Rigid-rod Polymers Research Articles

Compressive strength of coated rigid-rod polymer fibres

One limitation to the use of high-strength/high-modulus rigid-rod polymer fibres like poly-(p-phenylene benzobisthiazole) (PBZT) and poly-(p-phenylene benzobisoxazole) (PBZO) in composite structures is their low compressive strength. Various theories have been developed to predict compressive strength of rigid-rod fibres. In this study the critical buckling stress for rigid-rod fibres with stiff external coatings has been theoretically modelled assuming that the failure mode in compression is the microbuckling of the fibrils in shear. Our model predicts that significant improvement in fibre compressive strength will occur only when relatively thick coatings, with thickness to diameter (t/D) ratios in excess of > 0.05, are used. Experimentally measured compressive strength of aluminium coated PBZT fibres shows values in good agreement to the theory at t/D ratios of 0.006 and below. Factors related to the selection of suitable coating materials and problems associated with establishing coating performance are identified.

An organometallic polyimine copolymer prepared from {η 6-1,4-bis(CHO)C 6H 4}Cr(CO) 3 and 1,3-phenylenediamine

The organometallic comonomer {η 6-1,4-bis(CHO)C 6H 4}(CO) 3 ( 1) was prepared from {η 6-1,4-bis(Bu 3Sn)C 6H 4}Cr(CO) 3 by Seyferth transmetalation and then treatment with N, N-dimethylformamide. Complex 1 was characterized by a single-crystal X-ray diffraction study: triclinic, P 1 , a=6.860(1), b=12.649(3), c=13.480(6) A ̊ , α=111.10(3), β=90.30(3), γ=94.76(2)° , V=1086.8(6) A ̊ 3, Z=4, R=3.93%, R w =4.58%, GOF=1.15 . Complex 1 was copolymerized with 1,3-phenylenediamine to produce an organometallic-polyimine 2 (97%, T m=282°C). The organometallic-polyimine 2 possesses a fully-conjugated organic polymer backbone. The copolymer was insoluble in common organic solvents, typical of a rigid-rod polymer.

Void formation in coagulated rigid-rod polymer thin films

Large voids of about 100μm are often found in rigid-rod polymer thin films coagulated from isotropic solutions. To understand the mechanism of this void formation so as to improve the optical quality of coagulated rigid-rod polymer thin films, surface and internal structures of various coagulated poly( p-phenylene benzobisthiazole) solutions were investigated on freeze-dried films by high resolution scanning electron microscopy. The films coagulated immediately from doctor-bladed solutions exhibited surface crinkles and large internal voids, while the films coagulated from the doctor-bladed solutions that had undergone a surface treatment in an atmosphere containing the vapour of a non-solvent showed a surface network structure but no large internal voids. Results support that the large voids were formed due to a large-scale coagulant incursion during coagulation. The absence of the large voids in the films coagulated from the surface-treated solutions is attributed to the surface network structure being strong enough to regulate the incursion of coagulant during the film forming process at coagulation.

Geometrical effect on the nonlinear optical properties of model rigid-rod polymers. Ab initio time-dependent coupled Hartree-Fock studies

The linear and nonlinear optical (NLO) properties of the cis and trans isomers of diphenylbenzobisoxazole (PBO) and diphenylbenzobisthiazole (PBT) have been calculated by ab initio time-dependent coupled perturbed Hartree-Fock method using a split-valence basis set. The second-order NLO susceptibilities of the trans isomers are calculated to be larger by a factor of 1.5 or more compared to the cis isomers over a wide range of optical frequency. Between the two homologues (PBO and PBT), the linear and the NLO susceptibilities of the thiazole systems are calculated to be slightly higher than the oxazole systems.

Solid State Structure and Photoluminescence properties of poly(2,5-dialkoxy-p-phenyleneethynylene)s

ABSTRACTIn an effort to better understand the relationship between molecular structure and photophysical properties, we have prepared and investigated a series of novel poly(2,5-dialkoxy-p-phenyleneethynylene)s. Wide angle X-ray diffraction measurements show that the supramolecular structure can be easily and significantly influenced by the nature of substituents covalently linked to the rigid-rod polymer main chains. Polymers which have sterically hindered side chains are essentially amorphous, while those with only linear side chains can form lamellar structures with a significant degree of long-range order. High photoluminescence quantum yields, up to 0.86 in solution and 0.36 in the solid state, have been measured. While the solution quantum yields are independent of the functionalization, solid state quantum efficiencies were found to be related to the degree of long-range order in the samples. In samples with a high degree of long-range order, the close proximity of the coplanar oriented polymer backbones is assumed to lead to the formation of eximer complexes which provide non emissive decay channels and, hence, result in comparable low photoluminescence quantum yields. In samples that adopt only a small extent of long-range order, the rigid-rod conjugated polymer backbones behave as if they were ‘dissolved’ in a hydrocarbon solvent and consequently high quantum efficiencies are obtained. Preliminary results indicate the suitability of these polymers as the emitting layer in electroluminescent devices.

Analysis of residual phosphorus in poly( p-phenylene benzoxazole), PBO, film by x-ray fluorescence (XRF) spectrometry

Poly( p-phenylene benzoxazole), PBO, is a rigid rod polymer which is polymerized in polyphosphoric acid. Oriented POB film shows good mechanical strength, excellent thermal stability and solvent resistance, and low dielectric constant. The measurement of residual phosphorus in the film is necessary since residual phosphorus may impact the physical and electrical properties of the film. A rapid and non-destructive XRF method has been developed for the analysis of residual phosphorus content in PBO thin films (0.1–2 mil). The XRF method demonstrated good linearity over the range of 150–4100 ppm, with a detection limit of ca 40 ppm. The residual phosphorus in several PBO thin film samples was also measured using NMR spectroscopy, and excellent agreement with the XRF analysis was obtained.

In situ thermoset molecular composites

AbstractThe polymerization of rigid rod polymer precursors in a reactive matrix precursor, which is later cured in the mold, constitutes the in situ process. A poly‐azomethine (PAM) was used as the rigid rod molecule. The resin used was an epoxy. We discuss the prediction of mechanical properties using micromechanics equations for chopped fiber composites. The chemistry used to synthesize the rigid rod polymer PAM in the epoxy precursor is reviewed. Approaches to better control the cure of these epoxy systems through cure kinetics and cure rheology studies completes the thermoset in situ molecular composite process. There was a 71% increase in tensile modulus in comparison to that of the neat epoxy resin. Molecular modeling simulations and continuum mechanics are used to help understand these findings. PAM/epoxy systems were used as a matrix material in the fabrication of unidirectional glass fiber/(PAM/epoxy) structural composites. © 1994 John Wiley & Sons, Inc.

Photogeneration of Charge Carriers in Bilayer Assemblies of Conjugated Rigid-Rod Polymers

Abstract : The quantum yield and the mechanism of photogeneration of charge carriers are investigated in bilayer assemblies consisting of a pi-conjugated rigid-rod polymer layer and a triarylamine doped polycarbonate layer. The electric field dependent quantum efficiency of photocarrier generation, Phi(E), in the bilayers containing a series of conjugated polybenzobisazoles was measured by photoinduced discharge and was found to be in the range of 10(exp - 3) to 10(exp -2) at low fields (<10(exp 4) V/cm) and as high as 0.12 - 0.32 at approx. 10(exp 6) V/cm. The Phi(E) data were qualitatively in accord with Onsager's three-dimensional model for ion-pair dissociation. Transient (ps) absorption spectroscopy of single layer thin films of the polymers showed that the primary photoexcitations were excitons. However, picosecond photoinduced absorption and photoluminescence experiments on the bilayers revealed photoinduced electron transfer and exciplex formation at the bilayer interface. Thus photocarrier generation on photoexcitation of the conjugated rigid-rod polymers in the bilayer occurs by photoinduced electron transfer, forming intermolecular exciplexes which dissociate efficiently in electric field. This mechanistic picture of charge carrier photogeneration provided a satisfactory account for the observed field dependent quantum yields in the series of bilayer assemblies.

Electronic energy transfer in new polymer nanocomposite assemblies

New light-harvesting thin film supramolecular assemblies, consisting of rod-coil polymer nanocomposites as the light-absorbtion energy donors and a randomly dispersed conjugated rigid-rod polymer as the energy acceptor, have been prepared and shown to exhibit efficiency for singlet electronic energy transfer as high as 93%. The film thickness dependence of the energy-transfer efficiency allowed us to determine the contributions of both the Förster and radiative mechanisms to energy transfer in the polymer nanocomposite assemblies. The Förster energy-transfer efficiency was found to increase with increasing acceptor concentration, reaching an asymptotic maximum of 48% at ∼3 mol%. On the other hand, radiative transfer diminished to an insignificant contribution at low acceptor concentration (< 1 mol %). The Förster energy-tranfer efficiency varied significantly with the length of the flexible coil segment which regulates the supramolecular structure of the photoactive nanocomposite energy donor. The average intersite distance between donor and acceptor chromophores was measured spectroscopically and found to be in the range of 10–24 Å, with corresponding Förster rradii of 19–23 Å in the three series of supramolecular donor/acceptor assemblies investigated, depending on the acceptor concentration. The present results on these novel light-harvesting polymer nanocomposite assemblies represent the successful supramolecular regulation of efficient electronic energy transfer in thin films and hence are promising for potential optoelectronic applications.

Aromatic poly(pyridinium salt)s: synthesis and structure of organo-soluble, rigid-rod poly(pyridinium tetrafluoroborate)s

Abstract A series of phenylated, aromatic poly(pyridinium tetrafluoroborate)s has been prepared by the polymerization of 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrylium tetrafluoroborate) with aromatic diamines in a dimethylsulfoxide/toluene mixture at 145–150°C. The water generated by the transformation of the pyrylium rings to pyridinium rings was distilled from the reaction mixture as a water/toluene azeotrope. All- para -catenated, rigid-rod polymers with inherent viscosities as high as 4.9 dl g −1 were obtained that were soluble in polar aprotic solvents. The polymers could be solution cast into tough, flexible films. Although the glass transition temperatures of the poly(pyridinium salt)s were difficult to detect with differential scanning calorimetry, they displayed distinctive melting endotherms with minima above 380°C. Thermogravimetric analysis showed that the polymers began to decompose near 360°C prior to melting. Wide-angle X-ray diffraction analysis revealed that the chains were packed in a structure similar to that of a smectic liquid crystalline glass.

Electroabsorption Spectroscopy of Rigid Rod Polymers PBZT and PBTPV

Abstract The rigid rod polymers poly(p-phenylenebenzobisthiazole) and poly(benzobisthiazole-p-phenylenebisvinylene) have been prepared as thin film samples by spin coating Lewis acid complexes from solution and regenerating the uncomplexed polymer by washing with water and drying in vacuo. This approach allows fabrication of films that show well resolved vibronic structure in their linear absorption spectra. In this paper we present results of linear- and electro-absorption spectra. From the latter we are able to deduce the average exciton radius which we find to be 13Å, in PBZT and 15Å, in PBTPV. The average change in polarisability accompanying the lowest energy π-π* optical transition is also determined. Comparison of our results is made with previous studies.

Process for fabricating novel composites based on reinforcement with microfibrillar networks of rigid-rod polymers: Farris, R.J. (of Northampton (Leeds), MA, USA), Cohen, Y. (of Haifa, Israel) and DeTeresa, S.J. (of Livermore, CA, USA) US Pat 5 102 601 (7 April 1992)

Process for fabricating novel composites based on reinforcement with microfibrillar networks of rigid-rod polymers: Farris, R.J. (of Northampton (Leeds), MA, USA), Cohen, Y. (of Haifa, Israel) and DeTeresa, S.J. (of Livermore, CA, USA) US Pat 5 102 601 (7 April 1992)

Rigid‐rod polyelectrolytes: synthesis of sulfonated poly(p‐phenylene)s

Macromolecular Rapid CommunicationsVolume 15, Issue 9 p. 669-676 Article Rigid-rod polyelectrolytes: synthesis of sulfonated poly(p-phenylene)s Rudy Rulkens, Rudy Rulkens Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this authorMargit Schulze, Margit Schulze Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this authorGerhard Wegner, Corresponding Author Gerhard Wegner Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanyMax-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this author Rudy Rulkens, Rudy Rulkens Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this authorMargit Schulze, Margit Schulze Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this authorGerhard Wegner, Corresponding Author Gerhard Wegner Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanyMax-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanySearch for more papers by this author First published: September 1994 https://doi.org/10.1002/marc.1994.030150902Citations: 77AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume15, Issue9September 1994Pages 669-676 RelatedInformation

Processing of optical quality rigid-rod polymer thin films

A novel process for the fabrication of optical quality thin films of rigid-rod polymers by coagulation from an isotropic solution is reported. This process consists of the following steps: (1) extrusion or doctor-blading of an isotropic rigid-rod polymer solution into a uniform thin solution layer; (2) relaxation of the solution in an atmosphere containing the vapour of a non-solvent for an appropriate length of time; and (3) coagulation of the solution in a non-solvent bath. Thin films of rigid-rod poly( p-phenylene benzobisthiazole) (PBZT) thus prepared do not show the large voids or line defects commonly observed in the extruded and subsequently coagulated PBZT thin films. A processing window based on the solution thickness and relaxation duration is outlined for a 1 wt% PBZT solution in methanesulfonic acid to fabricate void-free PBZT thin films up to 6 μm in thickness at room temperature. Optical spectra and micrographs show that the PBZT thin films prepared by the current process compare favourably with those extruded and then coagulated in terms of low optical loss and fewer defects.

Calculation of the effects of protonation on rigid-rod polymers

Semiempirical molecular orbital calculations have been used to investigate the effects of protonation on the behaviour of the structural repeat units of poly( p-phenylene benzobisthiazole), PBZT, and poly( p-phenylene benzobisoxazole), PBO. Single and multiple protonations of the heterocyclic rings at the nitrogen, oxygen and/or sulfur atoms were examined. It was found that protonation at the nitrogen was more favourable than at the oxygen or sulfur atoms. Delocalization of the charge into the phenyl ring resulted in a higher bond order for the inter-ring bond. While the energy barrier for torsional rotation increased with protonation, the resistance to bending the rings in an out-of-plane fashion decreased somewhat. Results of the semiempirical calculations indicated that protonation of the oxygen in PBO might result in opening of the five-membered heterocyclic ring by breaking the carbon-oxygen bond. Ab initio calculations on relevant models, however, did not support this result.

Synthesis and properties of diarylsiloxane and (aryl/methyl)siloxane polymers: 2. Solution and rheological properties

Polydiarylsiloxanes and polydialkylsiloxanes, with alkyl groups larger than methyl, have liquid-crystalline states, presumably as the result of a chain-rigidifying effect from steric interactions of the bulky aryl or alkyl groups along the chain. In the first paper of this series, we reported on the thermal behaviour of a number of diarylsiloxane polymers with phenyl and/or p-tolyl substituents, all of which showed liquid-crystalline behaviour at high temperatures. The solution properties of several of the ‘mixed’ poly(phenyl p- tolyl)siloxane polymers have now been investigated in order to characterize their chain stiffness properties and to relate these to the tendency to form a liquid-crystalline state in bulk. The ‘mixed’ poly(phenyl p- tolyl)siloxanes were chosen for investigation since they have a major advantage in experimental convenience over the ‘unmixed parent’ polymers, polydiphenylsiloxane and polydi( p-tolyl)siloxane. The former are soluble at room temperature in common solvents, whereas the latter polymers are only soluble at temperatures above 150°C. The various diarylsiloxane polymers were prepared by anionic polymerization of the cyclic trimers, and the preservation of the triad sequences (absence of ‘scrambling’) was confirmed by 29Si n.m.r. Values of the Mark-Houwink-Sakurada exponent, a, for three different types of poly(phenyl p- tolyl)siloxanes are essentially equal, at ∼0.83. This value of the exponent is below the value expected for a rigid chain ( a>1.0) but is above the maximum value expected for a flexible random-coil polymer in a good solvent ( a⩽0.8). The shear viscosity of solutions of the mixed poly(phenyl p- tolyl)siloxane polymers increases monotonically with increasing polymer concentration up to 60 wt%, and does not show an abrupt drop in viscosity above a critical concentration, as is often observed with rigid-rod polymers. This observation, together with the value of the Mark-Houwink-Sakurada exponent, a<1, indicates that these polymers do not behave in solution as rigid-rod polymers, but most likely as worm-like chains with a relatively large persistence length.

Pseudo-ladder rigid-rod polymers: dihydroxy pendent benzothiazole aromatic heterocyclic polymer and copolymers

Anisotropic homopolymerization of 2,5-dihydroxyterephthalic acid (DHTA) and 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT.2HCl), and copolymerization of DHTA, terephthalic acid and DABDT.2HCl in polyphosphoric acid (PPA), afforded high molecular weight rigid-rod polymer and copolymers, with two hydroxyl groups as pendants per repeat unit. In PPA, the lyotropic liquid crystalline behaviour of the homopolymer was distinctly affected by the polymerization temperature. Spectroscopic evidence strongly suggested a completely planar and ribbon-like structure, the consequence of the strong intramolecular hydrogen bonds between the OH moieties and the N atoms of the nearby benzothiazole units. The homopolymer also exhibited the unusual capability, characteristic of BBL-type ladder polymers, to form directly from its precipitate an aggregated film which displayed little or no shrinkage when dried. Anisotropic dopes of the homopolymer (dihydroxy-polybenzothiazole (PBZT)) and certain dihydroxy-PBZT/PBZT copolymers were spun into fibres with typical tensile properties for modified PBZT polymers, but marginal compressive strength (4–30 ksi (1 ksi = 6.9 MPa) for homopolymer and 16–61 ksi for the copolymers). The intrinsic conductivity for the as-spun fibre of the homopolymer was 2.2 × 10 −7 S cm −1 and that for heat-treated (435°C) fibre was 5.6 × 10 −8 S cm −1.

Organic NLO Polymers. 2. A Study of Main-Chain and Guest-Host NLO Polymers: NLO-phore Structure Versus Poling

Several new dipolar main-chain χ (2) nonlinear optical (NLO) polymers were prepared. The NLO-phores, based on alkoxy substituted α-cyanoacrylates, were also placed as monomeric guests within a poly(methyl methacrylate) host. Polar alignment of the NLO-phores by corona poling and their relaxation behavior was monitored by detecting the optical signal resulting from the second harmonic generation. The study revealed that two dipolar rigid-rod main-chain NLO polymers (NLOPs), having solubilizing side chains, were not responsive to alignment by corona poling. We found that each main-chain NLOP prepared in the study showed a strong resistance to alignment, whereas virtually the same NLO-phore as a guest within a polymer host responded well to corona poling

Synthesis and Properties of Stiff-Chain Polyesters Based on the Terphenyl Moiety

Abstract The synthesis and the characterization of rigid-rod polyesters 2 and 3 deriving from 2′,5′-dihexyl-p-terphenyl-4,4″-diol 7 and from 2′,5′-dihexyl-p-terphenyl-4,4″-dicarboxylic dichloride 8 together with a facile synthesis of monomers 7 and 8 is described. It is shown that these polyesters exhibit a very good solubility in common organic solvents. Therefore these materials present interesting model compounds for comprehensive studies of rigid-rod polymers in solution.

Preparation and processing of molecular composites of rigid-rod and flexible-chain polymers from soluble complexes

Preparation and processing of molecular composites of rigid-rod and flexible-chain polymers from soluble complexes