Whiskers of poly(3-alkylthiophene)s

It is shown that poly(3-alkylthiophene)s may readily crystallize from poor solvents in the form of whiskers. The experimental conditions required for the formation of whiskers were found to depend upon the alkyl side-chain length, solvent quality, and temperature. In all cases studied for alkyl side-chain lengths of 3-12 carbon atoms, the widths of the whiskers were of the order of 15nm, while their lengths often exceeded tens of microns. The thickness of the whiskers formed under the experimental conditions employed was found to scale with side-chain length, and was approximately 2 or 3 times the a/2 lattice dimension of the polymer unit cell. Packing of the macromolecules within the whiskers was such that the polymer backbones were normal to the whisker length; that is, the b-axis was oriented parallel to the long axis of the whiskers. These results are thought to be relevant to known thermochromism phenomena associated with poly(3-alkylthiophene)s. © 1993 John Wiley & Sons, Inc.     

Effect of side-chain length on charge mobilities in neutral poly(3-alkylthiophene)s: Determination from dielectric measurement

For neutral poly(3-alkylthiophene)s (P3ATs), the electric modulus formalism of dielectric relaxation measurement together with the use of nonexponential decay function can be applied to describe the behavior of conductivity relaxation and carrier transport. The charge mobilities of neutral P3ATs calculated from conductivity relaxation with the use of the defect-diffusion model are in agreement with the data from field-effect transistor measurement. The temperature dependence of charge mobility exhibits a local maximum right after the end of glass transition region, which can be attributed to the transition of soft conformons in the disordered phase to localized conformons. The charge mobilities and activation energies of mobilities for P3ATs are dependent on conjugation length and volume fraction of conducting units. © 1994 John Wiley & Sons, Inc.     

Comparative study of photoelectric properties of a copolymer and the corresponding homopolymers based on poly(3-alkylthiophene)s

As semiconducting materials in organic light-emitting devices (OLEDs), a novel, highly soluble poly[(3-octylthiophene)-co-(3-(2-ethyl-1-hexylthiophene))] (P3OTIOT) and the corresponding homopolymers (poly(3-octylthiophene) (P3OT) and poly(3-isooctylthiophene) (P3IOT)) were prepared by an FeCl₃-oxidative approach to compare their photoelectric properties. Characterization of the polymers included FT-IR, ¹H NMR, gel permeation chromatography (GPC), thermo-gravimetric analysis (TGA), UV-vis spectroscopy, photoluminescence (PL) and electroluminescence (EL). P3OTIOT and P3OT depicted excellent solubility in common organic solvents. TGA studies showed that all of the materials exhibited very good thermal stabilities, losing 5% of their weight on heating to 300 °C. The optical property investigations showed that the band-gap energy of P3OTIOT was similar to that of P3OT (2.43 eV) at 2.45 eV and 6% lower than that of P3IOT (2.6 eV) in CHCl₃ solution. In PL spectra, the emission maxima of P3OTIOT and P3IOT were 50 nm and 130 nm blue-shifted with respect to that of P3OT, respectively. However, the PL intensity of P3OTIOT was seven times higher than that of P3OT. Single layer polymer light-emitting devices (PLEDs) with the ITO/polymer/Ag configurations were fabricated by the spin-coating method with P3OT, P3IOT and P3OTIOT as the EL materials, which exhibited red (650 nm), orange-red (610 nm) and yellow-green (525 nm) EL, respectively. The external EL quantum efficiencies (QE) of P3IOT and P3OTIOT devices are 6.4 × 10⁻³% and 5.1 × 10⁻³% which are about five and four times higher than that of the P3OT device (1.2 × 10⁻³%), respectively. The turn-on voltage of the P3OTIOT device (5 V) is between that of the P3OT (4.5 V) and P3IOT (6 V) devices. These results indicated that the P3OTIOT combined the photoelectric properties of P3OT and P3IOT with excellent solubility, processability, low band-gap energy, high QE and low turn-on voltage in the PLEDs, and they might be excellent polymeric materials for applications in organic light-emitting diodes, light-emitting electrochemical cells and polymer solar cells.     

Structure and thermochromic solid-state phase transition of poly (3-alkylthiophene)

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3-dodecylthiophene) [P3DT] and poly (3-hexylthiophene) [P3HT], the temperature dependence of x-ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit-cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a-axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a-axis direction. (2) The interplanar spacing, intensity, and integral width of the x-ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x-ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans-type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.     

Measuring molecular order in poly(3-alkylthiophene) thin films with polarizing spectroscopies

We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after melting through the combination of several polarized photon spectroscopies: infrared (IR) absorption, variable angle spectroscopic ellipsometry (SE), and near-edge X-ray absorption fine structure (NEXAFS). The data from the various techniques can be uniformly treated in the context of the dielectric constant tensor epsilon for the film. The combined spectroscopies allow determination of the orientation distribution of the main-chain axis (SE and IR), the conjugated pi system normal (NEXAFS), and the side-chain axis (IR). We find significant improvement in the backbone order of the films after recrystallization of the material at temperatures just below the melting temperature. Less aggressive thermal treatments are less effective. IR studies show that the changes in backbone structure occur without significant alteration of the structure of the alkyl side chains. The data indicate that the side chains exhibit significant disorder for all films regardless of the thermal history of the sample.     

Structural diversity in poly(disulfide)s

This article reports a synthetic methodology for single step preparation of telechelic poly(disulfide)s (PDS) by step‐growth polymerization between a di‐thiol and a commercially available monomer 2,2′‐dithiodipyridine in presence of a functional group appended pyridyl disulfide moiety as the “mono‐functional impurity” (MFI). Redox‐destructible well‐defined segmented PDSs with functional chain terminal, predicted and tunable degree of polymerization and narrow polydispersity index (<2.0) could be synthesized under a mild reaction condition. Using an appropriate MFI, PDS could be synthesized with trithiocarbonate chain terminals in a single step, which could be further used as macro chain‐transfer agent (CTA) for chain growth polymerization under RAFT mechanism producing ABA type tri‐block copolymer wherein the B block consists of the degradable PDS chain. By copolymerization between a hydrophobic di‐thiol monomer and a hydroxyl group appended di‐thiol monomer, PDS could be prepared with pendant hydroxyl functional group which was utilized to initiate ring opening polymerization of cyclic lactide monomers producing well‐defined degradable graft‐copolymer. The pendant hydroxyl groups were further utilized to anchor a polar carboxylic group to the degradable PDS backbone which under basic condition showed aqueous self‐assembly generating micelle‐like structure with hydrophobic guest encapsulation ability and glutathione responsive sustained release. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 194–202     

Structural investigations on lewis acid mediated solubilization of poly(p-phenylenebenzobisthiazole) in an aprotic solvent

Investigations on aluminum chloride-mediated solubilization of poly(p-phenylenebenzo-bisthiazole), PBZT, in nitromethane revealed that, in general, dilute solutions of the polymer prepared in nitromethane with a large molar excess of the Lewis acid with respect to PBZT were relatively stable and thus suitable for processing into films and coatings via regeneration with hydroxylic nosolvents while polymer solutions with minimum stoichiometrically required (PBZT:AlCl₃ molar ratio 1:4) or marginal molar excess of AlCl₃ relative to PBZT tended to gel during handling. Structural studies on polymer–Lewis acid complex solutions were performed using ¹H and ²⁷Al NMR. ¹H NMR of the protonated structure of the model compound 2,6-diphenylbenzo [1,2-d:4,5-d′] bisthiazole was useful for confirming the ¹H NMR assignments of PBZT-AlCl₃ complex solution in CD₃NO₂. ²⁷Al NMR was particularly useful in probing the different tetrahedrally coordinated environments of the Al nucleus in the polymer solution, pointing to a complexation interaction between the polymer molecule and the Lewis acid and also between the solvent and the Lewis acid. Direct evidence in the solid state for the presence of a reversible electron donor–acceptor complex (EDA complex) was obtained from FTIR spectra of complexed films, isolated and handled in an inert atmosphere. The structural changes upon PBZT complexation caused significant frequencly shifts in both aromatic as well as heteroring stretching modes relative to PBZT itself, and intensity variations indicative of changes in the resonance configuration between the 1,4-phenylene moiety and the aromatic heterocyclic ring were also observed upon complexation. A preliminary comparison between the pristine PBZT fibers and regenerated PBZT by dilute solution viscometry indicates that the process results, to some extent, in polymer degradation leading to a decrease in the molecular weight of the polymer © 1993 John Wiley & Sons, Inc.     

Mixed solvent effect on lithium-coordination to poly(ethylene oxide)

This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K⁺ solutions in acetonitrile are also found in the respective PEO/Li⁺ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*_water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕ_water = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006     

Synthesis,characterization and molecular weight studies of certain soluble poly(3-alkylthiophene) conducting polymers

Soluble conducting polymers of 3-hexylthiophene, 3-octylthiophene, 3-decylthiophene and 3-dodecylthiophene were synthesized by constant potential electrolysis. The resultant polymers were characterized by cyclic voltammetry, ultraviolet spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Molecular weights were studied with gel permeation chromatography on solutions of the polymers in toluene. Surface properties were investigated by scanning electron microscopy. Substituent groups lengths have been found to strongly influence the electronic properties of the resultant polymers. Poly(3-hexylthiophene) has shown the highest conductivity, with the highest degree of polymerization. The conductivity and the degree of polymerization values decrease as the substituent chain length increases.H.B. Mark Jr.: deseased     

Properties of poly(3-halidethiophene)s

The influence of the halogen atom on the intrinsic properties of poly(3-halidethiophene)s has been investigated using experimental and theoretical methodologies. Specifically, the electrochemical, electrical, electronic and morphological properties of poly(3-bromothiophene) have been determined and compared with those recently reported for poly(3-chlorothiophene) [Aradilla et al., Polym. Chem., 2012, 3, 436.]. The electrochemical stability and porosity are smaller for poly(3-bromothiophene) than for poly(3-chlorothiophene) while the π-π* lowest transition energy is higher for the former than for the latter. Moreover, quantum mechanical calculations on model oligomers have evidenced that the conformational properties of poly(3-halidethiophene)s, where the halogen is fluorine, chloride or bromine, are dominated by steric interactions and, therefore, are significantly influenced by the size of the halogen atoms. Both the ionization potential and the π-π* lowest transition energy have been predicted to increase slightly when the π-donor character of the halogen atom decreases, in agreement with experimental observations.     

Enhancement of electroluminescence intensity in poly(3-alkylthiophene) with different alkyl side-chain length by doping of fluorescent dye

Electroluminescent diodes utilizing poly(3-alkylthiophene) (PAT) containing fluorescent dyes have been fabricated and their unique enhancement of emission characteristics have been studied. Remarkable enhancement of the electroluminescence efficiency has been observed for diodes with PAT doped with oxadiazole derivative (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole; PBD) and perylene derivative (N,N′ - Bis(2,5 - di - tert - butylphenyl) - 3,4,9,10 - perylenedi- carboximide; BPPC). The mechanism of emission enhancement by doping of PBD into PAT has been discussed with different alkyl side-chain lengths. © 1997 John Wiley & Sons, Ltd.     

Structural correlation between the columnar mesophase and the melt in poly(di-n-alkylsiloxane)s

Phase transitions of poly(dialkylsiloxane)s substituted with propyl and butyl groups are reported based on X-ray diffractometry. The structure in the mesophase and in the melt of polymers with 2 to 10 carbon atoms in each side chain is compared. Both phases display a linear dependence of the molecular cross-section on the length of the alkyl group demonstrating their structural similarity. By means of differential scanning calorimetry it is shown that the temperature range of the mesophase remains practically unchanged in width as well as in absolute temperature for dibutyl up to dihexyl substituted polysiloxanes.     

Structural and end‐group effects on bulk and surface properties of hyperbranched poly(urea urethane)s

The hydroxy end groups of aromatic and aliphatic hyperbranched poly‐(urea urethane)s prepared with an AA* + B*B₂ one‐pot method were modified with phenylisocyanate, butylisocyanate, and stearylisocyanate. The success of the modification reaction was verified with ¹H NMR and IR spectroscopy. Linear model poly‐(urea urethane)s were prepared, too, for comparison. The bulk properties of OH functionalized hyperbranched poly(urea urethane)s, compared with those of linear analogues and modified hyperbranched poly(urea urethane)s, were studied with differential scanning calorimetry, thermogravimetric analysis, and temperature‐dependent Fourier transform infrared measurements. Transparent and smooth thin films could be prepared from all polymer samples and were examined with a light microscope, a microglider, and an atomic force microscope. The properties of the polymer surface were examined by measurements of the contact angle and zeta potential. For all samples, the properties were mainly governed by the strong interactions of the urea and urethane units within the backbone, whereas the influence of the nature of the end groups and of the branched structure was reduced in comparison with other hyperbranched polymer systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3376–3393, 2005     

FT-IR studies of solvent and temperature effects on poly(diglycidal ether of bisphenol A) (epoxy)

The infrared spectra of poly(diglycidal ether of bisphenol A) (epoxy) were studied in solutions of chloroform, benzene, and carbon tetrachloride separately to investigate the solvent effect through the behavior of the hydroxyl stretching band. The effect of temperature on the epoxy resin was also studied in this region. The results indicate that there is a varying degree of the weakening of the hydrogen bonding of the hydroxyl group in the epoxy, depending on the solvent. There is evidence also for the formation of hydrogen bonding between chloroform and the hydroxyl group of the epoxy and to a lesser extent between epoxy and benzene.     

Study on the conformations in poly(p-chlorostyrene)-endothermic solvent (n-propylbenzene) and poly(p-chlorostyrene)-exothermic solvent(tert-butyl acetate) at theta temperatures by X-ray small-angle scattering

Summary Conformations of linear poly(p-chlorostyrene) (PPCS) in an endothermic solvent (n-propylbenzene) and an exothermic solvent (tert-butyl acetate) at theta temperatures have been investigated by X-ray small angle scattering. By analyzing X-ray small-angle scattering data for the two systems, the determination of molecular parameters and the comparison between an angular dependence of experimental scattering curve and that of theoretical one have been made, with the discussion on the asymptotic behavior of the scattering curve.The values of persistence length and the radius of gyration of a cross section of polymer chain were 10.5–13.0 Å and 3.7 Å for PPCS-n-propylbenzen, and 11.1–13.7 Å and 5.2 Å for PPCS-tert-butyl acetate, respectively.The values of persistence length seem to be little affected in both systems, while those of radius of gyration of a cross section of polymer chain seem to be affected appreciably by the condition whether the system is endothermic or exothermic. The effect of the distribution of the electron density on the cross section is almost equal in both solvents. From the asymptotic behavior of scattering curves, the system of PPCS-n-propylbenzene has the area of interface larger than that of PPCS-tert-butyl acetate. Agreements between theoretical and experimental scattering curves are found over the experimental angular regions. Thus, it is considered that conformations of PPCS in both theta conditions are the same as that of an ideal chain and only a radius of gyration of the cross section of the polymer chain assumes different values in two solvents.

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Zusammenfassung Es wurde die Konformation vom linearen Poly(p-chlorostyrol) (PPCS) im endothermen Lösungsmittel (n-Propylbenzol) und im exothermen Lösungsmittel (tert-Butylacetat) bei den -Temperaturen untersucht. Die Bestimmung des molekularen Parameters, der Vergleich zwischen den Winkelabhängigkeiten der experimentellen und theoretischen Streukurven und die Diskussion über das asymptotische Verhalten der Streukurven wurden für die beiden Systeme durch Analyse der Röntgenkleinwinkelstreuungsdaten durchgeführt.Die Werte von Persistenzlängen und Querschnittsstreumassenradien waren 10.5–13.0 Å und 3.7 Å für PPCS-n-Propylbenzol, bzw. 11.1–13.7 Å und 5.2 Å für PPCS-tert Butylacetat.Es scheint, daß kein Einfluß auf die Persistenzlängen in den beiden Systemen existiert, während ein solcher auf die Querschnittsstreumassenradien der Polymerknäuel festzustellen ist, je nachdem das System endotherm oder exotherm ist. Die Verteilung der Elektronendichte hat die gleiche Wirkung auf den Querschnitt in den beiden Systemen.Nach dem asymptotischen Verhalten der Streukurven hat das System von PPCS-n-Propylbenzol die größere innere Oberfläche als die von PPCS-tert Butylacetat. Die Übereinstimmung zwischen den experimentellen und theoretischen Streukurven wird innerhalb der experimentellen Winkelbereiche festgestellt. Hieraus wird geschlossen, daß die Konformationen des PPCS unter Thetabedingungen dieselben sind, die Knäuel ideale Knäuel sind und nur die Werte von Querschnittsstreumassenradien der Polymerknäuel in den beiden Lösungsmitteln differieren.

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With 10 figures and 1 table     

The effect of casting solvent on the material properties of poly(γ-methyl-D-glutamate)

The effect of casting solvent on the material properties of poly(γ-methyl-D -glutamate), PMDG, was investigated. The specific solvents used were chloroform, trifluoroacetic acid, dichloroacetic acid, methylene chloride, hexafluoroisopropanol, and tetrachloroethane. The different nature of these solvents controlled the degree of α, β, or random coil contents of the final film. The effect of the morphology on material properties induced by the respective solvents was investigated by dynamic mechanical measurements of the dry films, stress strain behavior of both wet and dry films as well as by wide-angle x-ray diffraction, small-angle light scattering, and optical microscopy. Infrared spectroscopy was used to help determine α or β content. It was found that the casting solvent has considerable influence on material behavior and morphology. These differences are reflected in both the dynamical mechanical (small strain) and stress–strain (large strain) measurements as well as the x-ray scattering and optical microscopy. It was noted by light scattering that all films gave rise to anisotropic rod scattering with the exception of the β film cast from trifluoroacetic acid. This latter film appeared to be optically isotropic.     

Substituent effects on the polycondensation of quinones with aromatic amines to form poly(quinone imine)s

The effect of alkyl groups on the polycondensation of aromatic diamines and quinones to form poly(quinone imine)s was investigated. Models were synthesized under standard conditions: 1 equiv of quinone was reacted with 2 equiv of aniline in the presence of titanium tetrachloride and 1,4‐diazabicyclo[2.2.2]octane. Only modest yields of diimines were obtained when alkyl substituents were introduced. Likewise, alkyl substituents were harmful in the polycondensation of both anthraquinones and benzoquinones with aromatic diamines. As for fluorine substituents, model reactions with either 1,5‐difluoroanthraquinone or 1,4‐difluoroanthraquinone with aniline proceeded in high yields. These model compounds for aromatic poly(quinone imine)s were characterized with ¹H NMR spectroscopy, ¹⁹F NMR spectroscopy, variable‐temperature ¹H NMR spectroscopy, and X‐ray crystal structure determination. Polymers of the difluoroanthraquinones with aromatic diamines were obtained in high yields, although not in high molecular weights, and no stereocontrol was found. Both p‐benzoquinones and anthraquinones were used as monomers in these polymerizations, and a fundamental difference in reactivity was observed. With the former, the polymerization behaved as a classical polycondensation and demanded exact reagent equivalence. With the anthraquinones, however, the polymerization proceeded by a condensation chain polymerization and was much more forgiving. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 43–54, 2002     

Model studies on the structure of poly(amide oxime)s and their cyclodehydration reactions leading to poly(1,2,4-oxadiazole)s

To obtain an understanding of the low molecular weight character of wholly aromatic poly(1,4-arylene acyldiamide oxime)s (PAAs) having n-alkyloxymethyl side braches and the additional decrease in molecular weight during their cyclodehydration reaction leading to the corresponding poly(1,4-arylene-1,2,4-oxadiazole)s (PAOs), tautomeric structures of poly[1,4-phenylene-2,5-bis(n-octyloxymethyl)terephthaldiamide oxime] (C₈-PAA) were ¹H-NMR-spectroscopically investigated by using two model compounds: O,O'-dibenzoyl terephthaldiamide oxime (H-PAA-M, 4) and O,O'-dibenzoyl-2,5-bis(n-octyloxymethyl) terephthaldiamide oxime (C₈-PAA-M, 5). In solution H-PAA-M existed exclusively as oximino isomer, while C₈-PAA-M consisted only of imino tautomer and C₈-PAA contained both the oximino and imino form, the former being dominant in composition. It was found that the presence of imino tautomer caused serious effects both on the low molecular weight character of C₈-PAA and on the additional decrease in molecular weight during thermal cyclodehydration to C₈-PAO, whereas the presence of oximino tautomer showed practically little effect. A discussion on the results is provided from mechanistic viewpoint. © 1993 John Wiley & Sons, Inc.