Rheological properties in cholesteric and blue phases of cholesteryl isostearyl carbonate: viscosity and effect of electric field on the rheology

Rheological property (shear stress versus shear rate) of cholesteryl isostearyl carbonate (CISC) is measured as a function of temperature, finding that, like some other cholesteryl derivatives, CISC has blue phases (BPs) between the cholesteric (Ch) and the isotropic (I) phases. In the Ch and the BP phases, measurements of the electrorheological (ER) effect, of the electric field on the rheology, are made; a slight increase of the viscosity is observed in the BPs and no ER effect in the Ch phase, which is contrasted to the distinct ER effect in the nematic (N) and the smectic A (SmA) phases.     

Dipole-induced chiral smectic-C phase in a eutectic mixture of cholesterol esters

Both cholesteryl oleate (CO) and cholesteryl oleyl carbonate (COC) are thermotropic mesogens with a general cooling phase sequence: isotropic → cholesteric → smectic → crystal. They are almost identical with respect to molecular structure and the central location of molecular dipole. However, the orientation of the latter is axial for CO and transverse for COC. A eutectic mixture of these components shows a phase sequence like the above but involving an induced smectic-C* phase. We explain this discovery on the basis of computer simulation results involving rigid core-dipole-flexible tail model of a mesogen and argue in favor of a ferroelectric liquid crystal model of the induced phase.     

Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate): synthesis and characterisation

Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate) was investigated. The novel liquid crystal was synthesised via ring-opening polymerisation of trimethylene carbonate initiated by cholesteryl derivative with an alkyl spacer and end primary hydroxyl group, without any catalyst. The chemical structure of resulting polymers was verified by ¹H NMR. Liquid crystalline properties were validated by X-ray diffraction, differential scanning calorimetry, and polarising optical microscopy. The results showed that all the synthesised polymers Chol-(CH₂)₂-(TMC)_n exhibited mesomorphism in particular temperature ranges because of the introduction of the cholesteryl derivative moiety.     

Assembly of poly[N‐(2‐hydroxypropyl)methacrylamide] having cholesteryl moiety as terminal groups

Poly[N‐(2‐hydroxypropyl)methacrylamide]s (PHPMAs) with one pendant cholesteryl moiety at the polymer end and two pendant cholesteryl moieties at both polymer ends as terminal groups (PHPMA‐Chol and PHPMA‐2Chol) were prepared by the radical polymerization of N‐(2‐hydroxypropyl)methacrylamide initiated with 4,4′‐azobis‐[(3‐cholesteryl) 4‐cyanopentanoate] in the presence of 2‐mercaptoethanol and thiocholesterol as chain‐transfer reagents, respectively. The self‐organization of the PHPMAs was analyzed by fluorescence and ¹H NMR measurements. The critical micelle concentration (CMC) decreases with a decreasing PHPMA degree of polymerization. The CMC of PHPMA‐Chol is much larger than that of PHPMA‐2Chol. PHPMA exhibits an excellent blood compatibility, as determined from the Michaelis constant for the enzymatic reaction of thrombin and a synthetic substrate, S‐2238, in the presence of PHPMA‐2Chol. According to a small‐angle X‐ray scattering measurement, PHPMA‐2Chol can hold the cholesterol molecule as a lipophilic drug model in a hydrophobic layer formed by terminal‐located cholesteryl groups in PHPMA‐2Chol. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3369–3377, 2000     

螺环单体的合成、聚合及与环氧树脂的固化反应

合成了新螺环原碳酸酯单体：３，９－二（对甲氧基苄基）－１，５，７，１１－四氧杂螺环［５，５］十一烷．以ＢＦ３·ＯＥｔ２为催化剂，实现了其阳离子聚合．聚合产物的１ＨＮＭＲ、１３ＣＮＭＲ、ＩＲ及元素分析均表明发生了双开环聚合反应．探讨了其聚合历程．用ＤＳＣ和ＩＲ跟踪环氧树脂及其与螺环单体混合后的固化反应过程，研究了固化剂、反应条件对固化反应的影响     

Hybrid nanogels with physical and chemical cross-linking structures as nanocarriers

Polymerizable nanogels were prepared by self-assembly of cholesteryl group-bearing pullulan (CHP) with methacryloyl groups (CHPMA). The CHPMA nanogel was polymerized with 2-methacryloyloxyethyl phosphorylcholine (MPC) by radical polymerization in dilute aqueous solution. The solution properties of the polymers in water were investigated by TEM, SEC-MALS, and fluorescence quenching technique. Monodispersed hybrid nanogels of CHPMA-MPC (CM nanogels) (25-30 nm in radius of gyration) were obtained by using CHPMA nanogel as a seed-nanogel. CM nanogels have a dual cross-linking structure that is physically cross-linked with the cholesteryl groups and chemically cross-linked with the MPC polymer chains. CM nanogels trap heat-denatured carbonic anhydrase B (CAB) and prevent their aggregations. The nanogels maintained the ability of trapping and releasing enzymes by host-guest interaction of cholesteryl group and cyclodextrin.     

Rational Design of Diphenyldiacetylene-Based Fluorescent Materials Enabling a 365-nm Light-Initiated Topochemical Polymerization

Photopolymerization of diacetylenes usually requires stringent reaction conditions like high energy irradiation of 254-nm light or even γ-rays, which are generally harmful to the human body and thus mild conditions with lower energy irradiation are required. In this study, different diphenyldiacetylene (DPDA) derivatives were rationally designed followed by the investigation of their photopolymerization behavior. It was found that the para-substituted amino groups could render the absorption band of DPDA bathochromically shifted, ensuring a 365-nm light wavelength coverage. On this basis, an organogel system was constructed by chemically modifying cholesteryl and lipoic acid onto the DPDA moiety in aromatic solvents. Such uniform self-assemblies further facilitated to a rather high degree of polymerization by 365-nm irradiation. As a kind of fluorescent materials, the whole polymerization process of this system can be visualized by a photoluminescent signal.     

The first series of ferroelectric steroidal fluorinated liquid crystals

A series of cholesteryl p-perfluoroalkylphenyl carbonate (CPC) [C₂₇H₄₅OCO₂C₆H₄(CF₂)_nF, n=1,4,6,8] liquid crystals was synthesized and their phase transition behaviours were studied. The results show that the compounds containing a not too long perfluoroalkyl chain (n=6,8) have monotropic chiral smectic C phases.     

Thermal bulk polymerization of cholesteryl acrylate

The thermal bulk polymerization of cholesteryl acrylate was carried out in the solid phase, the mesomorphic phase, and the liquid phase to study the effect of monomer ordering on polymerization rate and polymer properties. The rate increased with decreasing ordering (or enhanced mobility) of the monomer. Formation of inhibitive by-products during the polymerization limited conversions to 35%. The sedimentation constant S₀ = 6.2 S was the same for the polymers obtained in the three phases. The weight-average molecular weight (M?_w) was 480,000 as determined by ultracentrifugation. Poly-(cholesteryl acrylate) formed in bulk is randomly coiled when dissolved in tetrahydrofuran. The thermal properties of the monomer are given.     

Controlled synthesis of polyepichlorohydrin with pendant cyclic carbonate functions for isocyanate‐free polyurethane networks

Poly(allyl glycidyl ether) and poly(allyl glycidyl ether‐co‐epichlorohydrin) were prepared by monomer‐activated anionic polymerization. Quantitative and controlled polymerization of allyl glycidyl ether (AGE) giving high molar mass polyether was achieved in a few hours at room temperature in toluene using tetraoctylammonium salt as initiator in presence of an excess of triisobutylaluminum ([i‐Bu₃Al]/[NOct₄Br] = 2?4). Following the same polymerization route, the copolymerization of AGE and epichlorohydrin yields in a living‐like manner gradient‐type copolymers with controlled molar masses. Chemical modification of the pendant allyl group into cyclic carbonate was then investigated and the corresponding polymers were used as precursors for the isocyanate‐free synthesis of polyurethane networks in presence of a diamine. Formation of crosslinked materials was followed and characterized by infrared and differential scanning calorimetry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Anionic ring-opening polymerization behavior of a seven-membered cyclic carbonate; 1, 3-dioxepan-2-one

Anionic ring-opening polymerization of a seven-membered cyclic carbonate, 1,3-dioxepan-2-one ( 1 ), was carried out to observe that the higher the polymerization temperature and lower the initial monomer concentration were, the lower the yield and molecular weight, and wider the molecular weight distribution of the obtained polymers were. The back-biting reaction and the formation of cyclic oligomers of 1 were observed during the polymerization of 1 . The relative polymerization rate of 1 was about 35 times faster than that of six-membered carbonate, 1,3-dioxan-2-one ( 3 ). The ΔHps of 1 and 3 estimated by MO (PM3) calculations were −9.8 and −4.4 kcal/mol, respectively. 1 could easily undergo the ring-opening polymerization based on larger ring strain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1375–1380, 1997     

Polycarbonate microspheres containing mitomycin C and magnetic powders as potential hepatic carcinoma therapeutics

The polycarbonate copolymer poly(trimethylene carbonate-co-5,5-dimethyl trimethylene carbonate) (P(TMC-co-DTC)) was synthesized by the polymerization of trimethylene carbonate (TMC) and 5,5-dimethyl trimethylene carbonate (DTC) using tin (II) 2-ethylhexanoate [Sn(Oct)(2)] as a catalyst. In vitro degradation tests indicated this polycarbonate copolymer degraded slowly in phosphate buffer saline solution (PBS, 0.1 mol/L, at 37°C). Magnetic polymer microspheres (MMC-PC-M) generated from the P(TMC-co-DTC) copolymer and containing Fe(3)O(4) magnetic ultrafine powders and an anticancer drug, mitomycin C (MMC) were prepared by a solvent evaporation technique. These anticancer magnetic polycarbonate microspheres showed strong magnetic responsiveness and high MMC loading capacity. In vitro drug release studies indicated that these microspheres sustained steady release rates of MMC in PBS. In vitro cytotoxicity assays demonstrated the microspheres were strongly inhibitory to human hepatic carcinoma (Bel-7204) cells. In vivo site-specific therapy in nude mice with human hepatic carcinoma indicated that the microspheres possessed markedly high antitumor activity against human hepatic carcinoma (Bel-7204).     

Radical polymerization behavior of a vinyl monomer bearing five‐membered cyclic carbonate structure and reactions of the obtained polymers with amines

Radical polymerization behavior of a vinyl substituted cyclic carbonate, 4‐phenyl‐5‐vinyl‐1,3‐dioxoran‐2‐one ( 1 ), is described. Radical polymerization of 1 proceeded through selective vinyl polymerization to produce polymers bearing carbonate groups in the side chain, in contrast to that of an oxirane analogue of 1 , 1‐phenyl‐2‐vinyl oxirane that proceeds via the selective ring‐opening fashion. Although the homopolymerization of 1 produce polymers in relatively lower yield, copolymerizations effectively provided cyclic carbonate‐containing copolymers. Nucleophilic addition of primary amines to the resulting homopolymers and copolymers produced the corresponding multifunctional polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 584–592, 2005     

Investigation on lipase-catalyzed solution polymerization of cyclic carbonate

In this study, 26-membered macrocyclic carbonate, cyclobis(decamethylene carbonate) [(DMC)₂] was attempted to undergo ring-opening polymerization by lipase catalysis in toluene. Novozym-435 exhibited even higher catalytic activity towards (DMC)₂ polymerization compared with SnOCt₂ while high molecular weight (M_n) of 5.4 × 10⁴ and yield of 99% was still achieved at ultra-low enzyme/substrate (E/S) weight ratio of 1/200. ¹H NMR spectra demonstrated the existence of terminal hydroxyl group. Solid phase polymerization in the absence of toluene unexpectedly took place at the temperature lower than (DMC)₂’s melting point of 110 °C. Compared with solvent-free case, the addition of toluene solvent resulted in marked increase in reaction rate. As to the polymerization during 48 h with the E/S weight ratio of 1/100, a region existed at around toluene/carbonate (vol/wt, ml/g) ratio of 1∼2 where the polymerizations gave optimal results in terms of both higher molecular weight and monomer conversion. It was found that much higher molecular weight polymers may be obtained by decreasing enzyme concentrations. Plots of ln{[M]₀:[M]_t} versus reaction time were in linear agreement, indicating no chain termination, and monomer consumption follows a first-order rate law. The Novozym-435 catalyzed polymerization of (DMC)₂ in toluene presented pseudo-living characteristic. Compared with 6-membered trimethylene carbonate, much lower reaction activity of large-sized (DMC)₂ is observed, which is opposite to the result concerning the enzymatic polymerization of lactones with different ring-size.     

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.     

Optical activity in the isotropic and blue phases of two cholesterics

Optical activity measurements were performed in the isotropic phase and blue phases of two short-pitch cholesteric liquid crystals (cholesteryl oleate and cholesteryl oleyl carbonate). The data in the isotropic phase are interpreted in terms of five structural modes of the order parameter. Coupling between these modes gives rise to an extremum and a change of sign in the pretransitional optical rotation. The intensities of the polarized and depolarized component of the transmitted beam were measured as an extral tool to locate the phase transitions.     

Optical activity in the isotropic and blue phases of two cholesterics

Optical activity measurements were performed in the isotropic phase and blue phases of two short-pitch cholesteric liquid crystals (cholesteryl oleate and cholesteryl oleyl carbonate). The data in the isotropic phase are interpreted in terms of five structural modes of the order parameter. Coupling between these modes gives rise to an extremum and a change of sign in the pretransitional optical rotation. The intensities of the polarized and depolarized component of the transmitted beam were measured as an extral tool to locate the phase transitions.     

Chromatographic characteristics of cholesterol-imprinted polymers prepared by covalent and non-covalent imprinting methods

Cholesterol-imprinted polymers were prepared in bulk polymerization by the methods of covalent and non-covalent imprinting. The former involved the use of a template-containing monomer, cholesteryl (4-vinyl)phenyl carbonate, while the latter used the complexes of template and functional monomer, methacrylic acid or 4-vinylpyridine prior to polymerization. Columns packed with these molecularly imprinted polymers (MIPs) were all able to separate cholesterol from other steroids. For different combinations of cholesterol and beta-estradiol concentrations in a total of 1 g/l, the peak retention times for both compounds were nearly constant. The adsorption capacity for cholesterol onto the MIPs was found to significantly depend on the use of functional monomers, but the selectivity factors were only slightly different from each other at 2.9 to 3.2 since the separation was all based on the specific binding of cholesterol to recognition sites formed on the imprinted polymers. The capacity factors for cholesterol were determined to be 3.5, 4.0 and 3.1, respectively, for covalently imprinted, 4-vinylpyridine-based, and methacrylic acid-based non-covalently imprinted polymers. However, the covalently imprinted polymer was found to have a higher adsorption capacity for cholesterol and about fivefold higher chromatographic efficiency for cholesterol separation, in comparison with non-covalently imprinted polymers. The use of covalent imprinting significantly reduced the peak broadening and tailing. This advantage along with constant retention suggests that the covalently imprinted polymer has potential for quantitative analysis.     

Ultraviolet-visible-near infrared and mid-Fourier transform infrared spectroscopic studies of intermolecular interaction in cholesteryl oleyl carbonate in mesophases

Ultraviolet-visible-near infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) spectroscopic studies are presented of molecular association between like molecules of cholesteryl oleyl carbonate, each containing suitable pi-donor (steroid ring C=C) and pi-acceptor (C-O single bonds united with a C=O bond to give a carbonate group) moieties. Frequency shifts and intensity enhancements of donor and acceptor oscillators appear to be governed by reduced mass, vibronic coupling constants, and a few other parameters such as relative change in force constants, etc. Donor-acceptor complex formation is characterized not only by the appearance of new bands in the mid-FTIR spectrum but also by the emergence of a new, intense electronic band centered at approximately 3700 cm(-1), the so-called charge-transfer band, in the UV-Vis-NIR spectrum. This band is strong in the smectic-A and solid phases, but progressively diminishes when temperature is raised to realize the upper end of the cholesteric phase and eventually the isotropic phase. Also, a new, small electronic band at approximately 360 nm, only seen in the entire thermal range of the cholesteric phase, is attributed to the Lifshitz-van der Waals interaction between pretransitional smectic-A domains existing in the cholesteric phase. It is argued that mesophases may owe their thermodynamic stability to both Lifshitz-van der Waals and vibronic coupling (or electron-phonon coupling in extended systems such as smectics and solids) interactions.     

Synthesis of carbonate-containing high temperature poly(arylene-siloxanylenes)

A method for the first synthesis of high molecular weight carbonate-containing siloxanylene polymers was successfully developed. The procedure covered the preparation and polymerization of pure carbonate-containing bis-silanols which included bis(4-hydroxydimethylsilylphenyl)-carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)-phenyl] carbonate, and their meta analogs. Because conventional siloxane polymerization methods, such as the heterocondensation of bis-silanols with diaminosilanes or homocondensation reactions catalyzed by alkali reagents, decomposed carbonate linkages, a new polymerization technique that involved the use of phosgene was used. The procedure was both facile and effective in the polymerization of other arylene bis-silanols.