Effect of trifluoromethyl substituents on birefringence of polystyrene

Transparent thermoplastic polymers that exhibit no birefringence are ideal for optical components such as optical films for liquid crystal displays and various lenses. Copolymerization of a positive birefringent monomer with a negative monomer is an effective technique for obtaining low birefringent polymers, especially zero‐photoelastic birefringence polymers that exhibit no photoelastic birefringence even during elastic deformation. We prepared four types of trifluoromethyl‐substituted polystyrenes. By substituting hydrogens at the ortho or meta positions of the benzene ring of polystyrene, we demonstrated that poly(2‐(trifluoromethyl)styrene), poly(3‐(trifluoromethyl)styrene), and poly(3,5‐bis(trifluoromethyl)styrene) had negative photoelastic coefficients. However, poly(4‐(trifluoromethyl)styrene) had a positive photoelastic coefficient similar to that of polystyrene. Based on these results, we synthesized a zero‐photoelastic birefringence polymer of poly(2‐(trifluoromethyl)styrene‐co‐4‐(trifluoromethyl)styrene) (55/45 wt.) exhibiting no photoelastic birefringence in elastic deformation, in which the positive photoelastic birefringence of the poly(4‐(trifluoromethyl)styrene) unit was compensated for by the negative photoelastic birefringence of the poly(2‐(trifluoromethyl)styrene) unit. The discovery of polymers having negative photoelastic coefficients is valuable for the design and synthesis of zero‐photoelastic birefringence polymers. The four types of trifluoromethyl‐substituted polystyrenes are promising optical materials because they have high transparency (transmittance > 89–92% for 27–34‐µm thickness films) in the visible and near‐infrared regions and a high decomposition temperature of approximately 400°C. Copyright © 2016 John Wiley & Sons, Ltd.     

Molecular orientation of aromatic polycarbonates containing fluorene side chains by polarized infrared spectroscopy and birefringence analysis

The molecular orientation of an aromatic polycarbonate containing fluorene side chains was investigated by polarized infrared spectroscopy and birefringence analyses. The copolymers were synthesized from 2,2‐bis(4‐hydroxyphenyl)propane (BPA), 9,9‐bis(4‐hydroxy‐3‐methylpheny)fluorene (BMPF), and phosgene by interfacial polycondensation. The 1449‐cm^?1 band of the uniaxially oriented films, stretched at the glass‐transition temperature (T_g) plus 5 °C, was assigned to various combinations of CC stretching and CH in‐plane bending vibrations in the fluorene ring, and the transition moment angle was estimated to be 90°. The intrinsic birefringence of aromatic polycarbonate films with BMPF molar ratios ranging from 0.5 to 1 was obtained with the 1449‐cm^?1 band. The copolymer was estimated to show zero intrinsic birefringence at the BMPF molar ratio of 0.75, and the BMPF homopolymer showed negative intrinsic birefringence. A linear relationship between the volume fraction of BMPF units and the intrinsic birefringence indicated that the two monomer units of BPA and BMPF in each copolymer were not independent, and an intrinsic birefringence could be defined even in the copolymer. The sign of the photoelastic coefficient in the homopolymer with BMPF units was positive. The different signs of the photoelastic coefficient and the intrinsic birefringence suggest that the fluorene side‐chain orientation induced by stress in the glass state is quite different from the orientation of the uniaxially oriented films stretched at T_g + 5 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1554–1562, 2003     

Simulation of phase‐separated structures of liquid‐crystalline polymer/flexible polymer blends

The phase‐separation kinetics of liquid‐crystalline polymer/flexible polymer blends was studied by the coupled time‐dependent Ginzberg–Landau equations for compositional order parameter ? and orientational order parameter S_ij. The computer simulations of phase‐separated structures of the blends were performed by means of the cell dynamical system in two dimensions. The compositional ordering processes of phase separation are demonstrated by the time evolution of ?. The influence of orientational ordering on compositional ordering is discussed. The small‐angle light scattering patterns are numerically reproduced by means of the optical Fourier transformation of spatial variation of the polarizability tensor α_ij, and the azimuthal dependence of the scattering intensity distribution is interpreted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2915–2921, 2001     

Mechanism of generation of photoelastic birefringence in methacrylate polymers for optical devices

We clarified the birefringence properties of poly(methyl methacrylate), poly(ethyl methacrylate), poly(isobutyl methacrylate), poly(cyclohexyl methacrylate), poly(isopropyl methacrylate), and poly(tert‐butyl methacrylate). We demonstrated that the conformational change in polymer molecules that causes orientational birefringence differs from that causing photoelastic birefringence. Orientational birefringence depends mainly on the orientation of the main chains of the methacrylate polymers above T_g. On the other hand, photoelastic birefringence in elastic deformation below T_g depends mainly on the orientation of the side chains while the main chains are scarcely oriented. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2029–2037, 2010     

Electric field‐induced birefringence,optical rotatory power and conoscopic measurements of a chiral antiferroelectric smectic liquid crystal

Using a photoelastic modulator‐based novel set‐up, the electric field‐induced in‐plane birefringence and the optical rotatory power (ORP) were measured of an antiferroelectric liquid crystalline compound (12OF1M7) in its various phases using 30 µm homeotropic cells. Some specific signatures of the in‐plane birefringence and of the ORP for the various phases are being established. A relatively small threshold field is needed for the unwinding process of the antiferroelectric phase with a unit cell of four layers [SmC_A*(1/2)] compared with that for two layers [SmC_A*(0)]. On application of the electric field on the high temperature side of the SmC_A*(1/2) phase (80.1–81.5°C), a field‐induced phase transition is shown to occur directly to the SmC* phase, whereas on the lower temperature side (79.4–80.1°C) the transition takes place to SmC* via the SmC_A*(1/3) phase. The in‐plane birefringence exhibits a critical power law dependence for the SmC*–SmA transition. The ORP changes sign within the temperature range of the phase with a unit cell of three layers, reflecting a change in the handedness during this phase. Using tilted conoscopy, the results for the biaxiality and the apparent tilt angle for a smectic liquid crystal with a tilt angle greater than 18° in the ferroelectric phase are reported. The biaxiality implies the difference in the refractive indices between the two minor axes of the refractive index ellipsoid. The optical transmittance at visible and IR wavelengths for free‐standing films reveal characteristic reflection bands for these phases. The modulated structures of the reflected bands appear just above the SmC_A* phase and below SmC_A*(1/3); these are possibly due to an easy deformation of the phase by the surfaces.     

Copolymers of methyl methacrylate with N‐trifluorophenyl maleimides: High glass transition temperature and low birefringence polymers

Copolymers of methyl methacrylate (MMA) with 2,3,4‐ and 2,4,6‐trifluorophenyl maleimides (TFPMIs) were synthesized by a free radical initiator, azobisisobutyronitrile, in 1,4‐dioxane and also in bulk. The refractive indexes of the copolymers were in the range of 1.49–1.52 at 532 nm. The T_gs were 133–195 °C depending on copolymer compositions. In addition, the copolymers were thermally stable, T_d > 350 °C. The orientational and photoelastic birefringence of the copolymers were also investigated. As both of the orientational and photoelastic birefringences of PMMA are negative, whereas those of poly(TFPMI)s are positive, we could obtain nearly zero orientational and photoelastic birefringence polymers when the ratios of 2,3,4‐TFPMI/MMA were 15/85 and 5/95 mol %, respectively. For 2,4,6‐TFPMI, zero orientational and photoelastic birefringences could be obtained when the ratios of 2,4,6‐TFPMI/MMA were 12/88 and 3/97 mol %, respectively. The T_gs of those copolymers with zero birefringences were in the range of 135–140 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Assessment of thermal expansion coefficient of methylsilsesquioxane thin film

For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006     

Fluorinated poly(arylene ether ketone)s bearing pentafluorostyrene moieties prepared by a modified polycondensation

The polycondensation of decafluorobenzophenone with hexafluorobisphenol A was modified by the addition of a molecular sieve dehydrating apparatus to the refluxing reaction system. This modification promoted the polymerization and enabled the reactions to be conducted in milder conditions and completed in a shorter time, thereby depressing side reactions such as branching and crosslinking. The resulting fluorinated poly(arylene ether ketone)s (FPAEK) were free of gel particles and possessed the designed molecular weights. This modified procedure was also suitable for introducing crosslinkable pentafluorostyrene (FSt) moieties into the polymers at the chain ends and/or inside the chain with the vinyl group of FSt being pendant. The resulting FSt containing fluorinated poly(arylene ether ketone)s (FPAEK‐FSt) can then be thermally crosslinked at 100 °C in the presence of 1% benzoyl peroxide (BPO) or at 250 °C without any initiator. The glass‐transition temperatures (T_g's) of FPAEK increased with increasing molecular weight and leveled off at about 147 °C for the polymer with a number‐average molecular weight of 18,600 Da, whereas the values were not apparently affected by the addition of FSt units. However, crosslinking of the FPAEK‐FSt resulted in an approximate 30 °C increase of the T_g. Spin‐coating FPAEK‐FSt onto silicon wafers followed by crosslinking gave films with excellent thermal stability, physical strength, and adhesion to the substrate as well as good reproducibility in terms of film preparation and optical properties. The refractive index and birefringence of the films measured at a wavelength of 1.55 μm were 1.502 and 2.5 × 10^?3, respectively. © 2002 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4205–4216, 2002     

Molecular orientation of rigid‐rod polyimide films characterized by polarized attenuated total reflection/fourier transform infrared spectroscopy

The variations in the molecular orientation of uniaxially drawn rigid‐rod polyimide films were systematically characterized in all three dimensions with polarized attenuated total reflection/Fourier transform infrared spectroscopy. The second‐order orientation coefficients were directly deduced from the anisotropy in IR absorptions of particular bands. With the draw ratio increasing, the state of the molecular orientation changed from being nearly planar to completely uniaxial via biaxial orientation, and the degree of orientation was much larger than that of a semirigid polyimide having an ether linkage at the same draw ratio, which originated from the rigid‐rod structure. In addition, the imide planes were rotationally oriented to the out‐of‐plane direction of the film geometry. Furthermore, the relationship between the molecular chain orientation and the in‐plane birefringence in the biaxial orientation state was examined. The intrinsic birefringence was estimated from biaxial orientation films to be 0.33 at a wavelength of 1307 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 418–428, 2003     

Synthesis and characterization of highly refractive polyimides from 4,4′‐thiobis[(p‐phenylenesulfanyl)aniline] and various aromatic tetracarboxylic dianhydrides

An aromatic sulfur‐containing diamine 4,4′‐thiobis[(p‐phenylenesulfanyl) aniline] (3SDA) was synthesized and polymerized with a sulfur‐containing dianhydride 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and three nonsulfur aromatic tetracarboxylic dianhydrides, respectively to afford four poly(amic acid)s (PAAs) with the inherent viscosities of 0.54–1.04 dL/g. Flexible and tough polyimide (PI) films obtained from the PAA precursors showed good thermal, mechanical, and optical properties. The glass transition temperatures (T_gs) of the PIs ranged from 179.1–227.2 °C determined by differential scanning calorimetry (DSC), and 173.8–227.3 °C by dynamic mechanical analysis (DMA), depending on the dianhydride used. The 10% weight loss temperatures were in the range of 500–536 °C, showing high intrinsic thermal‐resistant characteristics of the PI films. The PI films also showed good optical transparency above 500 nm, which agreed well with the calculated absorption spectra using the time‐dependent density functional theory. The average refractive indices (n_av) measured at 632.8 nm were 1.7191–1.7482, and the in‐plane/out‐of‐plane birefringences (Δn) were 0.0068–0.0123. The high refractive indices originate from the high sulfur contents, good molecular packing, and the absence of bulky structures. The relatively small birefringence mainly results from the flexible thioether linkages structures of the diamine. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5606–5617, 2007     

A rod‐like fluorinated polyimide as an in‐plane birefringent optical material 2: Control of optical retardation using spontaneous molecular orientation

Following previous work, a fluorinated polyimide with a rod‐like structure has been investigated as an in‐plane birefringent optical material whose birefringence and thickness can be precisely controlled. Poly(amic acid) films fixed in a metal frame by two sides and thermally cured without any drawing resulted in a polyimide film with an in‐plane birefringence (Δn) larger than 0.1 at 1543 nm. The optical retardation, which is defined as the product of Δn and the film thickness, was controlled by varying the curing and post‐annealing temperatures and by using reactive ion etching. In situ measurements of the tensile stress and the generated retardation showed that the initial orientation at below 200°C was due to the large tensile stress caused by the film shrinkage during imidization and that the increased Δn at higher temperatures was caused by the spontaneous orientation of the polyimide molecules. The curing temperature dependence of refractive indices, optical transmittance in the visible and near‐infrared region, and the wavelength dispersion of retardation of the in‐plane birefringent polyimide films are also reported. Copyright © 1999 John Wiley & Sons, Ltd.     

Structure and mechanical properties of talc‐filled blends of polypropylene and styrenic block copolymers

The structure–property relationships of isotactic polypropylene (iPP)/styrenic block copolymer blends filled with talc were examined by optical and scanning electron microscopy, wide‐angle X‐ray diffraction, and tensile‐ and impact strength measurements. The composites were analyzed as a function of the poly(styrene‐b‐ethylene‐co‐propylene) diblock copolymer (SEP) and the poly(styrene‐b‐butadiene‐b‐styrene) triblock copolymer (SBS) content in the range from 0 to 20 vol % as elastomeric components and with 12 vol % of aminosilane surface‐treated talc as a filler. Talc crystals incorporated in the iPP matrix accommodated mostly plane‐parallel to the surface of the samples and strongly affected the crystallization process of the iPP matrix. The SBS block copolymer disoriented plane‐parallel talc crystals more significantly than the SEP block copolymer. The mechanical properties depended on the final phase morphology of the investigated iPP blends and composites and supermolecular structure of the iPP matrix because of the interactivity between their components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1255–1264, 2004     

Thermally enhanced photoinduced in‐plane reorientation in photo‐cross‐linkable polymer liquid crystalline films and its application to linear polarizer

Thermally enhanced photoinduced in‐plane molecular reorientation in new photo‐cross‐linkable polymer liquid crystalline (PPLC) films comprising 4‐[ω‐(4‐methoxycinnamoyloxy)alkyloxy]biphenyl side groups is explored using linearly polarized ultraviolet (LPUV) light exposure and subsequent annealing. The influence of the alkylene spacer length between the photo‐cross‐linkable group and the biphenyl mesogenic moiety is investigated. The straight‐line characteristics of the photoreactive mesogenic side group and the 4‐methoxycinnamoyl group play important roles in the high photoreactivity and the large thermally enhanced molecular reorientation, where the in‐plane order and the birefringence of the reoriented film are 0.61 and 0.18 are obtained. Finally, cooperative molecular reorientation of dichroic dyes doped in PPLC films is also achieved to fabricate a linear polarizer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4712–4718, 2008     

Residual thermal birefringence in freely quenched plates of amorphous polymers: Simulation and experiment

Free quenching experiments were performed on thin plates of polystyrene (PS) and polycarbonate (PC). The thermal birefringence distribution along the thickness direction of the plates was measured. The birefringence data were compared with the results of a numerical simulation based on the linear viscoelastic and photoviscoelastic constitutive equations for the mechanical and optical properties, respectively, and the first‐order rate equation for volume relaxation. The effects of the initial temperature, quenching temperature, and quenching media on the development of residual thermal stresses and birefringence were evaluated. At higher initial temperatures (>105 °C), the thermal birefringence in quenched PS plates was negative at the center and positive at the surface, whereas at lower temperatures (close to the glass‐transition temperature), the birefringence became positive at the core and negative at the surface or positive through the entire cross section of the plate. The birefringence in freely quenching PC plates was positive at the center and negative at the surface at any initial temperature. These observations were in fair agreement with predicted data. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1850–1867, 2003     

Reduced stress‐optical coefficient of polycarbonate by antiplasticization

We have investigated the effect of antiplasticization on the stress‐optical behavior of polycarbonate (PC) containing terphenyls (tPh) and di(2‐ethylhexyl)adipate (DEHA). Addition of the three tPhs (p‐, o‐, and m‐tPh) and DEHA at contents of 5–10 wt % increases the tensile storage modulus (E' ) of PC owing to the antiplasticization effect. In particular, p‐tPh increases E' more than the other additives, suggesting that the rod‐like shape matches the free volume of PC in the glassy state. The three tPh isomers improve the glassy birefringence of PC while DEHA does not change the glassy birefringence, which corresponds to the polarizability anisotropy. The stress‐optical coefficient, a ratio of stress and birefringence, of PC decreases with increasing additive content in order of p‐tPh ? o‐tPh > m‐tPh = DEHA. This result is agreement with a restricted rotational motion of additive molecule in PC, which is observed in dynamic mechanical and birefringence data. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1837–1842     

Birefringence control by hydrogen bonding on compatible polymer pair composed of hydrogenated ring‐opening polymer and modified polystyrene

A new polymer blend composed of a hydrogenated ring‐opening polymer (HROP) with an ester group and hydroxyl functionalized polystyrene (HFP) produced the excellent transparent materials which enabled a precise birefringence control in keeping with the other physical properties for optical film use. The blend with a composition from 0.28 to 0.35 for the HFP weight fraction showed an extraordinary wavelength dispersion, transmitting through a zero birefringence point at the critical fraction of 0.45, while each polymer showed an ordinary wavelength dispersion. The observed excellent transparency even above those of the glass transition temperature was attributed to a depressed phase separation that resulted from strong hydrogen bond between the ester and hydroxyl groups. An IR analysis of the film demonstrated a remarkable red‐shift in the carbonyl peak with an increase of the hydroxylated polystyrene content, indicating a strong hydrogen bond between those groups. This new polymer blend provides a useful design to achieve practical demands for film use, both optical and mechanical under the fabrication conditions using the melt extrusion technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3132–3143     

Crosslinkable polymers for optical waveguide devices. II. Fluorinated ether ketone oligomers bearing ethynyl group at the chain end

Fluorinated ether ketone oligomers bearing a crosslinkable ethynyl group at the chain end have been investigated for low-loss polymer optical waveguide devices. These oligomers are designed to achieve low birefringence and were synthesized by the reaction of 4,4′-(hexafluoroisopropylidene)diphenol with an excess decafluorobenzophenone, followed by reaction with (phenylethynyl)phenol or ethynylphenol. The molecular weights (M_ns) and polydispersities of the oligomers determined by GPC with polystyrene standard are in the range of 6600–8500 g/mol and 1.79–2.04, respectively. By spin coating and thermal crosslinking, the polymer solutions easily provide the good optical quality thin films. The cured films show good chemical resistance and high thermal stability up to 460°C under nitrogen. At 1.55 µm wavelength, the refractive index and birefringence of the films show in the range of 1.5104–1.5172 and 0.0078–0.0014, respectively. The propagation loss of the single-mode channel waveguide was measured to be less than 0.5 dB/cm at 1.55 µm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2355–2361, 1999     

Thiophene‐cored 2,2‐bis(methylol)propionic acid dendrimers for optical‐power‐limiting applications

The synthesis and characterization of dendron‐coated 2,5‐bis(phenylethynyl)thiophene chromophores are described. The dendrimers were grown divergently on the arylthiophene core with the versatile anhydride of 2,2‐bis(methylol)propionic acid. The arylthiophene core was synthesized with Sonogashira coupling reactions. Structurally well‐defined dendrimers up to the fourth generation were grown, as confirmed by size exclusion chromatography, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight analysis. The different dendritic substitution did not influence the absorption spectra of the compounds in or near the visible region. Solutions of arylthiophenes had good transparency at wavelengths greater than 400 nm. The dendritic thiophenes exhibited an optical‐power limit at the laser wavelength of 532 nm. However, the magnitude of the optical‐power limit of these compounds was slightly lower than that of a nondendritic arylthiophene with n‐pentyl substituents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1177–1187, 2005     

Novel polyesters with amino‐sulfone azobenzene chromophores in the main chain

The synthesis and optical properties of a series of amorphous polyesters with amino‐sulfone azobenzene chromophores in the main chain are presented. The condensation of alkyl diacid chlorides with 4‐[(2‐hydroxyethyl)ethylamino]‐4′‐(2‐hydroxyethylsulfonyl)azobenzene (7) gave polymers that showed low and unstable photoinduced birefringence because of their low glass‐transition temperature. The condensation of 7 with mixtures of adipoyl chloride and terephthaloyl chloride gave a polymer with a higher glass‐transition temperature and a stable reversible photoinduced birefringence. A photostationary birefringence of 0.07 was observed. Surface profile gratings were optically inscribed and produced diffraction efficiencies less than or equal to 19%. Photostationary, long‐term stable birefringence and surface‐grating efficiency increased with polymer rigidity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2245–2253, 2000