摘要:

AbstractThe effects of high oscillatory shear on the viscosity of a model polymer dispersion of solid particles was investigated. A dispersion of glass beads in poly(dimethyl siloxane) (PDMS) is uniform and free of any agglomeration. When sheared at low stress levels, the dispersion remains uniform. At high stresses under oscillatory shear, two processes can take place. One is spatial ordering (threading) of the spherical beads that does not occur in steady shear. The other is molecular interfacial slip due to high interfacial stress in samples containing fluoro‐silane treated glass beads, leading to a lower suspension viscosity than that of samples containing bare non‐treated be

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370301

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe transformation of PTFE from phase II to phase IV at 19°C and atmospheric pressure has been investigated using wide angle X‐ray diffraction. Diffraction patterns were taken as a function of temperature. The integrated intensity of an equatorial peak present only in phase II was used to monitor the extent of the transformation. Peaks on the second and fifth layer lines were used to determine the effect of transformation and/or disorder. Integrated intensities on these three layer lines were shown to decrease differently with increasing temperature. The decrease in intensity on the second and fifth layer lines could be described in terms of a model comprising the initial integrated intensity, fraction transformed and the amount of rotational disorder present. Molecular modeling also was used to investigate the transformation. A commercially available force field was modified to represent the equilibrium solid state of PTFE. The modified force field was used to examine aspects of the transformation including the influence of neighboring molecules on the molecular conformati

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370302

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolymerization of butadiene and isoprene in hydrocarbon solvents initiated by unsolvated organosodium compounds was studied. It was found that the polymer molecular weight and the MWD are determined mainly by chain transfer to solvent and polymer, and no chain transfer to monomer was observed even in the case of isoprene. The overall polymerization rate is proportional to the concentrations of the monomer and the initiator. Apparent chain propagation rate constants were found to be 0.11 litre mol−1s−1for butadiene and 0.065 litre mol−1s−1for isoprene polymerization in heptane at 30°C. It is suggested that associated (dimeric) forms of polydienylsodium active centres play an important role in chain propagation, being responsible for a stronger chain transfer and a greater 1,2‐butadiene, or 3,4‐isoprene, unit content than in polymerization with other a

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370303

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractDehalogenative polycondensation of 3,6‐dibromo‐N‐alkylcarbazoles was catalysed by a Ni(O)‐based complex generated inN,N‐dimethylacetamide by electroreduction of NiBr2/2,2′‐bipyridine. The process involves three different reaction steps, which are successively: electrolysis of Ni(II) to Ni(O); insertion of the latter into a CBr bond of monomer leading to CNiBr* active species; dehalogenative coupling between active species and monomer yielding oligomers. From the kinetics of electrogeneration of the catalytic system in absence of monomer, a first‐order reaction was determined. Insertion and coupling reactions were found to be second‐order and comparison of the values of the corresponding rate constants clearly showed that coupling is the rate‐determining step of the process. Simultaneous size exclusion chromatography and cyclic voltammetry measurements were carried out in the course of the electrosynthesis of poly(N‐alkylcarbazole)s. The change in the molar mass population distribution as a function of electrolysis time revealed a step polymerization process, while showing a termination of the chain growth due to the occurrence of monobrominated species. The study of the effect of the [monomer]/[catalyst]ratio on the molar mass population change indicated that the coupling of active species (Ni(O)‐activated monomer) is res

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370304

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractCyclic oligomeric carbonates are prepared by a hydrolysis/condensation reaction from aromatic bis(chloroformate)s. Three methods for convenient preparation of bis(chloroformate)s have been developed: (1) use of diethylaniline to scavenge HCl, in a modification of an earlier procedure; (2) low pH, low temperature interfacial condensation of bisphenols with phosgene; and (3) use of Ca(OH)2in interfacial condensation with phosgene. Reaction parameters which control formation of monomeric bis(chloroformate)s versus higher oligomerization include temperature, pH, and rate of phosgene addition. For water‐soluble bisphenols such as hydroquinone, the phase ratio of water to CH2Cl2can also be importan

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370305

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe anionic polymerization of β‐lactones mediated by supramolecular complexes of alkali metal alkoxides and naphthalenides is demonstrated. The novel chemistry of the initiation and the propagation steps of polymerization is discuss

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370306

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of chemical composition of copolymers of acrylonitrile (AN) and methylacrylate (MA) on the hydration and thermal transition behaviour was investigated. An increase of the MA content considerably depressed bothTmandTcof the hydrated polymers. A double melting and crystallization transition behaviour was observed when the hydrated polymer was reheated after cooling from the molten state. The separation between primary and secondary peaks was more notable in the second heating scan than in the first heating scan. A novel solid‐state transition was observed in the dried acrylic polymers which had experienced hydration and melting in the wet state, followed by drying in the open state at 200

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370307

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA new method to prepare functionalized polyethylene involving borane intermediates and transition metal catalysts is described. Two processes, direct and post polymerizations, were employed to prepare borane‐containing polyethylene (PE‐B), which can be transformed to functionalized polyethylene (LLDPE‐f) with various functional groups, such as BR2, OH, NH2, OSi(CH3)3. In the direct process, the PE‐B copolymers were prepared in one step by copolymerization of ethylene with a borane monomer (ω‐borane‐α‐olefin). The post polymerization process requires two steps: copolymerization of ethylene and 1,4‐hexadiene, and subsequential hydroboration reaction of unsaturated PE. Three transition metal catalysts, including two homogeneous metallocene (Cp2ZrCl2[bis(cyclopentadienyl) zirconium dichloride] and Et(Ind)2ZrCl2[1,1′‐ethylenedi‐η5‐indenyl‐zirconium dichloride] with MAO (methylaluminoxane)) and one heterogeneous (TiCl3·AA/Et2AlCl) ones, were studied in the copolymerization reactions. The single site Et(Ind)2ZrCl2/MAO homogeneous catalyst, with a strained ligand geometry and opened active site, is by far the most effective system in the incorporation of high

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370308

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAn organo‐soluble aromatic polyimide has been synthesized from 3,3′, 4,4′‐bis(phenyltetracarboxylic) dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl)‐4,4′‐diaminobiphenyl (PFMB) via a one‐step polymerization inm‐cresol. The phase boundary diagram for this system has been established by differential scanning calorimetry, polarized light microscopy (PLM) and wide angle X‐ray diffraction (WAXD) experiments. A crystallosolvate form I has been found over the entire concentration region at low temperatures. When the temperature is increased, an isotropic phase has been observed below concentrations of about 40%. In the relatively high concentration region between 45 and 95%, a transition from the crystallosolvate from I to a crystallosolvate form II has been observed. Form II exhibits a different WAXD pattern. In a narrow concentration region between the isotropic and the crystallosolvate form II (40–45%), a biphase behavior has been found. The birefringence of this region may be an indication of a liquid crystalline phase. The BPDA–PFMB polymer crystal has been found in the very high concentration region (>95%) for temperatures>250°C. The morphologies of these phases have been investigated via PLM and transmission electron microscopy. Above the gel/sol transition temperature, the form I shows negative birefringent spherulites consisting of thin lamellae. The form II exhibits a tendency of positive birefringent spherulites. Possible mechanisms of the formation of the metastable phase morphology and their associations with the mechanical gel/sol t

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370309

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe monomers 1,13‐tetradecadiyne, 1,11‐dodecadiyne, 1,9‐decadiyne and 1,7‐octadiyne were cyclotrimerized, using niobium pentachloride as the catalyst, in the presence of 1,5‐hexadiyne, which co‐cyclotrimerizes to give a benzocyclobutene (BCB) capping group. Molecular weights of the BCB‐capped oligomers were in the 3100–8000 range, with fairly narrow polydispersities. The oligomers were characterized by1H NMR and IR spectoscopy, along with GPC and DSC studies. DSC studies on the end‐capped oligomers show that each exhibits an exotherm around 260°C, indicative of the formation of carbon–carbon bonds in a crosslinking reaction. The final, crosslinked materials may be regarded as thermosetting thermoplastics, since they are hard at room temperatu

ISSN:0959-8103    

DOI:10.1002/pi.1995.210370310

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY