Side-chain Copolymers Research Articles

Synthesis, characterization and photoreaction of photoreactive side-chain liquid-crystalline copolymers comprising 2-benzoylethoxybiphenyl and 3-methyl-2-butenyloxybiphenyl side groups

Synthesis, characterization and photoreaction of photoreactive side-chain liquid-crystalline copolymers comprising 2-benzoylethoxybiphenyl and 3-methyl-2-butenyloxybiphenyl side groups

Pulse poling of side-chain and crosslinkable copolymers

The growth of the macroscopic second-order nonlinear optical properties of side-chain and crosslinkable copolymer species is theoretically modeled. The model describes the rotational diffusion of nonlinear diazo-dye dipoles, in the presence of crosslinking sites randomly distributed in the copolymer matrix, under application of a periodic electric poling field. Solutions for the fundamental equations, describing the time-dependent orientational probability distribution for the crosslinked dipoles, have been obtained in the frame of two complementary approximations. Such distributions have been used in order to evaluate the temporal growth of the second-order nonlinear optical properties and their asymptotic value when saturation of the crosslinking process is attained. The two approximations are shown to give equivalent results, in the range of parameters where both are valid. The influence of the poling electric field frequency and of the volume density of crosslinking sites on the asymptotic second-order nonlinear optical properties is discussed. The results of the theoretical model are compared to the experimental ones, obtained for two copolymers species: A Disperse red 1 side-chain copolymer and a crosslinkable evolution of the latter, Red acid magly. In the experiments the r33 component of the electro-optic coefficient is measured by means of a modified electro-optic ellipsometry setup. The comparison shows a good agreement between experimental and numerical results. The model can be used in order to find the best values of the copolymer parameters, necessary in order to maximize the final second-order nonlinear optical properties.

Synthesis and characterization of polymers containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 4. Poly[(4,4‐dimethyl‐2‐vinyl‐5‐oxazolone)‐co‐(methyl methacrylate)

AbstractThis paper describes the synthesis, characterization and nonlinear optical properties of a series of side chain copolymers prepared by chemical modification of poly[(4,4‐dimethyl‐2‐vinyl‐5‐oxazolone)‐co‐(methyl methacrylate)]s (P(VDM‐co‐MMA)s) with 4,4′‐disubstituted biphenyl. First, a poly(4,4‐dimethyl‐2‐vinyl‐5‐oxazolone) (PVDM) and four P(VDM‐co‐MMA)s were prepared by free‐radical polymerization. Chemical transformation reactions were then performed on these polymer backbones with 4‐cyano‐4′‐(β‐aminoethoxy)biphenyl. This amine was synthesized according to a novel procedure. The functionalized polymers are isotropic and show glass transition temperatures up to 132°C. They can easily be processed by spin‐coating into thin films of optical quality. These films were oriented by a corona discharge process, and ultraviolet spectroscopic measurements were performed to study the axial ordering kinetics as a function of poling conditions. Second‐order nonlinear optical coefficients (d33 and d31) were measured at a fundamental wavelength of 1064 nm. The ratio d33/d31 was found to be close to 3, as expected for amorphous isotropic polymers. No significant relaxation was observed at ambient conditions in 2 months. Hydrogen bonding between CO‐NH groups of neighboring side chains are felt to contribute to the stability of the second‐order nonlinear optical properties in these PVDM systems.

NLO‐polymers containing tert‐butyloxycarbonyl protecting groups: Modification after processing leading to thermally stable nonlinear optical materials

A new polymer for nonlinear optics (NLO) based on male‐imide/methylvinyliscocyanate precursor polymers is introduced. This side‐chain copolymer is cured after spin‐coating and before poling, which, by a thermally activated fragmentation reaction, leads to increased glass transition temperature, increased density of NLO chromophores, and reduced solubility. NLO materials will play an important role in optical telecommunications, but the problem of the chromophores relaxing back into the isotropic state must first be solved.

Crystallization of side chains in copolymers of ethylene and 1-alkenes

The phase structure of random copolymers of ethylene and ethylene-d4 with 1-octadecene and other 1-alkenes has been investigated. CPMAS 13C NMR spectra show that a fraction of the central sections of C16H33 side chains in ethylene-d4 copolymers are in ordered environments at 298 K. They give rise to resonances from 32.9 ppm to 33.8 ppm, which show that they are in trans conformations; T1C values for this group of resonances range from 1 s to 7 s. The remaining side chains are in an amorphous environment, the internal methylenes having a chemical shift of 30.8 ppm and a T1C close to 0.4 s. A Raman band at 1062 cm−1 in the spectrum of an ethylene-d4-1-octadecene copolymer is consistent with partial crystallization of side chains. Some side-chain crystallization also occurs in a 1-tetradecene copolymer. X-ray diffraction studies suggest that smaller side chains do not crystallize to a significant extent at 298 K. © 1996 John Wiley & Sons, Inc.

Manipulation of the ferroelectricity in LC polymers via photomechanical isomerization of azobenzene moieties

AbstractWe report the synthesis and characterization of a new ferroelectric liquid crystalline side chain copolymer containing photoisomerizable chromophores and non‐photoisomerizable mesogenic units. On illumination with UV‐light a suppression of the polar order is obtained as indicated by a substantial drop of the spontaneous polarization (PS) compared to the dark state. We interpret this as the phase order being disrupted by the cis‐isomer of the chromophore. After illumination with VIS‐light only the major part of Ps is restored. The photochemical cis‐trans back‐isomerization (restoration of the phase) leads to a different stationary state than the dark state of the material. The thermal reisomerization (cis‐trans) in the liquid‐crystalline phase was observed to be faster than in solution by one order of magnitude.

Preparation of Langmuir−Blodgett Mono- and Multilayers of Copolymers of Isocyanides with NLO-Active Side Chains. Effect of a Spacer Group between the NLO Chromophore and the Polymer Backbone

The structure and properties of Langmuir−Blodgett films of copolymers of a hydrophilic isocyanide and an isocyanide containing an NLO-active moiety with a spacer group are studied. Depending on the ratio of the two monomers, the copolymers are able to form stable monolayer films. The orientations of the NLO groups in the copolymers with respect to the film plane have been derived from polarized transmission and grazing incidence reflection (GIR) IR spectra. Quantitative analysis of the spectra shows that the polymer main chains have no specific orientation in the plane of the film. The side chains of copolymers with a high NLO-dye content appear to be oriented perpendicular to the film plane.

Optical properties of side-chain liquid crystal copolymers of monosubstituted cholesteryl itaconate and a non-chiral mesogen

New mono- and disubstituted cholesteryl derivatives of itaconic acid have been prepared and their thermotropic liquid crystalline behaviour examined. The monosubstituted derivative has been homopolymerized, and also copolymerized with a non-chiral mesogen 4-cyanophenyl-4′-(6-acryloyl oxyhexyloxy) benzoate. Examination of the series of copolymers prepared, using differential scanning calorimetry and hot-stage polarizing microscopy, showed that when the content of the cholesteryl itaconate was high, both a smectic-A phase (SA) and a cholesteric phase (N*) were present. It was found that the SA phase could be eliminated by lowering the content of the cholesteryl itaconate in the copolymers, giving samples that displayed only the N* phase over a much wider temperature range. The samples in the N* phase also exhibited selective reflection of visible light that changed from short to long wavelengths as the samples were cooled from the isotropic melt. These colours can be locked into the glassy state of the polymer by quenching below the glass transition temperature, but only if the SA phase is absent. It was also noted that at high contents of the cholesteryl itaconate the selective reflection appears to occur in the ultraviolet region. Keywords: itaconic acid, copolymers, liquid crystalline polymers, cholesteric phases, selective reflection.

Poly(styrene‐graft‐ethylene oxide) as a compatibilizer in polystyrene/polyamide blends

AbstractPolystyrene (PS) blends containing a dispersed phase of either polyamide‐6 (PA‐6) or polyamide‐12 (PA‐12) were compatibilized by additions of 1, 3, or 5 wt % poly(styrene‐graft‐ethylene oxide). The graft copolymers were found to have a stabilizing effect on the domain sizes. Weight average radii of PA‐6 domains in compression molded samples were reduced by a factor of 5 with 3 wt % graft copolymer added. The corresponding size reduction for PA‐12 domains was by a factor of 3. Also, the domain sizes were more uniformly distributed in blends containing the graft copolymers. Thermal analysis of the blends revealed that compatibilization retarded the PA crystallization, with some PA crystallizing at the PS glass transition. This retarded crystallization is explained as a result of the domain size reduction and by the presence of graft copolymer at the interface. The graft copolymers had a toughening effect on the blends and the impact strength of a PS/PA‐12 blend was improved by 65% by adding 3 wt % of graft copolymer. Binary blends of the PA and poly(ethylene oxide) (PEO) were investigated in a separate study to verify miscibility of the graft copolymer side chains and the PA. Hydrogen bonding between PA‐6 and PEO was confirmed by IR spectroscopy and partial miscibility was indicated by melting point depressions. © 1995 John Wiley & Sons, Inc.

Synthesis of Second-Order Nonlinear Optical Polymers Containing Stilbazolium Salt Chromophore in the Side Chain

Abstract We synthesized novel side chain copolymers containing the stilbazolium tetraphenylborate for the linear electro-optic coefficient measurement. These polymers are very soluble in common organic solvents such as acetone, cyclohexanone, dimethylformamide etc. The second-order nonlinear optical properties of poly [1-[(N- ethylenepiperazyl)-stilbazolium tetraphenylborate]-N-[(1, l-dimethyl-m-isopropenyl)benzyl]carbamate-co-methylmethacrylate](POLYMER Ia & Ib), poly [l-[(N-ethylenepiperazyl)-stilbazolium tetraphenyl borate]-N-[(1,1-dimethyl-m-isopropenyl)benzyl]carbamate-co-N-vinylcarbazole](POLYMER II), and poly [1-[(N- ethylenepiperazyl)-stilbazolium tetraphenyl borate]-N-[(1, 1-dimethyl-m-Isopropenyl)benzyl]carbamate-co-4-hydroxyphenyl maleimide] (POLYMER III) were improved due to the change of the nonlinear optical chromophore in the side chain.

Ferroelectric, pyroelectric and electro-optic properties of a chiral side chain copolymer with high polarization and a broad C∗ phase

Abstract The synthetic route to a chiral side chain copolymer exhibiting broad smectic phases is described. The copolymer shows a smectic C∗ phase from below room temperature up to 105°C. Ferroelectric properties of this copolymer are reported as well as results showing electroclinic switching. The pyroelectric effect and the dielectric behaviour of the copolymer are also demonstrated.

Amorphous chiral smectic A phase of side chain copolymers

Abstract The chiral structure of the anomalous smectic phase recently observed in chiral copolymers has been studied by optical methods. The phase is amorphous, but shows a short range order, as a combination of smectic A and cholesteric structures. This phase is presumed to possess locally the TGBA structure.

The Synthesis And Optoelectronic Properties Of Oxadiazole-Based Polymers

ABSTRACTNew oxadiazole-based polymeric materials have been synthesized either as side chain copolymers with polymethacrylate or as main chain copolymers carrying solubilizing elements such as hexafluoropropylidene or meta-linked aromatic spacer units. Many of these materials exhibit blue luminescence in the solid state. The materials have been evaluated by photoluminescence and cyclic voltammetry studies, and as the electron transporting layer in a two-layer electroluminescent device with poly(p-phenylenevinylene) (PPV) as the emissive layer. The major conclusion is that these materials function by providing large heterojunction offsets at the Highest Occupied Molecular Orbital (HOMO) which block the passage of holes through the device.

Enzymatically Catalyzed Generation of Electronically Excited States in a Synthetic Copolymer with a Schiff Base in Pendant Groups

The copolymer of N-(2-hydroxypropyl)methacrylamide and N-[N-(N-methacryloylglycyl)glycyl]hexane- 1,6-diamine (17.6 mole %) was prepared as a model compound for investigation of the mechanism of enzymatically catalyzed generation of electronically excited states in proteins. The amino end groups of the copolymer side chains were transformed into a Schiff base by reaction with glycolaldehyde. The modified copolymer was characterized by its ultraviolet, visible and fluorescence spectra. The enzymatically catalyzed oxidation of the modified copolymer was carried out in a phosphate buffer at pH 7 using horseradish peroxidase as the enzyme. The generation of electronically excited states was demonstrated by chemiluminescence measurement and by a spectroscopic procedure based on transfer of the excitation energy to bilirubin.

Liquid-crystal side-chain copolymers composed of a non-chiral mesogenic monomer and a chiral non-mesogenic monomer

A series of copolymers was prepared from a mesogenic monomer, 4-cyanobiphenyl-4-(6-acryloyloxy-hexyloxy) benzoate (1) and a chiral non-mesogenic monomer (S)-methyl(2-methyl-3-methacryloyloxy) propionate (2). The reactivity ratios for the copolymerization of the two monomers were found to be r1 = 0.15 and r2 = 3.00, indicating the greater tendency for the less bulky chiral monomer to be incorporated into the copolymer chains preferentially. Examination of the mesogenic behaviour showed that samples with compositions of mole fraction F2 ≤ 0.6 exhibited a nematic phase which was stable over a temperature range of about 85°C. There was no evidence that the interaction of monomer 2 with mesogen 1 was strong enough to induce a chiral nematic phase in the copolymers. A crosslinked sample was also studied and it was observed that the alignment of the mesogenic phase was very sensitive to the application a uniaxial tensile force.

Photoassisted poling of polymer materials studied by Stark spectroscopy (electroabsorption) technique

Photoassisted poling of two polymer systems (i) a dilute solution of p'-diethylamino- p'-nitroazobenzene polycarbonate and (ii) the side chain copolymer poly[(ethylene)-co-(N-hexyl-N-(4-methacryloxy-butyl)-4-amino-4'-nitrostilbene)] was investigated. The poling was carried out at room temperature by a dc electric field under simultaneous irradiation of the samples with nonpolarized light absorbed by the azobenzene and stilbene chromophores. The long memory polar order parameter is shown to be of the order of 0.07 and 0.0023, respectively for the two chromophores mentioned. The higher value for the azobenzene moiety, comparable to the value calculated from the Boltzmann distribution of excited dipoles in the same electric field, has been attributed to a higher probability of its trans-cis isomerization.

Effect of chiral end group variation on the properties of ferroelectric copolymers

Abstract The effect of changing the chiral end chain on the phase behavior and physical properties of some lactate-based side-chain copolymers are reported. Two classes of polymers have been studied, one with hydrocarbon groups and the other with fluorocarbon groups as terminal chains attached to the chiral center through an ester linkage. While the hydrocarbon materials exhibit larger range of the ferroelectric smectic-C* phase than the corresponding fluorocarbon analogs, the spontaneous polarization of the copolymers with fluorocarbon tails are found to be substantially larger than the corresponding hydrocarbon derivatives. The phase behavior of the copolymers is also compared with that of the corresponding unattached low molar mass side-group mesogens.

Stabilization of the dipole alignment of poled nonlinear optical polymers by ultrastructure synthesis

A new approach to attaining long term and high temperature stability of second-order nonlinear optical effects has been developed. Two side-chain copolymers containing dipole-end cross-linkable chromophore pendants were synthesized from a double-end cross-linkable (DEC) chromophore monomer. The polymer solutions containing a cross-linker were spin cast into optical quality thin films, which were subsequently poled by an electric fiield, using a corona configuration, and thermally cross-linked. Second-order susceptibilities, χ (2) , on the order of 10 -7 esu, of the polymer films were measured by the second harmonic generation (SHG) at 1.06-μm fundamental wavelength

Observation of the photorefractive effect in a dialkylaminonitrostilbene copolymer

We report observations of the photorefractive effect in a 1:1 side-chain copolymer of N-methacryloxyethyl-N-methylaminonitrostilbene with methyl methacrylate. Without the addition of a photoconducting component, gratings were written in this polymer at 633 nm in 8-μm-thick films at low powers and were detected by use of a four-wave mixing measurement. Diffraction efficiencies of the order of 10−5 −10−4 were measured by four-wave mixing.

Mesomorphic behavior of side-chain copolymers containing chiral as well as nematogenic moieties comprising p-phenylene and trans-cyclohexylene rings

The effect of different ring systems on liquid crystalline (LC) mesomorphism has been addressed in terms of thermotropic side-chain acrylate polymers incorporating p-phenylene and trans-cycloherylene units. It was found that the nematogenic monomer based on a p-n-butylbenzoyl p'-phenyl ester core copolymerized with chiral comonomers containing (S)-(-)-1-phenylethanol and (-)-5-cholesten-3β-ol (i.e., cholesterol) gives rise to the cholesteric mesophase with selective reflection wavelengths in the visible region. However, partial or complete replacement of the p-phenylene moiety with the trans-cyclohexylene ring results in smectic mesephase formation