摘要:

AbstractPolymers of norbornenes with SiMe3and Si(Me2)CH2SiMe3groups were synthesized and mass transfer properties of the polymers were studied. Ring‐opening polymerizations of these monomers were realized in the presence of homogeneous WCl6‐based and heterogeneous Re2O7‐based metathesis catalysts. Introduction of silicon‐containing groups in the polynorbornene main chain results in a drastic increase of the permeability (P) and diffusion (D) coefficients for different biatomic and multiatomic gases. Comparison of polymers having SiMe3and Si(Me2)CH2SiMe3substituents shows lower permeability and diffusion coefficients in the latter case. The combination of transport properties (Pivalues) and separation factorsaij=Pi/Pjof the two new silicon‐containing polynorbornenes permits one to consider them as representatives of the most permeable and sufficiently permselective group of polymers. Transport properties of the polymers studied were analysed on the basis of the free volume

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920101

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPyrolysis gas chromatographic studies were carried out on two polyphosphate esters of bisphenolASystematic name: 2,2′‐isopropylidendiphenol.. The gaseous pyrolysis products were found to be mainly phenols and a few phosphate compounds. The identification of phosphorus compounds in the gas phase proves a gas phase mechanism of flame retardant action for polyphosphates. The presence of phosphoric acid in the char residue supports the existence of the conventional condensed‐phase mechanism. Thus, the study demonstrates that both condensed‐phase and gas‐phase mechanisms are operative in the flame‐retardant action of pol

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920102

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to improve our comprehension of the crystalline structure of polyamides, two regular odd terpolyamides containing 3‐aminopropanoyl, 5‐aminopentanoyl and 7‐aminoheptanoyl units were prepared by the active ester polycondensation method. The choice of the sequencing order in the starting compounds (called here heterotrimers) and the various routes leading to them are discussed. It was found that both the reactions and the purification of intermediates were most conveniently performed by combining the heterodimer of the lower amino acids with the higher amino acid. The polycondensation was carried out through a multiple step process either in solution or in the solid‐state at a temperature below 200°C.13C NMR spectra showed that no rearrangement during the polycondensation occurs under these conditions. The terpolyamides have sufficiently high molecular weights to provide good films for crystallographic studies. The two terpolyamides of inversed order do not cocrystallize even when coprecipitated from a solution, probably because of their different crystalline st

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920103

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractOligomerization of trichloroacetaldehyde (chloral) was carried out with the lithium salt of (1S, 2R, 4S)‐(–)‐borneol as the initiator. The unimer and dimer fractions consisted of two and four diastereomers, respectively; the individual isomers were isolated from the fractions by crystallization from methanol or by high performance liquid chromatography. The X‐ray single‐crystal analysis showed that the major isomer in the unimer fraction is the (R)‐form which has the acetal carbon in (R)‐configuration. The diastereomeric ratios were determined by1H NMR asR/S= 57/43 for the unimers andRS/SR/RR/SS= 34/25/23/18 for the dimers. The conformations of the meso‐dimers [(R,R)‐ and (S,S)‐isomers] in the crystalline form corresponded to a half turn of the 41‐helix of isotactic polychloral, whereas the conformations of the racemo‐dimers (the (R,S)‐ and (S,R)‐isomers) were different from the helical structure in the crystal and in solution. The trimer fraction consisted of six of the eight possible diastereomers; among these isomers, themmisomers (the (R,R,R)‐ and (S,S,S)‐isomers) were highly predominant. The amount of the (R,R,R)‐trimer formed was only slightly larger than that of the (S,S,S)‐isomer.(a)Part 42, cf. G. D. Jaycox, O

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920104

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe stereochemistry of polypropenes obtained in the presence of several MgCl2‐supported Ziegler‐Natta catalyst systems comprising different Lewis bases has been investigated by13C NMR spectroscopy, with special attention paid to the “less tactic” (heptane‐soluble) fractions. These have been found to consist of “tendentially isotactic” and “tendentially syndiotactic” stereosequences, in largely variable amounts (depending on the catalyst system). The microstructure of the former is in accordance with the enantiomorphic site model, whereas that of the latter suggests a stereocontrol arising from the asymmetry of the growing chain end. In both cases, propene insertion is primary (1–2). Polymerization conditions leading to the formation of “syndiotacticrich” polymers showing syndiotactic crystallini

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920105

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe photoinitiated bulk polymerization of macroscopically oriented 1,4‐phenylene bis{4‐(ω‐acryloyloxyalkyloxy)benzoate} produces densely crosslinked oriented polymer networks. The influence of the length of the alkylene spacer between the aromatic central core and the polymerizable acrylate end‐groups on the mesomorphic behaviour of the monomer, the molecular orientation in the monomeric and polymeric state and the process of photoinitiated polymerization in the ordered state is studied. Some optical properties of the oriented networks are p

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920106

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPartially acetylated cellulose was synthesized by homogeneous acidic and basic saponification of cellulose triacetate (fully acetylated cellulose) and by homogeneous acetylation of cellulose dissolved in moltenN‐ethyl‐pyridinium chloride. The result of1H NMR spectroscopic investigations was that acetylation and acid saponification lead to products with different esterification of the hydroxy groups at C2, C3and C6whilst basic saponification leads to uniform acetylation. Furthermore, the solubility of the cellulose acetates depends on the method of preparat

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920107

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractBlends of isotactic poly(propylene) (iPP) and trans‐polyoctenylene (TOR), prepared from solution, exhibit unexpected mechanical properties at specific mass fractions of TOR: While generally the elastic modulusEdecreases continuously with increasing TOR content, it surpasses a maximum for mass fractions of TOR around 0,10. The reason for this behaviour is investigated. It turns out that the crystallinity as well as the crystal morphology (which is investigated by evaluating small‐angle X‐ray scattering by interface distribution functions) does not explain the mechanical behaviour. The order of the lamellar stacks (number of orientation‐correlated crystals) proves to be well correlated with the course of the elastic modulus. This order is a consequence of the increasing dispersion of TOR at mass fractions between 0,075 and 0,20 creating interfaces and infecting subsequently the crystallization conditions in the

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920108

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe iniferter method of Otsu was studied for the synthesis of polyvinyl block copolymers of relatively low molecular weight using tetramethylthiuram disulfide (TD) and benzylN,N‐diethyldithiocarbamate (BDC) as initiator. Considering the low quantum yield of dissociation (ϕd) of TD (2,5 · 10−3in cyclohexane), TD was used as thermal initiator (95°C) for the synthesis of dithiocarbamate‐polystyrene (TD‐PS) telechelics.13C NMR analysis of this TD‐PS shows two13CS signals corresponding to two different end‐groups: Et2NCSSCH(C6H5)CH2 and Et2NCSSCH2CH(C6H5). Several styrene polymerizations were also carried out in presence of azoisobutyronitrile (AIBN) as thermal initiator and TD as chain‐transfer reagent. Depending on the mole ratio AIBN/TD, mono‐ and difunctional TD‐PS's are formed, as evidenced by NMR analysis. These TD‐PS's were used for the photochemical initiations of ethyl acrylate (EA), acrylic acid (AA) and methyl methacrylate (MMA). It is assumed that the quantum yield of dissociation of the dithiocarbamate end‐group is equal to that of BDC (ϕd: 0,06). TD‐PS nonfunctional polymers were also prepared, either photochemically by dissociation of BDC, or thermally in presence of AIBN and BDC as transfer agent. They were used for block copolymerization with MMA. Inversely, TD‐PMMA's were prepared in a first step; in this case ϕd= 0,026. They were then used for the polymerization of EA. The block copolymers were fractionated; their composition and molecular weights were determined by1

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920109

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractWell‐defined poly(4,4′‐isopropylidenediphenyl carbonate)‐block‐polystyrene multiblock copolymers, PC‐b‐PS, were prepared by condensation of PC prepolymers having chloroformyl end‐groups with PS prepolymers having hydroxyl end‐groups. Both prepolymers had narrow molecular weight distribution (PC prepolymer:M̄w/M̄n≤ 1,31, PS prepolymer:M̄w/M̄n≤ 1,03). The course of the polycondensation reaction depends on the molecular weight of the prepolymers used as substrates. After fractionation, the obtained multiblock copolymers are homogeneous in chemical composition and have a narrow molecular weight distribution. The mechanical properties of the copolymers depend on the weight fraction of the PS blocks. All copolymers exhibit two glass transition temperatures, close to those o

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920110

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY