

Abstract

Pursuing high strength and high modulus polymer fibers and novel electrooptical properties have motivated much research activity in rigid‐rod polymers in the past 40 years. In this review, we examine the synthesis, structures, and properties of rigid‐rod polymers with emphasis on polybenzobisoxazoles (PBO), polybenzobisthiazoles (PBZT) and polybenzimidazoles (PBI), beginning with their solution properties, especially lyotropic liquid crystallinity. High performance fibers spun from lyotropic liquid crystalline polyphosphoric acid (PPA) solution are described. The characterization of fiber properties including mechanical, thermal, electrical, and optical properties is summarized. PBO (Zylon) and PIPD (M5) fibers were successfully commercialized in high strength applications such as body armor, ropes, cables, and recreational equipment in the last 10 years, and we discuss the possible causes of rapid degradation of some PBO fibers. The concepts of molecular composites and nanocomposites provide new applications in antiballistic materials, fire protection, athletic equipment, cables, strings, ropes, cordage, sails, multilayer circuits, and catalyst supports. Recently, rigid‐rod polymer films have drawn attention in the electrooptical fields, especially for phosphoric acid (PA)‐doped PBI membranes (Celtec MEAs) in the applications of high temperature fuel cells. Computer simulation has been employed as a powerful tool to predict the properties of the rigid‐rod polymers.

Oligomerization of Silyl Ketene: Favoring Chain Extension over Backbiting

“…The NMR spectra of all products were similar, and functional groups were identified from the NMR spectra: the 1 H NMR spectra showed sp 3 C−H next to carbonyls (3.0−3.6 ppm) and alkenyl C−H (4.0−6.0 ppm), whereas the 13 C NMR spectra mainly revealed sp 2 C's of carbonyl (180−210 ppm) and enol ether groups (148−169 and 95−110 ppm, respectively). The presence of multiple peaks in these regions suggests multiple double bond geometries (cis and trans).…”

“…Of particular interest are rigid-rod polymers or polymers with permanently extended chains. These unique polymers have particle-like behavior and can densely pack to give materials with high strength and modulus . The extended geometry of rigid-rod polymers also provides a framework to build chiral superstructures, provided an appropriate polymer backbone and substituents are present.…”

Synthesis and Characterization of Rigid-Rod Polymers with Silsesquioxanes in the Main Chain

“…Rigid-rod polymer fibers can also be used in the production of protective garments or as reinforcing fibers for composite materials. Table lists the mechanical and thermal properties of common commercial rigid-rod polymers …”

Rigidification of Poly(p-phenylene)s through ortho-Phenyl Substitution

“…Poly( p -phenylene)s (PPPs) represent a unique class of conjugated rigid-rod polymers. 7 , 8 Unsubstituted PPPs exhibit exceptional mechanical strength, stiffness, and high thermal stability due to the rigid aromatic backbone of the para-connected phenylene units. 9 , 10 Nevertheless, their applications are hampered by their vanishing solubility, which also induces structural defects and leads to low molecular weights during their preparations, typically through a Ni-mediated polycondensation of aromatic dihalides 11 or an oxidative coupling of benzene in the presence of CuCl 2 and AlCl 3 .…”

“…Poly­( p -phenylene)­s (PPPs) represent a unique class of conjugated rigid-rod polymers. , Unsubstituted PPPs exhibit exceptional mechanical strength, stiffness, and high thermal stability due to the rigid aromatic backbone of the para-connected phenylene units. , Nevertheless, their applications are hampered by their vanishing solubility, which also induces structural defects and leads to low molecular weights during their preparations, typically through a Ni-mediated polycondensation of aromatic dihalides or an oxidative coupling of benzene in the presence of CuCl 2 and AlCl 3 . , To circumvent these drawbacks, several protocols have been employed: (i) chemical transformation of solubilized precursor polymers to yield unsubstituted PPPs and (ii) substitution of PPPs to enhance their solubility. − Especially, substituted PPPs bearing alkyl and/or additional functional groups have been studied as shape-persistent polymers. Notably, an additional concept used to prepare soluble PPPs with high molecular weights is to introduce regioirregularity through a suitable monomer choice or copolymerization, which unfortunately often lacks the structural perfection. − …”