摘要:

AbstractThe preparation of polyphosphazene random and block copolymers bearing trifluoroethoxy and alkoxyalkoxy groups by the anionically initiated polymerization of phosphoranimines and poly(diarylphosphazene)s from phosphine azide intermediates is discussed. The properties of these materials were studied by differential scanning calorimetry, wide‐ and small‐angle X‐ray scattering, thermogravimetric analysis, dynamic mechanical analysis, dielectric relaxation spectroscopy, single crystal X‐ray and electron diffraction, density measurements and optical microscopy, and were correlated with molecular architecture, molecular weight, composition and side groups st

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980301

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis article summarizes our recent experimental studies of an important class of polymer melt rheological phenomena including flow instabilities, stick‐slip transitions, interfacial melt/wall slip, gross extrudate distortion and sharkskin like surface roughening of extrudates. Our experimental results indicate that most aspects of the perplexing flow behavior of strongly entangled melts in polymer extrusion can be depicted in terms of melt/wall interfacial interactions at a molecular level. For high surface energy walls, a transition from no‐slip to slip hydrodynamic boundary condition (HBC) occurs through molecular disentanglement (coil‐to‐stretch) of adsorbed chains from unbound chains. For weakly adsorbing walls, interfacial slip takes place through a second molecular mechanism involving a stress‐induced polymer desorption process. Since the coil‐stretch transition of adsorbed chains is controlled by interfacial shear stress, the HBC can be unstable throughout the die wall under the condition of a constant flow rate, where the wall stress may fluctuate in time. Unstable HBC due to the interfacial molecular instabilities is shown to be the origin of a variety of global and local flow instabilities including the oscillating flow and the sharkskin like distortion of extrudate surface. With a set of new experiments to directly probe the interfacial molecular processes, we will be able to support the unified understanding of intriguing capillary melt flow characteristics summarized in t

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980302

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo new lyotropic solutions of cellulose derivatives are reported which can be polymerized upon γ‐irradiation. The first solution consists of hydroxypropylcellulose (HPC) inN,N‐dimethylacrylamide (DMAcr) and the second of 2‐(acryloyloxy)propylcellulose (APC; degree of substitution (DS) = 0.18) in water. Both solutions were characterized using refractive index measurements, polarizing microscopy and diffuse reflection spectroscopy. For solutions of HPC in DMAcr, it was demonstrated that they exhibit anisotropic phase behaviour at concentrations higher than 45 wt.‐% within a limited temperature range. Highly concentrated solutions of about 70 wt.‐% also showed cholesteric phase behaviour with iridescent colours. Upon γ‐irradiation, the solvent DMAcr rapidly polymerized. A conversion to 90% of polymer was reached at a dose of 5 kGy. Molecular composites of HPC in polymerized DMAcr were obtained in which the macroscopic order was preserved. Shear‐deformed samples were still birefringent and exhibited band textures, when viewed between crossed polarizers, and light reflection of the cholesteric samples still occurred at the same wavelength as before irradiation. The polymerized samples showed an extended temperature stability, the anisotropy being stable up to approximately 150°C. The second solution of APC in water also exhibits cholesteric phase behaviour at a concentration of 61.5 wt.‐%. Upon γ‐irradiation, the polymer chains undergo rapid cross‐linking via the reactive acrylate groups and form a network in which the cholesteric order is preserved. The cross‐linked APC films are swellable in water and retain their anisotropic order when the concentration of the solution is varied between 40 and 100 wt.‐% of APC. The materials properties of the two systems after

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980303

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe use of the phosphazene base P2‐Et(a)as a promoter for the anionic polymerization of hexamethylcyclotrisiloxane (D3Me) or hexaethylcyclotrisiloxane (D3Et) initiated by an organolithium compound leads to well‐defined polysiloxanes. At low conversion (

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980304

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractFour aromatic diamines containing aliphatic spacers andMetaandparaoriented oxyphenylene rings, and their corresponding hydrochlorides, were combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC) to give high molecular weight polyamides by interfacial and low‐temperature solution methods. The synthesis and characterization of monomers and polymers are reported, and the differences observed in polycondensation yields, molecular weights and molecular weight distributions, as a function of the method of synthesis, are discussed. Values of number‐average molecular weight (M̄n) up to 8 × 104g/mol and weight‐average molecular weight (M̄w) up to 1 × 105g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values ofM̄nup to 2 × 105g/mol andM̄wup to 3.6 × 105g/mol by using polystyr

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980305

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA random ethene/styrene copolymer containing 13.8 mol‐% styrene was prepared with the Ziegler‐Natta catalyst system Me2Si(Me4Cp)(N‐t‐butyl)TiCl2/methylaluminoxane and characterized by means of preparativetemperaturerisingelutionfractionation (TREF) combined with size exclusion chromatography, NMR, differential scanning calorimetry and wide‐angle X‐ray scattering analyses of the copolymer fractions. Efforts are made to describe the distribution of the styrene content of the copolymers using the Stockmayer‐Tacx distribution function. Both, comonomer distribution and molar mass distribution strongly support the presence of a single type of catalytically

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980306

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractNew bicyclic 2‐methylene‐1,3‐dioxepanes, were synthesized starting from 2‐bromomethyl‐5,6‐dihydroxy‐1,3‐dioxepanes. The structure of the 2‐methylene‐1,3‐dioxepanes was confirmed by elemental analysis, IR,1H NMR and13C NMR spectroscopy. Radical polymerization of 2‐methylene‐1,3‐dioxepanes in bulk with 2,2′‐azoisobutyronitrile (AIBN) and di‐tert‐butyl peroxide (DtBPO), respectively, gives highly viscous polymers. The polymerization of liquid monomers is accompanied by negative volume changes. The spectroscopic investigations of the formed polymers show that 2‐methylene‐1,3‐dioxepanes undergo primarily radical ring‐opening polymerization, whereas the cationic photopoly

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980307

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe synthesis of a new type of poly(vinyl sugar) is described whose polymer backbone is connected with the monosaccharide unit by a C—C bond. Such polymers can be obtained by radical initiation. They show good stability in polymer‐analogous reactions in contrast to common poly(vinyl saccharides) whose sugar residues are bound to the polymeric chain by ester, ether, or glycoside bonds. Starting from 7,8‐dideoxy‐1,2;3,4‐di‐O‐isopropylidene‐α‐D‐galacto‐oct‐7‐en‐1,5‐pyranos‐6‐ulose(1)polymers(P1)could be obtained by emulsion polymerization in high yields. Reduction of the keto group ofP1proceeded quantitatively and yielded poly(7,8‐dideoxy‐1,2;3,4‐di‐O‐isopropylidene‐D,L‐glycero‐α‐D‐galacto‐oct‐7‐en‐1,5‐pyranose)(P3). In contrast to the following polymers without protecting groups these poly(vinyl ketones), which were soluble in tetrahydro‐furan and toluene, did not follow a pure GPC‐separation mechanism. The protecting groups of the poly(vinyl saccharides), either with or without keto groups, could be removed completely to giveP2andP4. The solubility of the polymersP2with galactose‐functionalized side chains in water was limited to a weight‐average molecular weightM̄wof 1 500 000 due to association phenomena of the monosaccharide units. Reduction of the hemiacetal group and of the keto group ofP2yielded poly(1,2‐dideoxy‐D,L‐glycero‐D‐galacto‐oct‐1‐enitol) (P5) with sugar alcohol side chains instead of a cyclic monosaccharide unit. Oxidation of the hemiacetal group ofP2andP4furnished poly(7,8‐dideoxy‐D‐galacto‐oct‐7‐en‐6‐ulosonic acid sodium salt) (P6) and poly(7,8‐dideoxy‐D,L‐glycero‐D‐galacto‐oct‐7‐enonic ac

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980308

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis study concerns the synthesis of C60‐capped vinyl ether (VE) oligomers with well‐defined structure by living cationic polymerization technique. The VE oligomers bearing C60at the chain end were prepared by addition reaction between monoocynylfulleride anions and living cationic VE oligomers. Living oligo(isobutyl vinyl ether) (IBVE) and oligo(methyl vinyl ether) (MVE) were synthesized using CH3CH(OiBu)Cl/ZnI2as initiating system. The C60‐capped VE oligomers were obtained as dark brown gummy solid in 28% for IBVE and 34% for MVE. The UV/VIS and13C NMR spectra indicated the formation of C60‐capped oligomers via 1,2‐addition reaction. It was also found that the films of blends of C60‐capped oligomers with poly(IBVE) and polystyrene (5 wt.‐% C60) are homogeneous on a micron scale and transparent, resulting from a good dispersion of C60in the p

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980309

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPropagation rate constants (kp) for photo‐ and thermal‐initiated radical polymerizations of styrene were determined by electron spin resonance (ESR) spectroscopy. Thekpvalue for the former at 70°C ((420 ± 30) M−1· S−1) was more than twice as large as that for the latter ((190 ± 10) M−1· s−1) although the former value was almost the same as that obtained with the pulsed‐laser polymerization method. To evaluate the origin of the difference in thekpvalues between photo‐ and thermal‐initiated polymerization the absorption spectrum of a model of the propagating radical was measured and both the influence of the wavelength of the irradiation light onkpvalues and the activation energy of the photo‐initiated radical polymerization of styrene were determined.kpdecreases for wave‐lengths shorter than 370 nm and is in agreement with thekpvalue for thermal‐initiated polymerization. No wavelength dependence ofkpwas obtained for dienes whose propagating radical does not absorb above 300 nm. The difference inkpvalues for photo‐ and thermal‐initiated polymerizations is considered to be due to the photoactivation (photoinduced excitation) of th

ISSN:1022-1352    

DOI:10.1002/macp.1997.021980310

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY