bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of contamination by side‐chain precursor on the molecular dynamics of a smectogenic siloxane copolymer as studied by dielectric relaxation spectroscopy
Authors: Attard George Simon , Moura‐Ramos Joaquim J. , Williams Graham , Nestor Gary , White Michael S. , Gray George W. , Lacey David , Toyne Kenneth J.
Published: April 2003

Two samples of a statistical siloxane copolymer 1 having two different pendant side‐chains have been investigated in the liquid‐crystalline state using dielectric relaxation spectroscopy. Samples 1a and 1b differed only in the number of precipitations (3 and 12, respectively) used in the purification procedure. Sample 1a, contained side‐chain precursor, whereas this contaminant was not detectable in sample 1b. It was found that the dielectric absorption curves for homeotropically‐aligned and unaligned specimens of sample 1a, were far broader than those observed for corresponding specimens of sample 1b, and there was evidence of an extra highfrequency shoulder. In addition, the frequency‐temperature locations of the overall loss peak differed between the two samples, being consistent with a plasticization effect caused by residual side‐chain precursor in sample 1a. It is shown that dielectric relaxation spectroscopy provides a convenient method for monitoring local phase separation and overall plasticization in liquid‐crystalline polymers caused by side‐chain precursor contamination.
A study of the thermal decomposition of poly(vinyl chloride) prepared at low conversion
Authors: Cuthbertson M. J. , Bowley H. J. , Gerrard D. L. , Maddams W. F. , Shapiro J. S.
Published: April 2003

Aiming to prove that commercial, 50°CPVC consists of a dual population of chains, has led us to the investigation of the thermal stability of low conversion (0,1–2%) PVC. Bulk polymers prepared at very low conversion levels were shown to be different to high conversion material. The former are more syndiotactic, and have a greater tendency to be less thermally stable, unzippering to long polyene sequences (with n > 15). These findings are consistent with the idea that initially‐produced PVC is formed by homogeneous polymerisation and that such material is intrinsically different to PVC which is formed at subsequently higher conversions by a heterogeneous route.
Novel synthetic approach to poly(p‐benzenesulfonamide): Self‐polycondensation of active p‐aminobenzenesulfonic acid derivatives under mild conditions
Authors: Saegusa Yasuo , Ogawa Takeshi , Kondo Hiromune , Nakamura Shigeo , Chau Nguyen , Iwakura Yoshio
Published: April 2003

Three active p‐aminobenzenesulfonic acid derivatives, 1‐(p‐aminobenzenesulfonyl)imidazole (4a), 1‐(p‐aminobenzenesulfonyloxy)benzotriazole (4b), and 2‐phenyl‐4‐(p‐aminobenzenesulfonyl)‐1,3,4‐oxadiazoline‐5‐thione (4c) were synthesized by reacting p‐isocyanatobenzenesulfonyl chloride (1) with stoichiometrical quantities of water in the presence of dibutyltin didodecanoate and subsequently with imidazole, 1‐hydroxybenzotriazole and 2‐phenyl‐1,3,4‐oxadiazoline‐5‐thione, respectively. The self‐polycondensation of 4a–c, leading to poly(p‐benzenesulfonamide) (7), was carried out in solution using polar aprotic solvents, N‐methyl‐2‐pyrrolidone (NMP) and hexamethylphosphoric triamide (HMPA), and acidic media, dimethyl sulfoxide (DMSO) and m‐cresol, with or without an appropriate acid catalyst or acid acceptor under mild conditions. Poly(p‐benzenesulfonamide) having the highest reduced viscosity of 0,14 dl·−1 was obtained almost quantitatively from 4c by using m‐cresol as a solvent without any acid catalyst and acid acceptor at 25°C. The polymers are soluble in polar aprotic solvents such as NMP, HMPA and DMSO and in aqueous sodium hydroxide. These poly(p‐benzenesulfonamide)s are less thermally stable than completely aromatic polyamides, because the initial weight‐loss started at 250–350°C. Aminolysis of three benzenesulfonic acid derivatives, 1‐benzenesulfonylimidazole (5a), 1‐benzenesulfonyloxybenzotriazole (5b), and 2‐phenyl‐4‐benzenesulfonyl‐1,3,4‐oxadiazoline‐5‐thione (5c), with the same leaving groups was also carried out as a model reaction of self‐polycondensation to determine the reaction conditions.
Oligomerization and cyclization of 1‐phenoxy‐2,3‐epoxypropane induced by magnesium perchlorate
Authors: Tänzer Wolfram , Müller Heike , Wintzer Jana , Fedtke Manfred
Published: April 2003

During the reaction of 1‐phenoxy‐2,3‐epoxypropane (1) with catalytic amounts of Mg(ClO4)2 a variety of reaction products are formed which do not correpond to a normally distributed oligomer range. Essentially, three reaction paths can be distinguished which lead to oligo‐(hydroxyether)s of similar structure (6 and 8) and to cyclic, isomeric dimers (9 and 10) of very low reactivity. During the reaction of bifunctional 2,3‐epoxypropyl ethers, cyclic products act as nonreactive diluents decreasing the network density of the final crosslinked product.
Rigid rod polymers with flexible side chains, 4. Synthesis, structure and phase behaviour of polyimides prepared from pyromellitic anhydride and 2,5‐di‐n‐alkoxy‐1,4‐phenylene diisocyantes
Authors: Wenzel Markus , Ballauff Matthias , Wegner Gerhard
Published: April 2003

A series of rigid rod polyimides 1a–f derived from pyromellitic anhydride (PMDA) and 2,5‐di‐n‐alkoxy‐1,4‐phenylenediamine containing flexible alkoxy side chains with 4 to 16 carbon atoms was prepared by solution polycondensation. As demonstrated by model experiments full conversion to the imide structure is achieved by reaction of PMDA with 2,5‐dialkoxyphenylene diisocyanate, the latter compound being blocked by imidazole. The best solvent for the polycondensation, found in the course of the model reaction, is 1,3‐dimethyl‐2‐oxo‐perhydro‐pyrimidine together with 4‐dimethylaminopyridine as an accelerator. Wide‐angle X‐ray diffractograms showed that all polyimides under consideration here are highly crystalline at room temperature. The occurrence of a sharp reflection at the region of low angles together with its higher orders demonstrates the presence of a layered structure. The layer spacing was found to increase linearly with the length of the alkyl side chains. Polyimides bearing long side chains (n ≥ 10) exhibit two broad endotherms in the DSC analysis. As is revealed by wide‐angle X‐ray analysis the first transition is related to a disordering process of the side chains. The second transition leads to a layered high‐temperature phase akin to the modification (B) found in a recent study of a similar rigid polyester bearing flexible side chains.
Anodic polymerization of acrylamide in aqueous nitrate solution using an activated iridium electrode
Authors: Otero Toribio Fernández , Mugarza Maria Antonia
Published: April 2003

The flow of an electric current through an aqueous solution of acrylamide and NaNO3, using an activated iridium electrode as anode, induces the polymerization of the monomer in solution. The influence of the chemical and electrochemical variables on monomer conversion was studied. The experimental results point to the production of initiating radicals by charge transfer between the electrolyte and the electrode, followed by desorption of these radicals from the electrode into the solution. The electrode process is a mixed process in which all the species present take part. Electrode activation depolarizes the NO discharge and increases the polymerization rate.
Comportement au voisinage des conditions «théta» des solutions semidiluées et concentrées de poly(diméthylsiloxane) dans le styrène
Authors: Lapp Alain , Strazielle Claude
Published: April 2003

The thermodynamical properties of poly(dimethylsiloxane) (PDMS) were studied in the theta‐solvent styrene. Moderately diluted and semidiluted solutions of three PDMS samples with weight‐average molecular weights M̄w = 23 500, 160 000, and 860 000 were investigated by means of light scattering near the theta‐temperature. The dependency of the interaction parameter X on temperature and concentration was established for the three samples. The study of the third virial coefficient A3 showed that A3 is independent of molecular weight and temperature as predicted by theory. However, the experimental value of A3/(AM) was higher than expected. The critical properties, i.e., critical point and spinodal, were considered.
Electrochemical polymerization of derivatives from N‐methylpyrrole and thiophene to heteroarylenevinylene polymers
Authors: Berlin Anna , Wernet Wolfgang , Wegner Gerhard
Published: April 2003

The heteroaryl‐ and heteroarylenevinylene compounds 1, 2, 3, and 4 were investigated by means of cyclic voltammetry and submitted to oxidative electropolymerization under galvanostatic conditions; the products obtained were further characterized by means of elemental analysis, optical absorption spectroscopy and conductivity measurements. (E)‐1,2‐bis(N‐methyl‐2‐pyrrolyl)ethylene (1), 2,5‐bis[(E)‐2‐(N‐methyl‐2‐pyrrolyl)vinyl]thiophene (2) and N‐methyl2,5‐bis[(E)‐2‐(N‐methyl‐2‐pyrrolyl)vinyl]pyrrole (3) gave brittle to spongy films on electropolymerization with perchlorate as the counterion balancing the positive charge on the polymer backbone units. The d. c. conductivity of all three polymers (as perchlorates) was of the order of 10−3 Ω−1·cm−1. N‐methyl‐2,5‐bis[(E)‐2‐(2‐thienyl)vinyl]pyrrole (4) did not give a solid polymer.
Photosensitive polymers with pendent p‐dialkylaminobenzylideneacetophenone residues as photoinduced radical polymerization initiators
Authors: Ichimura Kunihiro , Kameyama Atsushi
Published: April 2003

Polymers with pendent p‐dialkylaminobenzylideneracetophenone (PABA) groups were prepared by copolymerization of 4‐(4‐dimethylaminobenzylidenemethylcarbonyl)phenyl methacrylate (1) with alkyl methacrylates and by the substitution reaction of poly(chloromethylstyrene‐co‐methyl methacrylate) with sodium 4‐(4‐dimethylaminobenzylidenemethylcarbonyl)phenolate (3). The polymers having PABA groups become insoluble upon photodimerization of PABA. Furthermore, the photosensitivity of the polymers increases considerably when mixed with vinyl monomers and diphenyliodonium hexafluorophosphate (DPI) during irradiation. The photocrosslinking may involve graft polymerization initiated by PABA which sensitizes the decomposition of DPI to form radicals. Introduction of unsaturated groups like maleate or crotonyl groups into the PABA polymer depresses the shrinkage of the photocured polymer film when the polymer was mixed with DPI. Sensitivity characteristics of PABA polymers toward Ar laser emitting 488 nm light are mentioned.
Spezifische Adsorbentien für das Peptidantibiotika synthetisierende Enzymsystem Gramicidin S Synthetase, 1. Darstellung niedermolekularer Spacer‐Ligand‐Verbindungen
Authors: Schlünsen Jürgen , Manecke Georg
Published: April 2003

Several amide derivatives of phenylalanin and prolin were prepared as spacer/ligand compounds by reaction of unprotected or monoprotected aliphatic and aromatic diamines and monoamines with the succinimido esters of the corresponding N‐protected amino acids. The formation of diacylated aliphatic diamines was fast under normal conditions. In the case of aromatic diamines the presence of a bases is necessary. For the preparation of monoacylated diamines best results were obtained with monoprotected diamines. The acylated diamines were purified by column chromatography or by extraction.
Poly(epichlorohydrin)s obtained by means of a new calcium complex as catalyst
Authors: Lamot Ryszard
Published: April 2003

A new catalytic complex was developed by reacting 1,1‐diphenylethylene with metallic calcium and submitting the resulting derivative [designated as (Ar)2Ca] to chemical modifications with 1‐chloro‐2,3‐epoxypropane (epichlorohydrin; ECh). From these reactions a series of (Ar)2Ca · x ECh catalysts resulted differing by the mole ratio ECh/Ca. A value of 0,7 was found to be the optimal one with regard to the catalytic efficiency of polymerizing epichlorohydrin. The poly(epichlorohydrin)s (PECh), obtained with yields of 46, 5 to 82, 4%, are distinguished by their chlorine content and cover a range of molar masses from 0,35 · 105 to 2,23 · 105 g/mol. The catalysts were characterized by elemental analyses and thermogravimetry. According to X‐ray patterns, PECh obtained by means of (Ar)2Ca · 0,7 ECh as catalyst displayes no crystallinity like PECh prepared in the presence of appropriate aluminium systems.
Study of the initiation mechanism of the vinyl polymerization with the system persulfate/N,N,N′,N′‐tetramethylethylenediamine
Authors: Feng Xin De , Guo Xin Qiu , Qiu Kun Yuan
Published: April 2003

The reaction mechanism of the redox initiation system persulfate/N,N,N′,N′‐tetramethyl‐ethylenediamine (TMEDA) was studied by spin trapping technique and ESR spectra. The free radical (CH3)2NCH2CH2(CH3)NCH (1) is one of the initial free radicals responsible for the initiation of the vinyl polymerization in addition to the sulfate free radical (HO3SO˙). The result of amino end group analysis confirmed the fact that the free radical 1 initiates vinyl polymerization and becomes the end group of the resulting polymers. The effect of TMEDA concentration on the final percentage of conversion of acrylamide polymerization and on the molecular weights of the resulting polymer were also studied. An initiation mechanism was proposed.
Synthesis of monomers and polymers by the Heck reaction
Authors: Heitz Walter , Brügging Wilhelm , Freund Lothar , Gailberger Michael , Greiner Andreas , Jung Holger , Kampschulte Uwe , Nießner Norbert , Osan Frank , Schmidt Hans‐Werner , Wicker Michael
Published: April 2003

The Heck reaction allows the synthesis of monomers in a one‐step reaction. Catalyzed by Pd, bromoarenes are reacted with ethylene to form substituted styrenes and symmetrical stilbenes. Unsymmetrical stilbenes are obtained from substituted bromoarenes and styrenes. Substituted hydroquinones and terephthalic acids are also available in high yields. Poly(1,4‐phenylenevinylene) is obtained starting from 4‐bromostyrene.
Conformational analysis of ß(1→4)‐linked polysaccharides in aprotic solvent solutions
Authors: Nardin Robert , Vincendon Marc
Published: April 2003

The 1H NMR parameters (chemical shift and coupling constant) of ß(1→4)‐linked polysaccharides xylan, cellulose, and chitin are compared in solutions of aprotic solvents. The following NMR parameters are analyzed: (1) Chemical shifts of labile protons, (2) their variation with temperature, (3) coupling constants through the HCOH moiety — for monomers, dimers, and the corresponding polymers. It is observed that the OH‐3 hydroxyl group for cellulose and chitin oligomers and polymers present a particular behaviour, which is in agreement with the existence of an intramolecular hydrogen bond between this hydroxyl of one monomeric unit, and the heterocyclic oxygen atom of the adjacent monomeric unit. This kind of intramolecular hydrogen bond is not observed in case of the xylan series. It can be concluded that substitution of an equatorial hydrogen atom at the C‐5 position of the sugar ring by a CH2OH group — when passing from xylan to cellulose and chitin — induces a rotation restriction around the glycosidic bond. This places the OH‐3 hydroxyl group in a favourable position to be hydrogen‐bonded. The consequent implication on the respective conformations of the chains in solution is discussed.
Synthesis and reactivity of 1,4‐disubstituted butadienes in the solide state
Authors: Augenstein Michael , Wegner Gerhard
Published: April 2003

A novel synthetic route to (2E,4E)‐6‐amino‐2,4‐hexadienoic acid (1) and related ω‐aminodiene compounds is reported. These substances form layer perovskites, CdCl4(NH3—R)2, that furnish stereoregular 1,4‐polybutadienes upon γ‐irradiation in a topochemical solid state reaction. The synthesis of a chiral derivative is also described, that can be crystallized in a perovskite structure and polymerized by γ‐rays. An ambivalent solid state reactivity is observed for the hydrochloride of 1: γ‐rays induce a chain reaction leading to a polymer of identical chemical structure and stereochemistry as reported for the perovskite, but with higher molecular weight. Upon UV‐irradiation, however, the hydrochloride undergoes a stereoselective (2+2)‐cycloaddition to a cyclobutanoic dimer as main product and oligomers after prolonged irradiation. In the case of γ‐irradiation at 273 or 300K significant contributions from postpolymerization are found both for the hydrochloride and the perovskite of 1.
Evaluation of the viscometric constants for chitosan
Authors: Maghami Ghobad G. , Roberts George A. F.
Published: April 2003

Viscosity‐average relative molecular masses have been determined for a series of chitosans having the same relative molecular mass and relative molecular mass distribution but differing extents of N‐acetylation. The results obtained show that the same viscometric constants in the Mark‐Houwink equation [η] = Km ·Ma are applicable to chitosans over the range between 0 and 40% N‐acetylation Comparison of literature values for number‐ and weight‐avepge rela‐tive molecular masses Mn, and Mw, with the viscosity‐average relative molecular mass M, values calculated using the related viscosity data and each of the three sets of viscometric constants that have been proposed for chitosan, confirms that the most accurate values currently available are km = 1,81 · cm−3 · 10−1 and a = 0,93, using 0,l M acetic acid/0,2M NaCl as solvent.
Temperature dependence of the pitch of the cholesteric helix of poly(γ‐benzyl‐L‐glutamate) in N,N‐dimethylformamide and N‐methyl‐2‐pyrrolidone
Authors: Sikora Antonín , Siromyatnikova Tatyana A. , Ginzburg Boris M. , Alumyan Yurii A. , Shepelevskii Andrei A. , Frenkel Sergei Ya.
Published: April 2003

Temperature depenences of the pitch of cholesteric helix in solutions of poly(y‐benzyl‐L‐glutamate) in N,N‐dimethylformamide and N‐methyl‐2‐pyrrolidone were measured for various molar masses of poly(γ‐benzyl‐L‐glutamate). It was found that in N‐methyl‐2‐pyrrolidone inversion of the cholesteric helix takes place, i. e., that the right‐handed helix changes to the lefthanded one. By using an equation derived by Kimura, the temperatures at which the system has a nematic order were determined. The results obtained allow the statement that an important role in the inversion of the cholesteric helix in poly(γ‐benzyl‐L‐glutamate) solutions is played by conformational changes in side chains of the polypeptide molecule.
Association of three‐block copolymers polycaprolactam‐block‐polystyrene‐block‐polycaprolactam
Authors: Tuzar Zdeněk , Stehlíček Jaroslav , Koňák Čestmír , Lednický František
Published: April 2003

Colloidal particles of three‐block copolymers polycaprolactam‐block‐polystyrene‐block‐polycaprolactam, formed in a solvent mixture toluene/2,2,3,3‐tetrafluoropropanol as a good solvent of polycaprolactam, were studied by static and dynamic light scattering and transmission electron microscopy. Two kinds of spherical multimolecular particles differing in size were found in the solution. The smaller particles containing tens of copolymer molecules were interpreted as regular copolymer micelles, and the larger particles formed from thousands of copolymer molecules were interpreted as associates of these micelles.
Eine erweiterung der gaußschen netzwerktheorie durch die berücksichtigung voll gestreckter netzbögen
Authors: Ortmann Reinhold , Dietrich Johann , Bonart Richard
Published: April 2003

The Gaussian network theory of Kuhn and Grün neglects the limited contour length of network chains connecting neighbouring crosslinking points. Therefore, in the unstrained material Treloar replaces Gaussian network chain statistics by a sperical shell distribution neglecting the random walk behaviour of chain segments. We try to overcome this discrepancy in the present paper. Starting from Gaussian end‐to‐end distance statistics in the unstrained material we calculate the strain dependent amount and orientation of fully extended chains in strained samples. Fully extended chains are supposed to behave as stiff rods during further elongation. Thus, we take into account randomly coiled and fully extended chains simultaneously. We, therefore, have to replace the conventional assumption of linear affine deformation by a more complex relation, i. e. by a geometrically averaged affine deformation. This is connected with a model strain ratio differing from the macroscopic strain. The model ratio refers to the orientation behaviour of the end‐to‐end vectors, which, in the case of already fully extended network chains, hardly contribute to the macroscopic elongation of the sample. The calculation leads to a bimodal orientation function. The orientation factor is similar to that which follows from the conventional theory, whereas the entropic retractive force deviates from the conventional result.
A convenient synthesis of functional monomers: Unsaturated spiroorthoesters using phase transfer catalysis
Authors: Isobe Naoki , Nishikubo Tadatomi , Tagoshi Hirotaka , Endo Takeshi
Published: April 2003

Unsaturated spiroorthoesters, which undergo no shrinkage on polymerization, were synthesized in high yield by an elimination reaction of the corresponding halomethylated spiroorthoesters with potassium hydroxide (KOH) or potassium tert‐butoxide (t‐BuOK) using a phase transfer catalyst. It was found that tetrabutylammonium bromide exhibits a catalytic activity higher than that of the other quaternary ammonium salts, 18‐crown‐6 and poly(ethylene glycol) (M̄w = 300) under equal conditions. The elimination reaction of halomethylated spiroorthoesters proceeds easily in toluene or diglyme with t‐BuOK and in tert‐butyl alcohol with KOH leading to the corresponding unsaturated compounds in high yields. In addition, the bromomethylated spiroorthoesters showed higher reactivity than the chloromethylated spiroorthoesters under equal conditions.
Transformation of polyester chains into dicationically living ones and synthesis of telechelic co‐oligomers thereof
Authors: Zhang Hongzhi , Feng Xinde , Fu Jingguo , Yang Huichang
Published: April 2003

Unliving chains of aliphatic polyester were transformed into dicationically living poly(THF)‐block‐polyester‐block‐poly(THF) chains, and four different telechelic triblock co‐oligomers with primary, secondary, tertiary amine, and hydroxyl end‐groups were synthesized. A novel approach to the exchange of hydroxyl or carbonyl ends of polyester for amino end‐groups is described. The primary amine‐terminated telechelic triblock was used to modify an epoxy resin to give a toughened product with high strength.
Preparation and characterization of unsymmetrical “liposomes in a net”
Authors: Ringsdorf Helmut , Schlarb Bernhard
Published: April 2003

Negatively charged lipid molecules were converted into polymerizable lipids by introduction of polymerizable mono‐ or bifunctional counterions. As an attempt to mimic the cytoskeleton of biomembranes, unsymmetrical polymeric vesicles were prepared, where the polyelectrolyte is attached either only to the inner or to the outer bilayer surfaces. Polymerizable cations were introduced to the outer surface of preformed small unilamellar vesicles via ion‐exchange. The outer counterions of vesicles bearing polymerizable counterions at both sides of the membrane were replaced by Na+. Polymerization of these systems leads to unsymmetrical vesicles. The introduction, separation and polymerization of the organic counterions was monitored by UV‐spectroscopy. Due to polymerization of the counterions, the phase transition temperature of the membranes is shifted remarkably to higher temperatures. For a comparison of ionically attached and covalently bound polymers, two cationic lipids were synthesized, which have a bifunctional polymerizable headgroup. In contrast to the lipids with “ionic” spacers, the polymerization of the covalently bound methacrylic units resulted in a decrease of the phase transition temperature. Thus, by application of ionically bound polymerizable units, unsymmetrical polymerized vesicle membranes are readily available. These systems may serve as models for mimicking the cytoskeleton of living cells.
Polylactones, 15. Reactions of δ‐valerolactone and ϵ‐caprolactone with acidic metal bromides
Authors: Kricheldorf Hans R. , Sumbél Movita‐Verena
Published: April 2003

δ Valerolactone and ϵ‐caprolactone were reacted with BBr3, AIBr3, TiBr4, SnBr4 or Bu2SnBr2 in dichloromethane or chloroform in a 1 : 1 mole ratio. When these exothermic reactions were conducted with cooling, complexation of the lactones at the exocyclic oxygen was detectable by means of IR and 1H NMR spectroscopy as the first reaction step. However, heating to 60°C causes in all cases ring cleavage, and after hydrolytic removal of the metal bromides ω‐bromocarboxylic acids or oligomers with ω‐bromoalkanoyl end groups were obtained. SnBr4, Bu2SnBr2 and ZnBr2 proved to be good initiators of the polymerization of both lactones. At low monomer/initiator (M/I)‐ratios (high initiator concentrations) most of the initiator remained unchanged, and the average degrees of polymerization of the resulting polylactones largely exceeded the value expected for the M/I‐ratio. By means of viscosity and GPC measurements weight‐average molecular weights up to 70 000 were found. All polylactones obtained by initiation with these three metal bromides contain ϵ‐bromoalkanoyl end groups. Furthermore, high‐molecular‐weight poly(ϵ‐caprolactone) could be prepared at polymerization temperatures up to 150°C. The results do not indicate a cationic polymerization mechanism, but an insertion mechanism involving the metal‐O bond formed after the first cleavage of the lactone rings.
Intrinsic viscosity of intramolecularly crosslinked polyelectrolyte: Poly(vinyl alcohol)/borax systems
Authors: Ochiai Hiroshi , Kurita Yuji , Murakami Ichiro
Published: April 2003

The intrisic viscosity [η] of poly(vinyl alcohol) (PVA) was determined in aqueous solutions with various concentrations cb of borax (Na2B4O7) as functions of molecular weight M and concentration cs of NaCl as an added salt. Polyelectrolyte viscosity behaviour was observed for the systems containing both borax and NaCl, due to the complexation with negatively charged borate ions B(OH)−4 · [η] changes depending on the ionic strength I. It was found that the Stock‐mayer‐Fixman treatment for the molecular‐weight dependence of [η] is valid in the lower molecular‐weight range (M < 105), even though the present PVA chain contains some intrachain crosslinks. Theta conditions can be attained at an appropriate concentration cs Θ of NaCl. The value of cs Θ is dependent on cb, but the conformational parameter from the Stockmayer‐Fixman treatment K0 is almost independent of cb. The effect of intrachain crosslinks becomes evident only as a considerably large negative value for the excluded volume parameter B at infinite ionic strength. In addition, the electrostatic part of the expansion factor α was found to be linearly correlated to a reduced parameter (M/I)1/2 for all cb systems, from the slope of which the charge density was estimated.
Decay of radical initiators in emulsion copolymerization of unsaturated polyesters and styrene
Authors: Bauer Harald , Ortelt Martina , Joos Betina , Funke Werner
Published: April 2003

Emulsion copolymerization of unsaturated polyesters (UP) with styrene was initiated by potassium peroxodisulfate and by azodiisobutyronitrile (AIBN). The decay rates of both initiators were compared and influences of temperature, electrolyte and concentration of the reaction components studied. Initiation radicals from the persulfate partly add to unsaturated UP units and decarboxylate terminal acid groups of the UP. Initiation by AIBN predominantly occurs in the aqueous phase, and side reactions with this initiator are neglectable.
Group transfer polymerization of methyl methacrylate in acetonitrile, 2. Initiation by trimethylsilyl cyanide
Authors: Speikamp Hans‐Dieter , Bandermann Friedhelm
Published: April 2003

Results of group transfer polymerization of methyl methacrylate (MMA) in acetonitrile with tetraethylammonium cyanide (Et4NCN) and tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF2SiMe3) as catalysts and trimethylsilyl cyanide as initiator are presented. It is shown, that both catalysts behave similarly with respect to catalysis of the initiation and the propagation step and of the termination step of the growing chains with the solvent, TASF2SiMe3 being more active than Et4NCN.
Structural study of compounds modelling elementary polymer units, 5. Molecular and crystal structures of C, C′‐disubstituted o‐carboranes
Authors: Lindeman Sergey V. , Khotina Irina A. , Teplyakov Mikhail M. , Struchkov Yurii T. , Korshak Vasilii V.
Published: April 2003

With the aim to determine the main structural characteristics of amorphous (branched and different‐unit) polymers of the polyphenylene type, prepared by polycyclocondensation of carborane‐containing mono‐ and diacetylaromatic compounds, an X‐ray structural study of four model compounds was carried out, viz. of 1,2‐bis[4‐(4‐acetylphenoxy)phenyl]‐1,2‐dicarba‐closo‐dodecaborane(12) (1) (triclinic crystals, a = 8,205 Å, b = 13,505 Å, c = 14,019 Å, α = 90,44°, β = 97,08°, γ = 97,24°, space group P1, Z = 2, R = 0,045 for 2663 reflections), 1,2‐bis(4‐phenoxyphenyl)‐1,2‐dicarba‐closo‐dodecaborane(12) (2) (monoclinic crystals, a = 14,813 Å, b = 17,133 Å, c = 11,211 Å, β = 112,43°, space group P21/c, Z = 4, R = 0,066 for 3 286 reflections), 1,2‐bis(4′‐acetylbiphenyl‐4‐yl)‐1,2‐dicarba‐closo‐dodecaborane(12) (3) (orthorhombic crystals, at −120°C a = 13,405 Å, b = 9,276 Å, c = 22,86 Å, space group Pnam, Z = 4 molecules on the m plane, R = 0,039 for 1 147 reflections), and 1,2‐bis(4‐acetylbenzyl)‐1,2‐dicarba‐closo‐dodecaborane(12) (4) (orthorhombic crystals, at −120°C a = 22,03 Å, b = 26,23 Å, c = 8,026 Å, space group Fdd2, Z = 8 molecules lie on the two‐fold axis, R = 0,051 for 577 reflections). The strained structure of the C,C′‐o‐diphenyl‐substituted carboranyl fragment is established, the high conformational flexibility of 4‐phenoxyphenyl linkages is confirmed and a tendency toward separate autoassociation of acetyl‐containing polar groups and carborane nuclei is shown, with the autoassociation of polar groups completely suppressing that of carborane nuclei in case of conformational rigidity and shortness of the arylene linkages. These and other structural characteristics of the investigated model compounds and their crystals, in case they turn out to be characteristic also for the corresponding polymers and their precursors, should largely determine the structure and physico‐chemical properties of their corresponding polymers.
Partitioned polymerization, 1. Transfer of initiator and/or monomer
Authors: Bartoň Jaroslav , Juraničová Viera , Hloušková Zuzana
Published: April 2003

The polymerization of acrylamide initiated by 2,2′‐azobisisobutyronitrile in the system water/benzene and water/ethyl acetate (vol. ratio 3 : 1), the emulsion polymerizations of methyl methacrylate, butyl methacrylate, styrene and acrylonitrile, and the emulsion copolymerization of butyl methacrylate with acrylonitrile and styrene with acrylonitrile initiated by ammonium peroxodisulfate in the presence and/or absence of the inhibitor 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl were studied. These systems represent a model of the partitioned polymerization. The partitioned polymerization is characterized by the deposition of a monomer and an initiator in different, mutually immiscible phases, e.g. water and oil phase, before polymerization. In order to start the polymerization the monomer (initiator) must transfer into the phase where the initiator (monomer) is situated. Application of the principle of partitioned polymerization led to the formulation of a novel approach to the initiation mechanism of emulsion polymerization of polar and non‐polar monomers initiated by water soluble or oil soluble initiators.
Studies in ring‐opening polymerization, 9. Co‐metathesis of cyclic alkenes and unsaturated esters
Authors: Amass Allan J. , Dale Audrey L. , Tighe Brian J.
Published: April 2003

The polymerization of cyclopentene in the presence of an unsaturated ester led to the synthesis of low‐molecular‐weight polypentenamer with a terminal functional group by ringopening metathesis polymerization using WCl6/AlEtCl2/EtOH as catalyst. Unlike most reactions of this nature the efficiency of the catalyst system is high because the ester used possesses an electron withdrawing group, the trichloromethyl group. The presence of this group ensures that the complex formed between the metal carbene complex and the ester group is reduced in stability and catalyst concentrations normally used for ring‐opening metathesis polymerizations can be used (mole ratio W : CP = 1 : 1000), the concentrations of ester being quite high (mole ratio ester : CP = 1 : 5). Under these conditions reasonably high yields of liquid polymers are obtained.
The formation of trans‐epoxides during the photochemical oxidation of cis‐polyisoprenes to liquid rubbers
Authors: Burfield David R.
Published: April 2003

Photochemical hydrogen peroxide catalyzed degradation of both natural rubber and synthetic cis‐polyisoprene is shown to result in the formation of a low‐molecular‐weight oil functionalised with hydroxyl, carbonyl and epoxide groups. Interestingly, the epoxide groups are shown to be of a trans‐configuration. A scheme is proposed to account for the formation of trans‐epoxide as well as concomitant mainchain isomerization. The preferential formation of trans‐epoxide in free radical oxidations strongly suggests that the naturally occurring cis‐epoxide, present in natural rubber, is due to a stereospecific enzymatic process, and is not the byproduct of radical oxidation.
Effects of ionenes on structure and catalytic activity of cobaltphthalocyanine, 3. Interaction of 2,4‐ionene with cobaltphthalocyanine and model compounds
Authors: van Welzen Joke , Van Herk Alex M. , German Anton L.
Published: April 2003

In order to obtain detailed information about the interaction between the constituents of the cobaltphthalocyanine‐tetrasodium sulfonate/ionene system, a catalyst used in thiol autoxidation, 2,4‐ionene was studied in combination with Fe(CN)4−6, Fe(CN)3−6, congo red, and several metal(II)phthalocyanines. In all cases, stoichiometric complexation was observed, at a ratio where the positive charges on the polymer were just matching those of the anionic species. The hexacyanoferrate complexes were found to be less stable than the dye complexes, due to the formation of dye aggregates in the latter systems. These aggregates appear to enhance the electrostatic interaction with the polymer to such an extent that even irreversible ionomeric “crosslinking” may occur. The results are discussed in relation to the catalytic activity of the polymeric catalyst.
Etude cinétique de la polymérisation en émulsion du styrène en présence d'éamulsifiants amphiioniques de type sulfobétaïne
Authors: Essaddam Hatem , Pichot Christian , Guyot Alain
Published: April 2003

Emulsion polymerization of styrene was carried out at 70°C with sodium persulfate as initiator in the presence of 3 different sulfobetaïne‐type amphoteric surfactants. Their micellar properties were well‐characterized as function of temperature, ionic strength and pH. The kinetic behavior, based on the analysis of monomer consumption, particle size and molecular weight, was found to depend on the emulsifier type and concentration. The results were compared with those obtained in the presence of sodium dodecyl sulfate (1) and under emulsifierfree conditions. With dodecyldimethylammoniopropanesulfonate (2), the kinetic behavior was similar to what is observed in 1‐emulsified polymerization, whereas with dimethyloctadecylammoniopropanesulfonate (3) and 3‐N‐acetyl‐N‐(dodecyldimethylammoniomethyl)aminopropanesulfonate (4), exhibiting lower critical micell concentration, the particle formation mechanism was also controlled by homogeneous nucleation associated with a limited flocculation period. The pH was found to affect the polymerization kinetics, however, the effect was more likely attributed to the initiator decomposition.
Aminolysis of low‐molecular‐weight and polymeric 4‐nitrophenyl esters
Authors: Frechet Jean M. J. , Mikeš František , Výprachtický Drahomír , Lam Hoang , Labský Jiří
Published: April 2003

4‐Nitrophenyl methacrylate (1a), 4‐nitrophenyl esters of some N‐methacryloyl‐ω‐amino acids (1b −d) and 4‐nitrophenyl esters of N‐acetyl‐ and N‐methacryloyltryptophane (2a and 2b) were prepared and characterized. Copolymers of 1 a −d and 2 b with N‐2‐hydroxypropylmethacrylamide (HPMA), N‐isopropylmethacrylamide (iPMA) and N‐ethylmethacrylamide (EMA) were also prepared. The 4‐nitrophenyl ester content of the copolymers was determined spectrophotometrically from their UV absorption and from the UV absorption of the 4‐nitrophenolate ion which is released upon hydrolysis of the active esters with 0,1 M sodium hydroxide. The difference between these values depends on both the type of polymerizable active ester used and the comonomer. The proportion of non‐hydrolyzable structure is especially high in the case of copolymers containing 4‐nitrophenyl esters of the methacryloylated α‐amino acids 1b and 2b. The formation of non‐hydrolyzable structures is likely due to side reactions which occur during polymerization. The polymers prepared by copolymerization of the polymerizable 4‐nitrophenyl esters were not found to be suitable for the preparation of polymeric fluorescent probes by a chemical modification route. It was found that the rate of aminolysis of low‐molecular‐weight and polymeric activated esters increases with increasing the number of methylene groups in the N‐(ω‐aminoalkyl)‐5‐dimethylamino‐1‐ naphthalenesulfonamides (dansylamines) 3a–f.
Liquid‐crystalline poly(β‐aminoester)s. Thermotropic mesomorphism and degradability in solution
Authors: Laus Michele , Angeloni Annino Sante , Galli Giancarlo , Chiellini Emo
Published: April 2003

Poly(β‐aminoester)s 7 – 12, containing in the repeating unit ethylenebis(carbonyloxy‐1,4‐phenylene)carbonyloxy groups interconnected by polymethylene segments of different length and coupled by diamino spacers, were synthesized from mesomorphic diacrylates and secondary diamines. The thermal behavior and the solution properties of the polymers were investigated. Depending on the structure of the repeating unit, the polymers were found to give rise to either isotropic or anisotropic melts. The incidence and extension of the mesophase are favored in poly(β‐aminoester)s based on even numbered methylene segments and 2‐methylpiperazinediyl spacers. The polymer samples were found to degrade at room temperature, when dissolved in solutions containing water, an organic base or an acid. Based on a macromolecular model compound (14) a degradation process is suggested involving a selective cleavage of the benzoate ester groups assisted by the amino groups in β‐position.
Preparation of metal‐free polyphthalocyanine thin films by an evaporation‐polymerization method
Authors: Abe Katsuya , Ohkatsu Yasukazu , Kusano Toru
Published: April 2003

A thin film (thickness: 200 nm) of metal‐free polyphthalocyanine, which is insoluble in organic solvents, was prepared by an evaporation‐polymerization process under mild conditions developed by us. The thin film is not only though, but it also resists chemicals and heat. Its conductivity is 1,1 · 10−4 S · cm−1, and it increases to 0,15 S · cm−1 on I2‐doping.
Synthèse, polymérisation et copolymérisation d'un dérivé 2h‐benzotriazolylphényl de l'acétate de vinyle
Authors: Camps Marcel , Monthéard Jean‐Pierre
Published: April 2003

1‐(4‐Acetoxy)‐3‐(2H‐benzotriazolylphenyl)vinyl acetate (4) was synthesized. The polymerization of 4 afforded polymer 5 with a relatively low molecular weight (= 2000). Copolymerizations of 4 (3,7 wt.‐%) were carried out with styrene and methyl methacrylate to copolymers 6 and 7, respectively. Polymer 5 and copolymers 6 and 7 were characterized by 1 H and 13 C NMR and by IR and UV spectroscopy. Their UV spectra show a strong absorption in the near UV spectrum. 4 may thus be considered as a potential comonomer for UV protection.
Physical behaviour of stereoblock‐isotactic polypropylene
Authors: de Candia Francesco , Russo Roberto , Vittoria Vittoria
Published: April 2003

Preliminary results regarding the physical behaviour of a stereoblock‐isotactic polypropylene are reported. The polymer was obtained using a soluble Ziegler‐Natta catalyst and films were prepared by pressure molding. The particular steric configuration is responsible of low crystallinity and small crystal size; the bulk structure can be represented by a fringed micellar model in which small crystallites act as physical crosslinks. The observed behaviour being typical of a thermoplastic elastomer well agrees with the suggested model.
13C NMR characterization of copolymers of ethylene and perdeuteroethylene
Authors: Cheng H. N. , Dziemianowicz Theodore S.
Published: April 2003

Copolymers of ethylene and ethylene‐d4 were prepared, and their composition and comonomer sequence distribution determined from high‐field 13C NMR spectra. For a conventional Ziegler‐Natta catalyst, deuterium was shown to decrease the reactivity of ethylene.
Thermal and rheological properties of poly(vinyl alcohol) hydrogels prepared by repeated cycles of freezing and thawing
Authors: Watase Mineo , Nishinari Katsuyoshi
Published: April 2003

Differential scanning calorimetry and scanning electron microscopy were carried out in order to study the relation between the structure and properties of poly(vinyl alcohol) hydrogels prepared by repeated cycles of freezing‐thawing. The effect of the number N of repeated cycles of freezing‐thawing, of the degree of saponification (DS), and of the degree of polymerization (DP) on structure and properties was examined. The elastic modulus and the endothermic enthalpy, estimated from the area surrounded by the endothermic peak, increase with increasing N, DS, and DP. The melting temperature Tm shifts to higher temperatures with increasing DS and DP, but it is almost independent of N for gels with high DS or DP. In PVA gels with lower DP or DS, Tm shifts to higher temperatures with increasing N. The temperature dependence of the elastic modulus is discussed on the basis of a theory on thermoreversible gels.
The structure of neutral polythiophene. An application of the rietveld method
Authors: Brückner Sergio , Porzio William
Published: April 2003

The crystal structure of polythiophene is analyzed by the Rietveld whole‐fitting method on the X‐ray diffraction powder profile. Experimental data allow only a bidimensional characterization of the structure in the plane orthogonal to the chain axis with a pgg symmetry (a = 7,79; b = 5,53 Å). Best fitting is obtained by assuming rigorous coplanarity of thiophene rings along the chain. The presence of few and weak layer‐peaks is interpreted in terms of only partial ordering of chains along their axes. The final disagreement factor, in terms of ∑|I0 − Ic|/∑ Inet, is 0,125.
Polymeric bound porphyrins and their precursors, 6. Syntheses of water‐soluble, negatively or un‐charged polymers with covalently bound moieties of porphyrin derivatives
Authors: Wöhrle Dieter , Krawczyk Gerhard , Paliuras Mihail
Published: April 2003

Water‐soluble polymers 6–17 containing covalently bound moieties of porphyrin derivatives were prepared by reaction of poly(methacrylic acid) (4) and poly(N‐vinylpyrrolidone‐co‐methacrylic acid) (5) with the low‐molecular‐weight substituted tetraphenylporphyrin 1 b, phthalocyanines 2 b and 2 d and naphthocyanine 3 c. Besides binding of one porphyrin derivative, also combined binding of two or three different porphyrin derivatives to the polymers could be achieved. The resulting polymers are negatively charged (polymers 6–11) or uncharged (polymers 12–17).
Immobilisierte tris(2,2′‐bipyridin)ruthenium(II)‐komplexe als photosensibilisatoren für die wasserphotolyse
Authors: Nußbaumer Walter , Gruber Heinrich , Greber Gerd
Published: April 2003

Crosslinked polymers containing pendant tris(bipyridyl)ruthenium(II) complexes [Ru(bipy)] were synthesized and examined as sensitizers for the light‐induced formation of hydrogen in the heterogeneous system H2O/immobilized Ru(bipy)/ethylenediamine‐tetraacetic acid/platinum. Hydrogen generation rates of 0,037 ml/h were obtained with Ru(bipy) ‐complexes immobilized with spacer groups onto hydrophilic carriers based on sucrose‐methacrylates as well as hydrophobic carriers based on crosslinked poly(4‐aminostyrene), whereas carrier bound complexes without spacer gave lower efficiencies in hydrogen production. The hydrogen generation rates were linear for more than 8 days.
Polymérisation induite par un plasma froid. Etude des mécanismes de polymérisation en fonction de l'épaisseur du film
Authors: Epaillard Fabienne , Brosse Jean‐Claude , Legeay Gilbert
Published: April 2003

The reactive species (radicals, ions, etc.) or the UV‐visible radiation emitted by the excitated species initiate the cold plasma induced polymerization of a monomer in the liquid or solid state. The residual CC double bond concentration of an acrylic monomer depends on the plasma characteristics (gas nature, pressure, discharge power, etc.), but also on the polymerization conditions. The UV‐visible radiation emitted in a cold plasma has more influence on the thickness of the film than the reactive species bombardment. Two simple mathematic laws describe these phenomena.
Influence of the interphase on mechanical properties in block copolymers
Authors: Bühler Fritz , Gronski Wolfram
Published: April 2003

Polystyrene‐block‐poly(styrene‐ran‐isoprene)‐block‐polyisoprene characterized by a morphology of spherical rubbery microdomains in a continuous polystyrene matrix is considered as a model for rubber‐toughened thermoplastics in which the volume fraction of the interfacial layer can be varied by varying the volume fraction of the interblock. Stress‐strain measurements of these systems are presented in relation to their morphology, interblock volume fraction and molecular weight of the polystyrene block. The results indicate that the energy of fracture is increased with increasing width of the interfacial layer without change of Young's modulus.
Relative reaction probabilities in polymer‐polymer reactions, 1. Investigations with Monte‐Carlo model chains
Authors: Olaj Oskar Friedrich , Zifferer Gerhard
Published: April 2003

Pairs of chains taken from ensembles of five‐way cubic lattice chains (athermal or theta) were analysed for the (relative) probability of contact formation between specified segments belonging to different chains within this pair. This probability may be taken as a measure of the rate constant which characterizes bimolecular polymer‐polymer reactions which occur between active sites attached to or localized at these segments, relative to the reaction between the same active sites, if these were not bound to the polymer chains. It turns out that the (expected) effect which results from the interaction between the chains as a whole (external shielding) is of comparatively small extent and is fairly independent of chain length. The much more important contribution, however, is made by a novel phenomenon which — exhibiting a strong dependence on chain length n — is responsible for an “internal” shielding: the compatible pair configurations (i. e. those which are free of intermolecular intersections) are characterized by largely increased segment‐segment distances. As a consequence, the probability of contact formation is much lower than it would be expected from a convolution of the (mutually independent) radial distributions of the segments participating in contact formation. The overall shielding factor K can be represented as a product of the fairly independent contributions of external (KG) and internal (Kw) shielding. The overall chain length dependence is described by a power law K = Dnd, where the exponent d depends on whether two (Type I contacts), one (Type II) or no endsegment at all (Type III) is involved in contact formation. For athermal chains the exponents are d = −0,16 (Type I), d = −0,30 (Type II), and d = −0,50 (Type III), the pre‐factor being of the order of unity throughout. Θ‐systems roughly show the same general characteristics as the athermal ones, however, to a lesser extent. Thus, neither shielding nor its chain length dependence vanish, the exponents being about −0,06 (Type I), −0,1 (Type II), and −0,2 (Type III), respectively.