摘要:

AbstractA survey is given on the effects of large amplitude oscillatory shear (LAOS) flow on the orientation behavior of lamellar polystyrene‐block‐polyisoprene (PS‐b‐PI) diblock copolymers with emphasis on the identification of key parameters that govern the observed behavior. For LAOS at temperatures close to the order‐disorder transition temperature,TODT, three orientation regimes related to the dynamic shear viscosity of the polymers are observed: parallel orientation at high frequencies, perpendicular orientation at intermediate frequencies, and parallel orientation again at very low shear frequencies. In annealing experiments it is found that the low frequency orientation behavior depends strongly on the thermal history of the samples. In conceptually new “dual frequency” experiments the effect of the superposition of two deformation components with frequencies in two different orientation regimes is described. From further studies identifying strain as the control parameter in these nonequilibrium experiments an orientation diagram for the long time orientation behavior of lamellar PS‐b‐PI diblock copolymers is constructed as a function of strain and frequency. For intermediate time scales in the experiments it is shown that the third orthogonal orientation component, the transverse orientation, can be obtained as a transient state. For all orientation components possible orientation mechani

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981101

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractVinylferrocene was polymerized by means of anionic initiators such asn‐BuLi,s‐BuLi and distyryl disodium in tetrahydrofuran as solvent. In all cases the polymerization shows the characteristics of a living polymerization. Depending on the sequence of the monomer addition, either block copolymers of the ABA or the AB type were synthesi

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981102

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCarboxy‐terminated oligostyrenes, prepared by radical polymerization using a dicarboxy‐functional initiator, can efficiently be separated by gradient high performance liquid chromatography (HPLC). On a normal phase chromatographic system, comprising a silica gel stationary phase and a tetrahydrofuran‐hexane eluent, elution occurs in the order of increasing polarity of the oligomers and separation into non‐, mono‐, and dicarboxy oligomer fractions is obtained. The chemical structure of the different functionality fractions is determined by matrix assisted laser desorption/ionization mass spectrometry (MALDI‐MS). The results indicate that further functionality fractions in addition to the carboxy oligomers are formed, due to contamination of the initiator or side reactions during the polymerizat

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981103

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA new orientation material for liquid crystals (LCs) based on modified ladder‐like polysiloxanes (LPSs) is investigated. The curing temperature (150–200°C) of these grafted LPSs is much lower than that of the traditionally used polyimides (PIs) (250–300°C). The pre‐tilt angles of a nematic liquid crystal (LC), 4‐pentyl‐4′‐cyanobiphenyl (5CB), are between 2–8°, depending on the rubbing conditions and the side chains. Annealing experiments at 100°C and 180°C demonstrated that the stability of these orientati

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981104

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe thermally‐reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) andD,L‐lactide (L), E42L12, E38L16, E39L20, E41L26, E78L14and E77L26, has been studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy. The solutions showed a high temperature gel‐sol boundary but no low temperature gel‐sol boundary. Polarised light microscopy showed that the gel phase was isotropic, and the dependence of sol‐gel temperature on concentration suggested that the micelles were prolate ellipsoidal, rather then spherical. NMR spectroscopy showed that below ca. 60°C, the L block in the micelle core become highly restricted. It is tentatively suggested that this is due to the L blocks forming an ordered structure, thus explaining the absence of a low temperature gel‐

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981105

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractAt least three kinds of stable paramagnetic species are formed in films of poly(triphenylcarbinol)1upon thermolysis in vacuo up to 500°C. “Low temperature” radicals of triarylmethyl type (RTAMT1) are created in the 120 ÷ 220°C temperature region. These radicals give rise to a symmetric ESR signal (g= 2.0026 ± 0.0003; ΔH≈ 1.0 mT) with poorly resolved hyperfine structure and to an absorption band (AB) of allowed transition with λmax= 407 nm in UV spectra. The spectral region of forbidden transitions, assumed for the RTAMT1, is masked by a nonradical AB, in particular by that of quinoid structure of Chichibabin hydrocarbon type with λmax= 595 nm. From 220°C to 280°C the “high temperature” radicals RTAMT2 appear, with a strong bathochromic shifted AB of forbidden transition (λmax= 710 nm). Maximum concentration of RTAMT2 (≈︁1020spin/g) is achieved at ≈︁280°C. Possible structures of both kinds of RTAMT are discussed. AtT≥ 300°C paramagnetic species that d

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981106

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractMultilayers of isopentylcellulose (systematic name: tri‐O‐isopentyl cellulose, IPC) were investigated by means of electron diffraction. Only the persubstituted cellulose ether showed some order in a multilayer as deposited. IPCs of lower degree of substitution (DS) form ordered layers when annealed at temperatures ≤150°C. IPC molecules adopt helix conformation; the lattices show in this temperature range 3‐fold screw axes. From analogy with known structures of cellulose derivatives we suggest left‐handed 32‐helices. At a temperature of about 210°C IPC multilayers undergo a transition into the liquid‐crystalline state and the feature of a stack of individual layers disappears. This was investigated for an IPC of DS = 3. By subsequent cooling a phase transition into a highly crystalline state takes place. From the huge increase of the crystalline density from initially 1.02 g/cm3in the multilayer system to 1.40 g/cm3in the bulk crystal at ambient temperature after having passed the liquid‐crystalline state we infer that the transition of the layered system into the liquid‐crystalline state is accompanied by selection of adjacent chains according to their polarity. Simultaneously the chain conformation is changed into a 4‐fold screw with 2 symmetry related chemical repeats forming the asymmetrical unit. Such a chain conformation is not known for other cellulose derivatives, only trimethylamylose adopts a similar conformation with

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981107

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe thermal degradation behaviour of two copolymers poly(acrylonitrile‐co‐methyl α‐acetoxyacrylate) and poly(methacrylonitrile‐co‐methyl α‐acetoxyacrylate) was studied by means of dynamic and isothermal thermogravimetry in the range 246–302°C and gas chromatography/mass spectrometry analysis. The main volatil products are acetic acid and methyl acetate and methanol in minor amounts. There is no monomer from the first copolymer. The global reaction order is zero over a wide range of conversion (α = 0,1 – 0,6), then it is one for α>0,7, with activation energies of 160,5 and 142,9 kJ ˙ mol−1, respectively. Some amount of comonomers was found in addition in the case of the second copolymer. The kinetic law may be written as:\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{{\rm d}a}}{{{\rm d}t}} = k(C + \alpha )(A - \alpha ) $$\end{document}whereAandCare constants for every temperature. The global activation energy was found to be 127,0 kJ ˙ mol−1. A kinetic model of a one order reaction with a partial auto catalytic character allows a very good fit of the experimental data with the theoretical curves over a wide range o

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981108

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe kinetics of the anionic ring‐opening polymerization of several cyclodisilazanes substituted with different groups on silicon atoms has been investigated in toluene/tetrahydrofuran (THF) using benzyllithium as initiator. Two different behaviours were observed: for hindered substituents (phenyl or allyl), the polymerization is not living; for less hindered groups, the polymerization is living but the rate constants differ markedly from one cyclodisilazane to another. They vary from 9 × 10−4L · mol−1· s−1for DNMeEtDNMe3to 0,1 L · mol−1· s−1for D NMe2ViDNMe(8). These variations show that the presence of vinyl groups on the monomers tremendously increases the rate of polymerization. In order to discriminate the monomer reactivity from the active center reactivity, a model reaction between lithium silylamides and triethylchlorosilane has been kinetically studied (each lithium silylamide was chosen to modelize one particular active center). Contrary to the corresponding monomers, the less hindered is the silylamide, the faster is the reaction. Thus, the difference of reactivity between the monomers and the reactive center models is so high that the polymerization of cyclodisilazanes can be considered as principally controlled by the reactivi

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981109

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPropagation rate coefficients (kp) for the homopolymerizations of butyl methacrylate (BMA) and dodecyl methacrylate (DMA) were determined by the pulsed laser polymerization (PLP)/size‐exclusion chromatography (SEC) technique. At amibient pressure, the polymerizations of BMA and DMA were studied between −20 and 50°C and between 9 and 60 °C, respectively. For DMA the pressure dependence of propagation rate has been measured up to 1500 bar. The propagation rate coefficients of three major methacrylates (MMA, BMA, DMA) are available over an extended pressure and temperature range. Thekpdata at identical pressurepand temperatureTare close to each other and exhibit a very pronounced family‐type behaviour with respect to both pressure and temperature dependence. The uncertainty of experimental data is estimated to be ± 10 per cent. The imperfect knowledge of the Mark‐Houwink coefficients may give rise to an increased error for the BMA and DMA data which should, however, stay below ±

ISSN:1022-1352    

DOI:10.1002/macp.1997.021981110

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY