Liquid crystalline side group copolymers containing cholesterol and methoxybiphenyl were synthesized and investigated by size exclusion chromatography, 1H NMR, polarization microscopy, X-ray diffraction, differential scanning calorimetry and additionally by measuring the birefringence and the optical reflection of the cholesteric phase. This cholesteric phase could be obtained by copolymerization of two monomers whose homopolymers exhibit only smectic phases. The cholesteric phase exists over a broad range of copolymer composition. For the cholesterol containing homopolymer an SA2 bilayer phase was observed, whereas the methoxybiphenyl homopolymer shows a highly ordered E phase below an SA1 monolayer phase. The layer periods of the SA phases of the copolymers depend on the composition. By measuring the birefringence the order parameter in the cholesteric phase could be determined. 相似文献
A number of new photosensitive copolyacrylates of different composition were obtained by the copolymerization of chiral photochromic
benzilidene-p-menthane- 3-one acrylic monomers with a smectogenic monomer containing a hexyloxyphenylbenzoate mesogenic group. The chiral,
photochromic monomers differ by the length of the aliphatic spacer and the aromatic fragment. It was found that the introduction
of a small number of chiral units into the copolymers (5 mol%) leads to the “degeneration” of the smectic C phase, which characterizes
the hexyloxyphenylbenzoate homopolymer, and to the formation of the smectic A phase. An unusual effect of chiral nematic phase
induction was observed for copolymers containing chiral side groups with two ring aromatic fragments. It should be pointed
out that the chiral nematic phase does not occur in the case of the homopolymers of both initial comonomers. An explanation
of this effect, based on the consideration of the chemical structure of the chiral and hexyloxyphenylbenzoate units, was suggested.
The optical properties of cholesteric copolymers were investigated; the helical twisting power of the chiral groups of different
structures was calculated. The possibility of using such copolymers as new photosensitive materials was demonstrated.
Received: 16 December 1999/Accepted: 1 February 2000 相似文献
The radical polymerization behavior of alkoxyallene containing the epoxy group, allenyl glycidyl ether ( I ), was investigated to obtain the more reactive polymer. The desired polymer was successfully synthesized only by the copolymerization of I with acrylonitrile (AN) at 80°C in DMF, although the homopolymer of I was converted to the crosslinked polymer during its purification. The same number of epoxy and two kinds of methylene groups were simultaneously introduced onto the polymer through propagating allyl radical. The obtained copolymer, therefore, was readily converted to the gelled polymer with methods such as heating and treating with Lewis acids or amines. Further, the copolymer containing two kinds of methylene groups was prepared similarly from methoxyallene ( II ) and AN, and was also converted to the crosslinked polymer with the cationic catalyst. These copolymers of I or II with AN will be expected to be new types of reactive polymers. 相似文献
A series of 3-[ω-(4-cyanobiphenyl-4'-yloxy)alkyl] ethers of estradiol 17-[ω(4-cyanobiphenyl-4'-yloxy)alkanoates] with variable spacers has been prepared as chiral triplet liquid crystals. The compounds show very broad range cholesteric phases and are transformed into cholesteric glasses at room temperature. They exhibit odd-even effects for their cholesteric-isotropic transition temperatures and the associated entropy changes as a function of spacer length. The odd-even effects are observed upon changing the parity of both the ester and of the ether spacer. The best ordering is observed for compounds with an even number of methylene groups both in the ester and the ether spacer. In these cases the three mesogen units are oriented more or less parallel when the alkyl spacers are in the all-trans-conformations. Odd-even effects are also observed for the selective reflection wavelength of the planar cholesteric phase, depending on the parity of both spacers. For several compounds with short spacers the selective reflection wavelength increases strongly with temperature, whereas for other compounds this is almost temperature independent. 相似文献
The photo-optical behaviour of two series of chiral photochromic acrylic copolymers with a chiral nematic phase has been studied. These copolymers contain identical chiral photochromic units, but have different structures of the phenyl benzoate mesogenic side groups which are responsible for the development of LC phases. This approach allowed us to examine specific features of the photo-optical behaviour of the copolymers as a function of the nature of the LC 'matrix' in which the cholesteric phase was induced. The action of UV irradiation was shown to lead to the E-Z isomerization of the chiral side groups and, as a consequence, to untwisting of the cholesteric helix of the copolymers. For copolymers of both series, the effective quantum yields of this photochemical process were calculated. In the case of copolymers in which the cholesteric mesophase is induced in a smectogenic matrix, the corresponding values of the quantum yield are lower and depend slightly on temperature. A plausible explanation of the above phenomena is suggested. 相似文献
The photo-optical behaviour of two series of chiral photochromic acrylic copolymers with a chiral nematic phase has been studied. These copolymers contain identical chiral photochromic units, but have different structures of the phenyl benzoate mesogenic side groups which are responsible for the development of LC phases. This approach allowed us to examine specific features of the photo-optical behaviour of the copolymers as a function of the nature of the LC 'matrix' in which the cholesteric phase was induced. The action of UV irradiation was shown to lead to the E-Z isomerization of the chiral side groups and, as a consequence, to untwisting of the cholesteric helix of the copolymers. For copolymers of both series, the effective quantum yields of this photochemical process were calculated. In the case of copolymers in which the cholesteric mesophase is induced in a smectogenic matrix, the corresponding values of the quantum yield are lower and depend slightly on temperature. A plausible explanation of the above phenomena is suggested. 相似文献
Biodegradable poly(sebacic anhydride-co-caprolactone) (PSA-co-PCL) multi-block copolymers were prepared by condensation of acylated PSA and PCL prepolymers with different weight ratios. The homopolymer and copolymers were characterized by 1H-NMR, gel permeation chromatography (GPC), differential scanning calorimeter (DSC) and atom force microscope (AFM). 1H-NMR and GPC has indicated the formation of PSA-co-PCL multi-block copolymers, in which PSA and PCL segments are randomly distributed. The incorporation of PCL segments into the molecule chains even at a content of 20 wt% could significantly decrease the molecular weight distribution of the copolymer and increase its weight average molecular weight, as compared with PSA homopolymer. DSC has revealed that the melting temperature and degree of crystallinity for both SA and CL components are strongly composition dependent, implying the hindrance effect of the two components on crystallinity of each other. AFM observation has shown the difference in crystalline structures between PSA and PCL phases in the copolymers. In-vitro degradation tests performed at 37 °C in PBS buffer solution (pH 7.4, 0.1 M) have demonstrated the acceleration of degradation rate of the sample with increasing SA content in the copolymer. 相似文献
Summary: The effects of copolymer sequence distribution on the dynamics of a copolymer in a homopolymer matrix are studied using computer simulations within the framework of the bond‐fluctuation model on blends containing low concentrations (10%) of copolymers dispersed in a homopolymer matrix. The sequence distribution of the two copolymer components was changed while maintaining the overall copolymer composition at 50/50. Our results indicate that copolymers with disordered sequence distributions exhibit dynamics that are faster than that of a homopolymer melt, while those with ordered sequence distributions exhibit a tendency to form aggregates that lead to slower dynamics as well as phase separation. Analysis of the structure suggests that copolymers with an alternating sequence distribution form large aggregates that are short‐lived, while diblocks form permanent micelle‐like structures. Analysis of the local composition around a copolymer molecule indicates that aggregation between copolymer chains has a direct impact on the local composition. This in turn has a significant impact on system dynamics. Our results indicate that the dynamics of random, random‐blocky, and alternating copolymers are nearly identical and are faster than that of a homopolymer melt. However, alternating copolymers form aggregates and hence are not uniformly distributed throughout the matrix phase. Thus, alternating copolymers are at a disadvantage in their ability to be effective compatibilizers. From a dynamic perspective, copolymers with random and random‐blocky copolymers seem to be ideal compatibilizers since they are distributed uniformly throughout the system and move rapidly through the matrix phase.
Snapshots of aggregates of alternating copolymer chains. Dark and bright spheres represent A and B monomers, respectively. 相似文献
Properties of a poly(arylene ether ketone) with carboxyl side groups, copolymers containing units of this homopolymer, and their salts with different degrees of neutralization by alkali metals were studied by the methods of dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. By varying the nature of a metal atom and the degree of neutralization of carboxylic groups of a homopolymer and their content in copolymers, one may change the properties of polymers, including their ability to form ion pairs and, hence, their glass transition temperatures. For polymer salts at the 100% neutralization of carboxylic groups, the storage modulus and the glass transition temperature are shown to increase with decreasing the radius of the metal ion. The thermal stability of poly(arylene ether ketone) with carboxylic side groups and copolymers with different contents of such groups may be controlled by varying the nature and content of the introduced metal. 相似文献
A liquid crystal comb polymer of potential interest for electro-optical applications has been synthesized and characterized. The polymer has a polyacrylamide main chain and two different types of side group, built up of 4'-undecanoyloxy-4-cyanobiphenyl groups (68 mol %) and of shorter aliphatic groups (32 mol %). The two types of side group occur randomly along the polymer's main chain. The preparation steps and the liquid crystalline structure of the resulting copolymer are compared with those of a homopolymer whose side groups (built up of 4'-undecanoyloxy-4-cyanobiphenyl groups) are all identical. X-ray diffraction shows that the polymers display different mesophases over different temperature ranges. However, the homopolymer exhibits two smectic phases (SmC2 and SmA2), while the new copolymer exhibits a SmC2 phase and a nematic mesophase at higher temperature. The mesophase thermal stability of the copolymer is significantly lower than that of the homopolymer. 相似文献
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
The effect of copolymer composition on the dynamics of random copolymers in a homopolymer matrix is studied using computer simulations within the framework of the bond-fluctuation model on blends containing low concentrations (10%) of A-B copolymers, where A and B are two different types of monomers, dispersed in a homopolymer matrix of chains with only A-type monomers. Four copolymer compositions were studied, phi(A)=0.33, phi(A)=0.5, phi(A)=0.66, and phi(A)=0.82, while maintaining a statistically random sequence distribution. For this study, we have only included intermolecular interactions between A and B monomers. Our results indicate, in agreement with experimental data, that copolymer composition has an impact on system dynamics. Analysis of the structure reveals that copolymers with majority A content are expanded in the homopolymer matrix, have fewer interchain copolymer-copolymer contacts, and are well dispersed in the homopolymer matrix. On the other hand, copolymers with lower A content form a more compact structure, have more interchain contacts, and form aggregates that are short lived. This in turn leads to slower system dynamics. Both the radius of gyration (Rg) and copolymer end-to-end vectors (Re) increase with increasing A content until phi(A)=0.66 and then decrease. Copolymers with lower A content form more compact structures as the repulsive interactions between unlike species are minimized by the copolymers folding back on themselves and forming aggregates of copolymer chains. Thus, these results provide insight into the variation of copolymer dynamics with composition in the system by documenting the correlation between the thermodynamics of this mixture, the conformation of a copolymer chain in a homopolymer matrix, and the dynamics of both components in this blend. 相似文献
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
New chiral photochromic cholesteric comb-shaped acrylic copolymers and low molecular mass dopants containing azobenzene photosensitive fragments and chiral groups based on menthol and menthone were synthesized. For the copolymers and their mixtures with low molecular mass dopants, the phase behaviour and optical properties were studied. Under irradiation with UV and visible light, the untwisting of cholesteric helix takes place, and the selective light reflection maximum is shifted to the long wavelength spectral region. This shift is related to the E-Z isomerization of the azobenzene chiral groups. For the copolymers and mixtures of the cholesteric polymer with the menthyl-containing dopant, this process is thermally reversible. The specific features of the kinetics of the forward and the reverse thermal processes were characterized. It was demonstrated, that the copolymers and mixtures of the cholesteric copolymer with the menthyl-containing dopant may be used for coloured reversible recording of optical information. For such materials, their resistance with respect to the repeated 'recording-erasing' cycles was tested, and the fatigue resistance was shown to be rather high. 相似文献
For the first time, a series of cholesteric copolymers containing combined chiral photochromic side groups has been synthesized and the phase behaviour and optical properties of the copolymers have been characterized. Specific features of the photochemical and photo-optical behaviour of such systems were studied, and the quantum yields of the photo-induced process in solution and in the condensed state of the cholesteric copolymers were calculated. The selective light reflection wavelength was found to be controlled by the UV radiation. The synthesized polymers were shown to be promising candidates for colour data recording. 相似文献