摘要:

AbstractSyntheses of segmented copoly(ether‐ester)s with (oxy‐2‐methyl‐1,4‐phenyleneoxycarbonyl‐1,4‐phenylene carbonyl)/(oxy‐2‐chloro‐1,4‐phenyleneoxycarbonyl‐1,4‐phenylene carbonyl) (methyl‐/chloro‐substituted) hard segments and poly(oxytetramethylene) soft segments, are reported. The methodology consisted of staged addition melt condensation of terephthaloyl chloride, poly(oxytetramethylene)glycol (POTMG;\[ \bar M_n\]= 250, 650, 1000, 2000) and methyl‐/chloro‐hydroquinone. Lengths of hard and soft segments were varied while the weight ratio of hard to soft segment was maintained constant. Copolymers were characterised for solubility behavior, and by infrared spectroscopy, x‐ray diffraction, DSC, and polarizing microscopy. Thermal properties were found to be dependent on length of soft segment as well as on the type of substituent in the mesogenic core. In both methyl‐ as well as chloro‐substituted copoly(ether‐ester)s soft segment glass transition temperature (Tgs) was obtained between −40 and −50°C. All copoly(ether‐ester)s are elastomeric at room temperature (25°C). These polymers exhibit thermotropic liquid crystalline behavior and were easily sheared and aligned in liqu

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321601

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTo obtain thermally stable and mechanically strong sodium and lithium conducting polymers, we prepared Na+and Li+poly(phenylene terephthalamide sulfonate salts) (MW ∼ 5500). We also synthesized oligo(ethylene oxide) (3, 5, or 7 units of ethylene oxide) substituted ethylene carbonate and poly[oxymethylene‐oligo(oxyethylene)]. These are high boiling point liquids with high dielectric constants as well as metal chelating properties. Polyelectrolyte systems were prepared by mixing Na+or Li+poly(phenylene terephthalamide sulfonate) salts with various amounts of modified ethylene carbonate and/or poly[oxymethylene‐oligo(oxyethylene)]. Films (0.1–0.5 mm thick) obtained from the blends were found to have considerable mechanical strength; forming free standing films. The ionic conductivities of the Na+and Li+polyelectrolyte systems were 10−6−10−5S/cm at 25°C. Thermal properties of these blend systems were investigated in detail. © 1994 John

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321602

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractSeveral batches of poly‐N,N‐diethylacrylamide were synthesized by anionic and by group transfer polymerization (GTP). A radical poly‐N,N‐diethylacrylamide prepared from the same monomer was also included in the comparison. According to matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) both types of living polymerization resulted in narrow molecular weight distributions withMw/Mnvalues below 1.5. Average molecular weights (Mn) between 888 and 4678 g/mol were calculated in these cases. The radical polymer had an average molecular weight (Mn) of approximately 130,000 g/mol. The dry anionic and GTP polymers were investigated by differential scanning calorimetry (DSC) and x‐ray diffraction spectrometry. Evidence for partial crystallinity in the solid state was found. The conformation of all polymers was examined by high resolution (600 MHz) NMR. According to these measurements, 75% of the CHR groups of the anionic poly‐N,N‐diethylacrylamide were located in an isotactic triade. The remaining 25% had heterotactic structure, while no indication for the presence of syndiotactic protons was found. Poly‐N,N‐diethylacrylamide prepared by GTP, on the other hand, had mainly syndiotactic structure. The aqueous solutions of the polymers showed phase separation upon heating. Whereas the lower critical solution temperature (LCST) was approximately 30°C in the case of the poly‐N,N‐diethylacrylamide prepared by GTP and by radical polymerization, uncommonly high LCSTs of more than 40°C were observed for the anionic poly‐N,N‐diethylacry

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321603

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance (EPR) spectroscopy using two spin‐trapping agents, 2‐methyl‐2‐nitrosopropane (MNP) and α‐(4‐pyridyl 1‐oxide)‐N‐tert‐butylnitrone (PyOBN). Through analysis of hyperfine structure of the spectra obtainedfrom the trapped radicals, the propagating radical is inferred to be the well known acrylate radical,  [CH2CH(COOC4H9)]nCH2CH(COOC4H9)

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321604

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo series of novel thermotropic liquid crystalline poly(imide‐carbonate)s were prepared by melt polycondensation from various arylene or alkylene bis(phenylcarbonate)s by usingN,N′‐bis(hydroxyethyl)pyromellitimide andN,N′‐bis(hydroxypropyl)pyromellitimide as monomers. Thermotropic liquid crystalline properties were characterized by a polarizing microscope with a heating stage and a differential scanning calorimeter (DSC). Nematic melts were found for the synthesized aromatic poly(imide‐carbonate)s. In order to investigate whether the pyromellitimide unit could be used as a mesogenic unit for preparing LC polymers, a series of aliphatic poly(imide‐carbonate)s was prepared in this study. However, no significant LC textures were found under the observation by polarizing microscope. It was suggested that the aspect ratio of the pyromellitimide unit was too short to form liquid crystalline poly(imide‐carbonate)s. In addition, it was interesting that the aliphatic poly(imide‐carbonate)s with a longer spacer (n= 3) in the pyromellitimide unit showed better crystallinity. Thermostabilities of all synthesized poly(imide‐carbonate)s were measured by thermogravimetric analysis (TGA). © 1994

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321605

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTo elucidate the particle growth mechanism in propylene polymerization with high‐yield MgCl2‐supported Ziegler‐Natta catalysts, observations have been carried out by electron microscopy on a series of samples having different degrees of polymer growth (from 0.1 to 1000 g/g of catalyst). Topics such as surface and bulk morphology, catalyst fragmentation, as well as distribution of the catalyst residues in the polymer have been investigated. The experimental data suggest that if the site distribution in the catalyst is uniform and the polymerization conditions are mild, the polymer growth starts uniformly throughout the catalyst particle, which then undergoes an even and progressive fragmentation into very fine units homeogeneously dispersed in the polymer matrix. The above results thus provide further experimental support to the particle growth mechanism outlined in the multigrain or polymeric flow models. © 1994 John Wiley&Son

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321606

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo new phenylethynyl endcapping compounds, 3‐ and 4‐amino‐4′‐phenylethynylbenzophenone, were synthesized and used to terminate imide oligomers from 3,4′‐oxydianiline and 4,4′‐oxydiphthalic anhydride at a calculated molecular weight of 9000 g/mol and from 3,4′‐oxydianiline (0.85 mol), 1,3‐bis (3‐aminophenoxy) benzene (0.15 mol), and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride at a calculated molecular weight of 5000 g/mol. Glass transition temperatures for the cured oligomers were ∼ 249°C for the former and 272°C for the latter. Films cured at 350°C for 1 h were tough and flexible and provided high tensile properties. The uncured oligomers were readily compression molded to provide tough, solve nt‐resistant

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321607

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPt‐and Pd‐catalyzed reactions of a set of allyloxyaromatic mono‐and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum‐1,3‐divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4‐allyloxy methylbenzoate gave relative reactivities (HSiO1.5)8≫ Et3SiH>HMe2SiOSiMe2H>Ph2SiH2. The cubic silsesquioxane, (HSiO1.5)8, is so reactive hydrosilylation is over in 1–3 h at 0°C. All other reactions required>40°C and longer reaction times. Initial efforts to form high polymers by Pt‐catalyzed reactions of bis‐allyloxy aromatics with Ph2SiH2provide polymers with bimodal MW distributions (polystyrene),Mws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of SiO bonds, “oxysilylation.” The same products appear (10–15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph3P[Pd(dba)2/Ph3P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph2SiH2>HMe2SiOSiMe2H>Et3SiH. Polymerization with Pd catalysts provides polymers withMws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO1.5)8with 4 equiv. of 4‐(4‐allyloxy‐benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [Mn≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321608

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolymers having pendant norbornadiene (NBD) moieties and rigid main chain were prepared from the reaction of partially brominated poly(2,6‐dimethyl‐p‐phenylene oxide) with a potassium carboxylate derivative of the corresponding NBD using a phase transfer catalyst in chlorobenzene. The photochemical valence isomerization of pendant NBD to quadricyclane (QC) moieties proceeded smoothly in the film state as well as polymer solution upon the irradiation by sunlight, xenon lamp, or high‐pressure mercury lamp. The rate of isomerization was affected by the structure of main chain in the polymer and the substituent groups of NBD derivatives. The catalytic reversion of the resulting QC moiety to the original NBD proceeded smoothly in the solution with (5,10,15,20‐tetraphenyl‐21H,23H‐por‐phine)cobalt(II) as the catalyst at room temperature; however, the reaction of NBD polymer containing poly(2,6‐dimethyl‐p‐phenylene oxide) (PPO) showed lower reactivity than that of the corresponding low molecular weight QC compound. When the cycle between the photochemical valence isomerization of NBD moiety to quadricyclane (QC) moiety and thermal reversion of QC moiety to NBD moiety at 160°C was repeated, the NBD polymer synthesized from PPO degraded gradually, whereas NBD polymer prepared from poly(4‐chloromethylstyrene) decomposed easily. Therefore, the rigid PPO structure showed high resistance for the degradation of NBD moiety. ©

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321609

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe antioxidant role of α‐tocopherol (vitamin E) in low‐density polyethylene (LDPE), and the nature of its transformation products formed during extrusion of the polymer are investigated. The melt stabilizing effectiveness of α‐tocopherol was found to be very high, higher than that of the commercial hindered phenol antioxidants, Irganox 1076 and 1010, after single and multiple extrusion. The high antioxidant activity of α‐tocopherol as a melt stabilizer is due, at least in part, to its transformation products. The importance of the processing history and the parent antioxidant concentration on the transformation products is discussed. Transformation products of α‐tocopherol were analyzed after each of the four extrusion passes of the polymer. These were fractionated, analyzed, and characterized by HPLC and spectroscopy, respectively. The main products formed are diastereoisomers of dimers and trimers, as well as aldehydes; the relative concentration of each was shown to depend on processing severity (number of extrusion passes) and the initial concentration of α‐tocopherol. The dihydroxydimer was found to be formed at a high concentration relative to the other products and proportional with the initial concentration of tocopherol. Based on both the identity and distribution of transformation products, a mechanism is proposed for the melt stabilization effect of α‐tocopherol in LDPE. © 1994

ISSN:0887-624X    

DOI:10.1002/pola.1994.080321610

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY