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1.
Four series of new poly(β-aminoester)s based on different mesogenic units and amino spacers were prepared and their properties examined. The polymers were obtained by a Michael-type polyaddition reaction of the diamines piperazine ( 5a ), 2-methylpiperazine ( 5b ), N,N′-dimethylhexamethylenediamine ( 5c ), and 4,4′-trimethylenedipiperidine ( 5d ) to diacrylates containing the anisotropic group, trans-4,4′-vinylenedi-p-phenylene diacrylate ( 1 ), 4-(4-acryloyloxybenzylideneamino)phenyl acrylate ( 2 ), 4,4′-diphenylylene diacrylate ( 3 ), and 4,4′-azoxydi-p-phenylene diacrylate ( 4 ). The mesophase behaviour of the resulting polymers 6–9 was strongly influenced by the nature of both the anisotropic and spacer groups. The 4,4′-azoxydi-p-phenylene unit appeared to be the most efficient in promoting liquid crystal properties, whereas no mesophases could be observed in polymers incorporating the 4,4′-biphenylylene unit. Doping of poly(β-aminoester)s, based on 4,4′-azoxydi-p-phenylene units, with a low-molar-mass cholesterogen allowed to obtain cholesteric structures extending over wide ranges of temperature. The molecular weight of the polymers was found to play a role in determining thermotropic mesomorphism by affecting the melting temperature of the polymer. In this context, some non-macromolecular model compounds were analyzed in respect of their thermal behaviour.  相似文献   

2.
Heterogeneous polymerizations of γ-methyl-L -glutamate N-carboxy anhydride (NCA), γ-benzyl-L -glutmate NCA, and β-benzyl-L -aspartate NCA were carried out using butylamine as initiator in acetonitrile at 30°C. The oligomer chains formed in the beginning of the polymerization crystallized into the antiparallel β-form and thereafter the α-helical chains grew from the active sites of the β-chains. The polymerization of γ-methyl-L -gultamate NCA proceeded to 100% conversion and accordingly gave rise to high molecular weight poly(γ-methyl-L -glutamate). The polymerizations of γ-benzyl-L -glutamate NCA and β-benzyl-L -aspartate NCA stopped at 54% and 16%, resp. The levelling-off of the conversion at such low values, in spite of the α-helical chain growth, may be due to the occlusion of the active chain ends of the resultant poly(γ-benzyl-L -glutamate) and poly(β-benzyl-L -aspartate) into the crystals. It was concluded that the interlamellar crystallization was induced by the intermolecular interaction between the benzyl groups of the polymer side chains, giving rise to the occlusion of the active growing chain ends into the interstices of the crystal formed during the polymerization.  相似文献   

3.
An improved method is described for the preparation of difunctional poly(hexafluoropropylene oxide) of moderate molecular weight (M n ≈ 6000) in good yield (>80 wt.-%). With the dependence of chain transfer constant on initiator concentration known, at least under controlled conditions, good molecular-weight control can be achieved.  相似文献   

4.
Crystal growth rates of spherulites of β-phase poly(propylene)s and of an ethylene/propene block copolymer, crystallized from the melt, have been investigated in the temperature range of 122 to 146°C. On the basis of the regime theory, a transition between regime II and III is found at ΔT ≈ 37–43,5 K. The nucleation constant for β-phase poly(propylene)based on the current theory of crystal growth was determined, and the fold surface free energy of β-phase poly(propylene) was estimated from the nucleation constant for different samples to lie between 48,2 and 55,2 erg/cm2 (1 erg = 10?7 J).  相似文献   

5.
Poly[γ-(β-N-carbazolylethyl)-L -glutamate] (PCLG) was prepared by polymerizing the monomer which was synthesized by adapting the NCA method to a reaction product between L -glutamic acid and N-(β-hydroxyethyl)carbazole. PCLG films were prepared on a quartz Nesa (In2O3) plate by casting technique. The charge-transfer complex could be successfully formed only near the surface of the PCLG film by immersing the PCLG film into either a benzene or a methyl ethyl ketone solution of 2,4,7-trinitrofluorenone (TNF), since both benzene and methyl ethyl ketone were poor solvents for PCLG and suitable solvents for TNF. A photocell was formed by depositing a translucent gold electrode with vaccum evaporation onto the immersed film. For a small content of TNF in both the immersed films and the homogeneously mixed films of PCLG with TNF, the photocurrent of PCLG was successfully sensitized by TNF, but the sensitized photocurrents retained the relation I>I in a similar way as the photocurrent of PCLG alone, where I was the photocurrent under illumination onto the positive Au electrode and vice versa. On the other hand, as the TNF content increased, I became remarkably greater than I. The PCLG polymer, therefore, can behave as a p-type photoconductor, while the well-doped PCLG-TNF complex can behave as an n-type photoconductor.  相似文献   

6.
A series of α,α-disubstituted β-propiolactams (substituted nylon 3 polymers) was prepared from non-optically active lactams. Their thermal characteristics, densities, and x-ray fiber diffraction patterns were recorded. One of the α-substituents was always a methyl group while the other was either CH3, C2H5, n-C3H7, or n-C4H9. The melting point for the dimethyl substituted polymer was 268°C; the others were respectively 76, 74, and 72°C. X-ray fiber diffraction data on all four samples yielded the same fiber repeat of ≈8,4 Å. A minimum energy based conformational analysis for the α,α-dimethyl derivative indicates that two conformations correspond to this repeat, each of which is a 21 helix.  相似文献   

7.
The synthesis of poly(γ-p-biphenylmethyl-L-glutamate), PBPLG, (poly{L-imino-1-[2-(4-biphenylylmethoxycarbonyl)ethyl]-2-oxoethylene}), ( 1d ) is described. The viscosity behavior of this polymer in benzene/dichloroacetic acid mixtures (c=0,2.10—3—1,4.10—3 g/cm3) at 25°CC is investigated. The results are compared with measurements on poly(γ-benzyl-L-glutamate), PBLG, (poly[L-imino-1-(2-benzyloxycarbonylethyl)-2-oxoethylene]), ( 1c ) under the same conditions. A transition from a rigid hydrogen bonded helix to a random solvated coil occurs in two stages for both: PBPLG (first stage 0—55%, second stage 55—100% dichloroacetic acid) and PBLG (first stage 0—70%, second stage 70—100% dichloroacetic acid). Therefore, the introduction of a p-phenyl substituent in PBLG leads to a less stable helix in benzene/dichloroacetic acid mixtures. The stability and viscosity behavior of PBLG in benzene/dichloroacetic acid mixtures (c=0,2.10—3—1,4.10—3g/cm3) is quite similar to the behavior of PBLG in m-cresol/dichloroacetic acid mixtures (c=1,0.10—3—4,0.10—3 g/cm3).  相似文献   

8.
9.
The synthesis of highly uniform (1,08 ≤ M w/M n ≤ 1,13) telechelic poly(ε-caprolactone) terminated at both ends with OH groups and its derivatization leading to poly(ε-caprolactone) with pyrene end-groups are described. The synthesis, carried out in THF at room temperature, involves initiation with (CH3CH2)2AlO(CH2CH2O)3Al(CH2CH3)2, leading to poly(ε-caprolactone) macromolecules growing at both ends. The active centers were deactivated with acetic acid, giving macromolecules with OH end-groups. Reaction of α,ω-dihydroxypoly(ε-caprolactone), HO-poly(εCL)-OH, with 4-(1-pyrenyl)butyryl chloride yields α,ω-di-1-pyrenylpoly(ε-caprolactone), Py-poly(εCL)-Py. Polymers are characterized by GPC, 1H NMR, and UV spectroscopies. The UV spectra of polymers with pyrene end-groups are compared with the UV spectra of the model compound.  相似文献   

10.
Ring-closing depolymerization of poly(ε-caprolactone) in toluene solution with catalytic amounts of Bu2Sn(OMe)2 results in a mixture of cyclic oligomers, the equilibrium concentration of which corresponds to the concentration predicted according to the Jacobson-Stockmayer theory. ε-Caprolactone, however, is absent from this reaction mixture. When poly(ε-caprolactone) is depolymerized in the melt at 260°C in the presence of a catalyst, beside ε-caprolactone its cyclic dimer and trimer are distilled off. The composition is dependent on the catalyst used, e.g., Bu2Sn(OMe)2 produces 95,4 wt.-% of ε-caprolactone and 3,7 wt.-% of its dimer while with Ti(OiPr)4 (iPr: isopropyl) 51,4 wt.-% ε-caprolactone and 49,6 wt.-% of its dimer are obtained. Block copolymers containing poly(ε-caprolactone) result in a similar product distribution, however, the second block may influence the rate of decomposition. The activation energy of the catalysed (0,5 mol-% Bu2Sn(OMe)2) and uncatalysed ring-closing depolymerization were determined to be 63 kJ/mol, and 87 kJ/mol, respectively.  相似文献   

11.
Novel segmented multiblock copolymers ( 7 ) were synthesized by linking poly(ethylene oxide) (PEO) blocks with poly(β-benzyl L -aspartate)(PBLA) blocks via urethane and urea bonds, which were formed by the reaction of 4,4′-methylenediphenyl isocyanate ( 5 ) with the terminal hydroxyl groups of α-hydro-ω-hydroxypoly(oxyethylene) ( 4 ) and the terminal amino groups of poly(β-benzyl L -aspartate)-block-iminohexamethyleneimino-block-poly(β-benzyl L -aspartate) ( 3 ) [prepared from 1,6-hexanediamine ( 1 ) and β-benzyl L -aspartate N-carboxy anhydride ( 2 )], respectively. Membranes with various water contents were obtained from these copolymers by changing the lengths of the PEO and PBLA segments. The study of the permeation of 1-phenyl-1,2-ethanediol, vitamin B12 and myoglobin through the membranes showed a high dependency of the permeability on the molecular weight of the solutes.  相似文献   

12.
Poly[γ-benzyl L -glutamate (BLG)-co-N5-(3-hydroxypropyl)-L -glutamine (HLG)] ( 3 ) and polyBLG/poly(ethylene glycol) (PBLG/PEG) block copolymers ( 6 ) were synthesized, and the adhesion behavior of rat lymphnode lymphocytes on these polymers was examined by the column method. An increase in the HLG content of polymer 3 caused a slight decrease in lymphocyte adhesivity. Lymphocyte subpopulation B cells were found to be more adhesive to polymers 3 than T cells, by a factor of 1,4 – 1,6. On the other hand, an increase in the PEG content of PBLG/PEG block copolymer caused a remarkable decrease inlymphocyte adhesivity and an increase in selectivity in the adhesivity between B cells and T cells up to a factor of 2,3.  相似文献   

13.
Novel biodegradable regular poly(ester urethane)s 2 (ηred ≤ 0,62 dL/g) were synthesized for the first time by polycondensation of di-p-toluenesulfonic acid salts of bis(phenylalanine) α,ω-alkylene diesters 1 with di-p-nitrophenyl trimethylenedicarbonate (4) under mild conditions in organic solvents in the presence of triethylamine as acid acceptor. The first synthesis of homopoly(ester urea)s 3 (ηred ≤ 0,33 dL/g) was carried out by polycondensation of 1 with di-p-nitrophenyl carbonate (5) under the same conditions. Preliminary in vitro evaluation of specific and nonspecific hydrolysis of the polymers obtained has been brought about using potentiometric titration.  相似文献   

14.
Isopropoxyethyne (1a) and tert-butoxyethyne (1b) were polymerized using group 5 and 6 transition metal catalysts to give poly(isopropoxyethyne) (2a) and poly(tert-butoxyethyne) (2b) , respectively. The weight-average molecular weight (M?w) of the resulting poly(alkoxyethyne)s was up to 1.0 × 104. Among the transition metal catalysts, a tungsten alkoxide or a molybdenum alkoxide having low Lewis acidity were found to effectively promote the polymerization without causing side reactions. Poly(tert-butoxyethyne) was successfully converted to poly(β-ketone) 3 by acid hydrolysis of the tert-butyl vinyl moiety.  相似文献   

15.
Commitment of the αβ and γδ T cell lineages within the thymus has been studied in T cell receptor (TCR)-transgenic and TCR mutant murine strains. TCRγδ-transgenic or TCRβ knockout mice, both of which are unable to generate TCRαβ-positive T cells, develop phenotypically αβ-like thymocytes in significant proportions. We provide evidence that in the absence of functional TCRβ protein, the γδTCR can promote the development of αβ-like thymocytes, which, however, do not expand significantly and do not mature into γδ T cells. These results show that commitment to the αβ lineage can be determined independently of the isotype of the TCR, and suggest that αβ versus γδ T cell lineage commitment is principally regulated by mechanisms distinct from TCR-mediated selection. To accommodate our data and those reported previously on the effect of TCRγ and δ gene rearrangements on αβ T cell development, we propose a model in which lineage commitment occurs independently of TCR gene rearrangement.  相似文献   

16.
Films of synthetic poly(β-hydroxybutyrate)s (PHB)s ranging from highly isotactic to moderately syndiotactic were cast from each of several polymer fractions isolated from ring-opening polymerizations of racemic β-butyrolactone and were subjected to degradation by the extracellular PHB depolymerases of the bacterium Pseudomonas lemoignei and the fungus Aspergillus fumigatus M2A. Films of bacterially produced PHB were also degraded for comparison. Gravimetric determinations of enzymatic degradation were measured relative to control experiments in which no depolymerase was added. Each sample was exposed to the same concentration of enzyme, as determined by the activity of the enzyme solutions towards bacterial PHB powder, and the degradation behavior varied strongly with the tacticity of the samples. Weight loss was greatest for the bacterial polymer, with films being completely degraded by either enzyme in 48 h. The degradation of the synthetic samples by both enzymes followed similar trends, although the fungal depolymerase effected less rapid degradation for all synthetic samples than did the bacterial enzyme. Of the synthetic PHB samples, those of intermediate tacticity (55–60% isotactic diads) exhibited the greatest rate of weight loss, while those most syndiotactic in nature (34–45% isotactic) degraded the most slowly. The observed rates are interpreted in terms of isotactic contents, tacticity sequence distributions, and sample crystallinities.  相似文献   

17.
Poly(β-hydroxybutyrate) (PHB) is a biotechnologically produced polyester, highly crystalline, totally biodegradable with low versatility in mechanical properties. To overcome this problem we performed a reactive blending procedure with a glassy acrylic polymer, poly(methyl methacrylate) (PMMA), via water suspension polymerisation of the acrylic monomer precursor onto poly(β-hydroxybutyrate). It was possible to isolate the co-polymeric phase formed between the two polymers and to characterize it using NMR and differential scanning calorimetry (DSC) techniques. Fracture tests on the blends gave a satisfactory response: in fact the Critical Energy Release Factor (Gc) calculated by Linear Elastic Fracture Mechanism (LEFM) theory of a PHB/PMMA 70/30 wt/wt blend is less than two times larger than that of neat PHB.  相似文献   

18.
Reactions of rabbit antisera to human β2-M against human platelets and man-mouse hybrid cells were studied by MA. tests and cytolvsis tests. Evidence is presented that the β2-M act as species-specific cell surface antigens, some of which are most likely shared bv cell surface proteins determined by genes on chromosomes other than the chromosome 15.  相似文献   

19.
Dimethyl 4-methyl-1-pentene-2,4-dicarboxylate ( 3 ) and trimethyl 4-methyl-1-octene-2,4,7-tricarboxylate ( 4 ) are not radically homopolymerizable. Dimethyl 1-hexene-2,4-dicarboxylate ( 5 ) polymerizes slowly to yield a small amount of oligomers. Homopolymerization of dimethyl 1-butene-2,4-dicarboxylate ( 6 ) affords a high-molecular-weight polymer. Radical copolymerization of these methyl α-substituted acrylates (M2) with styrene (M1) was carried out at 60°C using AIBN, and the following monomer reactivity ratios were obtained; 3 : r1 = 0,983, r2 = 0,000; 4 : r1 = 0,938, r2 = 0,000; 5 : r1 = 0,672, r2 = 0,119; 6 : r1 = 0,566, r2 = 0,195. The polymerizability of these methyl acrylate derivatives is influenced by the steric effect of the α-substituents.  相似文献   

20.
The 13C NMR spectra measured at 25 MHz of the methyl and propyl esters of isotactic and syndiotactic poly(α-bromoacrylate) were sufficiently resolved to be analysed for pentad tacticity sequences. The pentad tacticity of the syndiotactic polymers prepared with free radical initiators at ?40°C agreed with those calculated for Bernoullian sequence distributions based on Pr values of 0,83–0,87. The tacticities of the isotactic polymers prepared with heterogeneous catalysts were determined on the basis of these assignments. Good internal consistency was obtained between the calculated and observed pentad proportions from the quaternary and carbonyl carbon peaks in the spectra of these polymers. The order of chemical shifts for the meso and racemic dyads and tetrads in these polymers were opposite to those found in the equivalent methacrylate polymers, but as with the latter, the 13C-T1 values were longer in the isotactic than in the syndiotactic polymers.  相似文献   

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