摘要:

AbstractAggregation states and transient light scattering in the chiral smectic C phase of a ferroelectric liquid crystalline polymer (FLCP) were studied. The smectic phase shows an interlayer spacing of 38–39.5 Å, which is about 1.41 times the length of the side chain mesogenic group. The transient scattering mode obtained by repeated voltage polarity reversal. A reversible transparent‐opaque (light scattering) change was observed in the chiral smectic C state upon application of electric fields with low and high frequencies, respectiely. Both transparent and opaque states were maintained stably even when the electric field was turned off (bistable light swiching). A novel type of electro‐optical effect based on light scattering was obtained for the FLCP in the chiral smectic C

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980501

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractLiving cationic ring‐opening polymerization of ϵ‐caprolactone (CL), δ‐valerolactone (VL) and 1,3‐dioxepane‐2‐one (6) was achieved at room temperature by using zirconocene borate complex catalysts. Respective block copolymerization of CL with VL or with cyclic carbonate6was also successfully performed. The mechanism of the present cationic living polymerization

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980502

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTime‐resolved light scattering measurements performed in conjunction with the stopped‐flow method revealed information on the formation of polyelectrolyte complexes (PECs) of the weak polyelectrolyte (PE) couple poly(N‐ethyl‐4‐vinylpyridinium bromide) and poly(sodium methacrylate). The stability of the PECs depends, apart from other parameters, on the total ionic strength of the solution [I], the PE concentration and the concentration ratio (Φ) = [PVPE]/[PMA]. On the basis of Φ‐[I] diagrams, obtained for three PE combinations differing in average molar mass, the stability of PECs is characterized by the regimes A, B and C referring to conditions, where PECs are quite stable and water‐insoluble (A), PECs are not very stable and water‐soluble (B) and PECs are instable (not formed). The course of the curves separating regime A from regime B reflects the action of two competing effects regarding the stability of PECs, namely the increase in charge density and the increase in ion condensation with growing total ionic strength: Kinetic measurements revealed that, at low ionic strength right upon mixing, supramolecular complexes and later large aggregates are formed. The aggregates undergo rearrangements leading eventually to smaller complexes. At high ionic strength aggregates are formed rather slowly after mixing. This behavior is related to ion condensation. PECs can form only after the small ions occupying the charged sites at the PE chains are removed. Detachment of small ions from PE chains is a relatively slow process and is the rate‐determining step in PEC formation at moderately high ionic stren

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980503

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractRing‐opening polymerization of a new anhydro ribose‐type monomer, 1,4‐anhydro‐3‐azido‐3‐deoxy‐2‐O‐tert‐butyldimethylsilyl‐α‐D‐ribopyranose (A3ASR), was investigated. The monomer was synthesized from 1,4‐anhyro‐α‐D‐xylopyranose by three steps comprising Walden inversion at the C3 position into ribose configuration. Ring‐opening polymerization of A3ASR by Lewis acid catalysts such as boron trifluoride etherate and stannic chloride gave a stereoregular 3‐azido‐3‐deoxy‐2‐O‐tert‐butyldimethylsilyl‐(1→5)‐α‐D‐ribofuranan having specific rotations of +246 ∼ +271 deg · dm−1· g−1· cm3and number‐average molecular weights of 18,7 × 103∼ 25,1 × 103. When the polymerization was carried out by antimony pentachloride at 0°C, the resulting polymer exhibited a negative specific rotation of −6 deg · dm−1· g−1· cm3and the C1 absorption in the13C NMR spectrum shifted downfield to 107,5 ppm, suggesting that the polymer might consist of 1,5‐β furanosidic unit. The reduction of the azido group of the 1,5‐α and 1,5‐β furanosidic polymers into amino group and subsequent desilylation gave 3‐amino‐3‐deoxy‐(1→5)‐α‐ and ‐β‐D‐ribofuranans, respectively. In addition, copolymerization of A3ASR with 1,4‐anhydro‐2,3‐di‐O‐tert‐butyldimethylsilyl‐α‐D‐ribopyranose (ADSR) in various feeds was performed by boron trifluoride etherate as catalyst to give copolymers with different monomeric components. The structu

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980504

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractEthylene polymerizations and norbornene oligomerizations catalysed by Cp2Ti13CH3Cl/MAO (Cp: cyclopentadienyl; MAO: methylaluminoxane) mixtures have been carried out at different temperatures (from ‐20°C to 20°C), in order to test the validity of carbene mechanisms in α‐olefin polymerizations. Depending on the temperature, different ratios of the cationic species [Cp2Ti13CH3]+[Cl · MAO]−and precursors of the alkylidene Cp2Ti =13CH2exist. Thein situpolymerization of13C enriched ethylene was monitored by13C NMR spectroscopy. Moreover, catalytic activity was determined and polyethylene samples were analyzed by13C NMR and gel permeation chromatography (GPC). The following evidence has been provided against the carbene mechanism in the α‐olefin polymerization with titanocene based catalysts: (a) in thein situethylene polymerization experiments the appearance of polyethylene signals is concurrent with the decrease of cationic [Cp2Ti13CH3]+[Cl · MAO]−signals and is not related to the intensity of the alkylidene Cp2Ti =13CH2signals; (b) from the13C NMR analysis of polyethylene chain‐end groups the13C enrichment of Cp2Ti13CH3Cl has only been found in the methyl chain‐end group and not in the methylene of the propyl chain‐end group, as should have been the case if the carbene mechanism had been valid; (c) from norbornene oligomerization (at 0°C) the addition product 2‐13C enriched methyl‐norbornane has been identified. Moreover, the identification of a13C enriched methylidene‐norbornane dimer at higher temperatures has revealed the possibility of norbornene addition to titanium carbenes through the formation of titanacyclobutane without the opening of the norbornene ring. However, this process requires higher energies with respect

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980505

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractNovel regioselective substituted cellulose derivatives, suitable for investigations of their liquid crystalline phase behaviour, were synthesized. The derivatives, tricarbanilates with varying substituents at the phenolic residue, were characterized according to their molecular weight and molecular weight distribution by means of size exclusion chromatography coupled with low angle laser light scattering (SEC/LALLS). A simple new method is presented, which allows the calculation of the constantsKandaof the Staudinger‐Mark‐Houwink (SMH) equation, the viscosity‐average molecular weightMηas well as the intrinsic viscosity [η] from the light scattering calibration curve of an SEC experiment. The calculated values of the intrinsic viscosity are in good agreement with those derived from measurements with a low‐shear viscometer. A plot [η]vs. weight‐average molecular weightMwshows, that a substitution at the C‐2 and C‐3 position of the glucosic unit with 3‐chlorocarbanilate leads to a well pronounced enlargement of the polymer dimensions which is mirrored by larger values of [η] at the sameMwas compared with other ce

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980506

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis paper deals with the synthesis of polyamides based on the natural diamine,L‐lysine, on the one hand, and diacids, adipic or glutaric, on the other hand. They were obtained by polycondensation of active diesters, pentachlorophenyl and pentafluorophenyl esters.L‐Lysine being non‐symmetrical, aregic (random) and syndioregic (“head‐to‐head, tail‐to‐tail”) poly(adipoyl‐L‐lysine)s and poly(glutaroyl‐L‐lysine)s were obtained with molecular weights higher than 15000; isoregic (“head‐to‐tail”) poly(adipoyl‐L‐lysine)s and poly(glutaroyl‐L‐lysine)s w

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980507

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe ring opening metathesis polymerisation (ROMP) of (±)‐ and (−)‐exo, endo‐bis[(4′‐cyanobiphenyl‐4‐yl)oxyalkyl]norborn‐5‐ene‐2,3‐dicarboxylates using three different Schrock type molybdenum alkylidene complexes ([Mo(NAr)(CH‐t‐Bu)(OR)2] with RC(CH3)3, C(CH32)(CF3) or C(CH3)(CF3)2) resulted in the formation of side chain liquid crystalline polymers (SCLCP's). The different initiators caused changes in the backbone tacticity which were determined by means of NMR techniques. The influence of the type of tacticity on the thermotropic behaviour of the SCLCP's was investigated. The thermal properties were determined by differential scanning calorimetry (DSC). The transition temperatures increased with rising molecular weight up to a degree of polymerisation of about 40. Above this value the thermal properties remained constant with increasing molecular weight. The types of phases for the liquid crystalline polymers were elucidated by polarising optical microscopy (POM). In general, the highly tactic polymers showed a broader thermal range of the LC phase. The kind of initiator used caused changes of the thermal and thermotropic behaviour of the SCLCP's. A grafting ratio model is introduced to explain the findings. From the experimental data a structure/property relationship is developed which might help to predict liquid crystall

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980508

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe effect of Cu2+on the stability of the triple‐stranded helical structure of poly[(riboadenylic acid): 2 poly(riboinosinic acid)] poly(A : 21) was studied by means of circular dichroism spectroscopy and ultraviolet spectroscopy. The experimental results show that Cu2+induces the hyperchromicity of poly(A : 2I) and causes the melting temperatureTmof poly(A : 2I) to decrease with increasing Cu2+concentration. At the ratio of the concentration of Cu2+to that of phosphate in poly(A : 2I),rt= 0, poly(A : 2I) is stable, is stable, atrt= 0.27, poly(A : 2I) decays in poly(A) and 2 poly(I), and atrt= 1.6, there is a racemat

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980509

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this communication, we report the synthesis and ring‐opening metathesis polymerisation (ROMP) of a 5‐substituted cyclooctene‐derivative, (±)‐cis‐[11‐(4′‐cyanobiphenyl‐4‐yloxy)undecyl]cyclooct‐4‐enecarboxylate. A highly active molybdenum‐carbene was used as initiator. The prepared polymer is liquid crystalline and shows a nematic

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980510

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY