bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid‐crystalline polyimides, 23. Photoreactive, cholesteric copoly(ester‐imide)s derived from 1,4‐phenylenediacrylic acid and 4‐aminobenzoic trimellitimide
Authors: Kricheldorf Hans R. , Probst Nicolas 
Published: April 2003

AbstractThe dichlorides of commercial 1,4‐phenylenediacrylic acid3,3′‐(1,4‐Phenylene)di‐2‐propenoic acid.
and N‐(4‐carboxyphenyl)‐trimellitimide were polycondensed with a chiral spacer prepared from (S)‐3‐bromo‐2‐methylpropanol and 4‐mercaptophenol. Optical microscopy revealed that all the resulting copoly(ester‐imide)s form an enantiotropic cholesteric melt and adopt a Grandjean texture upon slight shearing. The WAXD powder patterns indicate the formation of a layered structure in the solid state. Irradiation with UV light of wavelength ⩽ 360 nm allows crosslinking at any temperature above 25°C.
Graft copolymers of poly(methyl methacrylate) and polythiophene
Authors: Hallensleben Manfred L. , Hollwedel Fred , Stanke Dietmar 
Published: April 2003

Abstract2‐(2‐Thienyl)ethyl methacrylate (2TEMA, 1), 2‐(3‐thienyl)ethyl methacrylate (3TEMA,2) and 2‐(N‐pyrrolyl)ethyl methacrylate (PEMA, 3) were synthesized and copolymerized with methyl methacrylate (MMA) by radical initiation with AIBN. The reactivity ratios for the system MMA/2TEMA were determined to be rMMA = 0,57 ± 0,09 and r2TEMA = 0,90 ± 0,03. Thiophen was grafted into the copolymers from 1–3 via oxidative polymerization in nitromethane. The graft copolymers were soluble as aggregates, and films cast from these solutions reached conductivities in the range of 0,2 to 0,4 S/cm.
A small‐ and wide‐ angle X‐ray scattering study on the smectic‐α‐monoclinic phase transition and on the melting behaviour of isotactic poly(propylene) cast films
Authors: Marigo Antonio , Marega Carla , Zannetti Roberto , Fichera Annamaria , Ferrari Paolo 
Published: April 2003

AbstractThe morphological changes of isotactic poly(propylene) cast films have been investigated during the smectic–α‐monoclinic phase transition and the following melting. The small‐and wide‐angle X‐ray scattering techniques allow to point out the different behaviour of a homopolymer sample and of two propylene‐ethylene copolymer samples as a function of the presence and concentration of the ethylene comonomer. During the smectic–α‐monoclinic phase transition the crystallinity increase appears to be directly connected to the lamellar thickening and/or to the formation of new lamellar stacks.
Compatibilization of high density polyethylene/polyisoprene blends with polyethylene/polyisoprene “thread‐through” copolymers
Authors: Zhang Xuequan , Chen Hui , Tang Tao , Huang Baotong 
Published: April 2003

AbstractThe compatibilization of high density polyethylene (HDPE)/polyisoprene (PI) blends with polyethylene/polyisoprene (PE/PI) “thread‐through” copolymers was investigated. The proliferating structure of PE/PI with segments chemically identical to HDPE and PI, respectively, is different from that of graft copolymers. Studies showed that the dispersed domain size in the blends was significantly reduced and interfacial adhesion was improved by the compatibilization action of the copolymer. In the differential scanning calorimetry (DSC) analysis, the crystallization peak of HDPE in the blends became broad with adding the copolymer and fractionated crystallization appeared in the HDPE/PI blend compatibilized with the copolymer at a weight ratio of 30/70 while it appeared in the blend without copolymer at a weight ratio of 20/80. DMA results showed that by adding the copolymer, both the glass transition temperature (Tg) of the PI component and the a‐ relaxation of HDPE shifted to lower temperature, demonstrating the enhanced penetration of the two components. Mechanical properties of the blends were improved, especially the elongation at break, by the presence of the copolymers. The characteristic yielding at the fractured surface of the blends compatibilized with the copolymer indicates the fractural behavior of the material changed from brittle to tough.
Interaction of N‐tert‐butylaziridine with π‐electron acceptors, 1. Zwitterion copolymerization with maleic anhydride
Authors: Christova Darina Ch. , Velichkova Rumiana S. , Panayotov Ivan M. 
Published: April 2003

AbstractZwitterion copolymerization of N‐tert‐butylaziridine (TBA) with the weak π‐electron acceptor maleic anhydride (MA) was investigated. It was demonstrated that the reaction proceeds by opening of both aziridine and anhydride rings, and copoly(ester‐amide)s of different composition were prepared depending on the polymerization conditions. On the basis of a model reaction it was assumed that charge‐transfer interaction is a stage of the zwitterion mechanism. The structure and the composition of the products obtained were investigated.
Phase‐inversion membranes. Characterisation of patterns of skin holes
Authors: Addad Jean‐Pierre Cohen , Pedro‐Bom Ricardo 
Published: April 2003

AbstractThe statistical structure of the two‐dimensional random pattern of holes which are formed through the skin of phase‐inversion membranes is analysed. Membranes were prepared from a polyetherimide solved in N‐methyl‐2‐pyrrolidone; solutions were quickly immersed in water, at room temperature. The random pattern was observed with videomicroscopy; it is shown that it can be described quantitatively from the analysis of the ensemble of all quadrilaterals drawn from nearest neighbouring holes. Perimeters and areas of quadrilaterals were found to obey a log‐normal probability distribution function. Several features characterize the random pattern of holes. (i) There is a characteristic minimum distance between nearest neighboring holes; its order of magnitude is 5 μm. (ii) This distance is shortened when the polymer concentration in the casting solution is increased. (iii) This distance is lengthened when the solvent concentration in the coagulation bath is increased.
Chain transfer by addition‐fragmentation mechanism, 5 Investigation of the chain transfer activity of several ethyl 2‐(substituted)cinnamates
Authors: Colombani Daniel , Chaumont Philippe 
Published: April 2003

AbstractA variety of ethyl 2‐(substituted)cinnamatesSystematic name: ethyl 3‐phenyl‐2‐(substituted)propenoate.
were synthesized and added to vinylic monomer polymerizations. These olefins are activated towards free radical addition and contain a homolytic leaving group in the allylic position. Thus, they exhibit chemical transfer properties in free radical polymerization. The compounds studied include bromide, iodide, sulfone, mercaptan and peroxide derivatives. Cinnamic iodide, however, exhibits degradative chain transfer activity. These compounds have an advantage over simple thiols in that they permit a good control of molar mass by an addition‐fragmentation mechanism involving difunctionalization of the resulting telomers. The methods of synthesis of ethyl 2‐(substituted)cinnamates are discussed through the nucleophilic substitution of various anions toward the allylic bromo derivative prepared from ethyl 2‐(α‐hydroxybenzyl)propenoate.
Curing kinetics of cyanated poly(ether sulfone)s of different molecular weight
Authors: Chang Jer‐Yuan , Hong Jin‐Long 
Published: April 2003

AbstractThree cyanated poly(ether sulfone)s (CPESs) with number‐average molecular weights of 910, 1550 and 3 240 were synthesized and their polycyclotrimerization kinetics studied by dynamic differential scanning calorimetry (DSC). The resulting apparent activation energies (Ea) are quite close and range from 87.5 to 92.0 kJ/mol. The corresponding curing reactions in relation to conversion (α) can be expressed with an autocatalytic first‐order kinetics dα/dt = A (1+ Bα) (1 – α) exp (–Ea/(RT)). This kind of kinetics can be explained by a mechanism consisting of both a hydroxyl‐catalyzed and an autocatalytic path. The lower pre‐exponential factor (A) and contribution of autocatalytic reaction (B) for high molecular weight CPES are due to the low concentrations of catalytic species in the starting CPES and the resulting sym‐triazine rings, respectively.
Temperature effect of TiCl4 impregnation of a recrystallized MgCl2 support on propene polymerization
Authors: Shin Ho Woo , Chung Jin Suk , Song In Kyu , Lee Wha Young 
Published: April 2003

AbstractThe MgCl2 support for a propene polymerization catalyst was prepared by the recrystallization method using ethanol as a solvent and ethyl benzoate as an internal electron donor. The recrystallized MgCl2 was impregnated with TiCl4 at various temperatures, and the effect of impregnation temperature on the catalytic activity and isotactic index (I. I.) of polypropene (PP) was investigated. It was found that ethanol and titanium chloride ethoxide (TCE) in the catalyst play an important role in the catalytic activity and I. I. The support treated with TiCl4 at high temperatures showed good performance but large activity reduction during polymerization. The enhanced performance is mainly due to activity Ti species containing small amounts of TCE. The large activity reduction is also mainly due to small amounts of ethanol and TCE, yielding small amounts of atactic sites with low Lewis acidity.
Thermal effects on the structure and relaxation properties of poly(monocyclopentyl itaconate)
Authors: Calleja Ricardo Díaz , Sanchis Maria‐Jesus , Gargallo Ligia , Radíc Deodato 
Published: April 2003

AbstractThe effect of thermal treatment and subsequent chemical structural modifications on the viscoelastic and dielectric properties of PMCPI (poly(monocyclopentyl itaconate)) was studied. The low temperature relaxation (γ‐relaxation) is unaffected by the thermal history or chemical modifications. The intermediate relaxation (β‐relaxation) is shifted by about 40°C to higher temperature after thermal treatment. The α‐relaxation (related to the glass transition temperature Tg) suffers more striking changes when moving to higher temperatures.
Characterization of strictly alternating hydrogenated poly[butadiene‐alt‐(1‐olefin)] copolymers
Authors: Gerum Werner , Höhne Günther W. H. , Wilke Wolfgang , Arnold Manfred , Wegner Tino 
Published: April 2003

AbstractThe crystallization behaviour of the series of hydrogenated poly(butadiene‐alt‐ethene) to poly[butadiene‐alt‐(1‐hexadecene)] copolymers was investigated with the aid of differential scanning calorimetry (DSC) and X‐ray measurements. Hydrogenated poly(butadiene‐alt‐ethene) corresponds to polyethylene and crystallizes in the same way. Hydrogenated copolymers poly(butadiene‐alt‐propene) through poly[butadiene‐alt‐(1‐decene)] are completely amorphous. In these cases the large branching degree prevents crystallization of the main chains, whereas the side chains are too short to be able to crystallize above the glass transition temperature. The critical length is obviously reached in case of hydrogenated poly[butadiene‐alt‐(1‐dodecene)]. The part of the series with large side chains (hydrogenated poly[butadiene‐alt‐(1‐dodecene)] through poly[butadiene‐alt‐(1‐hexadecene)], shows the most interesting effects, especially hydrogenated poly[butadiene‐alt‐(1‐dodecene)], which shows crystallization depending on thermal history. In these substances the side chains are long enough to cause side‐chain crystallization, which becomes more pronounced with increasing length of the side chains. The crystal structure is not excactly to be determined, but some data indicate a model, in which the side chains are packed in a manner as in unbranched alkanes, but are also possible orthorhombic. However, the quality of the crystals formed is not very good, so these regions are better described as ordered domains rather than as crystallites.
Temperature‐dependent Cu2+‐Cu2+ paired structure in ethylene/methacrylic acid copolymer neutralized with Cu(II). Ionic crystallite disordering and polyethylene crystallite melting
Authors: Yamauchi Jun , Narita Hidehiro , Kutsumizu Shoichi , Yano Shinichi 
Published: April 2003

AbstractTemperature‐dependent ESR spectra of Cu2+‐Cu2+ pairs in ethylene/methacrylic acid copolymer neutralized with Cu(II) were reexamined in detail. The resonance positions and the linewidths of one of the ESR fine‐structure lines showed thermal distension of the Cu2+‐Cu2+ distance, and the slopes in the temperature variations changed at the temperature associated with melting of the polymer crystallites. No meaningful anomalies were observed around the temperature at which the preceding endothermic transition takes place. In this transition, the Cu2+‐Cu2+ pairs seems to enter a disordered state, keeping almost the same paired structure. In contrast to this irreversible order‐disorder transition, the melting process in the most part of the polyethylene crystallite phases starts to impose stress upon the Cu2+‐Cu2+ pairs, accompanying the slope changes of the ESR parameters. These reversible variations with remarkable thermal hysteresis are compatible with the DSC analyses.
Homo and copolymerization of ethylene: improvement of supported vanadium catalysts performance by halocarbons
Authors: Ribeiro M. Rośario , Deffieux Alain , Fontanille Michel , Portela Manuel F. 
Published: April 2003

AbstractThe effect and the role of halogenated molecules as additives for supported vanadium catalytic systems has been investigated both in high temperature ethylene homopolymerization and in its copolymerization with 1‐hexene. Addition of CH3CCI3 to the {VCl3, xAICI3} or {VCl3, xCrCI3} system, leads to a strong productivity improvement. The intensity of the activating effect depends on the nature of the support. Results suggest that the activation involves both oxidation of V(II) deactivated species into potentially active trivalent ones, and generation of new active sites. Studies on the structure of ethylene/1‐hexene copolymers show that the addition of halocarbons leads to copolymers with a higher comonomer content (SCB) and a better homogeneity in composition.
Synthesis and structural characterization of chiral smectic C and smectic A poly(vinyl ether)s
Authors: Chiellini Emo , Dossi Eleftheria , Galli Giancarlo , Solaro Roberto , Gallot Bernard 
Published: April 2003

AbstractA new series of chiral liquid‐crystalline poly(vinyl ether)s was synthesized by cationic polymerization of the corresponding vinyl ether monomers. They consisted of a biphenyl mesogenic unit bearing an (S)‐2‐methylbutyl chiral substituent and spaced via an alkyl segment of varying number x of methylene groups. Different initiators and experimental conditions were used for the polymerization reactions. All the samples were semicrystalline, and smectic C and A sequential mesophases were formed in polymers comprising a sufficiently long spacer segment (x > 8). X‐ray diffraction measurements were performed on unoriented specimens. In the smectic C phase, the occurrence of different orders of X‐ray reflection on the smectic layers enabled drawing of the electron density profiles along the layer normal. By simple model considerations it was possible to choose the most physically acceptable one and to identify the low temperature mesophase as double layer smectic C.
Amino‐termined poly(L‐lactide)s as initiators for the polymerization of N‐carboxyanhydrides: synthesis of poly(L‐lactide)‐block‐poly(α‐amino acid)s
Authors: Gotsche Michael , Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractPoly(L‐lactide)‐block‐poly(L‐amino acids) block copolymers were prepared via polymerization of α‐amino acid N‐carboxyanhydrides with amino‐terminated poly(L‐lactide)s as macroinitiators. Two types of macroinitiators were used, one with an aminopropoxy head group (number‐average molecular weight Mn = 22000) and the other one with a phenylalanine end group (Mn = 18000). The first macroinitiator was obtained by polymerization of (L,L)‐lactide with an initiator prepared in situ from diethylzinc Et2Zn and N‐tert‐butoxycarbonyl‐1‐amino‐3‐propanol, followed by deprotection of the amino group. The second macroinitiator was obtained by endcapping of poly(L‐lactide) with N‐tert‐butoxycarbonylphenylalanine and deprotection of the amino group. 1H‐ and 13C NMR spectroscopies confirm the block structure of the copolymers obtained. In differential scanning calorimetry curves only one melting transition characteristic of the poly(L‐lactide) block is observed, on further heating decomposition occurs. By thermogravimetry two steps of decomposition are observed, the first one being assigned to the decomposition of the poly(L‐lactide) block, and the second one to that of the poly(amino acid) block, by comparison with the thermal behaviour of the corresponding homopolymers.
MALDI‐TOF mass spectrometry in polymer analytics, 1. Monitoring the polymer‐analogous sulfonation reaction of polystyrene
Authors: Räder Hans Joachim , Spickermann Jochen , Müllen Klaus 
Published: April 2003

AbstractIn the present paper, homologous series of polystyrenes, poly(styrenesulfonic acid)s and their corresponding sodium salts in a mass range between 2000 and 100000 Dalton were used as model systems, to check for the significance of matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF MS) in the analysis of synthetic polymers. These three different types of polymers were specially selected, because they are related to each other by polymer‐analogous reactions. The difference in molecular weight between the parent polystyrenes and the poly(styrenesulfonic acid)s or their sodium salts, respectively — prepared from the same sample — provides information on the sulfonation efficiency. It thereby appears that the mass spectrometric monitoring of a polymer analogous reaction proceeds with much greater accuracy than other methods, such as gel permeation chromatography. The measured polymer distributions supply exact values of peak molecular weight (Mp), number‐average molecular weight (Mn), weight‐average molecular weight (Mw) and polydispersity (D = Mw/Mn) which turn out to be close to those values calculated for a complete (100%) transformation in the given polymeranalogous reaction. Additional information is available in the mass range below 10000 Dalton, where single chains of the polymers are resolved. Based on the identified polymer ions, the ionization mechanism for poly(styrenesulfonic acid)s and their sodium salts seems to deviate from the mechanism proposed for the ionization of biomolecules. The exact assignment of all signals shows that there is virtually no fragmentation of the polymer ions during measurement. Even the polyionic sodium salt is analyzed together with the counterions.
Synthesis and thermal properties of poly(enaminonitriles) containing flexible ether units
Authors: Ha Jeong‐Hyup , Lee Seung‐Jae , Gong Myoung‐Seon 
Published: April 2003

AbstractPoly(enaminonitriles) containing flexible alkyl ether units were prepared by reacting p‐bis(1‐chloro‐2,2‐dicyanovinyl)benzene with various α,ω‐bis(4‐aminophenoxy)alkanes in N‐methyl‐2‐pyrrolidone (NMP). All the polymers are soluble in polar aprotic solvents such as N,N‐dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N‐dimethylacetamide (DMAc) and NMP as well as in common organic solvents such as tetrahydrofuran and acetone. High molecular weight polymers possessing inherent viscosities in the range of 0.82–1.20 dL/g were obtained and tough films were cast from a DMF solution. They showed a large exotherm around 340°C attributable to the chemical changes of the dicyanovinyl group. Thermogravimetric analyses exhibited a good thermal stability with a 10% weight loss around 450°C and 73–88% residual weight at 500°C under nitrogen.
Phase transition from a C‐centered to a B‐centered orthorhombic crystalline form of syndiotactic poly(propylene)
Authors: Auriemma Finizia , Lewis Russell H. , Spiess Hans Wolfgang , De Rosa Claudio 
Published: April 2003

AbstractSamples of highly syndiotactic poly(propylene) (s‐PP) crystallized in a C‐pseudo‐centered orthorhombic form are here characterized through high resolution solid state 13C NMR sepctroscopy and wide angle X‐ray diffraction. The 13C NMR CP MAS (cross‐polarization, magic angle spinning) spectra of highly disordered quench‐precipitated s‐PP samples (with a structure very close to a C‐pseudo‐centered orthrohombic form) yield additional resonances beside those already reported in the literature for s‐PP samples crystallized with the chains in a fully helical \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} (TTGG\rlap{--} )_n $\end{document} conformation (T: trans; G: gauche). From the correlation of 13C NMR CP MAS spectra with the X‐ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C‐ to the B‐pseudo‐centered orthorhombic form starts to occur. Correspondingly, the aforementioned additional resonances in the 13C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13C NMR CP MAS spectrum of samles crystallized in the B‐pseudo‐centered structure. NMR and X‐ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon; at temperatures below 140°C for our samples, the variously sized C‐pseudo‐centered orthorhombic crystallites melt and readily re‐crystallize in the B‐pseudocentered orthorhombic form.
Initiation of polymerization with substituted ethanes, 14 Free‐radical polymerization of methyl methacrylate and styrene with substituted adiponitriles
Authors: Braun Dietrich , Skrzek Thomas 
Published: April 2003

AbstractTetraarylsuccinonitriles 1 show an atypical “stepwise” initiation mechanism in freeradical polymerization, particularly in the case of methyl methacrylate (MMA) as monomer. In the prior phase of the polymerization reaction very high concentrations of primary radicals lead to the formation of short‐chain telechelics with both end groups originating from the initiator. In the further course of polymerization these telechelics are able to from radicals by release of initiator end groups and so to “re‐initiate” free‐radical polymerization (‘resusciatable’ radical polymerization). In this communication a general synthesis method of MMA telechelics with a formal degree of polymerization of one is presented. These 2,2,5,5‐tetraaryl‐3‐methoxycarbonyl‐3‐methyladiponitriles 4 dissociate with Arrhenius activation energies in the range of 150 ± 10 kJ/mol. When using these telechelics as initiators in free‐radical polymerization of MMA and styrene, respectively, above 80°C no repeated telechelic formation phase is observed and polymer formation starts immediately from the beginning. The polymers obtained have weight‐average molecular weights of 200 000 to 950000 (poly(methyl methacrylate)) and 50000 to 400000 (polystyrene), respectively.
Thermal and ferroelectric properties of two series of coloured chiral liquid crystalline side group copolymers
Authors: Niesel Frank Thomas , Rübner Joachim , Springer Jürgen 
Published: April 2003

AbstractTwo series of liquid crystalline side group copolymethacrylates were synthesized and their thermal and ferroelectric properties determined. All copolymers contain the same azobenzene mesogen spaced from the backbone by a heptamethylene sequence but different chiral co‐compounds were used. The samples show either a monolayer or a bilayer smectic C* phase but only four polymers with a low content of the azo‐dye could be switched ferroelectrically. The formation of the smectic C* phase of some samples was found to be hindered. In order to study this phenomenon as a function of the molecular weight one copolymer was fractionated.