bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential reordering in condensation copolymers, 3. Miscibility‐induced sequential reordering in random copolyesteramides
Authors: Fakirov Stoyko , Sarkissova Marianna , Denchev Zlatan
Published: April 2003

Binary and ternary blends of poly(butylene terephthalate) (PBT), Nylon 66 (PA66), bisphenol‐A‐polycarbonate (PC) and polyarylate (PAr) have been studied mostly by means of differential scanning calorimetry (DSC) after thermal treatment that enables transesterification. Thus, the entire cycle of sequential reordering is realized, namely: homopolymers → block copolymer → random copolymer → block copolymer. For this purpose the binary PC/PAr and PBT/PA66 blends are annealed in the molten state directly in the calorimeter until complete amorphization (as revealed by DSC). In the first blend the latter is proved by the appearance of a single glass transition temperature Tg and in the second — by the complete diappearance of the crystallization ability. At this stage a third component is added, miscible with one of the starting blend constituents — PBT for the PC/PAr and PAr for the PBT/PA66 blend. Subsequent annealing in the molten state results in amorphization of the PBT‐PC‐PAr and PBT‐PA66‐PAr terpolymers, as concluded from the loss of crystallization ability. Further annealing at 280°C and 290°C, respectively, leads to the recovery of the crystallization ability. This is documented by the reappearance of the melting temperature and the crystallinity in the DSC traces taken in heating mode. The crystallinity observed is only achieved during cooling of the melt to room temperature, i. e., crystallization‐induced sequential reordering is excluded. It is assumed that the driving force of the observed block regeneration in the melt is the trend of the PBT and PAr components of the two randomized copolymers to mix with each other. Mixing presumes the presence of longer PBT and PAr sequences. Thus, in addition to the crystallization‐induced sequential reordering in condensation copolymers, another example of transreactions is observed in the direction of an entropy decrease. It is called miscibility‐induced sequential reordering in random condensation copolymers.
Anionic polymerization of pentadecanolide. A new route to a potentially biodegradable aliphatic polyester
Authors: Jedliński Zbigniew , Juzwa Maria , Adamus Grażyna , Kowalczuk Marek , Montaudo Maurizio
Published: April 2003

The anionic polymerization of pentadecanolide (1‐oxa‐2‐cyclohexadecanone) initiated with potassium alkoxides was investigated. Polymerization proceeds under mild conditions (tetrahydrofuran, 35°C) to form high‐molecular‐weight polymer (number‐average molecular weight M̄n up to 100 000). The formation of cyclic oligomers, via back‐biting reaction, was demonstrated by means of gel‐permeation chromatography (GPC) and matrix assisted laser desorption ionisation‐time of flight (MALDI‐TOF) analyses.
Characterization of water‐soluble polymers and aqueous colloids with asymmetrical flow field‐flow fractionation
Authors: Tank Claus , Antonietti Markus
Published: April 2003

A study on the retention and separation of water‐soluble polymers and globular proteins by asymmetrical flow field‐flow fractionation (Asym. flow FFF) is presented. The applicability of only one carrier liquid to a great variety of samples with different charge stabilization and morphology (in order to simplify the handling and the data evaluation) is demonstrated. With this carrier liquid, the investigation of polystyrene latex beads with anionic as well as cationic surfactants, anionic polystyrene sulfonates and globular proteins in the hydrodynamic radius range 10–400 nm is presented, thus resulting in linear calibration curves as well as in the ability for the absolute determination of the diffusion coefficient as well as its distribution. The averaged plate number of the presented flow channel under the applied standard conditions is determined to be in the order of 1 500 which demonstrates the potential of this technique. Preliminary experiments with commerical, broadly distributed poly(1‐vinyl‐2‐pyrrolidone) samples show that the experiment performed at model systems can easily be extended to technical polymers of commercial interest.
Phase separation of blends of polydisperse polymers: Comparison between experiment and theory for the system poly(dimethylsiloxane)/poly(ethylmethylsiloxane)
Authors: Enders Sabine , Stammer Andreas , Wolf B. A.
Published: April 2003

Cloud point curves were measured turbidimetrically for blends (upper critical solution temperatures; UCSTs) of poly(ethylmethylsiloxane) (PEMS) and four different samples of poly(dimethylsiloxane) (PDMS); the weight average molar masses in kg/mol are 31.2 for PEMS and 10.4, 15.5, 18.1 and 24.0 for PDMS; all components have polydispersity indices D (= M̄w/M̄n) within the range from 1.82 to 2.67. Corresponding calculations on the basis of the Flory‐Huggins theory (three adjustable parameters) account for the poly‐dispersity; molecular weight distributions are represented by the generalized Schulz‐Flory equation. Calculated cloud point curves agree very well with those measured, if individual sets of parameters are admitted for each of the different mixtures. Even for an identical set of parameters the maximum deviations remain moderate. Realistic model calculations concerning the influences of D on cloud points and on critical points were performed with this set of parameters. For the present (only slightly endothermal) system, the precipitation threshold increases from 318 to 558.6 K as DPEMS is raised from 1.87 to 4.00, keeping the number average degree of polymerization constant.
Photoluminescence of a new water‐insoluble polysiloxane film containing pendant Ru(bpy) and its quenching by dioxygen
Authors: Nagai Keiji , Takamiya Nobuo , Kaneko Masao
Published: April 2003

A new water‐insoluble polysiloxane containing pendant Ru(bpy) (bpy = 2,2′‐bipyridine) was studied with respect to the photoluminescence and its quenching by dioxygen. The emission was quenched by O2 in water more efficiently than in gas phase, and the Stern‐Volmer plots showed a downward deviating curve. To determine which of several quenching models can be applied to the present system, the emission decays under various O2 concentration were measured, and analyzed by a double exponential decay. From the simulations of the decay using the kinetic parameters obtained from the model analysis, it has been concluded that the quenching by O2 is caused by static quenching (model 4). The O2 concentration in the film in contact with water estimated from the quenching parameters was much higher than the solubility of O2 estimated from the solubility coefficient in a dry film. These results suggest specific affinity of the polysiloxane for O2 molecule in water.
Physical gelation of polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene copolymer in paraffinic oil. Oscillatory shear and compression measurements
Authors: Quintana José R. , Díaz Esperanza , Katime Issa
Published: April 2003

The thermoreversible gelation of the triblock copolymer polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene (SEBS2) in paraffinic oil was studied. The solvent used is selective for the middle PEB block of the copolymer. The thermal behaviour as a function of copolymer concentration was investigated. The sol‐gel transition temperature increases with the copolymer concentration. The mechanical properties were examined through oscillatory shear and compression measurements. The concentration dependence of the elastic storage modulus, G′, was established. The relaxation rates observed were extremely high, indicating a considerable mobility in the gel during the measurement time.
Small‐angle X‐ray scattering on latexes
Authors: Ballauff Matthias , Bolze Jörg , Dingenouts Nico , Hickl Peter , Pötschke Dominic
Published: April 2003

Small‐angle X‐ray scattering (SAXS) is a tool which allows the study of the structure and the interaction of polymer latexes with great accuracy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the contrast by adding sucrose to the serum. Thus, scattering intensities measured at different contrast, i.e., at different excess electron densities can be evaluated (contrast variation). This yields precise information on the radial electron density of the particles. In this article recent SAXS‐investigations on latex particles are reviewed. It is demonstrated that core‐shell latexes can be analyzed precisely by contrast variation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phase. Here it is shown that the depletion of the polymer molecules near this boundary is very small which points to a minute wall‐repulsion effect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfactants dominates the measured intensity in this particular system. Therefore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene latex can be assessed by SAXS.
Polymers by 1,3‐dipolar cycloaddition reactions: the “criss‐cross” cycloaddition
Authors: Maier Gerhard
Published: April 2003

1,3‐Dipolar cycloaddition reactions have been used to prepare a large number of different heterocyclic and heteroaromatic polymers. Most of this work has been done in the 60's and 70's. Since then, interest in this field has vanished almost completely. While the number of polymer structures accessible by 1,3‐dipolar cycloaddition is very large, the high reactivity and tendency of the 1,3‐dipoles to undergo side reactions limits the successful applications in step growth polymer synthesis considerably.

The “criss‐cross” cycloaddition reaction also proceeds via two consecutive 1,3‐dipolar cycloaddition steps. Its starting compounds, azines and diolefins or diisocyanates, are stable, can be purified easily, and do not undergo side reactions if the reaction conditions are chosen properly. Initially, the reaction between hexafluoroacetone azine and various diolefins was studied. This work was aimed at the preparation and structural characterization of soluble polymers. Later on, the “criss‐cross” cycloaddition between aromatic aldazines and diisocyanates was included in this research. Different azines and diisocyanates were studied to find the best compromise between reactivity of the monomers and solubility and glass transition temperature of the products. Due to the special reaction mechanism, the polymers have exclusively isocyanate end groups, independent of stoichiometry of the monomers and the conversion. Thus, this reaction is ideally suited for the preparation of telechelics. Prepolymers obtained by “criss‐cross” cycloaddition between 4‐methoxybenzaldazine and 4,4′‐diisocyanatodiphenyl ether were used as hard segments in segmented block copolymers. Those block copolymers with a hard segment content below 36% showed elastomeric behavior with ultimate elongations above 700% and tensile strengths between 2 and 6 MPa.
The influence of the comonomer in the copolymerization of ethylene with α‐olefins using C2H4[ind]2ZrCl2/methylaluminoxane as catalyst system
Authors: Quijada Raúl , Galland Griselda Barrera , Mauler Raquel Santos
Published: April 2003

Copolymers based on ethylene with different incorporations of 1‐hexene, 1‐octene and 1‐decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From 13C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene‐comonomer‐ethylene‐comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1‐hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄w/M̄n) of the copolymers is rather narrow and dependent on the concentration of the comonomer incorporated.
Grafting reactions onto poly(organophosphazenes), 7. Light‐induced grafting of poly(vinyl acetate) onto catena‐poly[bis(4‐methyl‐, 4‐ethyl‐ and 4‐sec‐butylphenoxy)‐λ5‐phosphazene] and successive hydrolysis to phosphazenegrafted poly(vinyl alcohol)
Authors: Minto Francesco , Fambri Luca , Gleria Mario
Published: April 2003

In this paper we describe the light‐induced grafting reaction of poly(vinyl acetate) onto catena‐poly[bis(4‐sec‐butylphenoxy)‐λ5‐phosphazene], catena‐poly[bis(4‐ethylphenoxy)‐λ5‐phosphazene] and catena‐poly[bis(4‐methylphenoxy)‐λ5‐phosphazene], and the successive acid‐ (and base‐) catalyzed hydrolysis of the grafted macromolecule to poly‐(vinyl alcohol). The process was found to be dependent on the irradiation time, reaction temperature, relative monomer/methanol concentration in the reaction mixture, type of substituents present on the exploited phosphazene polymers, and on the crystallinity of these macromolecules. The new phosphazene grafted copolymers thus prepared have been characterized by IR spectroscopy, gravimetric analysis and contact angle measurements.
Synthesis of end‐functionalized polymer by means of living anionic polymerization, 5. Syntheses of polystyrenes and polyisoprenes with hydroxy and mercapto end groups by reactions of the living polymers with haloalkanes containing silyl ether and silyl thioether functions
Authors: Tohyama Mieko , Hirao Akira , Nakahama Seiichi , Takenaka Katsuhiko
Published: April 2003

Anionic living polystyrene and polyisoprene were allowed to react with six tert‐butyl‐dimethylsilyl ethers of ω‐halo‐1‐alkanols 1–6, the trimethylsilyl ether of bromohydrin (7), the tert‐butyldimethylsilyl ether of 4‐bromophenol (8), and tert‐butyldimethylsilyl 3‐chloropropyl sulfide (9), followed by acid‐catalyzed cleavage of SiO and SiS bonds to afford polystyrene and polyisoprene, respectively, with hydroxy or mercapto end groups. The alcoholic hydroxy groups were introduced quantitatively to the polymer chain end regardless of the kind of halogen atom, length of methylene spacer separating the protected hydroxy group from the halogen, and structure of protecting groups. The tert‐butyldimethylsilyl ether of 4‐bromophenol (8) was not suitable for this reaction, since most (≈90%) of the original living polyisoprene was dimerized due to metal‐halogen exchange followed by the coupling reaction of the polymeric allyl bromide derivatives thus formed with remaining living polyisoprene. Polystyrene and polyisoprene with tert‐butyldimethylsilyl sulfide end group were obtained quantitatively by the reaction of their anionic living polymers with 9. Generation of mercapto groups through deprotection was confirmed by I2 oxidation and reaction with acrylonitrile.
Synthesis of end‐functionalized polymer by means of living anionic polymerization, 7. Reaction of anionic living polymers with perfluoroalkyl halides
Authors: Sugiyama Kenji , Hirao Akira , Nakahama Seiichi
Published: April 2003

Reactions of anionic living polymers of styrene, tert‐butyl methacrylate, and 2‐(trimethylsiloxy)ethyl methacrylate with perfluoroalkyl (Rf) halides, such as C4F9(CH2)3I(1), (CF3)2CF(CF2)6I (2), C4F9(CH2)2I (3), C8F17(CH2)2O(CH2)4Br (4), were investigated to synthesize well‐defined polymers with Rf groups at the chain end. Nucleophilic attack of living polystyryl anions on 1 and 4 quantitatively proceeds to give the Rf‐terminated polystyrenes with predictable molecular weights and narrow molecular weight distributions, while low functionalities (0–50 mol‐%) were obtained in the cases of 2 and 3, on account of electron transfer and ß‐proton elimination. The anionic propagating ends of the methacrylates with potassium countercation react with 1 and 4 to afford the Rf‐terminated poly(methacrylate)s in high efficiency. Poly[2‐(trimethylsiloxy)ethyl methacrylate] produced was deprotected under acidic conditions to give poly(2‐hydroxyethyl methacrylate) bearing the Rf‐terminal group. However, the reactions of the propagating enolate with lithium countercation with 1 and 4 result in low yields of the Rf‐terminated polymers. From the surface analyses of the Rf‐terminated polymer films by X‐ray photoelectron spectroscopy and contact angle measurements, a remarkable enrichment of the Rf group at the dry surface and a surface restructuring corresponding to the environmental change are indicated.
The effect of terminal alkyl chains on hyperbranched polyesters based on 2,2‐bis(hydroxymethyl)propionic acid
Authors: Malmström Eva , Johansson Mats , Hult Anders
Published: April 2003

A hyperbranched hydroxyfunctional polyester based on 2,2‐bis(hydroxymethyl)propionic acid as AB2‐monomer and a tetrafunctional polyol as core was end‐capped with five different alkylacyl chlorides. Alkyl chain lengths ranging from three to sixteen carbons were used. Short alkyl chains (3–6 carbons) decrease the glass transition temperature from around 30°C for the hydroxyterminated polyester to temperatures well below zero. With a sufficiently long alkyl chain (12–16 carbons) the polymers tend to crystallize. The polyesters with C16‐chains as terminal groups exhibit several different crystalline phases as revealed by differential scanning calorimetry. From X‐ray data it was possible to suggest that the crystallization for the C16‐terminated samples occurs in a non‐interpenetrating fashion for the larger sample and in an interpenetrating way for the smaller polymers.
Ein neuartiges Verfahren zur Bestimmung der Molmassen Breit verteilter polymerer mit Hilfe der Gelpermeations‐Chromatographie und der viskosimetrie am Beispiel Hämoglobin‐hyperpolymerer
Authors: Pötzschke Harald , Barnikol Wolfgang K. R. , Domack Ulrike , Kirste Rudolf G.
Published: April 2003

An iterative, approximative procedure is presented, to calibrate the determination of molar masses of polymers with gel‐permeation chromatography, additionally using viscometry, and transformations, according to Benoit's concept of universal calibration, even if only polymers with broad molar mass distribution are available. The calculated (intermediate) values of the average molar masses from each step of iteration converge to final values. With at least two fractions of the polymers to be analyzed, and with measured intrinsic viscosities of the fractions, a calibration curve of gel‐permeation chromatography and Mark‐Houwink's constants can be determined. Assumptions for the use of the calibration procedure are the existence of linear calibration curves for gel‐permeation chromatography, constant Mark‐Houwink's exponents, and a common universal calibration curve according to Benoit, of the polymers of interest, and of another polymer for comparison. From this second polymer the Mark‐Houwink equation must be known (or measurable with acceptable expense), and sufficient uniform fractions for chromatography must be available. In aqueous saline the assumptions are fulfilled by hyperpolymers of human haemoglobin, and by native proteins, as shown in a previous paper. The new procedure was applied to fractions of those hyperpolymers, it was evaluated, and variants of the procedure were compared. The evaluation was done by comparison of the number‐and mass‐averages of the molar masses of the fractions of haemoglobin hyperpolymers, determined with gel‐permeation chromatography calibrated with the new procedure, with the values obtained from osmometry and light scattering. The goodness of the new procedure, especially the power of correction of molar masses, can be demonstrated with the application to fractions of haemoglobin hyperpolymers, it changes with their uniformity. Furthermore, the new procedure shows its efficiency, when three steps of iteration are enough to reach the final values. At last, with a Benoit transformation of the averages of molar masses, obtained by a theoretical consideration within the given marginal conditions, a rectification of the new procedure is given.
Coordination polymerization of lactides, 5. Influence of lactide structure on the transesterification processes in the copolymerization with ε‐caprolactone
Authors: Bero Maciej , Kasperczyk Janusz
Published: April 2003

The influence of lactide configuration on the chain microstructure of lactide/ε‐caprolactone copolymer was investigated. The copolymerization was carried out in the presence of Al(acac)3, AlEt3 and ZnEt2 as initiators. The chain microstructure analysis of the copolymers was performed by means of 13C NMR spectroscopy. The effect of lactide configuration on the transesterification and randomization of the copolymer chain was determined. The contribution of transesterification processes in the case of D,L‐lactide was found to be considerably higher than that observed when L,L‐lactide was used.
Liquid crystalline main‐chain polymers containing the ferrocene unit as a side group
Authors: Wilbert Götz , Zentel Rudolf
Published: April 2003

We have incorporated three new diethyl ω‐ferrocenylalkylmalonates into a smectic liquid crystalline main‐chain polymer in contents of about 10 mol‐%. As mesogenic unit 4,4′‐bis(6‐hydroxyhexyloxy)azoxybenzene was used as diol component and diethyl phenylmalonate as diacid component. Three ferrocene‐containing polymers were investigated in the oxidized and non‐oxidized state of the ferrocene unit varying the counterion. DSC data show a shift toward higher phase transition temperatures after oxidation, which increases with the length of the alkyl spacer between main chain and ferrocene unit. X‐ray measurements of the non‐oxidized species show an unusual increase of the smectic layer thickness with increasing length of the alkyl spacer.
Molecular structure of some model compounds for poly(aryl ether ketone)s
Authors: Shibata Mitsuhiro , Yosomiya Ryutoku , Zheng Yu‐Bin , Ke Yang‐Chuan
Published: April 2003

The molecular structure of a series of model compounds for poly(aryl ether ketone)s was investigated by means of 13C NMR spectroscopy, quantum chemical calculation, and wide‐angle X‐ray scattering. The comparison of the chemical shifts for the model compounds dissolved in 98% H2SO4 and CDCl3 (or CDCl3 + DMSO‐d6) suggested that their carbonyl groups are partially protonated by sulfuric acid and the induced positive charges are delocalized in their aromatic rings. This result was supported by the charge distribution obtained by quantum chemical calculations. The model compounds were also used to characterize the molecular structure of poly(aryl ether ketone)s. The length of the repeating unit of the polymer chain, which was calculated based on the whole chain length or fragment chain length of the model compounds obtained by semiempirical PM3 method, is compared with the c‐axis of the crystal unit cell of the polymer. For poly(aryl ether ketone)s containing biphenyl moieties, the length of the c‐axis of the unit cell is approximately twice that of the repeating unit of the macromolecule.
Electrosynthesis of poly(3‐methylthiophene) films with high strength and stabile conductive properties
Authors: Zhou Liang , Jin Shi , Xue Gi
Published: April 2003

The electrochemical polymerization of 3‐methylthiophene was significantly facilitated by the presence of freshly distilled boron fluoride‐ethyl ether as supporting electrolyte and stainless steel as electrode during the polymerization. The lower oxidation potential of the monomer led to high overall stereoregularity and stacking order of poly(3‐methylthiophene) chains. A current density of 1 mA/cm2 and a monomer concentration of 35–70 mmol/L turned out to be optimal electrosynthesis conditions. Poly(3‐methylthiophene) films had high tensile strength (73 MPa) and flexibility. The high stereoregularity of poly(3‐methylthiophene) resulted in high conductivity with improved environmental stability.
Reactive groups on polymer covered electrodes, 4. Lactate‐oxidase‐biosensor based on electrodes modified by polythiophene
Authors: Welzel Hans‐Peter , Kossmehl Gerhard , Engelmann Gunnar , Neumann Barbara , Wollenberger Ulla , Scheller Frieder , Schröder Werner
Published: April 2003

Electrocopolymerization of 3‐thiopheneacetic acid (1) and 3‐methylthiophene (2) under various conditions produces poly{(3‐methylthiophene‐2,5‐diyl)‐co‐[3‐(carboxymethyl)thiophene‐2,5‐diyl]} (3). By activation of the carboxy groups with dicyclohexylcarbodiimide (DCC) lactate oxidase (LOD) is covalently bonded to the surface of the electrode. In this way a lactate sensor was formed which is applicable for the determination of lactate in micromolar concentrations.
Liquid crystalline networks of polymethacrylates
Authors: Pfaffernoschke Matthias , Wolff Dietmar , Rübner Joachim , Springer Jürgen
Published: April 2003

LC networks on the basis of methacrylate and dimethacrylate components were synthesized via bulk and precipitation copolymerization. Up to an amount of crosslinking component of 1 mol‐% a smetic A phase is observed. The networks with 3 and 5 mol‐% only show a nematic phase. From X‐ray diffraction an orientation of the smectic phase was observed that derives from surface effects or biaxial swelling. It was found that the orientation can be increased by multiple swelling/deswelling cycles.
Crystallization from the melt of poly(lactide)s with different optical purities and their blends
Authors: Tsuji Hideto , Ikada Yoshito
Published: April 2003

Poly(lactide)s (PLA) with different optical purities (OP) were synthesized by copolymerization of D‐lactide and L‐lactide. Crystallization of D‐ and L‐lactide‐rich copolymers before and after 1 : 1 blending was studied from the melt over a wide range of annealing temperatures (Ta) using differential scanning calorimetry and polarizing microscopy. Melting temperature and crystallinity increased with an increase in OP for both the non‐blended and the 1 : 1 blended PLAs and they lost their crystallizability when their OP became smaller than 76%, suggesting that the critical isotactic sequence length of PLA for crystallization was approximately 15 isotactic lactate units. Normal spherulite formation was observed for both the non‐blended and the blended PLAs even when the OP of PLAs decreased to 76%, whereas the spherulitic size of the non‐blended PLAs was larger than that of the 1 : 1 blended PLAs when compared at the same OP and Ta. The highest Ta for crystallization increased with increasing OP and was higher for the 1 : 1 blended PLAs than for the non‐blended PLAs at a fixed OP, indicating that the crystallizable Ta range was extended to higher temperature by blending D‐ and L‐lactide‐rich PLAs. This is ascribed to stereocomplex (racemic crystallites) formation at high Ta from the 1 : 1 blended PLAs. Based on these results, the phase diagram for crystallization was depicted for the non‐blended and the 1 : 1 blended PLAs.
Polymerizations of butadiene with Ni(acac)2‐methylaluminoxane catalysts
Authors: Endo Kiyoshi , Uchida Yoshiki , Matsuda Yuichi
Published: April 2003

Polymerizations of butadiene (BD) with transition metals (MtX) and methylaluminoxane (MAO) catalysts were studied. Among the catalysts examined, nicke(II) acetylacetonate [Ni(acac)2] in combination with MAO revealed the highest catalytic activities for the polymerization of BD, giving high molecular weight polymers consisting of mainly cis‐1,4‐units in the microstructure. With Ni(acac)2‐MAO catalyst, the overall activation energy for the polymerization of BD between 0°C and 60°C was estimated to be 18 kJ/mol. From a kinetic study, the rate equation for the polymerization of BD with the Ni(acac)2‐MAO catalyst at 30°C can be expressed as follows: Rp = [BD]1.8 [Ni(acac)2‐MAO]0.9. The polymerization mechanism of the polymerization of BD with the Ni(acac)2‐MAO catalyst is discussed.
Anionic polymerization of 2‐vinylpyridine: a computational study of solvent effects on polymerization stereochemistry.
Authors: Pratt Lawrence M. , Khan Ishrat M. , Hogen‐Esch Thieo E.
Published: April 2003

Anionic polymerization of 2‐vinylpyridine shows significant solvent effects on the polymer stereochemistry. Polymerization with butyllithium in tetrahydrofuran (THF) yields a largely isotactic polymer, while polymerization with butyllithium in tetramethyl‐ethylenediamine (TMEDA) results in a material with nearly the same stereochemistry as radical polymerization. Semiempirical molecular orbital calculations were used to explain these solvent effects.
Enzyme‐catalyzed synthesis of poly(1,6‐hexanediyl maleate‐co‐fumarate) in organic medium. Study of macrolactone formation in relation to the composition of the initial monomer mixture
Authors: Mezoul Gilles , Lalot Thierry , Brigodiot Maryvonne , Maréchal Ernest
Published: April 2003

The lipase‐catalyzed synthesis of poly(1,6‐hexanediyl maleate‐co‐fumarate) from 1,6‐hexanediol, dimethyl maleate and dimethyl fumarate is described. No secondary reaction involving the double bounds takes place, so that the copolyester composition can be well defined by adjusting the mole fraction of the dimethyl esters in the initial monomer mixture. The average molar masses of the non‐fractionated copolyesters depend on the mole fraction of the dimethyl maleate and are correlated with the amount of macrocycles formed. The possibility that the reaction system obeys a ring‐linear chain equilibrium is discussed. Linear polyester chains and macrolactones are characterized by 1H NMR spectroscopy, steric exclusion chromatography and tonometry. A comparison is made with the homopolyester syntheses which were described in previous works.
Synthesis and characterization of polyoxetanes containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 2. Synthesis, characterization and polymerization of 3,3‐bis(4‐cyano‐4′‐biphenylyloxymethyl)oxetane
Authors: Guichard Bertrand , Poirier Véronique , Noël Claudine , Reyx Danièle , Le Borgne Alain , Leblanc Marc , Large Maryanne , Kajzar François
Published: April 2003

3,3‐Bis(4‐cyano‐4′‐biphenylyloxymethyl)oxetane was prepared by reaction of 3,3‐bis‐(chloromethyl)oxetane with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl. With highly purified dichloromethane, single crystals could be prepared. The X‐ray patterns could be indexed in terms of a monoclinic cell a = 13,87 Å, b = 14,74 Å, c = 13,91 Å and β = 118,68°. Some experiments were carried out to determine the cationic polymerization behavior of this oxetane. The initiating system BF3 ċ Et2O/dichloromethane was used and it was shown that unusually high initiator concentrations were necessary to observe polymerization. By means of steric exclusion chromatography and NMR spectroscopy, the formation of cyclic oligomers was evidenced. Upon heating, all the polymers showed a nematic phase. Some preliminary Corona poling experiments were performed and the second harmonic generation coefficients d31 and d33 were measured. It was shown that one can gain in net polar ordering by starting with a liquid crystalline system. The ratio d33/d31 was found to be much larger than 3 in agreement with the molecular statistical models for electric field poling of liquid crystals.
Thermodynamics of 5,5‐dimethylperhydro‐1,3‐oxazin‐2‐one, its polymerization in bulk and poly(5,5‐dimethyl‐2‐oxo‐1‐oxa‐3‐azahexamethylene) between 0 K and 500 K
Authors: Lebedev Boris , Smirnova Natal'ya , Telnoy Vadim
Published: April 2003

The thermodynamic properties of the six‐membered cyclic urethane, viz. 5,5‐dimethylperhydro‐1,3‐oxazin‐2‐one (DIO, 1) and the corresponding polymer, poly(5,5‐dimethyl‐2‐oxo‐1‐oxa‐3‐azahexamethylene) (PDIO, 2) were studied by calorimetry. The temperature dependence of the heat capacity at constant pressure Cp0 of the monomer and the polymer was studied between 5 K and 500 K. Temperatures and enthalpies of physical transitions were determined. The energies of combustion of the above compounds were measured. From the results the thermodynamic functions Cp0(T)–H0(O), S0(T) G0(T)–H0(O), were calculated for various physical states of the monomer and the polymer from 0 K to 500 K. The standard enthalpies of combustion ΔHcomb0 and the thermochemical parameters of formation of DIO and PDIO were estimated at temperature T = 298,15 K and pressure p = 101,325 kPa. The zero entropy Sgt0(O) and configurational entropy Sconf0 of PDIO in the glassy state were evaluated. The thermodynamic parameters of the bulk polymerization of DIO were calculated in the range of 0 K to 400 K at standard pressure. It was established that an equilibrium of the polymerization reaction of DIO to PDIO is shifted towards the formation of the monomer in the whole temperature range studied from 0 K to 450 K.
Bismaléimides et polybismaléimides à pont éther et thioéther—synthèse, réactivité et tenue thermique
Authors: Milano Jean Claude , Mekkid Said , Vernet Jean Louis
Published: April 2003

This paper describes the synthesis and characterization of six structurally different bismaleimides. They were prepared by reacting maleic anhydride with diamines containing ether and thioether bridges. Thermal polymerization of these monomers in the presence or absence of radical initiators was investigated by differential scanning calorimetry. Activation energy (E), kinetic order (n), rate constants (k) and heat of polymerization (ΔH) were determined. The cured resins are stable up to 334–418°C both in argon and air atmosphere.
Study on the enantioselective oligomerization of 1‐butene by chiral non‐racemic Ti complexes fixed on MgCl2
Authors: Fuhrmann Hans , Kortus Karin , Fuhrmann Christa
Published: April 2003

A number of chiral non‐racemic titanium complexes of the type (R*O)2TiCl2 (R* being an enantiomerically pure monosaccharide derivative) was incorporated in a MgCl2 matrix by coprecipitation from a non‐solvated n/iso‐Bu2Mg solution with CCl4. The precatalysts formed were activated with different organoaluminium cocatalysts and used for the oligomerization of 1‐butene. In dependence of the cocatalyst and the temperature various reaction pathways were observed. In most cases saturated oligomers were isolated. At −20°C with i‐Bu3Al2OBuCl2 as cocatalyst 55–65% olefinic oligomers with 50–70% enantiomeric excess (ee) are formed. If the growing chain is terminated by chain transfer to the Al cocatalyst, epimerization of the last inserted monomer occurs, possibly due to a rearrangement which might be favoured by an agostic interaction. The fixation of TiCl4 to a chiral modified MgCl2 support does not lead to enantiomerically enriched oligomers under the same reaction conditions.
Molecular dynamics in liquid crystalline N‐acylated oligoethylenimines as studied by broadband dielectric spectroscopy
Authors: Groothues Herbert , Kremer Friedrich , Plesnivy Thomas , Ringsdorf Helmut
Published: April 2003

The molecular dynamics and the charge transport in six liquid crystalline N‐acylated oligoethylenimines were investigated by dielectric spectroscopy. The dielectric spectra in the temperature range from 125 K up to 400 K and in the frequency range between 10−2 Hz and 107 Hz could be described by a conductivity contribution and three relaxation processes. The molecular assignment of the α‐process is a relaxation of the rigid benzamide unit. Its mean relaxation time is influenced by the length of the alkoxy side chains, the spacer length (ethylene or propylene groups) and the neighboring repeating units. In the columnar mesophase this process is cooperative due to sterical hindrance. A normalized g‐factor expressing the intermolecular cooperativity was calculated. The cooperativity increases when approaching the glass transition temperature. The γ‐process is assigned to local librational motions of the alkoxy side chain involving the ether linkage. It has an Arrhenius‐like temperature dependence (activation energy ΔEa = 22–32 kJ/mol). The β‐process is presumably a libration at the end of the alkyl chains. The conductivity contribution to the imaginary part of the dielectric function ε″ is frequency independent except for very low frequencies where electrode polarization causes a decrease in the measured conductivity. The charge transport is strongly influenced by the phase transitions isotropic to columnar and columnar to crystalline, but not by the glass transition.
New polymers by metallocene catalysis
Authors: Kaminsky Walter
Published: April 2003

Work in the field of application of metallocene‐based catalysis in olefin, diolefin and styrene polymerization has become a research topic of growing interest in recent years. A great number of symmetric and chiral zirconocenes have been synthesized, that give tailored polymers of totally different structures. Single site catalysts have the capability of permitting the user to control polymer tacticity, molecular weight and molecular weight distribution more efficiently. Beside the homopolymers of polyethylene and poly(propylene), new kinds of copolymers and elastomers can be synthesized.
Synthesis of thiol‐ and carboxyl‐terminated poly(p‐phenylene sulfide) oligomers
Authors: Yu Zili , Miao Guoxiang , Wu Qixian , Chen Yongrong
Published: April 2003

Poly(p‐phenylene sulfide) (PPS) oligomers were synthesized from sodium sulfide (SS) and p‐dichlorobenzene (p‐DCB) in hexamethylphosphoramide (HMPA) under atmospheric pressure. The effects of reaction time, temperature, and monomer ratio on end groups and molecular weight of PPS oligomers were investigated. The results show that the molecular weight is controlled by the above parameters. Thiol‐terminated PPS oligomers were prepared by two routes. One was the polycondensation of p‐DCB with equimolar SS followed by the reaction with an extra amount of SS. The other was the depolymerization of high molecular weight PPS with SS in HMPA. The results show that the second route is the best one for preparation of thiol‐terminated PPS oligomers. Carboxylterminated PPS telechelic oligomers were produced through the reaction of thiol‐terminated PPS oligomers with p‐chlorobenzoic acid.
Synthesis of ferroelectric liquid‐crystalline polymethacrylates containing 1,2‐diphenylethane based mesogens
Authors: Hsu Chain‐Shu , Her Bin‐Sheng
Published: April 2003

The synthesis of side‐chain liquid‐crystalline polymethacrylates containing (2S)‐2‐chloro‐4‐methylvaleric acid end groups and 1,2‐diphenylethane based mesogenic units is presented. Differential scanning calorimetry, optical polarizing microscopy and X‐ray diffraction were used to determine the thermal transitions and to analyze the anisotropic phases. Among the methacrylate monomers prepared in this study, those without lateral chloro substituent show only a smetic A phase while those with a lateral chloro substituent display a cholesteric phase. All polymers exhibit smectic mesomorphism and do not undergo side‐chain crystallization. All four polymethacrylates without lateral chloro substituents reveal enantiotropic smectic A and smectic B phases while the other four polymethacrylates with lateral chloro substituents reveal enantiotropic smectic A and chiral smectic C phases. The results seem to demonstrate that incorporating a lateral chloro substituent into the mesogenic core enhances the formation of a tilted chiral smectic C phase.
Synthesis and electro‐optical properties of polyurethanes with nitrostilbene side chains
Authors: Jin Shengyu , Wübbenhorst Michael , Turnhout Jan Van , Mijs Wim
Published: April 2003

Two side‐chain polyurethanes, HMDI‐PU (2a) and TDI‐PU (2b), have been synthesized from 2,2′‐iminodiethanol (“diethanolamine”) N‐substituted with a nitrostilbene group on a hexamethylene spacer with, respectively, hexamethylene diisocyanate and 1‐methyl‐2,4‐phenylene diisocyanate (“2,4‐toluenediisocyanate”). 2a showed a smectic liquid‐crystalline phase; 2b proved to be amorphous. The phase behavior was characterized by means of differential scanning calorimetry, polarization microscopy and wide‐angle X‐ray scattering. Thermally stimulated discharge current measurements (TSD) revealed at least two strong relaxation processes above the glass transition temperature Tg which are related to the dynamic glass transition involving the backbone part (α) and the mesogenic units (λ). Non‐linear optical analysis of 2a showed that the Pockels coefficient r13 was low in the mesophase and high in the isotropic phase. Contrary to expectation, poling in the mesophase did not enhance the Pockels effect. The amorphous 2b gave both a high and a stable Pockels coefficient (r33 around 6.0 pm/V). The stability could be improved by ageing and prolonged poling at the ageing temperature. However, the Pockels coefficient proved to be dependent on the temperature: high above 85°C, low below 85°C (provided that the sample had been heated once before). This was attributed to an antiparallel association of the chromophores. The role of hydrogen bonds influencing poling has been assessed by temperature‐dependent infrared spectroscopy.
Thermolysin‐catalyzed peptide synthesis in aqueous polymer two‐phase systems
Authors: Kitano Hiromi , Maeda Yasushi , Yamamoto Masayo , Izumida Rie
Published: April 2003

A proteolytic enzyme, thermolysin, was covalently immobilized to dextran which has a small number of carboxyl groups. Enzymatic synthesis of aspartame derivative (Boc‐Asp‐Phe‐OMe) using the dextran‐conjugated thermolysin was carried out in an aqueous polymer two‐phase system, where poly(ethylene glycol) (PEG) and dextran dissolved in water make a phase separation. The yield of the peptide catalyzed by the dextran‐conjugated thermolysin was higher than that using a native enzyme in the aqueous polymer two‐phase system partly due to the effect of the microenvironment around the modified enzyme and partly due to the “mass‐law” effect (the preferential dissolution of the peptide product into the PEG phase). The aqueous polymer two‐phase system would be very useful to carry out enzymatic organic syntheses in high yields.
Copolymerization of styrene and 1‐butene with a novel MgCl2‐supported Ti catalyst
Authors: Gao Feng , Lin Shangan
Published: April 2003

Copolymerization of styrene and 1‐butene was first conducted at 50°C with a novel Ti catalyst by using Al(iBu)3 (iBu = isobutyl) as cocatalyst. The Ti catalyst is composed of MgCl2/TiCl4/PhCOOEt/Ph2SiCl2/SiCl4/NdClx(OR)y/Al(iBu)3 (assigned as SN‐1 catalyst), which gave mixtures of poly(1‐butene), polystyrene, and a copolymer of both monomers. The catalytic efficiency is 1 200 ‐ 4 000 gp/(gTi · h). The monomer reactivity ratios were estimated to be rs = 0.47 and rb = 29.1. The polymers produced were fractionated successively, and a styrene‐1‐butene copolymer was obtained which was characterized in detail.
Photoresponse of polymethacrylamides bearing 1,3‐diphenyl‐2‐propen‐1‐one (chalcone) functions in the side chains
Authors: Goretzki Christian , Ritter Helmut
Published: April 2003

Synthesis and free radical polymerization of 1‐(4‐methacryloylaminophenyl)‐3‐phenyl‐2‐propen‐1‐one (2), 1‐[4‐(6‐methacryloylaminohexanoylamino)phenyl]‐3‐phenyl‐2‐propen‐1‐one (7) and 1‐[4‐(11‐methacryloylaminoundecanoylamino)phenyl]‐2‐propen‐1‐one (8) are described. The monomers and a model compound (1) were characterized by NMR and IR spectroscopy. The corresponding homopolymers (9–11) and a copolymer with methyl methacrylate (12) were characterized by DSC, GPC and TG analysis and also spectroscopically. Furthermore, the kinetics of E/Z‐isomerisations and [2 + 2] cycloadditions of chalcone functions in the polymers and the model compound were examined.
X‐ray investigation on melt‐crystallized bacterial poly(3‐hydroxybutyrate)
Authors: Gazzano Massimo , Tomasi Gianpaolo , Scandola Mariastella
Published: April 2003

Films of bacterial poly(3‐hydroxybutyrate), obtained by crystallization from the melt at different temperatures up to 120°C, were investigated by powder X‐ray diffraction analysis and optical microscopy. With increasing crystallization temperature (Tc) the diffraction patterns differed more and more from that of the “as received” powder in both relative intensity of the reflections and peak width. The relative peak intensities also varied in response to temperature changes of the melt from which the polymer was quenched to a selected Tc. The differences in the X‐ray diffraction patterns were correlated with changes of average spherulite size (0.1 mm to 2 mm) in films with limited thickness. When the spherulites were large the lamellar crystals were strongly oriented parallel to the film plane. Full profile Rietveld analyses allowed to quantify the preferred orientation effect and to extract additional morphological and structural informations.
Aggregation behavior and interaction with human serum albumin of 2‐oxazoline block copolymers in aqueous solutions
Authors: Naka Kensuke , Nakamura Tohru , Ohki Akira , Maeda Shigeru
Published: April 2003

The structure of the aggregates of block copolymers containing poly[(N‐acetylimino)ethylene] as hydrophilic block and poly[(N‐acylimino)ethylene]s as hydrophobic block was studied by size exclusion chromatography, dynamic light scattering, and transmission electron microscopy. The morphology of the aggregates, consisting of spherical and rod‐like micelles, depends on the chemical structure of the block copolymers. The adsorption behavior of human serum albumin (HSA) onto each polymer aggregate was studied by size exclusion chromatography. The maximum amount of HSA bound onto the polymer aggregates depends on the morphology of the polymer aggregates. Adsorption isotherms of HSA for each polymer aggregate are in good agreement with a Langmuir adsorption isotherm. The amount of HSA adsorbed onto the aggregates is not influenced by the fatty acid content in HSA. The electrophoretic mobility of the aggregates without HSA is close to zero, and the negative mobility increases when HSA is incorporated into the aggregates. The experimental results suggest that adsorption of HSA to the aggregates occurs mainly at the surface or at the hydrophilic shell of the polymer aggregates, not at the hydrophobic core of the polymer micelles.
Synthesis of new polymers involving deltahedral carborane units
Authors: Vohlídal Jiří , Vangani Veena H. , Plešek Jaromír , Rajabi Farzaneh H. , Blechta Vratislav , Němec Ivan
Published: April 2003

Aminocarboranes nido‐7‐NH3+‐(7‐CB10H12)− and closo‐1‐NH3+‐(CB11H11)− were copolymerized with α,ω‐dihalogenoalkanes to high‐molecular‐weight alternating copolymers. The nido‐compound copolymer was crosslinked by means of sandwiching two open cages with CoIII ion yielding bis(monocarbollide)‐cobaltate(III) units as the new type knot points. Metallacarboranes, 1,1′‐diaminobis(monocarbollide)nickelate(IV) and two bridged bis(dicarbollide)cobaltates(III) (8,8′‐μ‐imino‐ and 8,8′‐μ‐oxyimino‐), have provided hemipolymers of molecular weight up to a few thousands in the same type of copolymerization. A new methacrylic‐type monomer was prepared by reaction of glycidyl methacrylate with 8,8′‐(μ‐imino)‐(1,2‐C2B9H10)‐3‐CoIII and copolymerized with methyl methacrylate to high‐molecular‐weight statistical copolymers.