摘要:

AbstractThe interactions in binary liquid mixtures were studied. The Flory‐Huggins interaction parameters are calculated. When the effects of concentration fluctuation and free volume on the interaction parameter are taken into account, the interaction parameters are found to be much smaller than the corresponding critical parameter

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractSymmetrically and unsymmetrically substituted diorganodichlorosilanes have been prepared by hydrosilylation with dichlorosilane using two different platinum catalysts, i.e., hexachloroplatinic acid (“Speier's catalyst”) and a platinum cyclovinylmethylsiloxane complex. Hydrosilylation of unsubstituted 1‐alkenes proved to be very efficient, yielding anti‐Markonikov substituted di‐n‐alkyldichlorosilanes. However, no reaction was observed when electron‐deficient 1‐alkenes were used. Octacarbonyldicobalt enabled formation of the monoadduct of 1H,1H,2H‐perfluoro‐1‐hexene with dichlorosilane, which was employed in a second hydrosilylation of the olefin. Thus, the anti‐Markovnikov diadduct was obtained in 40% overall yield. The two‐step synthesis has also been applied successfully to obtain unsymmetrically substituted diorganodichlorosilanes containing

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA homologous series of hexa‐n‐alkylcyclotrisiloxanes and poly(di‐n‐alkylsiloxane)s has been prepared with alkyl side groups varying in length between 4 and 10 carbon atoms. Melting transition enthalpies of the hexa‐n‐alkylcyclotrisiloxanes indicated a reversed odd‐even effect, showing higher melting enthalpies for cyclotrisiloxanes with n‐alkyl side groups with an odd number of carbon atoms. The melting behaviour of the heptyl‐ and octyl‐substituted cyclotrisiloxanes was rather complex. Multiple melting transitions could be observed, which are presumably due to formation of a kinetically favoured crystalline phase next to the thermodynamically stable crystal modification. All hexa‐n‐alkylcyclotrisiloxanes could be polymerized by anionic or cationic ringopening polymerization. The observation of longer polymerization times and formation of relatively larger amounts of cyclic byproducts in the case of hexadecylcyclotrisiloxane compared to hexaethylcyclotrisiloxane indicated that with increasing side group length, the anionic polymerization propagation rate constantskpdecreased, whereas the rate constants of depolymerizationkdxincreased. Cationic polymerization with trifluoromethanesulfonic acid as the initiator, offered a way to enhancekprelative tokdx, which allowed the preparation of high molecular‐weight polymeric products in good yields even in case of cyclotrisiloxanes substituted with long n‐alkyl groups. Apart from poly(dimethylsiloxane), poly(diheptylsiloxane) and poly(dinonylsiloxane), all poly(di‐n‐alkylsiloxane)s showed two crystalline phases which were separated by a crystal‐crystal transition signifying melting of the side groups. Starting from poly(diethylsiloxane), poly(di‐n‐alkylsiloxane)s up to poly(dihexylsiloxane) displayed a hexagonal columnar mesophase as well, the stability of which increased with longer alkyl side groups. However, further elongation of the n‐alkyl side groups to decyl appeared to destabilize the columnar mesophase. Poly(didecylsiloxane) only exhibited a metastable columnar mesophase in combination with

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960113

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis and the thermal behaviour of different polysiloxanes containingcis,cis‐(3,5‐dihydroxycyclohexyl) 3,4‐bis(alkoxy)benzoate mesogens (“two‐chain” diol unit) in the side chain are described. Aggregation via intermolecular hydrogen bonding between different “two‐chain” diol units leads to the formation of mesomorphic supramolecular structures. The phase behaviour changes drastically by variation of the dimethylsiloxane content of the backbone. Thus, the homopolysiloxane is the first example of a polymer with a thermotropic cubic mesophase, being observed below a hexagonal columnar one. However, the copolymers exclusively form the hexagonal columnar mesophase. The thermal transitions of all polymers, investigated by means of differential scanning calorimetry (DSC) as well as by polarizing microscopy, are discussed. The mesophase structures have been determined by X‐ray measurements in combination with

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960114

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPoly(cycloalkyl[c]thiophene)s were synthesized by electrochemical or chemical oxidation of bicyclic, α,α′‐unsubstituted thiophenes. NMR measurements on neutral, soluble poly(cyclododeca[c]thiophene) indicate that the polymers have the expected linear structure. The optical spectra and the electrochemical properties of the films are reported. The electrical conductivity σ of salts of the polymers varies from 50 S/cm to 8 · 10−5S/cm depending on the ring size of the substituent and degree of oxidation of the polymer backbone. A linear correlation between log σ and the diameter of the alkyl substituent demonstrates that interchain contacts play a dominant role in the conductivity of these polymers. The temperature dependence of the conductivity was measured in the range of 300 to 5 K and its frequency dependence in the range of 1–107Hz at 300 to 120 K. The conductivity data were analyzed in terms of hopping of localized charge carriers and the localization length of the charge carriers wa

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960115

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of novel diazo dye containing nonlinear optical (NLO) polymers and model compounds are prepared and the influence of the chromophore length on polymer‐specific behavior such as solubility, glass transition temperature and decomposition temperature is describe

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960116

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA structural study was carried out on poly(α‐butyl β‐L‐aspartate), which is a stereoregular nylon‐3 derivative with an alkoxycarbonyl group attached to the β‐carbon of the main‐chain repeating unit. Two crystal forms, namely hexagonal and tetragonal, made of 13/4 and 4/1 helices, respectively, and bearing a structural resemblance to the polypeptide α‐helix, were characterized by X‐ray diffraction. Though these forms are basically identical to those previously reported for poly(α‐isobutyl β‐L‐aspartate), the crystal transition from hexagonal to tetragonal known to take place in this polymer by effect of heating, was not observed in the present case. Modeling calculations revealed that although similar conformations are favoured for the two polymers in both crystal forms, the relative stability of the 13/4 helix to the 4/1 helix was found to be significantly reduced in the case of the butyl derivative. The presence of helical conformation in solution has been evidenced by both1H NMR and circular dichroism and the helix‐coil transition promoted by acids was investigated

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960117

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAn epoxy‐terminated organosilicon polymer (denoted as ETOP) was used as modifier to blend with bisphenol A type epoxy resins. For uncured epoxy resins/ETOP blends, the miscibility is mainly the contribution of entropy. The phase boundary was investigated. The turbidity points were determined on the basis of optical microscopic observation. While the aromatic amine curing agents were added to the systems, curing at higher temperature, an obvious phase separation between cured bisphenol A type epoxy resins (DGEBA) and ETOP was observed. The structure of the resulting cured products was investigated by differential scanning calorimetry (DSC), dynamic mechanical property analysis (DMA) and scanning electron microscopy (SEM). It is the very elastomeric phase (0,1–5 μm) that enhances the toughness of epoxy resins. Another significant phenomenon is that the crosslinked epoxy‐rich phase (matrix) possesses a higher glass transition temperature (Tg) than pure epoxy resins cured with an aromatic amine, particularly at a higher content of ETOP. This may be considered as participation of epoxide groups on ETOP molecules in the crosslinking reaction of matrix and enhancing the crosslinking density of the matrix (i.e., increasing theTgs). The results provide ones a larger choice to improve the toughness of the epoxy resin without loss of substantial modulus and thermal resi

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960118

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

Abstract2‐(Dimethylamino)ethyl methacrylate (DMAEM) —N‐vinyl‐2‐pyrrolidone (VP) copolymers were synthesized and characterized. The copolymerization parameters were determined:rVP= 0,61,rDMAEM= 11,41. The tacticity of DMAEM sequences and the distribution of monomer units were estimated. Then, the experimental conditions for the quaternization of the copolymers with alkyl bromides were defined. The modified copolymers were characterized and the mechanism of the quaternization reaction was studied via pote

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960119

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractN‐Vinyl‐2‐pyrrolidone — 2‐(dimethylamino)ethyl methacrylate copolymers were quaternized with octyl bromide in tetramethylene sulfone. The quaternization kinetics was studied, varying the concentrations of reagents and the composition of copolymers. The initial rate constant is not disturbed by the concentration of reagents, but it is by the initial copolymer composition: the higher the initial octyl bromide concentration, the higher the maximal conversion rate. These kinetic results were interpreted, observing the influence of the steric effect, the electrostatic effect and the effect of solvation. The kinetic models proposed in the literature were applied to our data and discussed. None of them describes perfectly the behaviour of o

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960120

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY