Rodlike Poly Research Articles

Illumination of exciton migration in rodlike luminescent conjugated polymers by single-molecule spectroscopy

Single-molecule spectroscopy is used to study the time-dependent spectral behavior of a short rodlike Poly(phenylene vinylene) (PPV) derivative polymer spin cast in a polystyrene matrix. The fluorescent time trace is characterized by stepwise intensity emission with constant spectral composition, punctuated by abrupt intensity changes, which are usually accompanied by abrupt spectral changes. In contrast to coiled long chain polymers, defect-free rodlike polymers exhibit multiple-emission sites, each with its characteristic invariant spectrum. The distribution of spectral jumps in the emission spectrum reflects the distribution of the effective conjugation length. This implies the energy transfer (i.e., thermalized exciton migration) along the polymer backbone is inefficient. A static disorder induced conjugation length distribution model with limited energy transfer can be used in understanding the photophysics of an isolated polymer.

Studies on the texture of nematic solutions of rodlike polymers. 3. Rheo-optical and rheological behavior in shear

The texture in shear flow is discussed for nematic solutions of rodlike poly(1,4-phenylene terephthalamide), reported here, and poly(1,4-phenylene-2,6-benzobisthiazole), reported elsewhere. These are similar, with a sequence of scattering and visual features that develop with time, terminating at a level characteristic of the shear rate in steady state. With increasing shear rate in torsion between parallel disks, steady-state flow reveals sequentially a diffuse scattering with a turbid appearance, diffuse scattering with an opalescent appearance, a broad elliptical scattering along the radial direction with poorly-defined striations, a sharp scattering along the radial direction with well-defined striations along the flow, and a clear, highly birefringent sample, with little scattering. These same features are seen, in the same sequence in time, in transient behavior leading to steady state. This behavior is attributed to the development of striations with twist distortions alternating in angle relative to the flow, and essentially in the sample plane in the fast steady-state flow, reflecting the lower free energy of that distortion in comparison with bend and splay distortions, especially near the parallel plates of the rheometer. The deterioration of this texture at slower flows is associated with increasing distortions out of the sample plane, leading to an essentially chaotic spatial distribution of the order tensor at a slow flow.

Diffusion of Rodlike Polypeptides with Different Main-Chain Lengths in the Thermotropic Liquid Crystalline State As Studied by the Field-Gradient1H NMR Method

The self-diffusion coefficients (D) of rodlike poly(n-alkyl l-glutamate)s having n-dodecyl side chains in the thermotropic liquid crystalline state were measured as a function of the main-chain len...

Adsorption of anionic polyelectrolytes to dioctadecyldimethylammonium bromide monolayers

Monolayers of dioctadecyldimethylammonium bromide (DODA) at the air/water interface were used as model for charged surfaces to study the adsorption of anionic polyelectrolytes. After spreading on a pure water surface the monolayers were compressed and subsequently transferred onto a polyelectrolyte solution employing the Fromherz technique. The polyelectrolyte adsorption was monitored by recording the changes in surface pressure at constant area. For poly(styrene sulfonate) and carboxymethylcellulose the plot of the surface pressure as function of time gave curves which indicate a direct correlation between the adsorbed amount and surface pressure as well as a solely diffusion controlled process. In the case of rigid rod-like poly(p-phenylene sulfonate)s the situation is more complicated. Plotting the surface pressure as function of time results in a curve with sigmoidal shape, characterized by an induction period. The induction period can be explained by a domain formation, which can be treated like a crystallization process. Employing the Avrami expression developed for polymer crystallization, the change in the surface pressure upon adsorption of rigid rod-like poly(p-phenylene sulfonate)s can be described.

Moisture-induced stress relaxation of polyimide thin films

Four different polyimides: rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA), pseudo-rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), semiflexible poly(4,4-oxydiphenylene pyromellitimide) (PMDA-ODA) and poly(4,4-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA) were prepared from two different precursors, poly(amic diethyl ester) (PAE) and poly(amic acid) (PAA). For polyimides prepared from the PAE precursors, stress relaxation coefficient at 25°C, 100% RH was 14.76×10−10cm2/s for PMDA-PDA, 3.29×10−10cm2/s for BPDA-PDA, 24.91×10−10cm2/s for PMDA-ODA and 9.34×10−10cm2/s for BPDA-ODA. For polyimides prepared from the PAA precursors, stress relaxation coefficient at 25°C, 100% RH was 10.50×10−10cm2/s for PMDA-PDA, 1.91×10−10cm2/s for BPDA-PDA, 28.84×10−10cm2/s for PMDA-ODA and 9.10×10−10cm2/s for BPDA-ODA. The effect of bulky ethyl ester group on the stress relaxation behavior is significantly high in rodlike PMDA-PDA or pseudo-rodlike BPDA-PDA having high chain rigidity and intermolecular packing order. The decreased birefringence, crystallinity and the looser packing in amorphous region of rigid polyimide derived from PAE may induce fast stress relaxation compared to flexible polyimide. Specially, the different chain mobility of polyimide also induced significant effect on the stress relaxation.

Fully Rodlike Polyimides Containing Flexible Side Chains with Various Lengths and Their Ability to Align Liquid-Crystals on the Rubbed Surface

Rodlike poly(p-phenylene pyromellitimide)s with various side chains (Cm-PMDA-PDA Pis) were newly prepared in a good quality of films. The polyimide films were rubbed, and used in constructing liquid-crystal (LC) cells which were filled with a nematic LC containing a dichroic dye. For the LC cell, both pretilt angle and alignment director of LCs were dependent strongly on the side chain length as well as the rubbing density. On the polymer film, both homogeneous and homeotropic LC alignments were achievable by either changing the side chain length or varying rubbing density. Unlike polymers reported previously as a LC alignment layer material, the Cm-PMDA-PDA PI induced LCs to pretilt with a negative angle rather than a positive angle: this is a unique property characteristic of the Cm-PMDA-PDA PIs. In addition, film properties were measured.

Thermoreversible Gelation of Isotropic and Liquid Crystalline Solutions of a “Sticky” Rodlike Polymer

Thermoreversible gelation of rodlike poly(γ-stearyl-α-l-glutamate) in n-dodecane has been studied by differential scanning calorimetry, polarized light microscopy, visual observations, and temperature ramped fluorescence photobleaching recovery. Solutions spanning a wide range of concentrations can produce gels. In solutions that are initially liquid crystalline, long-range features such as cholesteric twist appear to be frozen by gelation. Although gelation is rapid, some of the polymer molecules retain significant mobility, allowing the gels to “cure” slowly.

Phase equilibrium studies on rod/solvent and rod/coil/solvent systems containing poly(?,L-glutamate) having oligo(ethylene glycol) side chains

Phase equilibrium studies for semiconcentrated solutions of rodlike poly(γ-benzyl L-glutamate) having oligo(ethylene glycol) as side chains (PBLG-g-OEG) have been investigated. The phase-boundary concentrations in isotropic and anisotropic phases for N,N-dimethylformamide (DMF) solution of PBLG-g-OEG with short side chains (PBLG2-g-380) are higher than those for solution of PBLG-g-OEG with long side chains (PBLG2-g-770). The lattice theory and the scaled particle theory for nematic solution, which don't distinguish the molecular architecture of the rodlike polymer, cannot explain this experimental result. Repulsive interaction between rodlike polymers by means of the attached side chains is proposed for the molecular orientation of PBLG-g-OEG in anisotropic state in order to describe the experimental result. Ternary phase diagrams of PBLG-g-OEG/poly(ethylene glycol) (PEG)/DMF show that the miscibility of rodlike PBLG-g-OEG and coiled PEG is most enhanced in the system of PBLG2-g-770, which has longest and largest amount of side chains. This experimental observation is explained by using the calculation based on the lattice theory and the repulsive interaction of side chains proposed above.

Self-Organization of Nitrogen-Containing Polymeric Supramolecules in Thin Films

ABSTRACTRigid rod-like poly(2,5-pyridinediyl), semi-rigid polyaniline and flexible poly(4- vinylpyridine) are nitrogen-containing polymers that with selected amphiphilic oligomers form self-organized comb-shaped supramolecules due to protonation, hydrogen bonding and polar- nonpolar effects combined. Luminescent or conductive ordered structures are demonstrated in thin films. The structures are characterized using small-angle x-ray scattering (SAXS) and grazing-incidence small-angle x-ray scattering (GISAXS). The uniformity is studied using atomic force microscopy and scanning near-field optical microscopy (SNOM).

Self-Organization of Nitrogen-Containing Polymeric Supramolecules in Thin Films

Rigid rod-like poly(2,5-pyridinediyl), semi-rigid polyaniline and flexible poly(4- vinylpyridine) are nitrogen-containing polymers that with selected amphiphilic oligomers form self-organized comb-shaped supramolecules due to protonation, hydrogen bonding and polar- nonpolar effects combined. Luminescent or conductive ordered structures are demonstrated in thin films. The structures are characterized using small-angle x-ray scattering (SAXS) and grazing-incidence small-angle x-ray scattering (GISAXS). The uniformity is studied using atomic force microscopy and scanning near-field optical microscopy (SNOM).

High-Spin Polyphenoxyl Based on Poly(1,4-phenyleneethynylene)

Rodlike poly(1,4-phenyleneethynylene) 2-substituted with multiple pendant phenoxyls 1 was synthesized by polymerizing 4-bromo-2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethynylbenzene 10a using the catalyst of a palladium−triphenylphosphine complex and cuprous iodide and subsequent heterogeneous oxidation. The corresponding dimer 2 was also synthesized; X-ray analysis of its precursor 4 indicated a linear phenyleneethynylene backbone and twisted dihedral angles of 50 and 77° for the pendant phenol groups. ESR spectra suggested a delocalized spin distribution from the pendant phenoxyl to the backbone. The diphenoxyl 2 had a triplet (S = 2/2) ground state. The spin concentration of the polyphenoxyl 1 could not be increased beyond 0.7 spin/unit due to its low solvent solubility; 1 with a spin concentration of 0.62 had an average S of 3/2.

Effects of precursor origins on water sorption behaviors of various aromatic polyimides in thin films

Poly(amic diethyl ester) [PAE] precursors of four different polyimides with various chain rigidities were synthesized and thermally converted to the polyimides in thin films: rodlike poly( p-phenylene pyromellitimide) [PMDA-PDA] and poly(4,4′-biphenylene pyromellitimide) [PMDA-BZ], pseudo-rodlike poly( p-phenylene biphenylenetetracarboximide) [BPDA-PDA] and semiflexible poly(4,4-oxydiphenylene pyromellitimide) [PMDA-ODA PAE]. For the polyimide films, water sorption behaviors were investigated by gravimetry and then compared with those of the polyimides prepared from the corresponding poly(amic acid) [PAA] precursors. In addition, their morphological structures were examined by X-ray diffraction. For all the polyimides, both water sorption and morphological structure were dependent upon the history of precursor origin. All the polyimides except PMDA-ODA revealed relatively higher diffusion coefficient of water, higher water sorption, lower intermolecular packing order and lower population of a more ordered phase in the PAE-derived polyimide films than the corresponding PAA-derived polyimide films. For PMDA-ODA, the variations in the water diffusion and sorption due to the precursor origin were relatively small in spite of a relatively large change in the morphological structure. Overall, the effect of precursor origin on the water diffusion and sorption is significantly high in the rodlike or pseudo-rodlike polyimides having a high chain rigidity and high intermolecular packing order, but relatively low in the semiflexible polyimide with a relatively low chain rigidity. In comparison, regardless of the precursor origins, the diffusion coefficient of water was in the decreasing order PMDA-ODA>PMDA-PDA>PMDA-BZ>BPDA-PDA and, however, the water sorption was in the decreasing order PMDA-PDA>PMDA-BZ>PMDA-ODA>BPDA-PDA. These water diffusion and sorption behaviors were understood by considering their chemical affinities to water in addition to the morphological structures.

Synthesis and characterization of fully rodlike poly(4,4?-biphenylene pyromellitimide)s with various short side groups

Fully rodlike poly(4,4-biphenylene pyromellitimide) (PMDA–BZ) is so brittle in spite of its extremely high modulus. In this study, the brittleness was attempted to be improved without a significant sacrifice of the high modulus by incorporating short side groups. For this, benzidine monomers, which contain methyl, methoxy, fluoro, and trifluoromethyl at the 2,2′-positions, were synthesized and then used for polycondensation reactions with pyromellitic dianhydride in N-methyl-2-pyrrolidone, producing soluble poly(amic acids)s. The synthesized poly(amic acid)s were converted to the fully rodlike polyimides in films by a conventional spin-coating on substrates, soft bake, and thermal imidization. The brittleness of PMDA–BZ was successfully healed with a small portion of sacrifice in the modulus by incorporating methyl, methoxy, and trifluoromethyl groups but could not be healed by the fluoro side group. The improvement in the brittleness might be contributed from the chain mobility and lateral chain packing order enhanced by the incorporation of the side groups, which are evident on the measured structures and properties. The structure and other properties were detected to be influenced by the incorporated side groups. The detailed structures and properties were interpreted by considering roles of side groups and the correlation between structure and properties, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 937–957, 1999

Structure and properties of rodlike poly(p-phenylene pyromellitimide)s containing short side groups

Fully rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA) exhibits a high modulus but is considered a useless polymer because of its high brittleness. In this study, the high brittleness was successfully healed with only a minor effect on the high modulus by incorporating short side groups, such as methyl, methoxy and trifluoromethyl, into the PDA unit of the polymer backbone. Furthermore, refractive indices, dielectric constants, and their anisotropies were all reduced by the incorporation of side groups. However, both in-plane thermal expansivity and thermal stability were relatively degraded by the incorporation of side groups. The polyimides exhibited relatively low packing coefficients because of the limited bulkiness of the side groups. They exhibited glass transition temperatures which are not expected for PMDA-PDA polyimide, indicating that the chain mobility was improved by incorporating side groups. With the improved chain mobility, molecular ordering was slightly improved, showing a bundle-like ordering without regular packing.

Synthesis and blue light-emitting characteristic of rod-like poly(4,4′-biphenylene pyromellitimide) with furyl side groups

A new 2,2′-bis(furyl)benzidine (FurylBZ) with a well-defined conjugation length was synthesized, and its polyimide was prepared through thermal imidization of the poly(amide acid) obtained from the polymerization with pyromellitic dianhydride. FurylBZ monomer and its polyimide film were characterized to exhibit intense blue light emission with a relatively narrow peak width in the photoluminescence. The relative fluorescence quantum yield was measured at room temperature to be 0.52 for FurylBZ in 1,4-dioxane and 0.074 for the polyimide in films. The polyimide was thermally stable up to 400°C. The polyimide is amorphous, due to the bulky furyl side groups. However, the polyimide chains were favorably aligned in the film plane due to the rod-like chain characteristic.

Water sorption and diffusion behaviours in thin films of photosensitive polyimides

Several photosensitive polyimide (PSPI) precursors were synthesised by the acid/base complexations of conventional poly(amic acid) precursors with photochemically cross-linkable 2-(dimethylamino)ethyl methacrylate. PSPIs in films were prepared from the photosensitive precursors by thermal imidisation, whereas the corresponding PIs in films were prepared from the conventional poly(amic acid)s: rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA), rigid (poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), semi-flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), semi-flexible poly(4,4′-oxydiphenylene pyromellit-imide) (PMDA-ODA), and flexible poly(4,4′-oxydiphenylene benzophenonetetracarboximide) (BTDA-ODA). Water sorption and diffusion behaviours in the PSPIs were gravimetrically measured at 25°C in 100% relative humidity and compared with those of the corresponding PIs. For the PSPIs as well as the PIs, the water sorption and diffusion behaviours were nearly Fickian, regardless of the backbone chemistry. However, those were strongly dependent upon the polyimide backbone chemistry and precursor origin. In addition, those in polyimides were affected by the bulky photosenistive groups, even though they were temporarily linked to the precursor polymers and then debonded from the backbones and ultimately outgassed during the thermal imidisation process. For PMDA-PDA, BPDA-PDA and BPDA-ODA, the PSPIs absorbed water more quickly than the corresponding PIs, whereas for PMDA-ODA and BTDA-ODA, the PSPIs absorbed water less quickly than the corresponding PIs. In contrast to the water diffusion, all the PSPIs absorbed slightly more or a great deal more water than the corresponding PIs, depending on the backbone chemistry. All the measured water sorption and diffusion behaviours in the PSPIs were understood by considering changes in the morphological structure (namely, chain order and orientation), voids, and residues possibly induced by the bulky photosensitive groups, in addition to the Tg as well as the chemical affinity to water.

Residual stress and optical properties of fully rod-like poly(p-phenylene pyromellitimide) in thin films: Effects of soft-bake and thermal imidization history

A soluble poly(amic acid) precursor solution of fully rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA) was spin cast on silicon substrates, followed by soft bake at 80–185°C and subsequent thermal imidization at various conditions over 185–400°C in nitrogen atmosphere to be converted to the polyimide in films. Residual stress generated at the interface was measured in situ during imidization. In addition, the imidized films were characterized in the aspect of polymer chain orientation and ordering by prism coupling and X-ray diffraction. The soft-baked precursor film revealed a residual stress of 16–28 MPa at room temperature, depending on the soft bake condition: higher temperature and longer time in the soft bake gave higher residual stress. The stress variation in the soft-baked precursor film was not significantly reflected in the final stress in the resultant polyimide film. However, the residual stress in the polyimide film varied sensitively with variations in imidization process parameters, such as imidization temperature, imidization steps, heating rate, and film thickness. The polyimide film exhibited a wide range of residual stress, −7 MPa to 8 MPa at room temperature, depending on the imidization condition. Both rapid imidization and low-temperature imidization generated high stress in the tension mode in the polyimide film, whereas slow imidization as well as high temperature imidization gave high stress in the compression mode. Thus, a moderate imidization condition, a single- or two-step imidization at 300°C for 2 h with a heating rate of < 10 K/min was proposed to give a relatively low stress in the polyimide film of < 10 μm thickness. However, once a precursor film was thermally imidized at a chosen process condition, the residual stress–temperature profile was insensitive to variations in the cooling process. All the films imidized were optically anisotropic, regardless of the imidization history, indicating that rod-like PMDA-PDA polyimide chains were preferentially aligned in the film plane. However, its degree of in-plane chain orientation varied on the imidization history. It is directly correlated to the residual stress in the film, which is an in-plane characteristic. For films with residual stress in the tension mode, higher stress films exhibited lower out-of-plane birefringence, that is, lower in-plane chain orienta-tion. In contrast, in the compression mode, higher stress films showed higher in-plane chain orientation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1261–1273, 1998

Studies on the texture of nematic solutions of a rod-like polymer 1. Distortion of the director field in a magnetic field

The growth of the distortion of the director in an external field, and its relaxation on removal of the field are studied for nematic solutions of the rod-like poly(1,4-phenylene-2,6-benzobisthiazole), PBZT, over a range of concentration, polymer molecular weight and temperature. The twist viscosity and the order parameter are more weakly dependent on concentration than predicted for charged rod-like chains. This behaviour implies a short-range translational order in a direction orthogonal to the chain axis, induced by electrostatic interactions among the polycations on protonated PBZT. The relaxation gives a normal temperature dependence for the splay curvature elasticity, but that for the twist curvature is unexpectedly strong. This behaviour is interpreted as a weakening of the surface anchoring with increased temperature.

Estimation of the linear thermal expansion coefficient in friction-deposited, oriented poly(tetrafluoroethylene) films by temperature-dependent lateral force microscopy

Preliminary lateral force microscopy (LFM) results are presented which were obtained at different temperatures on thin films of poly(tetrafluoroethylene) prepared by friction deposition. Chain-chain distances of rodlike poly(tetrafluoroethylene) macromolecules were determined as a function of temperature from LFM images which exhibit molecular resolution. The value of the linear thermal expansion coefficient in the chain-perpendicular direction was estimated to be 3.5x10-3 [1/°C] in the temperature range between+10°C and+40°C. This value is higher than the literature data quoted for the temperature range between 0 °C and 25 °C. Possible reasons for this deviation are discussed.

Electric polarization of polyelectrolyte and colloid media: dielectric versus electro-optic approach

The theories of dielectric dispersion and of electric birefringence as a representative of electro-optic methods are considered and it is shown that they both depend in a similar way simply on the real part of the complex electric polarizability of the macromolecules or the particles. The latter also contains the permanent dipole moment. Experimental data on dielectric dispersion, electric birefringence and electric light scattering of strongly elongated, rod-like poly(tetrafluoroethylene) particles are compared and an attempt is made to extend the dielectric dispersion curve to lower frequencies using electric birefringence and electric light scattering data. Further, the experimental data on dielectric dispersion, electric light scattering, electro-orientation and dipolophoresis for the more complicated Escherichia coli particles are compared. Again, the possibility to extend the 10 kHz–100 MHz dielectric dispersion curve down below 1 Hz by using electric light scattering data is examined. The good matching of the dielectric dispersion and electric light scattering frequency curves found in the overlapping frequency range (10 kHz-5 MHz) essentially enhances the chance that dielectric dispersion below 1 MHz is related to α dispersion and not to electrode polarization. Thus it is not only possible to obtain additional information on the mechanism of polarization at lower-frequency dielectric dispersion, but also to extend our knowledge about the effective dielectric properties of biological complex fluids to frequencies essentially below 1 MHz. This could be important for the understanding of the effect of low-frequency electromagnetic fields on living matter.