Chiral liquid crystalline side chain polymers

Summary Optically active liquid crystalline side chain polymers with dif ferent flexible spacer groups (n=2–11) and different main chains (acry lates, methacrylates and α chloroacrylates) are described. (+)-2-methyl butyloxyphenyl esters of benzoic acid were chosen as the mesogenic group.     

Synthesis and characterization of high molecular weight side chain liquid crystalline/photoactive polymers

Various liquid crystalline and photoactive azobenzene monomers were synthesized and attached to copoly(methyl methacrylate‐glycidyl methacrylate) [copoly (MMA‐GMA)] to get high molecular weight side chain liquid crystalline (LC)/photoactive copolymers. Further, spacers are generated in situ and reactive groups are obtained after the modification. All monomers and polymers were thoroughly characterized by FTIR, ¹H and ¹³C NMR, UV‐VIS spectrophotometry, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy. All side chain LC polymers showed higher thermal stability than that of copoly(MMA‐GMA). Three LC and one azo monomer exhibited characteristic nematic mesophase where as one LC monomer has shown nematic and sanded smectic‐A texture. The rate of trans‐cis isomerization of polymer was lower than that of the monomer and both monomers and polymers showed slow back isomerization. Present approach offers convenient way to synthesize high/desired molecular weight photoactive LC polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The structure of a cyanobiphenyl side chain liquid crystalline poly(silylenemethylene)

The structure of a side chain liquid crystalline poly(silylenemethylene) (-(SiCH₃R-CH₂)-: R=O(CH₂)₁₁O-Ph-Ph-CN, Ph=phenyl) (CN-11) has been studied by X-ray diffraction and differential scanning calorimetry (DSC). The DSC results showed that CN-11 has transitions at ∼92 °C (T₂) and ∼147 °C (T₁) during both cooling and immediate heating. A third transition occurred at ∼50 °C (T₃) during heating after annealing at room temperature. The X-ray fiber pattern of the CN-11 annealed at room temperature showed several wide and small angle reflections which were indexed by a monoclinic unit cell with parameters a=16.8 Å, b=7.42 Å, c=43.6 Å and β=102.1° (b: fiber direction), representing a crystal structure with layer thickness of ∼43 Å. Upon heating at T₃, the crystal structure became less ordered (but somewhat more ordered than smectic A (S_A) and smectic C (S_C)). This was followed by S_A (or S_C) phase at T₂, and ultimately an isotropic state (I) at T₁. The observed layer thickness (∼43 Å) is about ∼1.5 times the most extended side chain length, indicating a double-layer structure with tilted or interdigitated side chains. The X-ray fiber pattern had a four-point pattern at d=4.52 Å, suggesting that the side chains in the crystal are likely to be tilted by 56° from the polymer fiber axis.     

Thermal and morphological properties of main chain liquid crystalline polymers

Temperature modulated differential scanning calorimetry (TMDSC), variable heating rate DSC, and tapping atomic force microscopy (AFM) were used to study semi-crystalline liquid crystalline polymers (LCPs). Main chain LCPs included a random copolyester (Vectra® A950) and an azomethine alternating copolymer. For the azomethine LCP the TMDSC non-reversing signal detected broad exothermic transitions associated with melting and recrystallization as the slow DSC heating scan induced surprisingly large morphological changes. Non-isothermally crystallized Vectra® and some isothermally crystallized samples at lower temperatures exhibited different levels of DSC scan induced crystal reorganization. Such crystal metastability was also studied by variable heating rate DSC and an independent technique for estimating the melting point at very rapid heating rates. The TMDSC characterization of the scan induced crystal perfection in Vectra® was substantially different than for the other polymers studied. In most cases even though crystal perfection was occurring, no clear exotherm was detected in the non-reversing signal. High temperature annealing for long times resulted in degrees of crystal perfection which could be studied by DSC with minimal scan induced reorganization. High resolution tapping AFM was used to elucidate details of crystal morphology for mechanically oriented and non-oriented Vectra® before and after annealing. Structures resembling lamellae were found to be oriented perpendicular to the chain direction in the oriented Vectra®. In the non-oriented film broad and sometimes curved ‘lamellae’ were detected. They were about 1000 nm long and between 20 and 35 nm wide, with the width increasing slightly as a function of increased annealing time at 260 °C melt crystallization conditions. Substructure of the lamellae in both oriented and non-oriented Vectra® consisted of smaller stacked crystallites which are detected by AFM studies of these surfaces.     

Synthesis and characterization of liquid crystalline poly(p-vinylbenzyl ether)s

Summary The synthesis and characterization of poly(p-vinylbenzyl ether)s containing 4-oxybiphenyl or 4-oxy-4-methoxybiphenyl mesogens or a 4-oxy-4-methoxybiphenyl mesogen which is connected to the benzyl ether group through one, two or three oligo(oxyethylene) units, are presented. The first two polymers exhibit a nematic mesophase while the last three a highly ordered smectic mesophase.     

Influence of chirality on phase behaviour of side chain liquid crystalline polymers

Summary Two kinds of chiral side chain liquid crystalline polyacrylates were synthesized and characterized by DSC, POM and x-ray diffraction. The results indicated that chirality of side chain end group and spacer length strongly influence the phase behaviour of the polymers. The polymer P-I with one asymmetric carbon atom of end group exhibits enantitropic Smectic S_A and S_C phases. The polymer P-III having two asymmetric carbon atoms displays enantitropic Smectic S_A and S_B phases. Formation of liquid crystalline polymorphism of polymers depends on spacer length of side chains.     

Synthesis and properties of dimesogenic liquid crystalline side group polymers

Summary Liquid crystalline polymalonates with side groups consisting of two different mesogenic units separated by alkylene spacers from each other and from the polyester backbone have been prepared. According to microscopic observations, DSC measurements and X-ray studies, all polymers display smectic phases.     

Infrared-spectroscopic investigations of molecular order in liquid crystalline side chain polymers

Summary Infrared dichroism was used to determine the order parameters of liquid crystalline side chain polymers. By this the order parameters of the main chain, of the spacer and of the mesogenic group can be obtained separately. Therefore spectra of two liquid crystalline polyacrylates were recorded with polarized light at different temperatures. In a poly(acrylate) with 6 CH₂ groups in the spacer a high order parameter was found not only for the mesogenic group, but also for the spacer and the main chain. The orientation of the poly(acrylate) with a spacer of only 2 CH₂ groups is lower due to the stronger interaction of main chain and mesogenic group.     

Synthesis,characterization, and thermotropic properties of side-chain liquid crystalline polysiloxane polymers with an oligo(ethylene oxide) unit in the side chain

A series of new alkene and octenyloxy monomers containing 4′-[oligo(ethylene oxide)] n monomethyl ether 4-biphenyl ether carboxyl benzoate [MS3BDBE_n] (n = to 3) and 1- (p-methoxydiphenyl)–(carboxyl benzoate) [oligo(ethylene oxide)]n [MS_m+2BEnDB] (m = 1, 6; n = 1 to 3) as end groups were synthesized. The molecular structure of the monomers was charaterized using nuclear magnetic resonance (NMR) spectroscopy. These monomers were grafted onto poly(methylhydrosiloxane)s (PMHS) by the platinun-catalyzed hydrosilylation process. The thermal transition temeratures and mesophase textures of the monomers and the polysiloxane polymers have been determined by diffential scanning calorimetry (DSC) and by polarized optical microscopy. The effect of changes in chemical structure on the mesophase properties, glass transition temperature, isotropic temperature, and mesophase texture of the monomers and the polysiloxane polymers is discussed. Polymers PS3BDBEn showed smectic and nematic phases which were not analogous to their precursor nematic monomers MS3BDBEn. Both monomers MS_m+2BE_nDB and their polymeric homologous PS_m+2BE_nDB did not exhibit mesophase properties. This demonstrated that the polymer effect could not stabilize the mesophase obtained from mesogenic core which contained a flexible oligo(ethylene oxide) unit interconnecting aromatic group. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of thermotropic liquid crystalline poly(azomethine ether)s

Two series of monomers, namely 4,4′-diformyl-α,ω-diphenoxydecane and 4,4′-diformyl-3,3-methoxy-α,ω-diphenoxydecane, were prepared from 1,10-dibromodecane with p-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde (vanillin), respectively. The poly(azomethine ether)s were prepared by solution polycondensation using 4,4′-diformyl-α,ω-diphenoxydecane, 4,4′-diformyl-3,3-methoxy-α,ω-diphenoxydecane with various diamines. The monomers and polymers were characterized by intrinsic viscosity, FT-IR, ¹H, and ¹³C NMR spectroscopy. The thermogravimetric analysis reveals that the polymers are stable up to 320-500 °C and decomposed with good char yield. The thermotropic liquid crystalline properties of the polymers were examined by differential scanning calorimetry (DSC) and their textures observed under hot stage optical polarized microscopy (HOPM). All the polymers were exhibited thermotropic liquid crystalline properties except tetramethylene diamines-based polymers.     

Synthesis and characterization of bulky side chain methacrylate polymers

The synthesis, and dilute solution behavior of poly(2,4-dimethylphenyl methacrylate) (2,4DMP), poly(2,5-dimethylphenyl methacrylate) (2,5DMP), and poly(3,5-dimethylphenyl methacrylate) (3,5DMP) is described. Comparison is made with results reported for other bulky side chain polymers. The Kuhn-Mark-Houwink-Sakurada (KMHS) relationships were established. The unperturbed dimensions 〈r²〉 ${}_{\text{½}}^{\text{0}}$ , the rigidity factor σ, the characteristic ratio C_∞, and the thermodynamic parameters were determined, using the Stockmayer-Fixman equation, from viscometric data in good solvents. The high rigidity observed for these polymers is explained assuming that these polymers behave as kinked-chains.     

Synthesis and properties of a new side chain liquid crystalline polymer by methathesis polymerization

Summary Novel liquid crystalline monomer, 4-methoxybiphenyloxy-(N,N-dipropargyl)undecane amide, subjected to metathesis reaction with transition metal catalyst systems. It was found that the MoCl₅-EtAlCl₂ catalyst system was very effective for the cyclopolymerization of the monomer. Resulting polymers exhibited good solubility in common organic solvents such as THF, chloroform, etc. The number-average molecular weight (Mn) values of the polymers were in the range of 0.98x10⁴–1.4x10⁴, relative to polystyrene standard by GPC.Thermal properties of the monomer and the polymer synthesized were examined by differential scanning calorimetry (DSC) and cross-polarized optical microscopy. The polymer exhibited the enanfiotropic liquid crystallinity and smectic mesophase.     

Synthesis and characterization of ferroelectric side chain liquid crystal polymers bearing banana-shaped chiral mesogens

A series of ferroelectric liquid crystal polymers having banana-shaped side chain mesogens were synthesized through photo-polymerization of epoxide moiety. 2,5-disubstituted-thiophene sub-unit was used in synthesizing the banana-shaped monomers. These liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). Mesomorphism was investigated as a function of spacer units. All the synthesized low molar mass banana-shaped compounds exhibit smectic blue phase, but chiral smectic C phase could be observed only on compounds having longer spacer. The clearing temperature of low molar mass compounds fluctuated a little when spacer length varies. All polymers exhibit cholesteric mesophase and an observable glass transition. These liquid crystalline compounds reveal strong photoluminescence at visible region (λ_max = 475 nm for M9EPX) and have potential use in polarized organic light emitting diode materials.     

Studies on thermotropic liquid crystalline polymers part XIII. Synthesis and properties of fully aromatic liquid crystalline poly(amide-ester)s

Four series of novel fully aromatic thermotropic liquid crystalline high molecular weight poly(amide-esters were prepared by direct polycondensation from terephthalic acid (TPA) and 2,6-naphthalene dicarboxlic acid with various aromatic diols and diamines in the presence of diphenyl chlorophosphate (DPCP), LiCl, and pyridine. The structures and thermal properties of the synthesized poly(amide-ester) s were examined by FTIR spectrum, wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal optical polarized microscope and thermogravimetric analysis (TGA). The effects of the amounts and kinds of the aromatic diols and diamines (bisphenyl units, naphthalene and (un)substituted phenylene structures) on the molecular weight and thermal properties of the synthesized poly (amide-ester) s were investigated in this study. When a portion of the amide groups were replaced with the ester groups, most of the synthesized poly(amide-ester)s containing naphthalene or substituted hydroquinone units showed excellent mesophase and thermal stability, but the poly(amide-ester)s containing bisphenyl structures lost the mesophase behaviors. The P3 series of poly(amide-ester)s derived from TPA and 2,6-naphthalene dicarboxlic acid with phenylhydroquinone and various diamines possess liquid crystalline properties, even some of the diamines containing kink structures.     

Synthesis and properties of polymer brush consisting of poly(phenylacetylene) main chain and poly(dimethylsiloxane) side chains

A novel polymer brush consisting of poly(phenylacetylene) (PPA) main chain and poly(dimethylsiloxane) (PDMS) side chains was synthesized by the polymerization of phenylacetylene-terminated PDMS macromonomer (M-PDMS). The macromonomer was prepared by the esterfication of monohydroxy-ended PDMS (PDMS-OH, degree of polymerization (DP) = 42) with p-ethynylbenzoic acid. The polymerization of M-PDMS using [(nbd)RhCl]₂/Et₃N catalyst led to polymer brush, poly(M-PDMS), with M_n up to 349?000 (DP of main chain 104). Poly(M-PDMS) with narrow molecular weight distribution (M_n = 39?900, M_w/M_n = 1.11) was obtained with a vinyl-Rh catalyst, [Rh{C(Ph)CPh₂}(nbd){P(4-FC₆H₄)₃}]/(4-FC₆H₄)₃P. Poly(M-PDMS)s were brown to orange viscous liquids and soluble in organic solvents such as toluene and CHCl₃. The UV-vis absorptions of poly(M-PDMS) were observed in the range of 350-525 nm, which are attributable to the PPA main chain.     

Dielectric and optical properties of liquid crystalline side chain polymers. A MNDO-analysis

Semiempirical quantum mechanical MNDO-calculations were performed on side chain liquid crystalline polymers to predict their electronic properties and thus their anisotropic dielectric and optical properties. These predictions are compared with the corresponding experimental results. The conclusion is that the predictions are sufficiently accurate, which suggests to use such methods for screening potentially interesting polymer liquid crystals prior to synthesizing them.     

Structure and liquid crystalline phases of amphiphilic side chain polymers in aqueous solution

Functional amphiphilic molecules which form liquid crystalline (l.c.) phases in aqueous solutions, can be polymerized to amphiphilic side chain polymers. Depending on the formation of the polymer backbone via the hydrophobic (type A) or hydrophilic part (type B) of the monomer, it can be differentiated between two polymers. For both types of polymers a model is proposed which explains their micellar association in solution. In aqueous solutions polymers of type A should form normal spherical, rodlike and disc-like micelles, while polymers of type B should form the corresponding reversed micelles. The phase behavior in aqueous solutions is investigated with two model systems of monomer/side chain polymer of type A. It is shown that the polymers exhibit l.c. phases, which are stable within a broader concentration range, as well as to higher temperatures compared to the corresponding monomers. The structures of the l.c. phases are in accordance with the model considerations.     

Europium‐containing cholesteric liquid crystalline polymers in the side chain

Europium‐containing cholesteric liquid crystalline polymers were graft copolymerized using poly(methylhydrogeno)siloxane, cholesteryl 4‐(allyloxy)benzoate (M₁), cholesteryl acrylate (M₂), and a europium complexes monomer (M₃). The chemical structures of the monomers were characterized by Fourier transform infrared and ¹H‐nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermo gravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. With an increase of europium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) and mesophase temperature range (ΔT) decreased. All polymers showed typical cholesteric Grandjean textures, which was confirmed by X‐ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of europium complexes units did not change the liquid crystalline state of polymer systems; on the contrary, the polymers were enabled with the significant luminescent properties. With Eu³⁺ ion contents ranging between 0 and 1.5 mol %, luminescent intensity of polymers gradually increased and luminescent lifetimes were longer than 0.45 ms for the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40866.     

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by ¹H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.     

Synthesis of liquid crystalline rod-coil dimers based on poly(propylene oxide) coil

Summary The synthesis and characterization of 4-[poly(propyleneoxy)propyloxy]-4'-bis[4-decyloxycarbonylbiphenyl-4'-biphenylcarboxylate] with poly(propylene oxide) coil of seven (dimer-7), twelve (dimer-12), seventeen (dimer-17), twenty one (dimer-21) are described. Dimer-7 with short length of poly(propylene oxide) coil exhibits successively smectic C, smectic A and nematic mesophases, while dimer-12 and dimer-17 with longer lengths of coils exhibit a bicontinuous cubic mesophase with Ia3d symmetry. Further increasing the length of coil, as in the case of dimer-21, suppresses liquid crystallinity. Received: 22 February 2000/Revised version: 21 March 2000/Accepted: 29 March 2000