bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly(methyl methacrylate)‐block‐poly(2,2‐dimethyltrimethylene carbonate); site transformation from a group transfer polymerization to an anionic ring‐opening polymerization
Authors: Hovestadt Wieland , Keul Helmut , Höcker Hartwig
Published: April 2003

Poly(methyl methacrylate)‐block‐poly(2,2‐dimethyltrimethylene carbonate) was prepared by a group transfer polymerization (GTP) of methyl methacrylate (MMA), followed by an anionic metal‐free polymerization of 2,2‐dimethyltrimethylene carbonate (DTC). It was shown that the anionic metal‐free polymerization of DTC can be initiated either by the system silyl ether/tris(dimethylamino)sulfonium trimethylsilyldifluoride (TASF) or by the system 1‐methoxy‐1‐trimethylsilyloxy‐2‐methyl‐1‐propene (MTS) in combination with TASF. The latter can be considered as a model compound for the living PMMA end in a GTP polymerization. The transformation of the trimethylsilyl ketene acetal end into an anionic species was achieved by desilylation with TASF. In the presence of DTC the resulting enolate reacts as carbanion with the carbonyl group of the carbonate moiety. Thus, at the linkage of the two blocks a disubstituted malonic acid derivative is formed. GPC analysis of the copolymers reveals a unimodal and rather narrow distribution of molecular weights. The block structure expected from the way of preparation is confirmed by 13C NMR analysis. The 1H NMR analysis gives the composition of the block copolymers and reveals that the larger the PMMA block, the less efficient is the initiating ability, leading to a larger PDTC block as expected from the monomer to initiator ratio; correspondingly more homo‐PMMA is formed. Thermal analysis of the block copolymers shows a melting transition of the PDTC block which is by about 20°C lower than that of the homopolymer: the glass transition temperature of the PMMA block is hidden under the melting transition of the PDTC block.
Photo‐crosslinking of polymers bearing p‐(formylamino)‐styrene units
Authors: Shirai Masamitsu , Suzuki Masako , Saito Takayuki , Koyama Masaya , Tsunooka Masahiro
Published: April 2003

Photosensitive polymers were synthesized by radical copolymerization of p‐(formylamino)‐styrene

IUPAC name: p‐vinylformanilide.

(1) with styrene (2), butyl methacrylate (3) or methyl methacrylate (4). On irradiation with 254 nm light the polymers become insoluble in solvents. Effects of the fraction of 1 units in the copolymers and of the polymers structure on the photoinduced insolubilization of the polymers were studied. The insoluble fraction of the exposed polymer films was enhanced by post‐heating. The quantum yield of the photolysis of 1 units in polymers was almost independent of the polymer structure. From model reactions employing formanilide, a mechanism of insolubilization of the polymers was discussed.
Synthèse et caractérisation de polystyrènes siliciés
Authors: Madit Nicolas , Bonfils Frédéric , Giral Louis , Montginoul Claude , Sagnes René , Schué François
Published: April 2003

Poly(p‐trimethylsiloxystyrene) (1a), poly[p‐(tert‐butyldimethylsiloxy)styrene] (1b), poly[p‐(trimethylsiloxy)‐α‐methylstyrene] (1c), poly[p‐(tert‐butyldimethylsiloxy)‐α‐methylstyrene) (1d) and poly{p‐[2‐(tert‐butyldimethylsiloxy)ethyl]styrene]} (1e) were prepared by free‐radical or cationic polymerization of the corresponding monomers. Poly{[p‐[2(trimethylsiloxy)ethyl]styrene]‐co‐[p‐(2‐hydroxyethyl)styrene]} (2a) was synthetized by anionic polymerization of the corresponding trimethylsilylated monomer, followed by acid hydrolysis of the resulting polymer. Poly{[p‐[2‐(trimethylsiloxy)ethyl]styrene]‐co‐[p‐(tert‐butoxycarbonyloxy)styrene]} (2b) were prepared by free‐radical polymerization of the corresponding monomers.
Molecular weight control of linear polyethylenes prepared in gas phase with Ziegler catalysts
Authors: Pasquet Véronique , Spitz Roger
Published: April 2003

Linear polyethylenes covering the range from high to low density were prepared in gas phase using an MgCl2‐supported Ziegler catalyst deposited on silica (bisupported catalyst). The comonomer used was 1‐butene. Molecular weights are dependent both on 1‐butene concentration and hydrogen pressure. The interaction of these two factors can be interpreted by the enhancement of the transfer reactions after 1‐butene insertion.
Some aspects of the reactivity of photo‐dimerizable esters grafted onto silicone main chain polymers
Authors: Coqueret Xavier , Achari Ahmida El , Hajaiej Adel , Lablache‐Combier Alain , Loucheux Claude , Randrianarisoa Lili
Published: April 2003

The reactivity under UV light and at room temperature of two series of photo‐crosslinkable silicone polymers containing pendant cinnamic or α‐cyano‐β‐styrylacrylic

Systematic name: 2‐cyano‐5‐phenyl‐2,4‐pentadienoic.

(CSA) esters was examined by means of UV spectroscopy. Two types of behaviour were evidenced on the basis of qualitative spectrum observation and quantitative measurements of reaction rates. Polymers with trans‐cinnamic pendant groups were found to undergo during the first moments of 280 nm irradiation a fast photo‐isomerization, preceding the dimerization process which takes place with a smaller rate. The mobility of the reactive cinnamic chromophores attached to the highly flexible silicone main chain leads to a collision‐controlled process contrasting with the behaviour of the polymers containing more polar CSA esters. In this case, a clean dimerization with high reversibility suggests a matrix‐controlled process. This is supported by kinetic data indicating a levelled reactivity for several polymers containing different amounts of CSA esters.
Monte Carlo simulation of tetrahedral chains, 4. Size and shape of linear and star‐branched polymers
Authors: Zifferer Gerhard
Published: April 2003

Linear and star‐branched chains with F = 4 − 12 arms and N = 125 − 7685 segments covering points of a tetrahedral lattice were generated by use of a pivot algorithm. For large N, the acceptance fractions f̄ of attempted moves may be described by a power law f̄ = A · (N − 1)−α. Clearly, the factor A decreases with increasing functionality F, but the exponent α is independent of the number of arms and equal to the value obtained for linear chains, α ≈ 0,1. Due to the influence of the hard‐core (centre) of the star, the acceptance fraction f̄ for small N is lower than predicted by the scaling law, yielding a stronger dependence on F than for large chains. Meansquare dimensions, i. e. mean‐square radius of gyration, mean‐square end‐to‐end distance and mean‐square centre‐to‐end distance obey a power law dependence on chain‐length (N − 1), the exponent being ≈ 1,184 for 245 ≤ N ≤ 7685 in all cases; alternatively, the (quadratic) dimensions may be described by a corrected scaling law (N − 1)2v · (C0 + C1 · (N − 1)−Δ) with v = 0,588 and Δ ≈ 0,5 as proposed by renormalization group theory for linear chains. The shape asymmetry of star‐branched polymers (with the same total number of segments each) decreases with increasing number of arms, but is still appreciable for F = 12, the highest number of arms examined.
Thermal reactions of amphotropic copolymers studied by thermogravimetry and temperature‐resolved pyrolysis‐field ionization mass spectrometry
Authors: Plage Bernd , Schulten Hans‐Rolf , Ringsdorf Helmut , Schuster Andreas
Published: April 2003

The thermal degradation mechanisms of amphiphilic acrylic copolymers containing mesogenic pyrimidine side chains and hydrophilic 2‐hydroxyethyl acrylate (HEA) main‐chain spacer units were investigated by thermogravimetry (TG) and pyrolysis‐field ionization mass spectrometry (Py‐FIMS). The degradation behaviour of these polymers depends on the amount of HEA incorporated. Thermogravimetry revealed that the main decomposition occurs in a single step for the pyrimidine homopolymer, whereas with increasing HEA content a two‐step process evolves. The major products identified by Py‐FIMS are two alcohols and one olefin split from the aromatic side chains. Depolymerization is only a minor degradation pathway. The rather complex thermal behaviour can be explained by three different reaction mechanisms: (a) alcohol formation via reaction of the HEA hydroxyl groups with ester groups in the side chains, (b) intramolecular cis‐elimination forming a volatile olefin and carboxylic acid groups remaining at the polymer backbone, and (c) the reaction of these acid groups with ester bonds forming the alcohols. Steps (b) and (c) are dominant for the pyrimidine homopolymer. With increasing HEA content in the copolymers step (a) becomes more important and, in addition, chemical crosslinking occurs. The mesogenic monomer, which was also examined, polymerized under the experimental conditions and showed essentially the thermal features of the pyrimidine homopolymer.
Novel degradable methacrylate‐ and p‐vinylphenoxy‐based oligomers, 1. Synthesis and characterization
Authors: Ericsson Jan , Hult Anders
Published: April 2003

Procedures are presented for the synthesis of a series of dicarbonate oligomers with either methacrylate or p‐vinylphenoxy end‐groups as polymerizable units. In addition, the synthesis route is given for a novel precursor of p‐vinylphenoxy‐type carbonates, namely, p‐nitrophenyl 3‐p‐vinylphenoxypropyl carbonate. Polymerization of the new oligomers was studied by differential scanning calorimetry (DSC). The bis(p‐vinylphenoxy) dicarbonates were polymerized by thermally induced cationic polymerization, and the corresponding dimethacrylates by free‐radically initiated photopolymerization.
Batch emulsion copolymerization of butyl acrylate and methyl methacrylate in the presence of sodium dodecyl sulfate
Authors: Emlie Brigitte , Pichot Christian , Guillot Jean
Published: April 2003

Kinetics of batch emulsion copolymerization of butyl acrylate (BuA) with methyl methacrylate (MMA) have been investigated using sodium dodecyl sulfate as emulsifier and the redox system potassium peroxodisulfate (K2S2O8)/sodium disulfite (Na2S2O5) as initiator. Latexes have been characterized with regard to their copolymer composition through 1H NMR analysis and particle size distribution by a quasi‐elastic light scattering (QELS) technique or transmission electron microscopy. The effect of the monomer feed composition on the average copolymer composition vs. conversion was first studied in order to derive emulsion reactivity ratios. However, simulation of experimental data based on monomer partitioning (due to the high water solubility of MMA) and particle swelling was better accounted for when considering bulk reactivity ratios together with polymerization in the aqueous phase (in addition to that in the main locus of the polymer particles). Then, the influence of several pertinent parameters, such as emulsifier concentration, amount of initiator, monomer‐to‐water ratio and addition of an organic solvent has been examined in relation to the actual polymerization mechanism.
Luminescent characteristics of tris(2,2′‐bipyridine)‐ruthenium(II) adsorbed in a silk fibroin membrane
Authors: Yoshimizu Hiroaki , Asakura Tetsuo , Kaneko Masao
Published: April 2003

The emission characteristics of the excited state of tris(2,2′‐bipyridine)ruthenium(II), Ru(bpy), adsorbed on a silk fibroin membrane is studied. The life time of the excited state of the adsorbed Ru(bpy) is unusually longer (1 000 ns) than that of Ru(bpy) in aqueous solution (598 ns). The excited state of the adsorbed Ru(bpy)32+ is quenched by oxygen when dipped in methanol, but not in water. The quenching by oxygen in methanol follows the Stern‐Volmer equation. The luminescent characteristics of the adsorbed Ru complex is discussed in terms of binding in hydrophobic domains composed of tyrosine residues of the protein.
On the rectilinearity of copolymers
Authors: Jung Bernd , Depner Michael
Published: April 2003

The expression “stiffness” of a polymer chain is shown to be ambiguous, and the use of the word “rectilinearity” is proposed to replace it in certain contexts. The influence of non‐uniform curvature on Kuhn length and mean‐square end‐to‐end distance of (co)polymers is studied using the frameworks of the freely‐rotating‐chain model and the Porod‐Kratky model. It is shown that every fluctuation around the given mean curvature of a chain increases its overall rectilinearity. Specifically, it is concluded that the rectilinearity increases with increasing fluctuation magnitude and with increasing separation of the different curvatures along the chain, i. e., it becomes greater in the order: alternating, random and block copolymer.
Some fundamental studies of the reaction of poly(vinyl alcohol) with alkyl chlorophosphates
Authors: Arranz Félix , Sánchez‐Chaves Manuel , Baena Francisco , Fontaine Laurent , Brosse Jean‐Claude
Published: April 2003

The modification reaction of poly(vinyl alcohol) with diethyl chlorophosphate and ethyl dichlorophosphate is studied in homogeneous phase using tertiary amines as catalysts. The structure of the modified polymers was determined by means of 1H and 31P{1H} nuclear magnetic resonance (NMR) spectroscopy as well as by chemical analysis. The structure of the polymers resulting from the reaction with diethyl chlorophosphate greatly depends on the reaction temperature as well as the catalyst. For lower reaction temperatures (≤25°C) only acyclic phosphate ester groups were observed. The activation energy was found to be 24,9 kJ/mol. The presence of cyclic phosphate ester groups was found, when higher reaction temperatures (>25°C) were used. These results can be interpreted considering the existence of transesterification reactions. Crosslinking structures were obtained in case ethyl dichlorophosphate was used instead of diethyl chlorophosphate.
Polymerization reaction with diphenylphosphoryl azide. Preparation of poly(α‐amino acid)s by direct polycondensation of α‐amino acids
Authors: Nishi Norio , Tsunemi Masahiko , Hayasaka Hideki , Nakajima Bun‐ichiro , Tokura Seiichi
Published: April 2003

Polypeptides can be prepared by stirring an amino acid solution in the presence of diphenylphosphoryl azide (DPPA) and an adequate tertiary amine. Generally, 1,3 mol of DPPA and 2,3 mol of triethylamine per mol of amino acid gave the best result. Polymerization of various amino acids (Gly, Ala, Leu, Phe, Met, Glu(OBzl), Glu(OMe), Cys(Bzl), Ser(Bzl), His(Bzl), Lys(Z), Arg(Tos), Arg(NO2), Arg(Mts), etc.; cf. Tab. 2) in dimethyl sulfoxide, N,N‐dimethylformamide, 1,4‐dioxane, pyridine, etc. gave the corresponding polypeptides with molecular weights as estimated from their intrinsic viscosities between 3 000 and 16 000, in reasonable yields. The purity of the resulting polypeptides was confirmed by IR, elemental analysis and optical rotation measurements of their acid total hydrolysates.
Polymerization reaction with diphenylphosphoryl azide. Preparation of sequential polypeptides by direct polycondensation of peptides
Authors: Nishi Norio , Naruse Takumi , Hagiwara Kiyoshi , Nakajima Bun‐ichiro , Tokura Seiichi
Published: April 2003

Various kinds of sequential polypeptides were prepared by direct polymerization of peptides in the presence of diphenylphosphoryl azide (DPPA). Typically, polymerization reactions were carried out as follows; monomer peptide concentration: 300 mg/0,6 mL of DMSO (or some other solvent); amount of DPPA: 1,3 mol/mol peptide; amount of triethylamine: 2,3 mol/mol peptide (+1,0 mol/mol peptide in case of peptide hydrochloride); reaction time: 2 days at room temperature. Molecular weights of the resulting sequential polypeptides were estimated from their intrinsic viscosities in dichloroacetic acid and SDS‐polyacrylamide gel electrophoresis; they range from 4 000 to 30 000. The purity of the sequential polypeptides was confirmed by IR, elemental analysis and optical rotation measurements of their acid total hydrolysates.
Chiral liquid‐crystalline polymers by polymer‐analogous reactions
Authors: Kapitza Heinrich , Zentel Rudolf
Published: April 2003

A synthetic route to combined main‐chain/side‐group chiral liquid‐crystalline (lc) polymers via precursor polymers with phenolic groups is presented. A polymer‐analogous reaction with chiral acids (conversions 90–100%) led to 33 new chiral lc polymers, which exhibit chiral smectic C*, smectic A, and cholesteric phases.
Copolymers and terpolymers of sulfur dioxide with allyl monomers comprising groups absorbing ultraviolet irradiation
Authors: Florjańczyk Zbigniew , Zygadło Ewa
Published: April 2003

Alternating copolymers are obtained of sulfur dioxide with allyl phenyl ether, allyl p‐nitrophenyl ether, N‐allylbenzamide, N‐allyl p‐nitrobenzamide, allyl cinnamate and allyl o‐benzoylbenzoate. Copolymerizations proceed in high yield at ‐78°C in the presence of tert‐butyl hydroperoxide as initiator. However, copolymer yield is small for reactions initiated with 2,2′‐azoisobutyronitrile at 50–60°C. Ultraviolet spectra of the copolymers obtained show the presence of intense absorption bands in the range of 220 to 305 nm. SO2 terpolymers have been obtained with allyl ethers, allyl amides or allyl esters and 1‐heptene, 2‐methylpropene or methyl acrylate. The effect of the structure of the monomers on the reactivity in polymerizations involving SO2 is discussed on the basis of the composition of the products.
Etude de la dégradation thermique du poly{acétoxy‐1 [(chloro‐2 éthyl)‐4 phényl]‐1 éthylène}
Authors: Boinon Bernard , Brigui Jamal , Monthéard Jean‐Pierre
Published: April 2003

A kinetic study of the thermal decomposition of poly{1‐acetoxy‐1‐[4‐(2‐chloroethyl)phenyl]‐ethylene} (1) was carried out by thermogravimetry. Two stages, well separated, are observed. The first one begins at 140°C. The corresponding decomposition reaction is a superposition of two reactions: loss of acetic acid and partial depolymerization. The main volatile products released in this first stage, identified by gas chromatography/mass spectrometry coupling, are chiefly acetic acid and a small quantity of p‐(2‐chloroethyl)acetophenone; there is no monomer from the monomeric unit. As in case of other poly(para‐substituted α‐acetoxystyrenes) the solid residue is poly[p‐(2‐chlorethyl)phenylacetylene] (5) of low molar mass, soluble in all usual organic solvents. No auto‐catalytic mechanism was found during this first stage, unlike in case of poly(vinyl acetate). The reaction order is one, over a wide range of conversion. The activation energy was found to be about 145,6 kJ/mol and the pre‐exponential factor 1,6 · 1015 min−1. An explanation for the insolubility of the residues, obtained by thermal degradation of some poly(p‐chloroalkylstyrenes), is proposed.
Cationic polymerization of bis(1‐alkylvinyl)benzenes and related monomers, 3. Telechelics containing indane units
Authors: Nuyken Oskar , Yang Dazhong , Gruber Freddy , Maier Gerhard
Published: April 2003

The synthesis and characterization of linear telechelics containing 1,1,3‐trimethylindane units via cationic polymerization is described. 1,4‐Diisopropenylbenzene (1) was polymerized in the presence of 1‐isopropenyl‐4‐methylbenzene (3a) to give a polyindane with methyl end‐groups, which was then oxidized to the corresponding carboxy‐telechelic polymer. As an alternative route for the preparation of polymers with indane units in the main chain, the step growth polymerization of suitably substituted indane derivatives was studied. In this way a polyindane with amino end‐groups was synthesized. It melts at 172°C and in DSC is stable up to ca. 300°C.
A kinetic study of the emulsion copolymerization of N,N′‐methylenebis(acrylamide) and an unsaturated polyester
Authors: Capek Igńc , Funke Werner
Published: April 2003

The emulsion copolymerization of N,N′‐methylenebis(acrylamide) (MBA) and an unsaturated polyester (UP) initiated by potassium peroxodisulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization, the size of latex particles and the number of polymer particles were determined as a function of MBA concentration. The rate of MBA polymerization was found to be proportional to the 0,8th (at 0–15% conversion) and 0,9th (at 20–40% conversion) order with respect to [MBA] at 0,0231 mol · dm−3 of UP. The values of the reaction order on the monomer concentration are discussed in terms of homogeneous and emulsion polymerization and crosslinking effects. The rate of UP polymerization in the emulsion copolymerization of MBA and UP does not depend on the total monomer concentration. The specific rate of MBA (or UP) polymerization increases with increasing monomer concentration and reaches a maximum at a certain concentration of monomer. The size of polymer particles decreases and the number of particles increases with increasing UP fraction. The stability of polymer particles increases with increasing UP fraction in the monomer feed. The ratio (kp/kt0,5)0 of the relative rate constants for propagation kp and termination kt calculated for the MBA or UP polymerizations at zero conversion increases with increasing MBA concentration. The growth of the polymer particles proceeds via polymerization in particles and by interparticle crosslinking reactions.
Crystallinity of uniform tri(oxyalkylene)s
Authors: Bedells Alison D. , Booth Colin , Viras K.
Published: April 2003

The crystallinities of uniform $ {\rm HO}\rlap{--} [\left( {{\rm CH}_2 } \right)_x {\rm O\rlap{--} ]}_{\rm 3} {\rm H} $ with x = 3 to 6, were investigated by small‐angle X‐ray diffraction, low‐frequency Raman spectroscopy, infra‐red spectroscopy and differential scanning calorimetry. It is shown that the C4 to C6 trimers adopt a trans‐planar conformation in their layer crystals, whereas the C3 trimer adopts a different chain conformation. In all cases the hydroxy end groups are extensively hydrogen bonded.
Oligomerization of 1‐hexene initiated by Zr(OnPr)4‐AlEt2Cl, 2. Mechanistic aspects
Authors: Liu Hua Qin , Deffieux Alain , Sigwalt Pierre
Published: April 2003

The mechanistic aspects of 1‐hexene oligomerization, initiated by Zr(OnPr)4‐AlEt2Cl at 20°C, are discussed on the basis of the product structures and distributions, the stability and reactivity of Mt‐alkyls (Mt = metal) formed during 1‐hexene oligomerization, the reaction behaviour of an internal olefin (cis‐2‐hexene) and the investigation of interactions between Zr (OnPr)4‐AlEt2Cl. After comparing the different possible initation routes for 1‐hexene oligomerization, a mechanism via insertion of 1‐hexene into Al‐alkyl bonds activated by zirconium is proposed. It was found that the olefin addition is not regiospecific. Primary addition into a linear alkyl‐metal bond leads to an olefin insertion, whereas secondary addition only leads to elimination; when α‐ or β‐ branched alkyl‐metal bonds are involved, only transfer to monomer takes place.
Synthesis and properties of polyamides derived from anhydro‐ and dianhydroalditols
Authors: Thiem Joachim , Bachmann Frank
Published: April 2003

The three isomeric 1,4:3,6‐dianhydroalditols with D‐gluco‐ (2), D‐manno‐ (11) and L‐ido (17) configuration and both 1,4‐anhydroalditols with threo (22) and erythro (27) configuration were efficiently transformed into the corresponding diamino derivatives. Interfacial polycondensation of these chiral heterocyclic diamines with purchasable aromatic and aliphatic carboxylic acid chlorides gave polyamides 35 and 36a–f, 37, 38 and 39a–d. The polymers were characterized using IR and 1H/13C NMR spectroscopy. Number‐average molecular weights were obtained from gel‐permeation chromatography to be M̄n ≈ 5000–25000 corresponding to a number‐average degree of polymerization up to P̄n ≈ 100. Inherent viscosities were measured, and differential scanning calorimetry gave information on the thermal properties of the polymers.
Kinetic and ESR studies of the radical‐initiated polymerization of N‐(2,6‐dimethylphenyl)itaconimide
Authors: Sato Tsuneyuki , Takarada Akira , Tanaka Hitoshi , Ota Tadatoshi
Published: April 2003

The polymerization of N‐(2,6‐dimethylphenyl)itaconimide (1) with azoisobutyronitrile (2) was studied in tetrahydrofuran (THF) kinetically and spectroscopically with the electron spin resonance (ESR) method. The polymerization rate (Rp) at 50°C is given by the equation: Rp = K[2]0,5 · [1]2,1. The overall activation energy of the polymerization was calculated to be 91 kJ/mol. The number‐average molecular weight of poly(1) was in the range of 3500–6500. From an ESR study, the polymerization system was found to involve ESR‐observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (kp) and termination (kt) were determined at 50°C. kp (24–27 L · mol−1 · s−1) is almost independent of monomer concentration. On the other hand, kt (3,8 · 104–2,0 · 105 L · mol−1 · s−1) increases with decreasing monomer concentration, which seems mainly responsible for the high dependence of Rp on monomer concentration. Thermogravimetric results showed that thermal degradation of poly(1) occurs rapidly at temperatures higher than 360°C and the residue at 500°C was 12% of the initial polymer. For the copolymerization of 1 (M1) with styrene (M2) at 50°C in THF the following copolymerization parameters were found; r1 = 0,29, r2 = 0,08, Q1 = 2,6, and e1 = +1,1.
Liquid‐crystalline polymers containing macrocyclic polyethers, 2. Side‐chain liquid‐crystalline copolysiloxanes containing mesogenic units based on 1,3‐dioxane‐2,5‐diyl and benzo[15]‐crown‐5
Authors: Hsiue Ging‐Ho , Wen Jiunn‐Shyang , Hsu Chain‐Shu
Published: April 2003

Synthesis and characterization of a series of copolysiloxanes containing crown ether and trans‐1,3‐dioxane based mesogens are presented. The phase behaviour of the copolymers was studied using differential scanning calorimetry and optical polarizing microscopy and compared with the phase behaviour of the corresponding copolysiloxane‐containing crown ether and biphenyl‐based mesogens. Two copolysiloxanes containing trans‐2‐(benzo‐[15]crown‐5)‐5‐(ω‐alkan‐1‐yloxy)‐1,3‐dioxane side groups present no liquid‐crystalline behaviour. The other four copolysiloxanes exhibit a nematic mesophase and undergo side‐chain crystallization at low temperature. Two of the four copolysiloxanes which contain a trans‐1,3‐dioxane‐2,5‐diyl group in the mesogenic unit present lower isotropization temperatures and narrower mesophase ranges than the other two. This result reveals that replacing a phenyl ring in the mesogenic unit of a liquid‐crystalline polymer by a trans‐1,3‐dioxane ring will decrease the thermal stability of the mesophase exhibited by this polymer.
Mechanism of whisker growth of poly(4‐hydroxybenzoate)
Authors: Taesler Christian , Petermann Jürgen , Kricheldorf Hans R. , Schwarz Gert
Published: April 2003

Needle‐like crystals (whiskers) of poly(4‐hydroxybenzoate) were prepared by thermal condensation of 4‐acetoxybenzoic acid in Marlotherm‐S® at 300, 350 and 400°C. In addition to the temperature, also reaction time and concentration were varied. Wide‐angle X‐ray scattering powder patterns show that the “300°C whiskers” contain nearly equimolar fractions of orthorhombic modifications I and II, “350°C whiskers” and “400°C whiskers” only consist of modification I. Differential scanning calorimetry measurements revealed a phase transition at 325, 346 and 359°C for the “300°C”, “350°C” and “400°C whiskers”, respectively. Electron microscopy shows that with increasing conversion the thickness of the whiskers passes through a maximum. The previously proposed whisker growth model along a central screw was not confirmed and a new crystal growth model is proposed.
Catalytic hydrolysis of phenyl esters in cyclodextrin/poly(allylamine) systems
Authors: Seo Toshihiro , Kajihara Taketoshi , Miwa Keishi , Iijima Toshiro
Published: April 2003

The hydrolysis of phenyl esters in systems containing poly(allylamine) {poly[1‐(aminomethyl)‐ethylene]} (1) carrying pendant β‐cyclodextrin (CD) moieties with selective inclusion ability was investigated. In the mixture of 1 (or its N‐benzyl derivative) with CD, CD retards the hydrolysis of p‐nitrophenyl acetate. It was estimated that the substrate which is included in CD is difficult to be attacked by 1, and in the case of N‐benzylated poly(allylamine) there occurs competitive inhibition with CD. On the other hand, poly(allylamine) containing covalently bound CD (2) has much higher hydrolysis activity for various phenyl esters than 1 and shows a kinetics of Michaelis‐Menten type. In the case of p‐nitrophenyl hexanoate and p‐nitrophenyl benzoate, high substrate inclusion and a change in catalytic ability were observed. It was also shown that polymer 2 develops a remarkable catalytic effect for p‐nitrophenyl L‐N‐acetylphenylalanine ester for which CD and 1 alone show no catalytic activity. It is suggested that a highly selective recognition of the substrate by the CD side group and an effective cooperative action between (1) amino group and CD, and (2) two neighbouring CD rings on the polymer chains occur.
Synthesis and characterization of a homologous series of chiral smectic C side‐chain polymers
Authors: Messner Bernfried , Finkelmann Heino
Published: April 2003

The synthesis and characterization of a homologous series of liquid‐crystalline side‐chain polymers with a chiral smectic C phase are described. The polymer backbone consists of methacrylate monomeric units which link the mesogenic moieties of the chiral cinnamic acid 2S‐ (−)‐4‐(2‐chloro‐4‐methylpentanoyloxy)phenyl ester via a flexible spacer of six to eleven CH2 groups. The influence of this variation on this variation on transition temperatures, phase structure and range of the l. c. phases is studied. In contrast to the monomers, the chiral smectic C phase of the polymers is significantly broadened with respect to the temperature regime and can be vitrified in the glassy state.
Synthesis of a liquid‐crystalline polysiloxane with a diol mesogen in the side chain
Authors: Staufer Günter , Lattermann Günter
Published: April 2003

The synthesis and thermal behaviour of a cis,cis‐(3,5‐dihydroxycyclohexyl) 3,4,5‐tris(alkoxy)‐benzoate, functionalized by one terminal C‐C double bond is described. Its mesophase of the hexagonal columnar type is formed by a “supramolecular” unit, consisting of six single molecules aggregated via hydrogen bonding. Subsequently, a liquid‐crystalline side‐chain polymer with a siloxane backbone was synthesized. Its mesophase behaviour, investigated by means of differential scanning calorimetry (DSC) measurements and polarizing microscopy, is discussed.
Synthesis and properties of well‐defined multiblock copolymers: polystyrene‐block‐polydimethylsiloxane
Authors: Dems Andrzej , Strobin Grażyna
Published: April 2003

Polystyrene (PS)‐polydimethylsiloxane (PDMS) triblock copolymers with well‐defined block lengths and silanol reactive end‐groups were synthesized by anionic polymerization as prepolymers for condensation reactions. Multiblock PS‐PDMS copolymers characterized by molecular and chemical homogeneity could be obtained either by self condensation of the silanol groups of by reaction with dichlorodimethylsilane. The kinetic constants, the activation energy, the extent of reaction and the molecular characteristics of the multiblock copolymers were determined as a function of the molecular weight of the prepolymer, the water content of the reaction medium and the concentration of HCl acting as catalyst in the dehydration reaction. The kinetic constants and the ultimate extent of the reaction could be correlated to the molecular weight of the prepolymer and to the viscosity of the reaction medium. DSC measurements of the multiblock copolymers show clearly the presence of two‐phase materials with mechanical properties depending on the PDMS content.
Effect of SnCl4 on the radical‐initiated polymerization of diethyl itaconate: Kinetical and ESR studies
Authors: Sato Tsuneyuki , Nakamura Hiroyuki , Tanaka Hitoshi , Ota Tadatoshi
Published: April 2003

The effect of SnCl4 on the polymerization of diethyl itaconate (1) with dimethyl 2,2′‐azoisobutyrate (2) in benzene was investigated kinetically and ESR spectroscopically. The polymerization rate (Rp) at 50°C shows a flat maximum on varying the SnCl4 concentration. The molecular weight of the resulting polymer decreases with increasing SnCl4 concentration. The overall activation energy of the polymerization is lowered from 52 to 33 kJ · mol−1 by the presence of SnCl4, (0,342 mol · L−1). An NMR study revealed that 1 and SnCl4 form 1:1 and 2:1 complexes with a large stability constant in benzene. The propagating polymer radicals in the absence and presence of SnCl4 are ESR‐observable as a five‐line spectrum under the actual polymerization conditions. The complexed polymer radicals show further three‐line splitting due to two methylene hydrogens of the ethyl ester group. The polymer radical concentration increases with the SnCl4 concentration. The rate constant (kp) of propagation was determined using Rp and the polymer radical concentration. kp (6,3–2,9 L · mol−1 · s−1 at 50°C) decreases with increasing SnCl4 concentration. The presence of SnCl4 (0,342 mol · L−1) reduces the activation energy of propagation from 29 to 21 kJ · mol−1. The rate constant (kt) of termination was estimated from the decay curve of the polymer radicals, kt (3,1–1,1 · 105 L · mol−1 s−1) also decreases with the SnCl4 concentration. The activation energies of termination in the absence and presence of SnCl4 (0,342 mol · L−1) are 30 and 24 kJ · mol−1, respectively. Suppression of propagation and termination by SnCl4 seems to be explicable in terms of an entropy factor.
Quasi‐elastic light scattering by polystyrene‐poly(methyl methacrylate) diblock copolymer solutions in a non‐selective solvent in the vicinity of the overlap concentration
Authors: Haïda Houcine , Lingelser Jean‐Paul , Gallot Yves , Duval Michel
Published: April 2003

The dynamic properties of a styrene (S)‐methyl methacrylate (MMA) diblock copolymer in semidilute solutions of toluene have been investigated by quasi‐elastic light scattering. One relaxation mode has been found in the low‐concentration regime near the overlap concentration C*. This mode is identified as the cooperative mode which is observed in semidilute solutions of the equivalent polystyrene (PS) homopolymer. A second mode appears simultaneously at higher concentrations. This slower diffusive mode is ascribed to the diffusion of the center of mass of the clusters formed by the copolymer molecules. The fast structural mode which is predicted by the theory1–3 is not observed. It is suggested that this mode, which must have a small amplitude, is hidden by the other two relaxation modes.
The synthesis of siloxane‐based polymers containing photoactive cinnamate moieties
Authors: Barley Susan H. , Gilbert Andrew , Mitchell Geoffrey R.
Published: April 2003

Three ways of synthesizing cinnamate‐based siloxane polymers suitable for photoisomerization purposes have been employed. The route involving direct hydrosilation of the photoactive unit and a non‐photoactive alkene with the homopolymer poly(methylsiloxane) has the severe disadvantages that the polymer is coloured, crosslinking during work‐up or storage commonly occurs and also some of the cinnamate CC double bonds are reduced during the hydrosilation. This loss of the chromophore can be decreased but not eliminated by its hydrosilation with the copolymer poly(dimethylsiloxane‐co‐methylsiloxane). All of the available SiH sites are now reacted with the cinnamate ester but a low concentration of active units on the polymer is still maintained. The most successful method of preventing loss of the chromophore is best achieved by functionalising the polymer via hydrosilation with allyl acetate, followed by hydrolysis of the acetate to the alcohol and finally esterification with the acid chloride of the chromophore. This procedure in contrast to the other methods, yields the photoactive polymer as an almost colourless, mobile liquid which is stable on storage and in which no reduction of the chromophore has occurred.
Polymer thin films and interfaces characterized with evanescent light
Authors: Knoll Wolfgang
Published: April 2003

This paper describes the use of evanescent light for the optical characterization of polymer thin films and interfaces. Firstly, a few basic concepts of evanescent wave phenomena, including total internal reflection, plasmon surface polaritons and guided optical modes, are reviewed. It is shown that the excitation of these waves allows for a sensitive determination of the optical architecture of the interface(s) involved. This “surface light” can then be used for the same broad range of optical techniques as it is known from experimental set‐ups designed for the investigation of various optical properties of polymer samples using plane electromagnetic waves, i.e. “normal” photons. This is demonstrated for diffraction experiments, microscopic investigations, inelastic scattering, e.g. Brillouin‐ or Raman‐spectroscopies, etc. The examples given include thin polymer films prepared by spin‐coating or by the Langmuir‐Blodgett‐Kuhn technique. It is shown that properties and processes at solid‐solution interfaces can be investigated equally well, and even surfaces of bulk samples can be characterized.
Copolymerization of ethylene with propene in the presence of Ti‐Mg catalysts of different compositions
Authors: Zakharov Vladimir A. , Yechevskaya Lyudmila G. , Bukatov Gennadii D.
Published: April 2003

Comonomer reactivity ratios (from kinetic and 13C NMR data), compositional homogeneity of ethylene‐propene copolymers, and molecular structure of individual fractions of the copolymers obtained with supported Ti‐Mg catalysts of different compositions were determined. The copolymerization reactivity of these systems was found to increase upon introduction of ethyl benzoate and dibutyl phthalate to the catalyst system. It was found that both lowly stereospecific and highly stereospecific catalysts have a broad distribution of active sites with respect to copolymerization reactivity. The composition of the catalysts (titanium content and stereoregulating additives) was shown to influence the reactivity ratios of the comonomers and the microstructure of the copolymers.
Untersuchungen zur Thiol/En‐Polymerisation: elektronenspinresonanzspektroskopischer Nachweis spontaner Radikalbildung
Authors: Sensfuß Steffi , Friedrich Manfred , Klemm Elisabeth
Published: April 2003

By means of ESR (electron spin resonance) spectroscopic investigations it is shown, that in dithiol/diene‐mixtures, in the absence of daylight and oxygen, radicals are formed spontaneously. Using the spin trapping technique and nitrosodurene (ND) as the trapping agent the existence of sulfur and carbon radicals could be proved unambiguously. Oxygen has no significant influence on the reaction. Spin trapping experiments have shown, that the aliphatic dithiols investigated do not form any traceable quantity of RS. and .OOH radicals in the presence of air. Radicals are detected only after addition of an ene‐compound.
On the determination of double‐bond contents of linear and crosslinked liquid‐crystalline polyesters including the corresponding monomers by differential pulse polarography
Authors: Peter Karin , Peter Ralf , Rätzsch Manfred
Published: April 2003

Unsaturated liquid‐crystalline polymers are synthesized with the aim to fix the liquid‐crystalline state which causes the favourable polymer properties by means of subsequent crosslinking. The elucidation of the influence of crosslinking on the liquid‐crystalline properties of such polyesters is possible using the determination of the double‐bond content in the polymer. Because the CC bonds of fumaric acid units are determined analytically by electrochemical reduction, a polarographic determination of the double‐bond content appears to be a favourable method. The treatment of the polymeric material and the choice of a solvent system which is suitable both in respect to electroanalytical use and sufficient solvent power are of first importance.
Microspheres prepared from temperature‐sensitive graft polymers
Authors: Kitano Hiromi , Yan Changhong , Nakamura Katsunori
Published: April 2003

Polyallylamine‐graft‐poly(N‐isopropylacrylamide) was prepared by coupling polyallylamine with poly(N‐isopropylacrylamide) (the latter with an end‐standing carboxyl group). The graft polymer obtained showed a temperature‐responsive phase transition under alkaline conditions, whereas the starting poly(N‐isopropylacrylamide) with end‐standing carboxyl group showed temperature‐sensitivity under acidic conditions. With an increase in the degree of grafting the temperature‐sensitivity of the polymer under weakly alkaline conditions increases. Microspheres were prepared by cross‐linking the graft polymers with glutaraldehyde in water‐in‐oil emulsion. Trypsin immobilized to the microspheres showed temperature‐responsiveness in its catalytic activity. The graft polymer can be used as a component of temperature‐sensitive devices in various forms.
Acrylamide‐co‐methacrylamide copolymers carrying peptide side chains: application to asymmetric catalysis
Authors: Boulahia Jalel , Carrière François , Sekiguchi Hikaru
Published: April 2003

The stereoselective epoxidation of chalcone, catalyzed by poly(L‐alanine) (PLA)‐grafted N‐benzylacrylamide‐co‐N‐aminopropyl methacrylamide copolymers, was carried out in the ternary system water/CCl4/polymer catalyst. The resulting oxirane was obtained with about 60% yield with an enantiomeric excess (e. e.) of 80%. A good catalytic efficiency was observed even under conditions of high dilution. When the same catalyst was used a third time, an important racemization of supported PLA gave a strong decrease of yield and e. e. values of the resulting epoxide. Better results with a lower benzylacrylamide moiety content in the copolymer backbone might be due to a higher density of PLA chains.
Telechelic polystyrene α,ω‐macrozwitterions, 1. Synthesis and characterization
Authors: Antonietti Markus , Heyne Joachim , Sillescu Hans , Lindner Peter
Published: April 2003

Telechelic α,ω‐macrozwitterions — narrowly distributed polystyrene chains oppositely charged at each end — were synthesized via anionic polymerization using direct functionalization with the initiator and the termination agent. The resulting products were purified (zwitterion content ≥ 0,95) and characterized with gel permeation chromatography, viscometry, static and dynamic light scattering and small‐angle neutron scattering. In unpolar solvents as toluene, the polymeric zwitterions form clusters with molecular weights depending on concentration. In the dilute case, the clusters are relatively small and consist of approximately 8 zwitterions. The structure of these clusters is discussed by their scattering behaviour. Above a critical concentration being in the range of 0,05 g/cm3, an infinite aggregate is formed. Zwitterions in N,N‐dimethylformamide behave differently: due to the attenuation of dipolar forces, no clusters are formed. In this case, the behaviour in dilute solution can be described by the formation of polymeric rings consisting of one polymer molecule, only.
Mixed (electronic and ionic) conductive solid polymer matrix, 1. Synthesis and properties of poly(2,5,8,11,14,17,20,23‐octaoxapentacosyl methacrylate)‐block‐poly(4‐vinylpyridine)
Authors: Li Jean , Khan Ishrat M.
Published: April 2003

Poly(2,5,8,11,14,17,20,23‐octaoxapentacosyl methacrylate)‐block‐poly(4‐vinylpyridine) semicomb polymers were synthesized using anionic living polymerization techniques. The polymers are white, powdery materials and were characterized by 1H and 13C nuclear magnetic resonance spectroscopy and gel‐permeation chromatography. The polymers display monomodal molecular weight distributions which are relatively narrow. The block copolymers show microphase separation as indicated by the presence of two glass transition temperatures (Tg), a soft (oxyethylene) phase Tg is observed between −60°C and −45°C and a hard (4‐vinylpyridine) phase Tg is observed between 135°C and 150°C. The soft oxyethylene phase has been doped with LiClO4 to obtain ionic conductors with electrical conductivities around 5 · 10−6 S · cm−1 at 25°C and the hard 4‐vinylpyridine phase has been complexed with 7,7,8,8‐tetracyano‐1,4‐quinodimethane (TCNQ, 2,5‐cyclohexadiene‐1,4‐diylidenedimalonitrile) to obtain electronic conductivities around 10−6 S · cm−1 at 25°C. The mixed (electronic and ionic) conductivities are intermediate between the ionic and electronic conductivities. Higher electronic conductivities (≈ 10−5 S · cm−1 at 30°C) are obtained for the polycation TCNQ−/TCNQ0 complexes.
Synthesis and cation‐sensitive fluorescence of polyelectrolytes bearing crown ether side groups
Authors: Shirai Masamitsu , Ishimaru Shinichi , Tsunooka Masahiro
Published: April 2003

Polyelectrolytes bearing crowned acetophenone moieties were prepared by radical copolymerization of 4′‐acryloylbenzo‐18‐crown‐6

System. name of benzo‐18‐crown‐6: 1,2‐benzo‐1,4,7,10,13,16‐hexaoxa‐2‐octadecene.

and methacrylic acid or lithium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate. On excitation with 330 nm light the polymers showed fluorescence at 410 nm in a mixed solvent of methanol and water (1:9 v/v) at 30°C. When cations were added, the fluorescence intensity of the polymers decreased in the orders Li+ > Na+ > Cs+ > Rb+ > K + for alkali metal cations, Ca2+ > Sr2+ > Ba2+ for alkaline earth metal cations and C2H5NH2 > CH3(CH2)3NH2 > C6H5CH2NH2 for alkylamine hydrochlorides used. The concentration effect for cations in the neighborhood of the polymer‐bound crown ether groups by electrostatic and/or hydrophobic binding induced significant complex formation between cations and crown ethers in aqueous solutions, resulting in a decrease of the fluorescence intensity.
Structure and mechanical properties of films of rigid‐rod polymers having flexible side chains
Authors: Schrauwen Cornelius , Pakula Tadeusz , Wegner Gerhard
Published: April 2003

A series of rigid‐rod polyesters with flexible alkoxy side chains of different length has been studied in order to determine the structure and properties of the polymers in various states (solid state, mesophase, melt). Various supermolecular structures can be obtained depending on the length of the side chains and on the preparation conditions of the samples. The relaxation behavior of the polymers has been investigated by dynamic mechanical measurements. Complex relaxation spectra have been observed, and types of molecular motions and structural rearrangements have been assigned to the observed mechanical relaxation transitions. The rheological behavior was studied in the mesophase and in the melt. In some polymers typical liquid‐crystalline properties have been observed, as for example the flow‐thinning effect. Large deformation of polymer films as well as the structure and mechanical strength of oriented samples have also been studied.
Benzoxazole‐2‐thiol/dibenzoyl peroxide combination as photoinitiator for methyl methacrylate polymerization
Authors: Sengupta Pranab K. , Ray Gour M. Singha
Published: April 2003

Benzoxazole‐2‐thiol (1)/dibenzoyl peroxide (Bz2O2) was used as photoinitiator for the polymerization of methyl methacrylate (MMA) in bulk and in solution. The study of initiator decomposition was conducted spectrophotometrically. Kinetic studies of the photopolymerization indicated the formation of a complex between 1 and Bz2O2 in the stoichiometric ratio 2:1. The initiation is believed to occur via in situ formation of bis(benzoxazol‐2‐yl) disulfide in the presence of light.
Thermal degradation of polybutadiene, 2. Overall thermal behaviour of polymers with different microstructures
Authors: Luda Maria Paola , Guaita Marino , Chiantore Oscar
Published: April 2003

The thermal decomposition at volatilization temperatures of polybutadiene samples with different initial microstructures was investigated i. vac. and under nitrogen atmosphere by thermogravimetry, differential scanning calorimetry, thermal volatilization analysis and infrared spectroscopy. The decomposition of cis‐1,4‐, trans‐1,4‐ and random polybutadienes occurs in two stages, whereas only one stage is shown by 1,2‐polybutadiene. Chemical changes and amounts of weight loss in the first degradation stage are dependent on the sample heating rates. The volatile degradation products were collected, fractionated and compared for the different polymers.