Liquid Crystalline Polycarbonate Research Articles

Self-assembly and in vitro drug release behaviors of amphiphilic copolymers based on functionalized aliphatic liquid crystalline polycarbonate with pH/temperature dual response

Amphiphilic copolymers Pn (n = 1–3) with mPEG as hydrophilic segment and aliphatic polycarbonate as hydrophobic segment were designed and synthesized successfully, and the results of POM, XRD and DSC showed that only P3 showed liquid crystalline (LC) phase. Due to the carboxyl and cholesteric LC groups in the side chain of the polycarbonate, the micelles prepared in this study were endowed with pH and temperature dual response. The effects of different conditions such as selective solvents, copolymer concentration, pH, temperature, the structure and LC mesophase on the self-assembly behavior and drug loading properties of the copolymer micelles were explored. It was found that the critical water concentration for self-assembly, the particle size and morphology of the micelles could be effectively controlled by changing the above conditions. Moreover, introducing LC properties into the copolymer could effectively decrease the critical water concentration for self-assembly and elevate the drug loading content. The DOX was conjugated to the copolymers by hydrogen bonds, and the copolymer P3 could form regular fusiform micelles after loading with DOX. Moreover, P3-DOX micelles could be endocytosed into cells and the drug release behavior could be triggered by the weak acid condition and elevated temperature. Therefore, the P3-DOX micelles could achieve a pH-triggered rapid drug release under weakly acidic conditions of the tumor cells. This kind of controllable micelles will have a potential application as drug-carriers in drug delivery.

Synthesis and phase behaviour of new biodegradable liquid crystalline polycarbonate derived from side chain cholesteryl derivative

ABSTRACTA new cholesterol side-functionalised polycarbonate was synthesised through a coupling reaction between the terminal carboxyl group of the monomer 6-cholesteroxy-6-oxocaproic acid (COHA) and side hydroxyl group of the polycarbonate (PHTMC). The chemical structures of the intermediate compounds, monomers and polymers obtained in this study were characterised with FT-IR and 1H NMR spectrum. Their phase behaviour and thermal stability were investigated using polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis. The monomer COHA showed a cholesteric phase, while the corresponding cholesterol side-functionalised polycarbonate P(TMC-g-COHA) revealed a smectic A phase. This behaviour was attributed to an increased density of the mesogenic units in side chain and hence an ordered organisation into the mesophase. Furthermore, P(TMC-g-COHA) could exhibit a liquid crystalline state below body temperature (≈37°C). This fact indicated it could be used clinically as a self-assemble material with orientational-order mesophase. In addition, P(TMC-g-COHA) had a good thermal stability, the corresponding thermal decomposition temperature was 241°C.

Electrochromic and liquid crystalline polycarbonates based on telechelic oligothiophenes

The triphosgene carbonate synthesis is adapted towards an alternating main-chain rod/coil polycarbonate based on a telechelic sexithiophene oligomer, yielding an electrochromic material displaying morphological behaviour typical of a liquid-crystalline polymer.

Synthesis of a side chain liquid crystalline polycarbonate with a chiral backbone

We report the experimental demonstration of a novel and environmentally benign supercritical carbon dioxide (ScCO2) technique that yields an optically active, side chain liquid crystalline polycarbonate in a single-step reaction. The obtained polymer is worthwhile, since it is highly stereoregular and can find applications in an enlarged mesomorphic temperature range compared to its acrylic analogues. The synthesized materials were characterized by IR, 1H-NMR, and 13C-NMR, while the thermal properties were measured by DSC. Polarized optical micrograph and wide angle X-ray diffraction were used for the mesogenic property characterization of the copolymer. The transfer chirality from the backbone to the mesophase is demonstrated on the optical microscopy textures. Being consistent with the 13C-NMR, X-ray implies an ordered polymeric structure. The DSC analysis of the copolymer indicates that the Ti (the clearing point temperature) value does not change dramatically, whereas a pronounced decrease in Tg (the glass transition temperature) value is observed from that of its acrylic analogues. Hence, the obtained polymer exhibits another practical benefit by widening the mesomorphic temperature range. This study is the insightful combination of material processing and chemical design that elucidates the advantages of ScCO2 application, in terms of liquid crystallinity and the tacticity of the obtained polymer.

Miscibility study of polymer blends composed of semirigid thermotropic liquid crystalline polycarbonate, poly(vinyl alcohol), and chitosan

AbstractMiscibility of binary and ternary polymer blends composed of thermotropic liquid crystalline polycarbonate (LCPC), poly(vinyl alcohol) (PVA), and chitosan was investigated by viscosity method, FTIR spectrum, and scanning electron microscope techniques. Effect of addition of chitosan as a compatibilizer on miscibility and morphology of binary LCPC/chitosan and PVA/chitosan and ternary LCPC/PVA/chitosan polymer blends was discussed. These measurements indicated that addition of chitosan into the blends of LCPC with PVA leads to an increase of miscibility and a formation of clear fibril structures on fractured surfaces, which are due to intermolecular hydrogen‐bonding interaction between LCPC, PVA, and chitosan chains. It was suggested that side‐chain hydroxy group of PVA and amino and hydroxy groups of chitosan play an important role in the formation of miscible phase and improvement of morphology in binary and ternary blends composed of LCPC, PVA, and chitosan. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1616–1622, 2004

Miscibility of Semirigid Liquid-Crystalline Polycarbonate with Poly(vinyl alcohol), Partially Saponified Poly(vinyl acetate) or Poly(vinyl acetate)

The miscibility in blends of semirigid liquid-crystalline polycarbonate (LCPC) with poly(vinyl alcohol) (PVA), partially saponified poly(vinyl acetate) (PVAc75) and poly(vinyl acetate) (PVAc) was investigated by means of differential scanning calorimetry and scanning electron microscopy. These measurements suggested that LCPC forms partially miscible blends with PVA and PVAc75. Blends of PVAc are immiscible. The side-chain hydroxy groups play an important role in improving the miscibilities of the blends.

Studies on the synthesis and properties of thermotropic liquid crystalline polycarbonates. VII. Liquid crystalline polycarbonates and poly(ester-carbonate)s derived from various mesogenic groups

Studies on the synthesis and properties of thermotropic liquid crystalline polycarbonates. VII. Liquid crystalline polycarbonates and poly(ester-carbonate)s derived from various mesogenic groups

Studies on the synthesis and properties of thermotropic liquid crystalline polycarbonates. VII. Liquid crystalline polycarbonates and poly(ester-carbonate)s derived from various mesogenic groups

Three series of thermotropic liquid crystalline polycarbonates and poly(ester-carbonate)s were prepared by solution polycondensation of 4,4′-biphenyldiol (BP), 4′-hydroxybiphenyl-4-hydroxybenzoate (HHB), or 4-hydroxyphenyl-4″-hydroxybiphenyl-4′-carboxylate (HHBP), as mesogenic unit, with 1,10-bis(p-hydroxybiphenoxy)decane (N10), bisphenol A (BPA), 4,4′-dihydroxy-diphenyl ether (BPO), 4,4′-[phenylbis(oxy)]bisphenol (BPOO), methylhydroquinone (MeHQ), or phenylhydroquinone (PhHQ). One series of cholesteric poly(ester-carbonate)s were also prepared by using HHBP, the aromatic diols mentioned above and isosorbide as the chiral moiety. All polycondensations were implemented in pyridine by using triphosgene as the condensation agent. The synthesized polycarbonates were characterized by viscometer, FTIR, DSC, TGA measurements, polarizing microscopy equipped with a heating stage, and WAXD powder pattern. In this study, it was found that the liquid crystalline properties of polycarbonates strongly rely on the mesogenic unit applied. HHBP-series exhibits a wide temperature region of liquid crystalline (LC) phase even with 50% of bisphenol A (BPA), which is a V-shaped structure and usually destroys liquid crystalline properties. In addition, homopolycarbonate with HHBP structure possesses extraordinarily low phase-transition temperature and wide liquid crystalline phase range, due to its asymmetric structure. This asymmetric structure results in head-to-tail, head-to-head, and tail-to-tail random conformation of polymer chain. The isosorbide containing poly(ester-carbonate)s formed cholesteric phase, which showed homogeneous blue, green, or red Grandjean texture upon shearing in molten state and the Grandjean texture could be frozen easily while quenching the sample to the room temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1852–1860, 2000

Synthesis and characterization of novel side-chain liquid crystalline polycarbonates, 4. Synthesis of side-chain liquid crystalline polycarbonates with mesogenic groups having tails of different lengths

Side-chain liquid crystalline polycarbonates with alkoxyphenylbenzoate side groups, having a short spacer and tails ranging from 1 to 8 C-atoms, were synthesized. The polymers were prepared by an organo-zinc catalysed copolymerization of carbon dioxide and mesogenic 4-alkoxyphenyl 4-(2,3-epoxypropoxy)benzoates. Model polycarbonates were prepared by copolymerization of glycidyl phenyl ether (GPE) and carbon dioxide and by terpolymerization of GPE, propylene oxide and CO2. The copolymerizations of LC monomers were carried out at 70°C in an autoclave at 60 atm CO2 pressure in dioxane as the solvent. Catalysts based on diethylzinc and water or diethylzinc and resorcinol were used. High catalyst concentrations (up to 20 mol-% on the basis of diethylzinc with respect to epoxide) and long reaction times (72 h) were found to be necessary for acceptable yields and reasonable molar masses. The resulting polymers had a high polydispersity and the maximum yield was about 30%. A major side product, formed directly from CO2 and epoxide, as well as indirectly by depolymerization, was the corresponding five-membered cyclic carbonate. The polymers on average contained about 30 mol-% of ether units and 70 mol-% of carbonate units due to a weak tendency of the epoxides to undergo homopolymerization. 1H and 13C NMR analysis revealed detailed information about the overall ether content and the distribution of the ether and carbonate groups in the chain, as well as the tacticity of the polymers. Surprisingly, the monomer distribution and the tacticity were molecular weight dependent. Some possible explanations for these phenomena are suggested.

Synthesis and characterization of novel side-chain liquid crystalline polycarbonates, 5. Mesophase characterization of side-chain liquid crystalline polycarbonates with tails of different lengths

The mesomorphic properties and thermal stability of side-chain LC polycarbonates with alkoxyphenyl benzoate side groups having a short spacer and alkoxy tails ranging from 1 to 8 carbon atoms were studied by DSC, X-ray diffraction and polarized light optical microscopy. All polymers have a smectic A structure. Mesogens having short tails organize preferably in a monolayer structure, and mesogens having long tails in a double layer structure. A sharp increase in the clearing temperatures and enthalpies as a function of tail length was observed. No clear relation between the tail length and the glass transition temperature was found. Both the Tg and the clearing temperature show a strong dependence on the molecular weight. Up to about Mw = 20000 a rapid increase in phase transition temperatures with increasing molecular weight was observed, eventually levelling off to a constant maximum value. The LC polycarbonates were found to be thermally stable up to about 200°C. At higher temperatures, random chain scission, resulting in a rapid decrease in molecular weight, and unzipping, resulting in the formation of a five-membered cyclic carbonate, are the main initial degradation mechanisms. The degraded polymers have lower transition temperatures than the original ones.

Mechanical and viscoelastic properties of extruded sheets from blends containing liquid crystalline copolyesters and polycarbonate

Sheets from blends containing liquid crystalline polymer (LCP) and bisphenol-A polycarbonate (PC) were prepared using a twin screw extruder at various take-up speeds. Thermal behavior, mechanical properties, and viscoelastic properties of sheets with various compositions were investigated using differential scanning calorimetry (DSC), dynamic mechanical analysis measurement (DMTA), and sonic velocity measurement. DMTA studies showed the blends to have two glass transition temperatures (Tg) corresponding to those of the PC-rich and LCP-rich phases. Blends of PC and LCP were immiscible, although their Tgs varied slightly with composition. The dynamic and sonic moduli increased with increasing LCP content owing to the high modulus of LCP. The modulus remained unchanged with increasing LCP content at low LCP wt% (<20 wt% LCP).

Thermotropic Liquid Crystalline Polycarbonates VI. Synthesis and Properties of Fully Aromatic Liquid Crystalline Polycarbonates by Interfacial or Solution Polycondensation

Several series of fully aromatic liquid crystalline polycarbonates were synthesized by interfacial or solution polycondensation from triphosgene with aromatic diols, such as hydroquinone, 4,4′-biphenyldiol, 2,6-naphthalenediol, Bisphenol A, 4,4′-dihydroxydiphenyl sulfone, 4,4′-dihydroxydiphenylsulfide, 4,4′-dihydroxydiphenylmethane, 4,4′-dihydroxydiphenyl ether, methylhydroquinone, t-butylhydroquinone, phenylhydroquinone, and resorcinol, respectively. The structures and thermal properties of the synthesized polycarbonates were examined by FT IR spectroscopy, differential scanning calorimetry (DSC), thermal optical polarized microscopy, and thermogravimetric analysis (TGA). The effects of the structures of polycarbonates on liquid crystalline properties and thermal stability were investigated. The thermotropic LC properties of polycarbonates are strongly dependent on the structures and content of the bent units. The non-linearity of carbonate linkage can be compensated for by bent units in some case.

Synthesis and Characterization of Novel Side-Chain Liquid Crystalline Polycarbonates, 3. Dynamic Mechanical Analysis of the Secondary Relaxation Processes

The dynamic mechanical properties of two homologous series of side-chain liquid crystalline polycarbonates were studied. One series with oxynitro-stilbene mesogenic groups and alkyl spacers of diff...

X-Ray Scattering and Thermal Characterization of α,β-Dimethyl Stilbene Polycarbonates

Abstract Structural and thermal characterization is reported for a series of recently synthesized1 liquid crystalline polycarbonates based on di-methyl substituted stilbene mesogen and methylene-containing flexible spacer of length n. In this work, we focus on the α, β-dimethyl stilbene (DMS-n) polycarbonates and on the comparison between them and α-methyl stilbene (HMS-n) polycarbonates2–4, especially those with heptane spacer. Wide angle X-ray scattering patterns show that DMS polycarbonates are able to form a nematic liquid crystalline phase. However, the liquid crystalline phase is generally not stable with respect to the crystalline phase. In the DMS polycarbonates, no distinct isotropic-to-nematic (i → lc) transition is seen either by polarizing optical microscopy or by differential scanning calorimetry (DSC). We suggest that the steric effect of the second lateral substituent results in a less stable, virtual mesophase. For DMS-n, an odd-even effect is observed in the crystallization and melting te...

Miscibility of semirigid thermotropic liquid crystalline polycarbonate with poly(vinyl chloride)

AbstractMiscibility and morphology of polymer blends of semirigid thermotropic liquid crystalline (LC) polycarbonate (LCPC) with three commercial amorphous poly(vinyl chloride)s (PVC) having various molecular weights were investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No phase separation was observed in the LCPC/PVC polymer blends. LCPC forms miscible polymer blends with the PVCs independent of molecular weight. The dynamic storage modulus of the LCPC/PVC polymer blends changes systematically with blend composition.

Small‐angle X‐ray scattering study of liquid crystalline polycarbonates based on α‐methyl stilbene mesogen and methylene‐containing flexible spacer

AbstractCrystallization and melting behavior are studied by small‐angle X‐ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α‐methyl stilbene mesogen and methylene flexible spacer. The one‐dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz‐corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real‐time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd‐even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide‐angle X‐ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 John Wiley &amp; Sons, Inc.

Synthesis and characterization of novel side‐chain liquid crystalline polycarbonates, 2. Polycondensation of mesogenic diols and diphosgene

AbstractA series of new side‐chain liquid crystalline polymers was prepared with a polycarbonate backbone, bearing (E)‐4′‐nitrostilbene mesogenic groups, connected to the backbone by spacers of different length. The polymers were synthesized in 1,4‐dioxane by polycondensation of diphosgene and diol monomers with the general structure 2‐[ω‐(4′‐nitrostilben‐4‐ylcxy)alkyloxy]‐1,3‐propanediol in the presence of pyridine as a proton trap and catalyst. The mesomorphic properties of all monomers, polymers and intermediates were studied by polarized optical microscopy and differential scanning calorimetry (DSC). The polymers were also studied by X‐ray diffraction of non‐oriented and oriented samples (fibres). All monomers were liquid crystalline with nematic and/or smectic phases. For the polymers a clear relation was found between spacer length and glass transition temperature (Tg), which decreases with increasing spacer length and between spacer length and clearing temperature, which increases with increasing spacer length. X‐ray diffraction measurements indicated the presence of a smectic A double layer structure (SAd) for all polymers at room temperature, with an antiparallel of overlapping mesogenic groups. A distinct difference in the orientation of the mesogens was found when fibres were drawn from the smectic phase or from the nematic or isotropic phase. In the first case the mesogenic groups were oriented perpendicular to the fibre axis and in the second case the mesogenic groups were oriented parallel to the fibre axis. By gel‐permeation chromatography (GPC) measurements of heated samples and by thermogravimetric analysis (TGA) and DSC the polymers were found to be thermally stable up to temperatures well above their clearing point.

Synthesis and Characterization of Novel Side-Chain Liquid Crystalline Polycarbonates

Abstract Side-chain liquid crystalline (SCLC) polycarbonates were prepared by copolymerization of carbon dioxide with epoxides, carrying a nitrostilbene mesogenic group and spacers of different lengths. The polymerization, carried out in an autoclave at high carbon dioxide pressure, was catalyzed by an organozinc catalyst. The number average molecular weight of the polymers, as determined by GPC, was in the range of 4,300 to 38,000. The polydispersity of the polymers ranged from 5.9 to 80. 1H NMR and 13C NMR studies revealed that the obtained polymers contain carbonate linkages (67-94%) as well as ether linkages in their backbone. Liquid-crystalline properties of the polymers were investigated by DSC, X-Ray diffraction and polarized optical microscopy.

Crystallization of Monotropic Liquid Crystalline Polycarbonates Based on a Methylstilbene Mesogen and a Methylene-Containing Flexible Spacer

Crystallization behavior has been studied for a series of recently synthesized liquid crystalline polycarbonates [PhCH=C(Me)PhOCOO(CH 2 ) m OCOO] n (m= 4-10, 12). The stability of the nematic phase and its relationship to three-dimensional crystallinity were studied. Development of crystallinity was followed by isothermal and nonisothermal crystallization using DSC and polarizing optical microscopy. A monotropic liquid crystal phase is identified for these polycarbonates. The multiple melting endotherms seen in the heating scan are assigned to the melting of crystals forming either from the mesophase (melting at higher temperature) or from the isotropic phase (melting at lower temperature)

Compatibilizing effect of a thermotropic liquid‐crystalline compatibilizer on liquid‐crystalline polycarbonate/poly(p‐phenylene oxide) blends

AbstractThe compatibilizing effect of a thermotropic block‐graft copolymer (LCBG) as a compatibilizer on thermotropic liquid‐crystalline (LC) polycarbonate (LCPC)/poly(p‐phenylene oxide) (PPO) blends was studied. Compatibility, morphology and mechanical properties of the blend systems were investigated by differential scanning calorimetry (DSC), thermal mechanical analysis (TMA) and scanning electron microscopy (SEM). The blend without the compatibilizer formed thermotropic LC phases, based on LCPC domains, and had a phase‐separated structure. The LC temperature ranges of the blends with LCBG were wider than that of the blend without the compatibilizer. DSC, SEM and TMA data showed that in the blends containing the compatibilizer the compatibility and the viscoelasticity were improved, because LCBG segments penetrate into both the PPO matrices and the LCPC domains in the blends. These results suggest that LCBG acts as a good compatibilizer for blends.