bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of indenyl ligand substitution pattern on metallocene‐catalyzed propene copolymerization with 1‐octene
Authors: Schneider Martin Julius , Mülhaupt Rolf
Published: April 2003

Copolymerization of propene with 1‐octene (1 mol/1 mol) was performed in toluene at 40°C in the presence of homogeneous methylaluminoxane (MAO)‐activated ansa‐metallocenes in order to study the role of benzannelation and 2‐methyl‐substitution of the silylene‐bridged bisindenyl ligand on comonomer incoporation, molecular mass, molecular mass distribution, and end groups. While 2‐methyl‐substitution promoted higher degree of polymerization without affecting copolymerization parameters, benzannelation improved markedly 1‐octene incorporation. Only with MAO‐activated rac‐Me2Si(2‐MeBenz[e]Ind)2ZrCl2 catalysts vinylidene end groups were formed exclusively. Molecular weight distribution remains narrow in all experiments.
Aggregation states and bistable light switching effects in a side chain ferroelectric liquid crystalline polysiloxane
Authors: Hwang Jenn Chiu , Shu Ming Chin , Moritake Hiroshi , Yoshino Katsumi
Published: April 2003

Aggregation states and transient light scattering in the chiral smectic C phase of a ferroelectric liquid crystalline polymer (FLCP) were studied. The smectic phase shows an interlayer spacing of 38–39.5 Å, which is about 1.41 times the length of the side chain mesogenic group. The transient scattering mode obtained by repeated voltage polarity reversal. A reversible transparent‐opaque (light scattering) change was observed in the chiral smectic C state upon application of electric fields with low and high frequencies, respectiely. Both transparent and opaque states were maintained stably even when the electric field was turned off (bistable light swiching). A novel type of electro‐optical effect based on light scattering was obtained for the FLCP in the chiral smectic C state.
Living ring‐opening polymerization of lactones using cationic zirconocene complex catalysts
Authors: Hayakawa Michiya , Mitani Makoto , Yamada Tohru , Mukaiyama Teruaki
Published: April 2003

Living cationic ring‐opening polymerization of ϵ‐caprolactone (CL), δ‐valerolactone (VL) and 1,3‐dioxepane‐2‐one (6) was achieved at room temperature by using zirconocene borate complex catalysts. Respective block copolymerization of CL with VL or with cyclic carbonate 6 was also successfully performed. The mechanism of the present cationic living polymerization is discussed.
On the mechanism of olefin polymerization by titanocene/MAO catalysts: Relationships between metathesis and addition polymerization
Authors: Tritto Incoronata , Li San Xi , Boggioni Laura , Sacchi Maria Carmela , Locatelli Paolo , O'Neill Aideen
Published: April 2003

Ethylene polymerizations and norbornene oligomerizations catalysed by Cp2Ti13CH3Cl/MAO (Cp: cyclopentadienyl; MAO: methylaluminoxane) mixtures have been carried out at different temperatures (from ‐20°C to 20°C), in order to test the validity of carbene mechanisms in α‐olefin polymerizations. Depending on the temperature, different ratios of the cationic species [Cp2Ti13CH3]+[Cl · MAO]− and precursors of the alkylidene Cp2Ti = 13CH2 exist. The in situ polymerization of 13C enriched ethylene was monitored by 13C NMR spectroscopy. Moreover, catalytic activity was determined and polyethylene samples were analyzed by 13C NMR and gel permeation chromatography (GPC). The following evidence has been provided against the carbene mechanism in the α‐olefin polymerization with titanocene based catalysts: (a) in the in situ ethylene polymerization experiments the appearance of polyethylene signals is concurrent with the decrease of cationic [Cp2Ti13CH3]+[Cl · MAO]− signals and is not related to the intensity of the alkylidene Cp2Ti = 13CH2 signals; (b) from the 13C NMR analysis of polyethylene chain‐end groups the 13C enrichment of Cp2Ti13CH3Cl has only been found in the methyl chain‐end group and not in the methylene of the propyl chain‐end group, as should have been the case if the carbene mechanism had been valid; (c) from norbornene oligomerization (at 0°C) the addition product 2‐13C enriched methyl‐norbornane has been identified. Moreover, the identification of a 13C enriched methylidene‐norbornane dimer at higher temperatures has revealed the possibility of norbornene addition to titanium carbenes through the formation of titanacyclobutane without the opening of the norbornene ring. However, this process requires higher energies with respect to the Cossee type insertion.
Side chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerisation, 3. Influence of backbone microstructure and grafting ratio on the thermotropic behaviour
Authors: Ungerank Markus , Winkler Berthold , Eder Elisabeth , Stelzer Franz
Published: April 2003

The ring opening metathesis polymerisation (ROMP) of (±)‐ and (−)‐exo, endo‐bis[(4′‐cyanobiphenyl‐4‐yl)oxyalkyl]norborn‐5‐ene‐2,3‐dicarboxylates using three different Schrock type molybdenum alkylidene complexes ([Mo(NAr)(CH‐t‐Bu)(OR)2] with RC(CH3)3, C(CH32)(CF3) or C(CH3)(CF3)2) resulted in the formation of side chain liquid crystalline polymers (SCLCP's). The different initiators caused changes in the backbone tacticity which were determined by means of NMR techniques. The influence of the type of tacticity on the thermotropic behaviour of the SCLCP's was investigated. The thermal properties were determined by differential scanning calorimetry (DSC). The transition temperatures increased with rising molecular weight up to a degree of polymerisation of about 40. Above this value the thermal properties remained constant with increasing molecular weight. The types of phases for the liquid crystalline polymers were elucidated by polarising optical microscopy (POM). In general, the highly tactic polymers showed a broader thermal range of the LC phase. The kind of initiator used caused changes of the thermal and thermotropic behaviour of the SCLCP's. A grafting ratio model is introduced to explain the findings. From the experimental data a structure/property relationship is developed which might help to predict liquid crystalline properties of unknown polymers.
Termination kinetics of free‐radical polymerization of styrene over an extended temperature and pressure range
Authors: Buback Michael , Kuchta Frank‐Dieter
Published: April 2003

The termination rate coefficient kt of the free radical bulk polymerization of styrene is determined between 30 and 90°C up to a maximum pressure of 2800 bar. The majority of polymerization experiments has been carried out at monomer conversions up to 20 per cent. In this range a single value of kt is sufficient to describe termination rate at constant pressure and temperature. Toward higher conversion, significant changes in kt are observed. The data are measured by a pulsed laser polymerization technique and partly by conventional chemically initiated experiments, both with 2,2′‐azoisobutyronitrile (AIBN) as the initiator. Online spectroscopy is applied toward measurement of styrene conversion. The experimental termination rate coefficients up to 20 per cent monomer conversion are adequately represented by the expression:

Activation volume and activation energy of kt are very close to the corresponding activation parameters that characterize the pressure and temperature dependence of the inverse of styrene monomer viscosity. Varying laser pulse repetition rate has been used to investigate a potential chain‐length dependence of kt at low conversion. It turns out that effects of this kind are not sufficiently pronounced to be safely established in view of the experimental precision of ±25 per cent that is reached in the kt determinations.
Soluble poly(1,4‐phenylenevinylene)s and poly(1,4‐phenyleneethynylene)s via suzuki coupling
Authors: Koch Friedrich , Heitz Walter
Published: April 2003

Poly(1,4‐phenylenevinylene) and poly(1,4‐phenyleneethynylene) were prepared fromtrans‐1,2‐dibromoethylene and 1,4‐bis(2‐bromoethynyl)benzene respectively with aryldiboronic acids by a Suzuki cross‐coupling reaction. The polymers were synthesized in a two‐phase system at room temperature using silver oxide and a Pd catalyst. 3% of biaryl formation is observed as a defect structure in the PPV polymers resulting from coupling of arylboronic acid. Soluble polymers were obtained when the aryldiboronic acid is substituted with long‐chain alkoxy groups.
Characterization of chitosan and rare‐earth‐metal‐ion doped chitosan films
Authors: Jiang Hao , Liang Jim , Grant John T. , Su Weijie , Bunning Timothy J. , Cooper Thomas M. , Adams W. Wade
Published: April 2003

A systematic study has been made on the influence of doped rare‐earth metal ions (Er3+ and Nd3+) on the molecular interaction present in thin films fabricated from chitosan‐acetic acid solutions (chitosan/HAc). FT‐IR spectroscopy (including NIR, MIR and FIR) coupled with X‐ray photoelectron spectroscopy (XPS) indicate a weak complexation between the metal ions and amine groups of chitosan. Specifically, the FIR spectra show broad bands near 550, 480 and 250 cm−1 for the doped films suggestive of metal ion‐ligand vibrations. XPS indicates multiple chemical states of N with an increased percentage of a higher binding energy state nitrogen caused by a weak interaction with the doped metal ions. Slight differences in microroughness between the doped and undoped films as observed by X‐ray reflectometry may also be related to the doping. The NIR and MIR spectra do not show any significant changes for all the doped and undoped films, implying that the basic molecular conformation of chitosan is not changed by the weak complexation.
Stepped‐up reactivity of a simple lanthanoid initiator. Polymerization of methyl methacrylate initiated with a lanthanoid alkoxide – ketene system
Authors: Sugimoto Hiroshi , Kato Makoto , Inoue Shohei
Published: April 2003

Polymerization of MMA is achieved by using a novel initiator, most probably the lanthanum enolate growing species formed in the polymeritation of ketene with La(OiPr)3. The design of this simple initiator is based on the stimulation of the reactivity of La(OiPr)3, which by itself is inactive, upon the reaction with ketene.
Polymers from coumarins, 2. Design and synthesis of novel main‐ and side‐chain coumarin‐containing polymers
Authors: Fomine Sergei , Pérez Heriberto , Fomina Lioudmila , Tlenkopatchev Mikhail , Ogawa Takeshi
Published: April 2003

Two novel coumarin‐containing monomers, 3,3′‐bis(ethoxycarbonyl)‐6,6′‐bicoumarin (3) and 7‐[(2‐norbornenyl)methoxy]coumarin (7), were prepared and characterized. They give polymers with Mw up to 350 000 and are soluble in common organic solvents. Polymers were prepared by high temperature transesterification reaction (poly‐3) and metathesis polymerization (poly‐7). Poly‐10 was prepared by direct activated polymidation of 6‐aminocoumarin‐3‐carboxylic acid (10). All polymers are amorphous with glass transition Tg of 121 and 64°C for poly‐3 and poly‐7, respectively. High optical quality films can be prepared by solution casting, and in the case of poly‐3 fibers can be drawn from the melt. All polymers show strong photoemission in the region from violet (poly‐7) to blue‐green (poly‐10) (410–510 nm). An electroluminescent device was fabricated from poly‐3 with turn‐on voltage of 4 V.
Random coil dimensions of poly(1‐hexadecene)
Authors: Peña Begoña , Aroca Marcelo , Pérez Ernesto , Bello Antonio , Riande Evaristo , Benavente Rosario
Published: April 2003

The characteristic ratios of three samples of poly(1‐hexadecene) with different tacticities were evaluated from intrinsic viscosity and molecular weight data obtained with a size exclusion chromatograph with dual (concentration plus viscosity) detector. No significant differences were found for the characteristic ratio in the studied range of tacticities. Theoretical calculations for the unperturbed dimensions were also performed for these samples by using the rotational isomeric state model, and compared with the experimental results.
Monomer reactivity vs. regioregularity in polythiophene derivatives
Authors: Fréchette Martin , Belletête Michel , Bergeron Jean‐Yves , Durocher Gilles , Leclerc Mario
Published: April 2003

It has been recently reported that a simple chemical oxidation of 3‐alkoxy‐4‐methylthiophenes leads to highly regioregular polymers with enhanced electrical and optical properties. A joint experimental and theoretical study on different alkyl‐, alkylthio‐, and alkoxy‐substituted thiophenes and bithiophenes has revealed a strong correlation between the distribution of the unpaired electron π‐spin density in the oxidized starting compounds and the regionchemical structure of the resulting polymers. In particular, these calculations have clearly indicated that an asymmetric reactivity of the oxidized monomers or dimers at the 2‐ and 5‐positions can lead to polymers with a high head‐to‐tail content. This theoretical tool should be useful for the future design of regioregular and nonregioregular polymers from chemical or electrochemical oxidative polymerization reactions.
Chiral methacrylic polymers containing permanent dipole azobenzene chromophores. 13C NMR spectra and photochromic properties
Authors: Altomare Angelina , Ciardelli Francesco , Ghiloni Maria S. , Solaro Roberto , Tirelli Nicola
Published: April 2003

Dynamics in solution and photochromic properties of radical copolymers of (S)‐4‐[N‐(2‐methacryloyloxyethyl)‐N‐(2‐methylbutyl)]amino‐4′‐cyanoazobenzene with butyl methacrylate were investigated. 13C NMR and 2D heteronuclear correlated (HETCOR) spectroscopy allowed assignment of 13C NMR signals and evaluation of main chain tacticity. 13C relaxation times T1 evidenced a rather limited mobility of azobenzene chromophores. Mobility increases with increasing content of butyl methacrylate units, that acts as an internal plasticizer. The limited mobility of the spacer between azobenzene and methacrylate groups is attributed to an interaction between carbonyl oxygen and aminic nitrogen stabilized by the internal charge transfer from the amino to the cyano group. Trans to cis photoisomerization rates turned out to be independent of molecular weight and chemical composition of the investigated photochromic polymers, whereas cis to trans thermal isomerization rates increase with the content of aromatic units. These data suggest that photo‐ and thermal isomerization processes imply an in‐plane inversion and an out‐of‐plane rotation of one of the phenyl rings of the azobenzene chromophores, respectively. Preliminary second harmonic generation measurements indicate that the investigated polymers are endowed with significant non‐linear optical properties.
Polylactones, 37. Polymerizations of L‐lactide initiated with Zn(II) L‐lactate and other resorbable Zn salts
Authors: Kricheldorf Hans R. , Damrau Dirk‐Olaf
Published: April 2003

Zn(II) L‐lactate (ZnLac2) was prepared either from ZnO and ethyl L‐lactate or with slightly higher optical purity from ZnO and L‐lactide. Using water‐free ZnLac2 L‐lactide was polymerized in bulk at 120°C or 150°C. Higher yields and higher molecular weights were found at 150°C. The highest number average molecular weights (M̄n around 70 000) were obtained at monomer/initiator (M/I) ratios of 4000. Despite the high reaction temperature the isolated poly(L‐lactide)s were 100% optically pure. Analogous polymerizations were also conducted with Zn(II) L‐mandelate or Zn(II) stearate with inferior results. Poor yields and molecular weights were found, when zinc glycolate salt was used as catalyst. Furthermore, numerous polymerizations were conducted with ZnCl2, ZnBr2 or ZnI2 as initiators. Again poly(L‐lactide)s with 100% optical purity were isolated, but most molecular weights were lower and never higher than those obtained with ZnLac2. Therefore, ZnLac2 proved to be the most favorable and fully resorbable (biocompatible) initiator of this study. Finally, the combination of ZnLac2 with a primary alcohol, which plays the role of a coinitiator, allows a broad variation of the molecular weight and the introduction and modification of an ester endgroup. This approach also allows the incorporation of bioactive alcohols such as α‐tocopherol, stigmasterol or testosteron in the form of covalently bound ester endgroups.
Synthesis and characterization of acrylate‐terminated unsaturated copolyesters
Authors: Zlatanic Alisa , Djonlagic Jasna
Published: April 2003

The reaction of the potassium salt of acrylic acid with the potassium salt of a dicarboxylic acid and 1,4‐dibromobutane was applied to the synthesis of three series of acrylate‐terminated copolyesters: poly(tetramethylene maleate‐co‐tetramethylene phthalate) (BMPA), poly(tetramethylene fumarate‐co‐tetramethylenephthalate) (BFPA) and poly(tetramethylene phthalate‐co‐tetramethylene succinate) (BPSA). The monofunctional monomer, the potassium salt of acrylic acid, was used for the introduction of double bonds at the end of the chains and for the regulation of the molecular weight of the polyesters. The telechelic copolyesters were characterized by 1H and 13C NMR spectroscopy, in almost all cases providing an acrylate functionality of two.
Ion‐aggregation in poly[ethylene‐co‐(2‐(4‐carboxyphenoxy)ethyl methacrylate)] and poly[ethylene‐co‐(2‐(3‐carboxypyridin‐6‐yloxy)ethyl methacrylate)] based ionomers
Authors: Iwatsuki Yasuhito , Tsuchida Shigeo , Yano Shinichi
Published: April 2003

Two new ethylene ionomers were synthesized, poly[ethylene‐co‐(5.4‐mol‐% 2‐(4‐carboxyphenoxy)ethyl methacrylate)] partially neutralized with Zn(II) (EMAA‐BZnX), and poly[ethylene‐co‐(5.4 mol‐% 2‐(3‐carboxypyridin‐6‐yloxy)ethyl methacrylate)] (EMAA‐N) and its hydrochloride (EMAA‐NHCl). Differential scanning calorimetric (DSC), X‐ray diffraction, and dielectric and dynamic mechanical relaxation studies were made for the two ionomers to investigate the formation and structure of ionic aggregates. In EMAA‐BZnX, DSC, dielectric and dynamic mechanical data suggest the formation of ionic aggregates in the neutralization range above 40%; X‐ray diffraction data, however, did not show any ionic peak, while the ionic groups were not aggregated at all in EMAA‐NHCl. From these results, the ion‐aggregation in ionomers is discussed with respect to chemical structure and the nature of ionic groups.
Dynamo‐optical and conformational properties of poly(biphenylsulfoneterephthalamide) in concentrated sulfuric acid
Authors: Filippova Tatjana V. , Shtennikova Irina N. , Lavrenko Peter N.
Published: April 2003

Optical and hydrodynamic properties of poly(biphenylsulfoneterephthalamide) (PPhSTPhA) (systematic IUPAC name: poly(iminoterephthaloylimino‐2,2′‐sulfonylbiphenyl‐4,4′‐diyl)) in sulfuric acid were investigated by means of flow birefringence and viscometry. Analysis of experimental molecular weight dependence on the shear optical coefficient made it possible to determine optical anisotropy of a monomer segment and a monomeric unit and the rigidity of the macromolecules. It was established that the molecules of this heterocyclic polyamide have the conformation of a kinetically rigid coil.
Studies on the phase separation of polyetherimide‐modified epoxy resin, 1. Effect of curing rate on the phase structure
Authors: Cui Jun , Chen Wenjie , Zhang Zhicheng , Li Shanjun
Published: April 2003

The effect of the curing rate on the phase structure of a new polyetherimide‐modified epoxy systems was studied. Through changing cure agents and cure temperature, selecting different molecular weights and end groups of the polyetherimide (PEI) polymers, the curing rates, the phase separation processes and the morphology of the cured blends were observed employing differential scanning calorimetry, time‐resolved light scattering and scanning electron microscopy. The highly active cure agent 4,4′‐oxydianiline leads to phase separation in the early stage of spinodal decomposition and to a co‐continuous phase structure. As to the 4,4′‐diaminodiphenyl sulfone cured systems, not only the curing rate, but the mobility of the PEI molecule also affected the final morphology of the PEI‐modified epoxy resin.
Anionic ring‐opening polymerization of cyclodisilazanes, 2. Influence of additives on the kinetics of polymerization
Authors: Bruzaud Stéphane , Mingotaud Anne‐Françoise , Soum Alain
Published: April 2003

The kinetics of the anionic ring‐opening polymerization of the DDNMe cyclodisilazane, initiated by benzyllithium, has been investigated in different experimental conditions. In non‐polar solvents, the active centers are aggregated ion pairs which are in equilibrium with a small amount of monomeric species. In the presence of additives such as THF, dioxane or tetramethyl‐ethylenediamine, there is only one type of active center. The aggregates are dissociated into light ion pairs externally solvated by the additive. The paper demonstrates also that the kinetics of the polymerization (i.e., rate constant of propagation kp) is a function of both the nature and the amount of additives.
Gas permeation properties of polyarylates synthesized with bromine‐ and methyl‐substituted bisphenols
Authors: Kharul Ulhas K. , Kulkarni Sudhir S.
Published: April 2003

The effect of bromine substitution on the bisphenol moiety is investigated in terms of the physical and gas permeation characteristics of the resulting polyarylates prepared with aromatic and naphthenic acids. A comparison of polyarylates based on tetrabromobisphenol‐A (TBrbisA) and tetramethylbisphenol‐A (TMbisA) shows that both substituents increase chain rigidity; however, bromine substitution increases packing density while methyl substitution reduces it. The tetrabromo substitution leads to high selectivities for small gases while the tetramethyl substitution leads to high permeabilities. In order to combine both high permeability and selectivity, both bromine and methyl substitutions were combined in the same polyarylate in two ways: (1) A copolymer based on TMbisA and TBrbisA and (2) a polyarylate based on dibromodimethylbisphenol‐A, (DBrDMbisA). These two hybrid polymers have intermediate permeabilities and higher selectivities than either TMbisA‐ or TBrbisA‐based polyarylates. The copolymer is more selective for CO2 while the polyarylate based on DBrDMbisA is more selective for He.
The possibility of living or long‐lived cationic polymerization in the butyl vinyl ether/iodine/liquid sulfur dioxide system
Authors: Oliveria Marcia G. , Moreira Ana C. F. , Brandão Georgia T. , Gomes Ailton S. , Soares Bluma G.
Published: April 2003

The polymerization of butyl vinyl ether (nBuVE) initiated by iodine in the presence of liquid sulfur dioxide has been investigated. The number‐average molecular weight increased with monomer concentration and after the addition of a fresh feed of the monomer at the end of the first polymerization step. This behavior has been observed in media of different polarity, that is, SO2/toluene = 80 : 10 or 50 : 40 v/v and SO2/CH2Cl2 = 20 : 70 v/v 1H NMR spectroscopy revealed the presence of aldehyde terminal group derived from acetal end group, indicating the presence of living or long‐lived propagating species. The average number of polymer chains carrying aldehyde end groups is higher than the initial iodine concentration, suggesting that an additional initiation process by hydrogen iodide is taking place.
The stability of polyelectrolyte complexes of Calf‐Thymus DNA and synthetic polycations: Theoretical and experimental investigations
Authors: Schindler Thomas , Nordmeier Eckhard
Published: April 2003

Complexes of Calf‐Thymus DNA and some polycations such as PDADMAC, IONEN, and P4VP were formed and investigated with respect to their stoichiometry and stability. The central part of the study are two theoretical models, the E‐model and the T‐model. It is assumed that a complex molecule consists of two linear polyion strands connected by electrostatic forces. One strand is a DNA molecule and the other is built by the polycations. Both strands carry equal number of charges, so that the complex molecule is electrically neutral. In the E‐model the complex binding distance, r1, is a constant, while in the T‐model r1 depends on the system parameters, such as the concentration, CS, of added salt or the dielectric constant, ε, of the solvent. Both theories predict a critical salt concentration, CS,d where a complex molecule becomes instable and dissociates in its single strands. According to the E‐model CS,d is 0.6 mol/1 for a 1 : 1 salt if the solvent is water and the temperature 298.16 K. This value agrees quite well with those obtained experimentally, which are 0.5 mol/1 for LiCl, 0.6 mol/1 for NaCl, 0.56 mol/l for KCl, and 0.68mol/1 for CsCl. If the dielectric constant of the solvent decreases, CS,d should decrease. This is also confirmed by the experiment. The T‐model predicts that the complex binding distance, rl,d, at which a complex molecule dissociates, is correlated with CS,d r1,d is large at low CS,d and vice versa. Using the experimental data of CS,d the T‐model predicts that r1 increases from r1 ≈ 3.8 · 10−10 m when the complex is built to r1 = r1,d ≈ 8 · 10−10m when the complex dissociates. This value is nearly as large as the average distance of a counterion bound territorial to a DNA molecule. However, for the divalent cations, Ca2+ and Sr2+, r1,d is only 4 · 10−10 m. This may be unrealistic.
Polymerization of acrylamide in aqueous medium initiated with a redox system composed of cysteine and potassium bromate
Authors: Okaya Takuji , Kikuchi Kenji , Morii Yukiko
Published: April 2003

Aqueous polymerization of acrylamide initiated with a redox initiator system composed by cysteine and potassium bromate was investigated as a model of the redox initiator system composed of poly(vinyl alcohol) having a thiol groups at one end and potassium bromate. The rate of polymerization was proportional to almost the square root of cysteine and potassium bromate concentration, indicating the initiation system is a usual free radical polymerization initiator. On the other hand, the rate was proportional to the 1.8th power of the monomer concentration. The activation energy of the rate of polymerization was about 5 kcal · mol−1, indicating also a typical redox initiation system. Chain transfer constant of polyacrylamide radical to cysteine was calculated to be 0.4. From these results, it is concluded that cysteine exerts two important roles: (1) as a reductant of the redox initiation and (2) as a powerful chain transfer reagent.
Langmuir‐Blodgett films of photochromic polyglutamates, 10. The influence of the side chain architecture on the thermal and monolayer forming properties of “hairy rod”‐like polymers
Authors: Menzel Henning , Rambke Birgit
Published: April 2003

The phase behavior of so called “hairy rod”‐like polymers with mesogenic elements in the side chains was investigated by means of differential scanning calorimetry and X‐ray diffraction and correlated with the properties of their monolayers at the air/water interface. The side chains of the polymers form a highly ordered (crystalline?) structure. The degree of crystallinity and the temperature of the phase transition to a less ordered liquid crystalline structure depend strongly on the side chain architecture. A higher degree of crystallinity is found for a decyloxy tail group than for a hexyl tail group, since alkoxy groups at the mesogenic elements can be packed more tightly. X‐ray diffraction proves that the side chains with a hexyl tail form a liquid crystalline phase, which may provide a fluid matrix for the rigid rod like backbones. The monolayers of these polymers with the side chains in a liquid crystalline phase at room temperature consist of soft domains and can be transferred to homogeneous Langmuir‐Blodgett films. By way of contrast the polymers in which the side chains are in a more highly ordered (crystalline) phase form stiff domains in the monolayers, resulting in isotherms with a shallow increase in surface pressure. Furthermore, a strong temperature dependence is found for the isotherms which can be interpreted to be a result of domain softening. The monolayers of the polymers with highly ordered side chains can be transferred only after inducing some disorder either photochemically or by increasing the temperature.
Polymorphism in an oligo(aryl ether ketone)
Authors: Rueda Daniel R. , Zolotukhin Mikhail G. , André Isabel , Ripoll Martin Martinez , de Abajo Javier , Alvarez Julio C.
Published: April 2003

1,3‐Bis(4‐phenoxybenzoyl)benzene (1) shows a single melting peak at T1 = 120°C when rapidly crystallized from a methanol/benzene mixture (10:1 v/v) (sample A) and a double melting peak at T1 = 120°C and T2 = 130°C when crystallized slowly (overnight) (sample B). Slow recrystallization of 1 using ethanol instead of methanol induces the formation of large single crystals which only show a single melting peak at T2 = 130°C (sample C). Analysis of powder X‐ray diffractograms obtained for A, B and C samples clearly point out the coexistence of two crystalline phases in sample B: phase 1 (observed for sample A) and phase 2 (sample C). From optical microscopy and thermal (DSC) observations, it can be concluded that, upon heating, phase 1 melts at T1 and the molten material converts itself into phase 2 if some crystals of phase 2 are present. Single crystal structure determination of, both, phase 1 and 2 reveal conformational differences of the molecule in both phases which pack in an orthorhombic and a monoclinic unit cell, respectively.
Synthesis and properties of polyamides based on a spirobichroman bis(ether‐carboxylic acid)
Authors: Hsiao Sheng‐Huei , Yang Ching‐Yen
Published: April 2003

High molar‐mass aromatic polyamides were obtained from 7,7'‐bis(4‐carboxyphenoxy)‐4,4,4′,4′‐tetramethyl‐2,2′‐spirobichroman, a novel dicarboxylic acid monomer, by direct polycondensation reaction in N‐methyl‐2‐pyrrolidone (NMP) with various aromatic diamines, using triphenyl phosphite and pyridine as condensing agents. Polyamides having inherent viscosities of 0,73–1,08 dL/g were obtained in quantitative yield. All the polyamides, even that derived from benzidine, are completely amorphous and readily soluble in a variety of organic solvents such as NMP, N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide (DMF), and m‐cresol. Their solutions can be cast into transparent, flexible and tough films. All the polyamides show distinct glass transitions in the range of 182–235°C on their differential scanning calorimetry (DSC) traces. The 10% weight loss temperatures in nitrogen and air are above 416 and 422°C, respectively.
Multilayer build‐up of a reactive polymer with α,ω‐functionalized chromophores
Authors: Hausch Marcus , Zentel Rudolf
Published: April 2003

Alternating multilayers with up to ten layers have been prepared by sequential reaction of a reactive polymer (poly[(1‐methylvinyl isocyanate)‐alt‐(maleic anhydride)]) with α,ω‐functionalized chromophores. For this purpose new chromophores were synthesized varying the length of the hydrophobic spacer. The analysis of the multilayer build‐up shows that physisorption is more important than chemisorption for fixation of new polymer layers. Thus, a multilayer build‐up is only possible with the shorter, more hydrophilic chromophore and not with the long hydrophobic spacer.
Molecular design of biodegradable functional polymers, 5. Enzymatic degradation of polycarboxylates containing vinyl alcohol blocks as biodegradable segment
Authors: Matsumura Shuichi , Shimagami Youko , Kanamaru Minako , Toshima Kazunobu , Tsuji Masao
Published: April 2003

Poly(sodium carboxylate)s containing vinyl alcohol blocks were prepared, and their microbial degradability and the poly(vinyl alcohol) (PVA) dehydrogenase activity as a function of vinyl alcohol block length in the polymer chain were analyzed. A clear relationship between the biochemical oxygen demand (BOD) biodegradability using the activated sludge and the relative activity of PVA dehydrogenase of a PVA‐assimilating strain, Alcaligenes faecalis KK314, was observed. A vinyl alcohol block length of about 7 monomer units corresponds to the minimum chain length of the vinyl alcohol block length which acts as a biodegradable segment in the poly[(disodium fumarate)‐co‐(vinyl alcohol)]. The enzymatic cleavability of polycarboxylates containing vinyl alcohol blocks was estimated using the cell‐free extracts of a PVA‐assimilating microbial strain, A. faecalis KK314, as the PVA‐cleaving enzyme source for both PVA dehydrogenase and hydrolase. The molecular weight of the polycarboxylates was reduced depending on the vinyl alcohol block length, and a similar molecular weight reduction tendency was observed with respect to the BOD values and PVA dehydrogenase activities.
The photoactive diazosulfonate group and its role in polymer chemistry
Authors: Nuyken Oskar , Voit Brigitte
Published: April 2003

Diazosulfonates are water soluble, highly photoactive but thermally stable compounds which are prepared from appropriate diazonium salts and sodium sulfite in a diazo coupling reaction. Upon irradiation, the stable trans‐isomer is converted into the instable cis‐isomer, followed by decomposition via a radical or an ionic mechanism with phenyl radicals or diazonium salts, respectively, as intermediates, depending on the reaction conditions. These chromophores could be incorporated as side groups into polymers via copolymerization, copolycondensation or via polymer analogous reaction. Reaction conditions as well as advantages and disadvantages of these different techniques and the photochemistry of the polymers are discussed. Diazosulfonate polymers have been applied successfully as photoresins in offset printing techniques. The use in test stripes in quick assays for the detection of phenolic compounds is discussed based on the coupling reaction of the diazonium salt intermediates. In addition, diazosulfonate containing surfactants could be synthesized and were used as photoactive stabilizers in emulsion polymerization and as partners in photoactive polyelectrolyte‐surfactant complexes.
Poly(ether ketone)s with cyclohexyl‐substituted indan groups in the main chain
Authors: Maier Gerhard , Wolf Martin
Published: April 2003

Poly(ether ketone)s containing 1,3‐dicyclohexyl‐1‐methyl‐3‐phenylindan groups in the main chain were prepared from different bisphenols and a bisfluoride monomer which contains the indan group. The bisfluoride monomer was synthesized in a three‐step process, starting from cyclohexyl phenyl ketone. All polymers are soluble in tetrahydrofuran, chloroform and N,N‐dimethylpropyleneurea. No melt transitions were detected by differential scanning calorimetry. Glass transition temperatures are relatively high (218°C to 255°C). In gel‐permeation chromatography with polystyrene calibration, 8400 < M̄n < 17900 and 34500 < M̄w < 76600 were found. The thermooxidative stability of these polymers is fairly low with decomposition starting at 400°C in air. This was attributed to the methine group of the cyclohexyl ring since the major decomposition products proved to be cyclohexane and cyclohexene.
Miscibility and specific interactions in blends of poly(vinyl acetate‐co‐vinyl alcohol) with poly(ethyloxazoline)
Authors: Parada Luis G. , Cesteros Luis C. , Meaurio Emilio , Katime Issa
Published: April 2003

Miscibility of poly(ethyloxazoline) (PEOX) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate‐co‐vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. In some blends, due to the small difference between the glass transition temperatures of the components, the enthalpic relaxation method was used as miscibility criterion. Differential scanning calorimetry (DSC) results indicate that PEOX is immiscible with PVAC and PVAL but is miscible with ACAL copolymers in a certain range of compositions. The ACAL/PEOX phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.
Synthesis of symmetric and asymmetric carbazolyl monomers and their siloxane polymers. Effect of the 2,3,6,7,9‐substitution in the carbazole unit on its mesomorphic behaviour
Authors: Dobarro Alicia , Velasco Dolores , Arnim Volkmar v. , Finkelmann Heino
Published: April 2003

A general synthetic route toward symmetric and asymmetric side‐on and end‐on carbazolyl monomers has been developed. The effect of the nature of the core on the induction of liquid‐crystal phases in side‐on carbazolyl polysiloxanes has been studied. Chromophores have been introduced into the carbazole core to produce materials with improved second‐order non‐linear optical (NLO) properties. The mesomorphic behaviour of all the polymers has been investigated by optical microscopy, differential scanning calorimetry (DSC) and X‐ray diffraction. The side‐on polymers are isothropic or crystalline except one of them that presents a metastable nematic phase.
Oligosaccharide‐based thermotropic liquid crystals, 4. Synthesis of cellobiose‐based twin and triplet derivatives and their mesophase properties
Authors: Takaragi Akira , Sugiura Makoto , Minoda Masahiko , Miyamoto Takeaki , Watanabe Junji
Published: April 2003

Previous work from this laboratory has shown that cellobiose octaalkanoate (COA) functions as a thermotropic discotic mesogen, forming a hexagonal ordered columnar phase (Dho). In this work, we prepared the COA‐based discotic twin and triplet derivatives and examined the mesomorphic properties of the derivatives by DSC, polarization microscopy and X‐ray diffraction. In the former derivative, two cellobiose heptadecanoate (CHD) molecules (monomers) are combined through an alkyl spacer of varying length by ether and ester linkages at the C‐1 position of the reducing end units of the monomers. Three CHD molecules having an alkyl spacer are connected with a coupling agent for the latter derivative. The results revealed that (i) all the twin derivatives form a distinct discotic columnar phase, (ii) the thermal stability of the mesophases of the twins is enhanced, compared with that of the monomer, when the length of the flexible spacer is appropriate, (iii) the twins with a relatively short spacer form a discotic rectangular ordered (Dro) phase, while those with a longer spacer form a pseudo‐Dho phase, (iv) the triplets also form a discotic columnar mesophase, but not a hexagonal ordered columnar (Dho) phase, (v) the thermal stability of the mesophases of the triplets strongly depends on the chemical nature of coupling cores, and (vi) the packing structures of the cellobiose cores within the columns of both derivatives are markedly different from that of the monomer.
New thermotropic copoly(keto esters) based on 3,4′‐disubstituted benzophenones
Authors: Stagnaro Paola , Tavella Flavio , Costa Giovanna , Valenti Barbara
Published: April 2003

Two isomeric benzophenone derivatives, 3‐hydroxy‐4′‐carboxy‐ and 4‐hydroxy‐3′‐carboxybenzophenone, were synthesized and used to prepare new homo‐ and copoly(keto esters) with some commercial comonomers. Polymerizations were performed both by solution and melt polycondensation methods which affect the inherent viscosity and solubility of the resultant products. Yields were always almost quantitative independently of the synthetic method employed. All the samples exhibited very high thermal stability. Phase behaviour and morphology of the polyesters have been investigated by differential scanning calorimetry (DSC) analysis and optical microscopy. A liquid‐crystalline (LC) phase was observed in most of the specimens containing commercial hydroxy acids in percentages higher than 30 mol‐%, while both homopolymers melt to an isotropic liquid. Preliminary gravimetric sorption experiments, using acetone as a penetrant, were carried out on films prepared from some of the copolymers able to give both isotropic non‐crystalline and nematic LC morphologies. The penetrant sorption was strongly reduced by the presence of the frozen nematic LC phase that behaves similarly to the conventional crystalline ordered state.
Study on the cationic polymerization mechanism of 1,3‐dioxepane in the presence of ethylene glycol
Authors: Liu Ye , Wang Hengbin , Pan Caiyuan
Published: April 2003

The cationic polymerization of 1,3‐dioxepane (DOP) initiated with trifluoromethanesulfonic acid (I) in the presence of ethylene glycol (EG) was investigated. At sufficiently low concentration of the initiator ([I] > 0.01 mol/L vs. [EG] < 0.20 mol/L), the molecular weights of the obtained polyacetal oligodiols are controlled by the mole ratio of consumed DOP to initial EG. Gel‐permeation chromatography studies revealed that the concentration of cyclic oligomers in the products are negligible. The mechanism of the polymerization was investigated by means of kinetic studies. The results showed that the polymerization proceeds according to the active chain end mechanism (ACF) in combination with the activated monomer mechanism (AM); thus the cyclic oligomer in the obtained polymer is reduced, and intermolecular chain transfer to EG in ACE is dominant. It was also demonstrated that as [DOP]2[I]/[EG] decreases the contribution of ACE to the polymerization decreases and that of AM increases. In addition, 1H and 13C NMR data illustrated that each macromolecule of polyDOP oligodiols contained one EG unit on average and that no EG end groups exist.
Novel chiral poly(para‐phenylene) derivatives containing cyclophane‐type moieties
Authors: Fiesel Rainer , Huber Joachim , Apel Ute , Enkelmann Volker , Hentschke Reinhard , Scherf Ullrich , Cabrera Karin
Published: April 2003

The introduction of cyclic ansa‐substituents allows for the synthesis of soluble poly‐(para‐phenylene)s PPP's possessing main chain chirality. The novel chiral PPP's represent an attractive combination of π‐conjugated character and chirality. We have synthesized open chain (single‐stranded) as well as ladder‐type chiral PPP's. The single‐stranded chiral PPP's exhibit temperature‐dependent changes of chiroptical properties. The behaviour should be assigned to conformational changes. The chiral ladder polymers contain the cyclophane loops exclusively on one side of the molecular board and are characterized by an unexpectedly high chiroptical activity of the π‐π*‐transition. They are potential candidates to study non‐linear chiroptical properties and to investigate circulary polarized luminescence (photo‐ and electroluminescence) effects.
New polymer syntheses, 91. Hyperbranched poly(ester‐amide)s derived from 3,5‐dihydroxybenzoic acid and 3,5‐diaminobenzoic acid
Authors: Kricheldorf Hans R. , Bolender Oliver , Stukenbrock Thomas
Published: April 2003

A new pentafunctional monomer (3a) was prepared by acylation of silylated 3,5‐diaminobenzoic acid (DABA) with 3,5‐bisacetoxybenzoyl chloride. The polycondensation of this monomer or its trimethylsilyl ester yielded a hyperbranched poly(ester‐amide) having a nearly alternating sequence of one DABA and two 3,5‐dihydroxybenzoic acid (DHBA) units. However, due to ester‐amide interchange reactions, ca. 15–25% of the DABA units lose their role as branching units. When 3,5‐bisacetoxybenzoic acid and 3,5‐bisacetamidobenzoic acid were copolycondensed in a 2:1 ratio, the resulting polymer and endgroup structures were different. Furthermore, hyperbranched copoly(ester‐amide)s with a variable DHBA/DABA ratio from 10:0 down to 3:7 were prepared. The glass transition temperature (Tg) increased by approx. 90°C (up to 250°C) at higher molar fractions of DABA. Furthermore, monomer 3a was copolycondensed with 3‐acetoxybenzoic acid or its trimethylsilyl ester. The resulting copoly(ester‐amide)s were again amorphous, showing a continuous decrease of the Tg down to the value of the poly(3‐hydroxybenzoic acid) (poly(3‐HBA)) around 136–140°C.
Novel benzo‐15‐crown‐5 functionalized α‐olefin/CO terpolymers for membrane applications
Authors: Klok Harm‐Anton , Eibeck Peter , Schmid Markus , Abu‐Surrah Adnan S. , Möller Martin , Rieger Bernhard
Published: April 2003

The synthesis of a benzo‐15‐crown‐5 functionalized α‐olefin (4′‐(undec‐10‐enylcarboxylate)benzo‐15‐crown‐5, 5) and its terpolymerization with carbon monoxide and various α‐olefins are described. A decline of the glass transition temperatures (Tg) of the corresponding terpolymers was observed upon incorporating compound 5 into the polymer main chain. Ion‐selective membranes were prepared by encapsulating the benzo‐15‐crown‐5 functionalized α‐olefin/CO terpolymers in a microporous polyethylene support. Preliminary ion‐transport experiments demonstrate the ability of these novel crown ether substituted polyketones to transport NaClO4 across the membranes. Adjusting the polarity of the polyketones via the length of the olefinic side chain offers a means to control the ion‐permeation‐rates.
Relationship between structure and gas permeation properties of polyimides prepared from oxydiphthalic dianhydride
Authors: Li Yuesheng , Ding Mengxian , Xu Jiping
Published: April 2003

Gas permeability coefficients of a series of aromatic polyimides, which were prepared from oxydiphthalic dianhydride (ODPA) with various aromatic diamines, with respect to H2, CO2, O2, N2, and CH4 were measured under 10 atm and in the temperature range from 30 to 150°C. A significant change in gas permeability and permselectivity resulting from systematic variation of the chemical structure of the polyimides was found. Among the polyimides which were prepared from phenylenediamine and its derivatives as well as bridged diamines without side groups on the benzene rings of the diamine residues, the increase of the gas permeability is accompanied by a decrease of the permselectivity. However, both the gas permeability and the permselectivity of the polyimides which were prepared from bridged diamines with methyl or methoxy groups on the benzene rings of the diamine residues simultaneously increase.
Influence of the molecular structure on the dynamics in poly(ester‐imide)s
Authors: Abdallah Merenga , Groothues Herbert , Kremer Friedrich , Kricheldorf Hans R.
Published: April 2003

Dielectric spectroscopy in the frequency range from 0.1 to 105 Hz was employed to study the molecular dynamics of main‐chain poly(ester‐imide)s (PEIMs) with varying spacer lengths from 5 to 12 methylene units. For all samples three relaxation processes were observed. The β‐process shows an Arrhenius‐like temperature dependence with activation energies between 50 and 55 kJ/mol. This process is assigned to a local libration of the ester groups. The α*‐process shows a WFL‐like temperature dependence. It is assigned to a main‐chain‐coupled motion of the mesogens around their short molecular axes. The α‐process also follows a WFL‐like temperature dependence. It is assigned to cooperative main‐chain motion of PEIM and it is correlated to the glass transition.
Radical polymerization of a trimer of methyl acrylate as polymerizable α‐substituted acrylate
Authors: Kobatake Seiya , Yamada Bunichiro
Published: April 2003

The radical polymerization of a trimer of methyl acrylate was investigated in relation to the steric hindrance‐assisted polymerization of an α‐(substituted methyl)acrylic ester. The trimer can also be regarded as a model of the unsaturated end group formed by the addition‐fragmentation chain transfer of methyl α‐(bromomethyl)acrylate during methyl acrylate polymerization. The trimer polymerizes slowly to a low‐molecular‐weight polymer at 30–60°C, and electron spin resonance (ESR) quantification of the propagating radical of the trimer allowed the determination of the absolute rate constants of propagation (kp) and termination (kt). The kp and kt values for the trimer indicate slow propagation and slow termination of polymerizable acrylates bearing a bulky α‐substituent. In conformity with a higher reactivity of the trimer of methyl acrylate than the corresponding trimer of methyl methacrylate, poly(methyl acrylate) bearing an unsaturated end group, which is produced by the polymerization of methyl acrylate in the presence of methyl α‐(bromomethyl)acrylate, was confirmed to copolymerize with methyl acrylate to yield a branched homopolymer.