bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo‐driven liquid crystal cell using azobenzene‐grafted ladderlike polysiloxane as command layer
Authors: Tang Yongxin , Liu Dongsheng , Xie Ping , Zhang Rongben
Published: April 2003

A novel photo‐driven liquid crystal (LC) cell was fabricated by sandwiching nematic LC molecules between two quartz plates whose surface was modified with 4‐hexyloxy‐4′‐undecanyloxyazobenzene (6Az11)‐grafted ladderlike copoly(methylhydrosilsesquioxane) (PMHSQ). Reversible changes of the alignment between homeotropic and planar modes were achieved. The transmittance through the cell and crossed polarizers could be controlled by the irradiation intensity of 365 nm UV light. A high contrast ratio over 100:1 was obtained.
Polymerization of 1,3‐butadiene, 4‐methyl‐1,3‐pentadiene and styrene with catalyst systems based on biscyclopentadienyl derivatives of titanium
Authors: Ricci Giovanni , Bosisio Carlo , Porri Lido
Published: April 2003

1,3‐Butadiene, 4‐methyl‐1,3‐pentadiene and styrene were polymerized with dicyclopentadienyltitanium dichloride/methylaluminoxane (Cp2TiCl2/MAO) and dicyclopentadienyltitanium chloride/MAO (Cp2TiCl/MAO). These systems are less active than cyclopentadienyltitanium trichloride/MAO (CpTiCl3/MAO), but show the same stereospecificity as the latter; they give predominantly cis‐1,4‐polybutadiene, 1,2‐syndiotactic poly(4‐methyl‐1,3‐pentadiene) and syndiotactic polystyrene. Cp2TiCl/MAO is much more active than Cp2TiCl2/MAO; this is probably due to the fact that in the reaction of Cp2TiCl2 with MAO, only a small amount of Ti(IV) is reduced to Ti(III), which is the active species in the polymerization of styrene and 1,3‐dienes. An interpretation of the structure of the active species in Cp2TiCl/MAO is reported.
Potassium hydride — the new initiator for anionic polymerization of oxiranes
Authors: Stolarzewicz Andrzej , Neugebauer Dorota , Grobelny Janusz
Published: April 2003

Potassium hydride with 1,4,7,10,13,16‐hexaoxacyclooctadecane (18‐crown‐6) was used in the anionic polymerization of (butoxymethyl)oxirane. Polymers with low ratio of mass‐ to number‐average molar masses (M̄w/M̄n < 1.1) were obtained, each macromolecule being terminated (after hydrolysis) with a hydroxyl group on both of its ends. Chain transfer reactions to the monomer were not observed to operate in this system.
Thermal polymerizations of alkali 4‐(1‐bromoethyl)benzoates
Authors: Inoki Mari , Akutsu Fumihiko , Kitayama Yasuyuki , Shinoda Koichi , Kasashima Yoshio , Naruchi Kiyoshi
Published: April 2003

Thermal reactions of alkali salts of 4‐(1‐bromoethyl)benzoic acid in bulk were investigated. These reactions were found to produce unexpectedly the graft copolymer, poly(4‐vinylbenzoate)‐graft‐oligo(oxycarbonyl‐1,4‐phenylenethylidene) (1). The relative reactivity of the oligocondensation as well as the vinyl polymerization of the salts decreased in the following order: K > Na > Li. The reaction polymerization rate proceeded rapidly during the initial 15 min, and then slowed down.
Synthesis of new smectic C* liquid‐crystalline block copolymers
Authors: Zheng Wen Yue , Hammond Paula T.
Published: April 2003

A series of smectic C* liquid‐crystalline (LC) block copolymers were successfully synthesized via the living anionic polymerization of polystyrene with optically active methacrylate monomers containing (S)‐2‐methylbutyl 4‐(4‐hydroxyphenylcarbonyloxy)‐biphenyl‐4′‐carboxylate mesogens. These materials are the first reported smectic C* block copolymers. Anionic polymerization in tetrahydrofuran (THF) at −70°C leads to LC block molecular weights of approximately twenty repeating units. The number‐average molecular weight of the polystyrene block was varied from 7000 to 20000 to adjust the composition in the block copolymers. Differential scanning calorimetry and optical microscopy indicate that the smectic C* phase is present in the systems over broad temperature ranges.
Copolymerization of ethylene and 1‐octene with Cp*TiCl3 as catalyst supported on 3‐aminopropyltrimethoxysilane treated SiO2
Authors: Uozumi Toshiya , Toneri Tatsuya , Soga Kazuo , Shiono Takeshi
Published: April 2003

Two kinds of SiO2‐supported Cp*TiCl3 (Cp* = η5‐1,2,3,4,5‐pentamethylcyclopentadienyl) catalysts were prepared, using SiO2 modified with 3‐aminopropyltrimethoxysilane (NSiO2) and the ordinary SiO2 as the carrier. The copolymerization of ethylene and 1‐octene was conducted over them combined with methylaluminoxane (MAO) as cocatalyst. From a detailed analysis of the produced copolymers, it was found that the NSiO2 supported Cp*TiCl3 catalyst gives poly(ethylene‐co‐1‐octene) with a higher content of 1‐octene and a narrower molar mass distribution as well as a narrower chemical composition.
Poly(divinylsiloxyethylene glycol) — synthesis and photoresist characteristics
Authors: Aoki Hidetoshi , Tokuda Takashi , Nagasaki Yukio , Kato Masao
Published: April 2003

Poly(siloxyethylene glycol)

The term “poly(siloxyethylene glycol)” was used by us in our previous paper10 for the following polymer skeleton:
magnified image

with pendant vinyl groups (PVSE) was synthesized by polycondensation of oligo(ethylene glycol) (MW = 300) and diaminodivinylsilane. PVSE300 thus obtained is soluble in cold water. The PVSE300 coupled with a polythiol compound shows properties of a negative working photoresist. A negative tone image was obtained by development with water at 4°C. PVSE300 is a new type of Si‐containing polymer resist which can be developed by water.
Characteristics of liquid‐crystalline cholesteryl and cyanobiphenyl side chains pendent to trans‐polypentenamer
Authors: Cho Iwhan , Chang Kyeongho
Published: April 2003

trans‐Polypentenamers with thermotropic liquid‐crystalline side chains cholesteryl and cyanobiphenyl were prepared by ring‐opening polymerization of vinylcyclopropane monomers with proper substituents. Molecular weights of the polymers were in the range of 25000 to 80000 and the ratios of weight‐ to number‐average molecular weights Mw/Mn were between 3.3 and 3.8. The glass transition temperature values of the polymers were 35°C (4a) and 39°C (4b). Monomers 3a and 3b present cholesteric and smectic mesomorphism, respectively. On the other hand, polymers 4a and 4b present only a smectic mesophase.
Side‐chain liquid crystalline copolymers with non‐mesogenic comonomers – influence of comonomer content on the nature of the mesophase
Authors: Sänger Jörg , Gronski Wolfram
Published: April 2003

Statistical copolymers with mesogenic and non‐mesogenic comonomer units were synthesized by partial hydroboration of the 1,2‐units of polybutadiene and subsequent conversion of the alcohol groups to mesogenic units. The nature of the LC phase proves to be dependent on the mesogen content. Below a certain content the smectic C phase vanishes, and the polymer becomes cypotactic nematic. Tg, Ts,n, Tn,i and ΔHs,n depend on the mesogen content, whereas ΔHn,i is independent. No difference can be detected between the phase behaviour of homopolymers and ABA‐triblock copolymers with a liquid crystalline B‐block and 10 wt.‐% polystyrene A‐blocks.
NMR study of doped poly(2,5‐dimethylaniline)
Authors: Geng Yanhou , Jing Xiabin , Li Ji , Wang Fosong
Published: April 2003

Structure changes and charge transfer in the doping process of poly(2,5‐dimethylaniline) (PDMA) were studied by NMR technique. It was shown that not only the polymer chain but also the hydrogen atoms and methyl groups on the aromatic rings were involved in the charge transfer process. A “four ring BQ derivatives” model was proposed to explain the NMR results.
Light emitting diodes based on a discotic main chain polymer
Authors: Christ Thomas , Stümpflen Volker , Wendorff Joachim H.
Published: April 2003

We prepared light emitting diodes with a discotic main chain polymer doped with a tristilbene amine derivative. X‐ray investigations showed the formation of a hexagonal columnar structure in the annealed devices. This increased order leads to a significant reduction of the onset voltage for light emission down to 4 · 105 V/cm.
Cloud point of poly(N‐isopropylmethacrylamide) solutions in water: is it really a point?
Authors: Netopilík Miloš , Bohdanecký Miloslav , Chytrý Vladimír , Ulbrich Karel
Published: April 2003

Time‐dependent phase separation/transition was observed in aqueous solutions of poly(N‐isopropylmethacrylamide) in the temperature range 38–42°C. The time before the second phase appears is a function of temperature and may reach up to several hours.
Synthesis of amphiphilic graft copolymers by ring‐opening polymerization of 2‐methyl‐2‐oxazoline initiated by poly[isobutene‐co‐(p,m‐chloromethylstyrene)] macroinitiators
Authors: Nuyken Oskar , Sanchez Juan Rueda , Voit Brigitte
Published: April 2003

poly[isobutene‐co‐(p,m‐chloromethylstyrene)]‐graft‐poly(2‐methyl‐2‐oxazoline) graft copolymers (GP) were prepared by the “grafting from” method throught the cationic polymerization of 2‐methyl‐2‐oxazoline (MeOXA) initiated by a statistical copolymer is isobutene and chloromethylstyrene. The unusual viscosity behavior in chloroform solution of these polymers, the dynamic laser light scattering analysis in aqueous solution, as well as the solubility in polar solvents like water and methanol demonstrate the amphiphilic character of the graft copolymers and indicate the formation of aggregates in solution.
Thermal stability of syndiotactic polypropene
Authors: Mori Hideharu , Hatanaka Tomoyuki , Terano Minoru
Published: April 2003

Thermal stability of syndiotactic polypropene (syn‐PP) was investigated by comparison with isotactic polypropene (iso‐PP). Heat treatments were carried out in air at 160–220°C for 10–30 min. Under these conditions, molecular weight and molecular weight distribution of syn‐PP were almost kept constant, indicating the high stability of syn‐PP. Iso‐PP was degraded drastically under the same conditions. Thus, it is confirmed that the stereoregularity is one of the dominant factors to determine the stability of PP.
Effect of cocatalysts on the character of a constrained geometry catalyst
Authors: Shiomura Tetsunosuke , Asanuma Tadashi , Sunaga Tadahiro
Published: April 2003

A constrained geometry catalyst (CGC) precursor, Me2Si(Flu)(N‐t‐Bu)ZrX2 (X = Cl or NMe2), behaved as a single site catalyst with methylaluminoxane (MAO) as cocatalyst, while it developed much diversified catalytic species with AIR3/Ph3CB(C6F5)4 as cocatalyst. The catalytic performance was not affected if X is Cl or NMe2.
Chemoselectivity in 4‐methyl‐1,3‐pentadiene polymerization in the presence of homogeneous Ti‐based catalysts
Authors: Longo Pasquale , Grisi Fabia , Proto Antonio , Zambelli Adolfo
Published: April 2003

The homogeneous catalyst CpTiCl3‐MAO is able to produce a random copolymer of 4‐methyl‐1,3‐pentadiene with ethylene. 13C NMR analysis of the copolymers shows that after insertion of ethylene units, the next 4‐ymethyl‐1,3‐pentadiene unit can be inserted in either 1,2 or 1,4 arrangement. The high chemoselectivity observed in the 1,2‐syndiotactic homopolymerization of 4‐methyl‐1,3‐pentadiene with respect to the lower one observed in the copolymerization with ethylene is attributed to a back‐biting coordination to the Ti of the active species of the penultimate monomer unit of the growing chain.
Effects of poly(methyl methacrylate)‐block‐poly(vinyl acetate) copolymer on the spinodal decomposition of corresponding homopolymer blends
Authors: Chen Wenjie , Shen Zhong , Huang Xiaoyu , Huang Junlian
Published: April 2003

Effects of adding a small amount of poly(methyl methacrylate)‐block‐poly(vinyl acetate) (PMMA‐b‐PVAc) to poly(methyl methacrylate)/poly(vinyl acetate) (PMMA/PVAc) blends with a lower critical solution temperature (LCST) phase diagram on the kinetics of late‐stage spinodal decomposition (SD) were investigated by time‐resolved light scattering at 160°C. It is found that the coarsening process of the structure was slowed down or accelerated upon addition of PMMA‐b‐PVAc depending on the composition of the block copolymer and the blend. The effect of the block copolymer on the domain size were interpreted as compatibilizing and incompatibilizing effects of the block copolymer on PMMA/PVAc blends based on the evaluation of changes in the stability limits of PMMA/PVAc with the addition of block copolymer using random phase approximation (RPA).
Gas phase polymerization of ethylene with a silica‐supported metallocene catalyst: influence of temperature on deactivation
Authors: Roos Peter , Meier Gerben B. , Samson Job Jan C. , Weickert Günter , Westerterp K. Roel
Published: April 2003

Ethylene was polymerized at 5 bar in a stirred powder bed reactor with silica supported rac‐Me2Si[Ind]2ZrCl2/methylaluminoxane (MAO) at temperatures between 40°C and 80°C using NaCl as support bed and triethylaluminium (TEA) as a scavenger for impurities. For this fixed recipe and a given charge of catalyst. the average catalyst activity is reproducible within 10% for low temperatures. The polymerization rate and the rate of deactivation increase with increasing temperature. The deactivation could be modeled using a first order dependence with respect to the polymerization rate.
Improved synthesis of cyclic and polymeric phosphazenes based on facile chlorine substitution with phenols promoted by cesium carbonate
Authors: Carriedo Gabino A. , Alonso Francisco J. García , González Pedro A.
Published: April 2003

In this report we describe a very convenient synthetic method for the preparation in high yields and purity of cyclic [N3P3(OCH2CF3)6] and [N3P3(OC6H4R)6] (R = Br, CN, CHO, COC6H5, COCH3, H, OCH3), and polymeric [NP(OC6H4R)2]n (R = Br, CHO, COC6H5, H, But) phosphazenes from the direct reaction of the trimer [N3P3Cl6] or the high polymer [NPCl2]n and the alcohol HOCH2CF3 or the para‐substituted phenols HOC6H4R, using Cs2CO3 as proton abstractor and acetone or tetrahydrofuran as solvent.
A novel synthesis of acrylic acid containing polymers
Authors: Xiang Maoliang , Jiang Ming , Kong Xiangming , Yang Yiquing , Lu Wenkui
Published: April 2003

A novel synthesis of linear acrylic acid containing polymers, poly(styrene‐co‐acrylic acid) and poly(acrylic acid), was accomplished through hydrolysis of the respective parent polymers, i.e. poly(styrene‐co‐methyl acrylate) and poly(methyl acrylate), with trimethylsilyl iodide under mild conditions. Combination of 1H NMR, 13C NMR, FTIR, DSC and chemical titration confirms that the conversion from methoxycarbonyl to carboxyl is almost complete. This method is further successfully applied to synthesize poly‐(ethyl methacrylate‐co‐acrylic acid) through selective hydrolysis of the methyl acrylate units in poly(ethyl methacrylate‐co‐methyl acrylate).
Ethylene polymerization with homogeneous Ziegler‐Natta catalysts: theoretical study on the role of ion pairs in the polymerization mechanism
Authors: Fusco Roberto , Longo Luca , Masi Francesco , Garbassi Fabio
Published: April 2003

The thermodynamics of the reaction of an ethylene molecule with the Cp2TiCH3Cl/Al(CH3)2Cl system (Cp = η5‐C5H5), as a model for olefin polymerization with homogeneous Ziegler‐Natta catalysts, was investigated via quantum mechanical DFT calculations. The comparison of the calculated energies for three possible titanium‐olefin coordinated intermediates, the ionic complex Cp2TiCH3(C2H4)+/Al(CH3)2Cl, the bimetallic complex Cp2TiCH3(C2H4)δ+ · Al(CH3)2Cl and the olefin‐separated ion pair Cp2TiCH/C2H4/Al(CH3)2Cl, shows that the most feasible polymerization mechanism occurs via olefin‐separated ion pair.
Photoinitiators and photoinitiation, 12. The aromatic ketone/t‐amine Type‐II photoinitiating system. Identification of the initiating species
Authors: Hageman Hendrik J.
Published: April 2003

The system benzophenone/N,N‐dimethylaniline (DMA) representing a typical Type‐II photoinitiating system is irradiated in the presence of 1,1‐di(p‐tolyl)ethylene (DTE) as a non‐polymerising model substrate. In the presence of DMA the excited triplet state of benzophenone is not quenched by DTE and N‐[3,3‐di(p‐tolyl)propyl]‐N‐methylaniline is isolated as the major product, indicating the DMA derived radical as the main initiating species in such Type‐II systems. The mechanism of the reaction and its implications are discussed.
13C‐enriched end groups of poly(3,7‐dimethyl‐1‐octene) prepared in the presence of isotactic specific catalysts
Authors: Longo Pasquale , Oliva Patrizia , Oliva Leone
Published: April 2003

Polymerizations of (R,S)‐3,7‐dimethyl‐1‐octene in the presence of heterogeneous or homogeneous isotactic specific catalysts give very similar products with a homopolymeric isotactic structure. The insertion of (R,S)‐3,7‐dimethyl‐1‐octene into the metal‐CH3 bond (both heterogeneous and homogeneous catalysts) is highly stereospecific and stereoselective.
Polypeptide‐synthetic polymer hybrids, 1. Miscibility of poly(vinyl alcohol) with poly(sodium α,β‐D,L‐aspartate)
Authors: Takasu Akinori , Aoi Keigo , Okada Masahiko
Published: April 2003

The present paper describes materials of polypeptide‐commodity polymer hybrids from poly(vinyl alcohol) (PVA) and poly(sodium α,β‐D,L‐aspartate) (1). Miscible blend films of polypeptide 1 and PVA were prepared by the solvent‐cast method from a homogeneous aqueous solution. Differential scanning calorimetry. Fourier transform infrared, and scanning electron microscopy combined with energy dispersive X‐ray spectroscopy (EDX) were used to investigate the blends. It was revealed that 1 and PVA are miscible in a wide range of compositions.
Silylation of cellulose and low‐molecular‐weight carbohydrates with hexamethyldisilazane in liquid ammonia
Authors: Mormann Werner , Wagner Thomas
Published: April 2003

Silylation of cellulose and some low‐molecular‐weight hydroxy compounds (1,2‐propanediol, D‐glucose, methyl α‐D‐glucoside, sucrose and β‐cyclodextrin) has been performed with hexamethyldisilazane (HMDS) in liquid ammonia at elevated temperature in an autoclave. No salt‐like by‐products are formed and no tedious purification of the products is necessary. As indicated by size‐exclusion chromatography the silylation of cellulose with HMDS/NH3 proceeds without degradation of the polymer chain. The degree of silylation of the trimethylsilylcellulose obtained is higher than with other silylation procedures reported in the literature. The temperature/composition diagram of HMDS/NH3 proved complete miscibility above 24°C.
Synthesis and properties of polyamides based on (±)‐norbornane‐2 endo, 3exo‐dicarboxylic acid
Authors: Flugel Michael , Heitz Walter
Published: April 2003

A series of polyamides was synthesized by interfacial polycondensation of (±)‐norbornane‐2‐endo,3exo‐dicarbonyl dichloride with various aliphatic diamines, H2N(CH2)mNH2 with m = 2, 3, 4, 6, 8, 10. The use of chlorobenzene as organic solvent is favourable for the preparation of high molecular weight polymers. Inherent viscosities of 0.51 – 1.63 dL/g were obtained. Differential scanning calorimetry of polymers with m = 3, 4, 6, 8, 10 revealed glass transition temperatures between 119 and 189°C, whereas no Tg could be determined for m = 2. The 5% weight loss temperatures ranged from 295 to 371°C in nitrogen atmosphere. The polymers are amorphous as shown by X‐ray and DSC experiments.
Coupling of benzyl halides mediated through alkali metal supramolecular complexes. A novel route to poly(p‐xylylene)
Authors: Jedliński Zbigniew J. , Janeczek Henryk , Matuszowicz Andrzej , Grobelny Janusz
Published: April 2003

Coupling of benzyl bromide giving 1,2‐diphenylethane was demonstrated to proceed at room temperature in THF solution mediated by the potassium/18‐crown‐6 supramolecular complex. Based on this model reaction a novel method for the low temperature synthesis of poly(p‐xylylene) from α,α′‐dibromo‐p‐xylene is proposed. Experimental evidence of the polymer structure was provided by solid‐state 13C NMR and IR spectroscopy.
New polymer syntheses, 88. Thermosetting cholesterin oligocarbonates with propargyl endgroups
Authors: Kricheldorf Hans R. , Sun Shih‐Jieh
Published: April 2003

Thermosetting cholesteric oligocarbonates were prepared by polycondensation of mesogenic diphenols such as 4,4′‐dihydroxybiphenyl (DHB) or hydroquinone 4‐hydroxy‐benzoate (HQHB; system. name: 4‐hydroxyphenyl 4‐hydroxybenzoate) with methylhy‐droquinone and isosorbide. Trichloromethyl chloroformate served as condensing agent and propargyl alcohol (system. name of propargyl: 2‐propynyl), 4‐propargyloxybenzoyl chloride or 6‐propargyloxy‐2‐napthoyl chloride served as chain stoppers. Most oligocar‐bonates form a cholesteric phase over a broad temperature range. Depending on the mole fraction of isosorbide these oligocarbonates form Grandjean textures when sheared in the molten state.
A new theoretical formula for the determination of the copolymer composition distribution measured by gel permeation chromatography
Authors: Xu Jian , Wu Guanying , Sun Yufeng , Shen Yibing
Published: April 2003

A new theoretical formula, used for the determination of the chemical composition distribution of copolymers, is proposed in this paper. The composition distribution of styrene in chlorinated butyl rubber/polystyrene comb graft copolymer was obtained by gel permeation chromatography utilising a combination of refractive index and ultraviolet detection. It is a more convenient and time‐saving method for the characterization of the molecular structure parameters of a copolymer compared to the conventional experimental method.
Synthesis of silsesquioxanes having photochromic diarylethene pendant groups
Authors: Nakashima Hisataka , Irie Masahiro
Published: April 2003

Silsesquioxanes having 1‐(2‐methylbenzo[b]thien‐3‐yl)‐2‐[5‐(4‐butylphenyl)‐2,4‐dimethylthien‐3‐yl]perfluorocyclopentenes as the pendant groups were synthesized. Photochemical conversion from the open‐ring to the closed‐ring form of diarylethenes chemically bonded to polymers was by 15–25% lower than the conversion of the chromophores dispersed in the same matrix. No appreciable difference in the photoconversion of the fixed chromophores was observed below and above the glass transition temperature (Tg) of the polymer films.
Microsphere synthesis by dispersion copolymerization of methyl methacrylate with poly(acrylic acid) macromonomers: pH effect on microsphere formation
Authors: Ishizu Koji , Yamashita Masao , Ichimura Ayako
Published: April 2003

The pH effect on microsphere formation in the dispersion copolymerization of methyl methacrylate with vinylbenzyl‐terminated poly(acrylic acid) (PAA) macromonomers is studied. The diameter of poly(methyl methacrylate) (PMMA) microspheres is minimum around pH = 8. Dynamic light scattering data indicate that the shell thickness of PAA‐grafted chains shows a maximum around this pH. The degree of expansion of PAA chains drastically affects the particle size of PMMA microspheres during the dispersion copolymerization.
Gel permeation chromatographic determination of activation rate constants in nitroxide‐controlled free radical polymerization, 2. Analysis of evolution of polydispersities
Authors: Fukuda Takeshi , Goto Atsushi
Published: April 2003

The dissociation rate constant kd of the PS‐TEMPO adduct, where PS is polystyrene and TEMPO is 2,2,6,6‐tetramethylpiperidin‐1‐oxyl, was determined by the gel permeation chromatographic tracing of the evolution of polydispersities at an early stage of styrene polymerization with a model PS‐TEMPO adduct as initiator. The results agree with those obtained by the direct method in Part 1.
Chiral ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl) complexes of zirconium and hafnium: separation and application to asymmetric polymerization
Authors: Habaue Shigeki , Sakamoto Hiroshi , Baraki Hideo , Okamoto Yoshio
Published: April 2003

Optical resolution of ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl) complexes of zirconium and hafnium was performed by using cellulose tris(3,5‐dimethylphenylcarbamate) coated on silica‐gel (Chiralcel OD) as a chiral stationary phase for HPLC. The biphenyl‐2,2′‐diolate complexes were completely resolved with the highest separation factor. The isolated enantiomerically pure hafnocenes were applied for the asymmetric cyclopolymerization of 1,5‐hexadiene.
Pressure effects on termination mechanisms during ethene polymerization catalyzed by dicyclopentadienylzirconium dichloride/methylaluminoxane
Authors: Thorshaug Knut , Rytter Erling , Ystenes Martin
Published: April 2003

Polymerization of ethene catalyzed by dicyclopentadienylzirconium dichloride/methylaluminoxane was performed in toluene at 50°C under 0.38–8.95 bar ethene. Both Fourier‐transform infrared spectroscopy and gel‐permeation chromatography showed that the molecular weight is independent of the ethene pressure (concentration). The trans‐vinylene unsaturation content increased as the pressure decreased. Termination by β‐H transfer to a coordinated monomer and a kinetically controlled isomerization reaction are suggested, in order to explain the observations.
Preparation of amphiphilic networks by Diels‐Alder reactions between oligo(butyl methacrylate) with furan end‐groups and a poly(ethylene oxide‐co‐acetylenedicarboxylate)
Authors: Delerba Mark , Ebdon John R. , Rimmer Stephen
Published: April 2003

A butyl methacrylate oligomer with furan end‐groups was synthesized by ozonolysing a poly(butyl methacrylate‐co‐butadiene) latex. The end‐groups of this oligomer were amidated with aminomethylfuran to give a coagulated mass of derivatized oligomers. This furan functional oligomer was then mixed with poly(ethylene oxide‐co‐acetylenedicarboxylate) and heated at 60°C or 125°C. The material cured at 125°C was found to contain a higher gel fraction (55 wt.‐%) than that cured at 60°C (30 wt.‐%).
Static density gradient centrifugation; extended Hermans‐Ende equation
Authors: Lechner M. Dieter
Published: April 2003

An extended Hermans‐Ende equation for real solutions has been derived in order to calculate the density as a function of the radial distance in a density gradient mixture (light/heavy medium) inside an ultracentrifugal cell. The equation has been tested with equilibrium density gradient measurements of the system water/metrizamide/polystyrene latex where metrizamide is the heavy medium. The solvent compositions were 8 to 15 mass‐% metrizamide (2‐(3‐acetamido‐5‐N‐methylacetamido‐2,4,6‐triiodobenzamido)‐2‐deoxy‐D‐glucose). The latex concentration was 0.03 mass‐%. It is demonstrated that the density gradient is highly influenced due to monideality effects with respect to the solvent composition and due to the pressure gradient in the ultracentrifuge.
Carboxy‐terminated homo‐ and copolymers of styrene using dicarboxylic acid‐functional azo initiator and 2,2,6,6‐tetramethyl‐1‐piperidyloxyl (TEMPO)
Authors: Baumert Martin , Mülhaupt Rolf
Published: April 2003

Carboxy‐terminated polystyrene, poly(styrene‐co‐acrylonitrile), and polystyrene‐block‐poly(styrene‐co‐acrylonitrile) with ratios of weight‐ to number‐average molar masses M̄w/M̄n below 1.3 were synthesized via a controlled radical polymerization mechanism. The polymerizations were initiated with 4,4′‐azobis(4‐cyanopentane‐carboxylic acid) and 2,2,6,6‐tetramethyl‐1‐piperidyloxyl radical and conducted in bulk at elevated temperatures. The polymerization was monitored by nuclear magnetic resonance, size‐exclusion chromatography, end‐group titration and differential scanning calorimetry.
Study of molecular size in ethylene‐propene copolymerization with zirconocene and hafnocene catalysts
Authors: Naga Naofumi , Ohbayashi Yoshiaki , Mizunuma Kooji
Published: April 2003

Ethylene‐propene copolymerization was carried out with Cp2MCl2 (Cp = cyclopentadienyl), rac‐Et(Ind)2MCl2, rac‐Me2Si(Ind)2MCl2 (Et = ethylene, Me2Si = dimethylsilyl, Ind = indenyl, M = Zr or Hf)/methylaluminoxane. In the case of using ansa‐hafnocenes, the minimum molecular size (extended chain length) of ethylene‐propene copolymer was obtained at about 50 mol‐% of propene content in the copolymer. The polymerization activity decreased with increase of propene feed ratio in non‐bridged non‐specific metallocenes. Higher polymerization activities were observed for the copolymerization compared to ethylene and propene homo‐polymerization with ansa‐isospecific metallocenes. The factor of molecular size lowering was studied by the chain propagation and chain transfer reaction.
Enhanced velocity of surfactant binding after the volume collapse of an oppositely charged gel
Authors: Narita Tetsuharu , Gong Jianping , Osada Yoshihito
Published: April 2003

This paper is a kinetic study of the interaction between an ionic surfactant and an oppositely charged polymer gel. The volume collapse of the gel enhances substantially the velocity of surfactant uptake, despite the decreased free volume for diffusion. This indicates that the increased charge density of the polymer network accelerates the surfactant binding.
ESR study on SiO2‐supported half‐titanocene catalyst for syndiospecific polymerization of styrene
Authors: Xu Junting , Zhao Jian , Fan Zhiqiang , Feng Linxian
Published: April 2003

Monocyclopentadienyltitanium trichloride (CpTiCl3) was directly immobilized on silica surface. The resulting CpTiCl3/SiO2‐MAO was investigated in view of its suitability for syndiospecific polymerization of styrene using ESR spectroscopy. Polymerization results show that both the syndiotacticity and the activity decrease upon immobilization. A possible explanation is that the active sites may become aspecific after immobilization and part of the immobilized active sites can be leached into the solution in the presence of MAO.
Alternating copolymerization of ethylene and 1‐octene with meso‐[dimethylsilylbis(2‐methyl‐1‐indenyl)]zirconium dichloride‐methylaluminoxane as catalyst system
Authors: Uozumi Toshiya , Miyazawa Kohji , Sano Tsuneji , Soga Kazuo
Published: April 2003

Copolymerizations of ethylene and α‐olefins with homogeneous metallocene catalysts generally give the corresponding random copolymers with narrow molecular mass distributions. In this study, we have conducted the copolymerization of ethylene and 1‐octene with the meso‐Me2Si(2‐Me‐1‐Ind)2ZrCl2‐methylaluminoxane (MAO) catalyst system, and analyzed the microstructure of the resulting copolymers in detail. The content of the alternating [EO] sequence increases markedly with an increase in the feed ratio of 1‐octene to ethylene, reaching over 95% under appropriate copolymerization conditions. We have thus succeeded in preparing the first sample of alternating olefin copolymers.
End‐group evidence of zwitterionic species in the anionic polymerization of cyanoacrylates by Lewis bases
Authors: Costa Gianna , Loonan Conleth , Pepper David
Published: April 2003

X‐ray fluorescence (XRF) spectra of poly(butyl cyanoacrylate) initiated, in tetrahydrofuran, by triphenylphospine and terminated by SO3, show the persistent presence of phosphorus and sulfur in the polymer, in near‐equivalent proportions, with the sulfur content partially removable by anion‐exchange. It is concluded that all chains have initial phosphonium groups, and, in abesence of any hydrolysis‐formed H2SO4, are macrozwitterions with terminal SO3−. Acid‐terminated chains should have proton‐capped ends and initial phosphonium+ · HSO4− ion‐pairs.
Simple methods for assessing the conformational sensitivity of infrared bands by dichroism
Authors: Ou‐Yang Wen‐Chung , Chen Hsin‐Lung
Published: April 2003

In characterizing the overall orientation of polymers by infrared (IR) dichroism, the orientation function must be obtained from the dichroic ratios of conformationally insensitive bands. Identification of such bands is thus necessary prior to the calculation of the orientation function. In this study, we devise two simple methods for evaluating the conformational sensitivities of IR bands from the measurement of the dichroic ratio. Both methods are based on the fact that the orientation function calculated by all conformationally insensitive bands should be identical, while this is not true for conformationally sensitive bands. Poly(ether ether ketone) (PEEK) is used as an example to demonstrate the use of these methods.
“Living” free radical copolymerization of styrene and N‐vinylcarbazole
Authors: Baethge Heike , Butz Sören , Schmidt‐Naake Gudrun
Published: April 2003

Poly[styrene‐co‐(N‐vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide‐mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene‐co‐(N‐vinylcarbazole)]/polystyrene block copolymers via a controlled chain‐extension reaction of the prepared copolymers with styrene.
Saccharide modified silica particles by enzymatic grafting
Authors: Loos Katja , von Braunmühl Volker , Stadler Reimund , Landfester Katharina , Spiess Hans Wolfgang
Published: April 2003

The surface of silica particles has been chemically modified with oligo‐ or poly‐(α,1←4)‐D‐glucopyranose (amylose) chains of various length by covalently attaching maltoheptaose derivatives to the solid support and enzymatic polymerization of glucose‐1‐phosphate with potato phosphorylase (E.C. 2.4.1.1) as catalyst. The characterization of the products by solid‐state NMR spectroscopy showed an interesting dependence of the linewidth with the grafting density of the glucan chains. The modified silica particles showed chiral discrimination in liquid chromatography.
Structural effects in poly(3‐alkylthiophene)s on the exposition to poor solvent
Authors: Caronna Tullio , Catellani Marinella , Luzzati Silvia , Meille Stefano Valdo , Romita Valeria
Published: April 2003

The exposure to pentane vapour of poly(3‐alkylthiophene)s with different alkyl chains produces a modification in the optical properties of the thin films. The treatment induces a red‐shift of the electronic absorption maximum and the appearance of vibronic structure in the UV spectra. We have followed these changes with IR and Raman spectroscopies to monitor the modification of the backbone conjugation, and with X‐ray diffraction to evidence the structural order of the chains.
Novel amphiphilic linear polymer/dendrimer block copolymer: Synthesis of poly(2‐methyl‐2‐oxazoline)‐block‐poly(amido amine) dendrimer
Authors: Aoi Keigo , Motoda Aki , Okada Masahiko , Imae Toyoko
Published: April 2003

Novel linear polymer/dendrimer block copolymers, poly(2‐methyl‐2‐oxazoline)‐block‐poly(amido amine) dendrimers (water‐soluble full‐generation type 4 (G = 4.0 and 5.0) and amphiphilic half‐generation type 5 (G = 3.5, 4.5, and 5.5)), were synthesized by divergent‐growth dendrimer construction with ω‐ethylenediamine‐terminated poly(2‐methyl‐2‐oxazoline), which was prepared by living ring‐opening polymerization of 2‐methyl‐2‐oxazoline. Assembly of the amphiphilic dendrimer‐based block copolymer (G = 5.5) was investigated by surface tension measurements (critical micelle concentration, 0.49 wt.‐%) and by small‐angle neutron scattering analysis (spherical particles; assembled number, ca. 103).
Chain‐length dependent termination in pulsed‐laser polymerization, 2. On the prospects of determining the bimolecular termination constant kt from the second moment of the chain‐length distribution
Authors: Olaj Oskar Friedrich , Kornherr Andreas , Zifferer Gerhard
Published: April 2003

The correct (event weighted) average of kt, 〈kt〉, has been calculated for pseudostationary laser‐induced polymerization for a kinetic scheme with chain‐length dependent termination and compared to the average k̄t obtained by formally solving for kt the expression for the second moment of the chain‐length distribution valid for chain‐length independent termination (represented by the product of rate of polymerization νp and weight average degree of polymerization P̄w). It is shown that there is a fair agreement between the two quantities. This may be used to recover experimentally the power‐law governing the dependence of kt on chain‐length, especially its exponent.
Quinoxaline‐based conjugated polymers containing ruthenium(II) bipyridine metal complex
Authors: Ng Po King , Gong Xiong , Wong Wing Tak , Chan Wai Kin
Published: April 2003

A series of novel quinoxaline‐based conjugated polymers which contain a ruthenium(II) bipyridine complex were synthesized by the Suzuki coupling reactions. UV/VIS spectroscopy showed that the spectral features of the polymers are dependent on the amount of metal complex present. Results from excitation and emission spectroscopy suggest an energy transfer between the backbone and the metal complex. The polymers exhibit hole carrier mobilities of ≈ 10−5 cm2 · V−1 · s−1, which is comparable to organic photoconductors.
Synthesis of well‐defined azido and amino end‐functionalized polystyrene by atom transfer radical polymerization
Authors: Matyjaszewski Krzysztof , Nakagawa Yoshiki , Gaynor Scott G.
Published: April 2003

Mono and difunctional polystyrenes containing active halogenated end groups were prepared by atom transfer radical polymerization (ATRP). Substitution reactions were explored to convert the halogen termini to azido groups, followed by readuction to form the amino functional polymer. Quantitative conversion of the end groups was observed in each transformation reaction. 1H NMR demonstrated the formation of the azide from the bromide functionality without elimination. The difunctional α,ω‐diaminopolystyrene was reacted with terephthaloyl chloride in a condensation process to produce chain‐extended polystyrene containing amide bonds along the polymer backbone.
Preparation and characterization of cyclic poly(oxypropylene)
Authors: Yu Ga‐Er , Sinnathamby Prash , Sun Tao , Heatley Frank , Price Colin , Booth Colin
Published: April 2003

Poly(propylene glycol) [α‐hydro‐ω‐hydroxypoly(oxypropylene)] of number‐average molar mass M̄n ≈ 2000 g · mol−1 (PPG2000) was cyclised with high conversion (ca. 75%) by reaction with dichloromethane in the presence of powdered KOH. The cyclic product was separated from chain extended polymer by preparative GPC, giving an overall yield of polymer (M̄n ≈ 2000 g · mol−1, narrow molar mass distribution) in excess of 50%. Characterisation by analytical GPC and 13C NMR spectroscopy confirmed cyclisation. DEPT and 1H‐coupled NMR spectra were used to show that the links in cyclic poly(oxypropylene) were 77% single acetal, 12% double acetal and 11% triple acetal (or higher). This complexity probably results from competitive reaction with water introduced with KOH.
Self‐organization of ionic surfactants controlled by oppositely charged polyelectrolytes
Authors: Kabanov Victor A. , Zezin Alexander B. , Kasaikin Victor A. , Zakharova Julia A. , Litmanovich Ekaterina A. , Ivleva Elena M.
Published: April 2003

Formation and structure of water‐soluble complexes of poly(acrylic acid) (PA) and poly(diallyldimethylammonium chloride) (PDADMAC) with oppositely charged surfactants: tetradecyltrimethylammonium bromide and sodium dodecylsulfate correspondingly have been studied by elastic and quasi‐elastic laser light‐scattering, high‐speed sedimentation and viscometry techniques. It was shown that minimum aggregation number of the surfactant ions in the complex micelle is controlled by the chemical nature of the polymer. A shift from dilute to semi‐dilute solution regime with respect to a free polyelectrolyte results in drastic rearrangement in PDADMAC‐SDS complex structure.
Interplay of chemical and physical factors in reacting polymer blends. Theoretical considerations
Authors: Platé Nikolay A. , Litmanovich Arkady D. , Kudryavtsev Yaroslav V. , Govorun Elena N.
Published: April 2003

Various effects produced by copolymers in polymer blends are discussed, with an emphasis on the role of interchain interactions. Simple theoretical models are considered to study the following problems: the interplay of diffusion and macromolecular reaction in compatible and incompatible blends, the stabilizing effect of premade diblock copolymer on the system of minor phase particles in incompatible blends, the kinetics of transesterification in a homogeneous blend. The effect of diblock copolymer on the Ostwald ripening in a polymer blend is stated in more details; the possibility of narrowing the size distribution of minor phase particles is predicted.
Molecular order and dynamics in block copolymers of poly(oxybutylene) and poly(oxyethylene)
Authors: Fragiadakis Daniel , Bouga Maria , Kyritsis Apostolos , Pissis Polycarpos , Viras Kyriakos , Mingvanish Withawat , Booth Colin
Published: April 2003

Broadband dielectric spectroscopy (10−2‐109 Hz) was employed to investigate the dynamics of poly(oxybutylene) chains in solid semicrystalline poly(oxybutylene)‐poly(oxyethylene)‐poly(oxybutylene) (BEB) triblock copolymers. The results are compared with those obtained for B homopolymers, EB diblocks and EBE triblocks. The B blocks were dipole‐inverted in the homopolymers and the EBE triblocks, however not in the EB and the BEB copolymers. The segmental α relaxation, caused by local chain motion, and the normal mode relaxation, due to chain motions of larger length scale, were studied in detail with respect to time scale, relaxation strength and shape of the response. The α relaxation in the BEB copolymers shows similar behavior to that in the other three systems, whereas the normal mode relaxation shows characteristic differences in the four systems.
A meanfield approach to the thermodynamics of a protein‐solvent system with application to the oligomerization of the tumor suppressor p53
Authors: Noolandi Jaan
Published: April 2003

The thermodynamic stability and oligomerization status of the tumor suppressor p53 tetramerization domain have been studied experimentally and theoretically. A series of hydrophilic mutations at Met‐340 and Leu‐344 of human p53 were designed to disrupt the hydrophobic dimer‐dimer interface of the tetrameric oligomerization domain of p53. Meanfield calculations of the free energy of the solvated mutants as a function of interdimer distance were compared with experimental data on the thermal stability and oligomeric state [tetramer, dimer, or equilibrium mixture of both] of each mutant. The calculations predicted a decreasing stability and oligomeric state for the following amino acids at residue 340: Met [tetramer] > Ser Asp, His, Gin, > Glu, Lys [dimer], whereas the experimental results showed the following order: Met [tetramer] > Ser > Gln > His, Lys > Asp, Glu [dimers]. For residue 344, the calculated trend was Leu [tetramer] > Ala > Arg, Gln, Lys [dimer], and the experimental trend was Leu [tetramer] > Ala, Arg, Gln, Lys [dimer]. The discrepancy for the lysine side chain at residue 340 is attributed to the dual nature of lysine, both hydrophobic and charged. The incorrect prediction of stability of the mutant with Asp at residue 340 is attributed to the fact that within the meanfield approach, we use the wild‐type backbone configuration for all mutants, but low melting temperatures suggest a softening of the α‐helices at the dimer‐dimer interface. This initial application of meanfield theory toward a protein‐solvent system is encouraging for the application of the theoretical model to more complex systems.
When tethered chains meet free ones; the stability of polymer wetting films on polymer brushes
Authors: Maas Joost H. , Leermakers Frans A.M. , Fleer Gerard J. , Stuart Martinus A. Cohen
Published: April 2003

We present a combined experimental and theoretical self‐consistent field (SCF) investigation of the wetting behavior of a polystyrene melt (composed of chains with degree of polymerization P) on top of a polystyrene brush (composed of chains with length N) grafted onto a silica surface. The control variables are the grafting density σ of the brush chains and the length of mobile chains P. Experiments show in agreement with the theory that there is a window of complete wetting. Both at very low and at high grafting densities the system remains partial wet. At large degree of polymerization P, there is a difference between the experimental and theoretical results. Theory predicts partial wetting only, whereas the window of complete wetting persists in the experiments even when P >> N. This difference is attributed to the double‐well structure of the disjoining pressure as revealed by the SCF theory. With this type of disjoining pressure it is conceivable that a metastable zero contact angle remains present for very long times.
Effects of temperature on neutron scattering from aqueous solutions of hydrophobically modified poly(ethylene oxide)
Authors: Beaudoin Emmanuel , Borisov Oleg , Lapp Alain , François Jeanne
Published: April 2003

The effect of temperature on the structure of aqueous dispersions of hydrophobically end‐capped poly(ethylene oxide) (PEOM) was investigated by small angle neutron scattering (SANS). Polymers with hydrogenated or deuterated n‐octadecyl end‐groups were studied in heavy water or in a mixture heavy water / water, respectively. In the latter case the PEO chains were selectively matched. In all the cases, the scattering curves were characterised by a main peak which revealed organisation of polymers into micelles consisting of hydrophobic cores surrounded by repulsive PEO coronae. Measurements were performed in the semi‐dilute regime where micelles coronae overlap. At constant polymer concentration, an increase in temperature leads to decreasing solvent strength of water for the PEO chains and decreasing repulsion between the PEO coronae. As a result, the intensity of the peak in a mixture of water /heavy water decreases with temperature On the contrary, in heavy water, the peak of the scattered intensity increases with increasing temperature. This scattering behaviour is interpreted on the basis of a scaling theory of the semi‐dilute solutions of star‐like polymer micelles.
New poly(silanes‐siloxanes) via hydrosilation in supercritical CO2 and subsequent crosslinking
Authors: Zhou Hui , Venumbaka Sreenu R. , Fitch III John W. , Cassidy Patrick E.
Published: April 2003

In order to obtain crosslinkable, low dielectric, low Tg materials, the hydrosilation polymerization was carried out in supercritical carbon dioxide (SC CO2) using Karstedt's catalyst, and a series of new fluorine‐containing poly(carbosilane/siloxane) were synthesized and characterized. The molecular weights of polymers obtained in SC CO2 were notably greater than those obtained in benzene. Hydrolysis and thermal curing of these polymers leads to materials considerably higher molecular weight which retain their low Tg values.
Novel silicon‐based alternating copolymers: synthesis, photophysical properties, and tunable EL colors
Authors: Kim Hwan Kyu , Paik Kyung Lim , Baek Nam Seob , Lee Youngil , Yoshino Katsumi
Published: April 2003

We synthesized novel silicon‐based alternating copolymers for tunable electroluminescent (EL) colors by Heck synthetic method. Their thermal, photophysical and electroluminescent properties were studied. Most of them exhibited a blue‐green EL color at the operating voltage of lower than 12 V. Unusually, we observed the white EL color from a EL device based on SiPhPVK. From photophysical studies and the time‐resolved PL spectroscopies, it might be attributed to the formation of stabilized excited state in SiPhPVK. Furthermore, in order to reduce the operating voltage of their LED with increasing the electron affinity of the main chain in silicon‐based alternating copolymers, we synthesized the silicon‐based copolymers containing electron transporting oxadiazole units in main chain. We also studied their photophysical and electroluminescent properties.
Formation of intragap states and achieving balance in carrier mobilities for a PPV derivative bearing the carbazole pendants
Authors: Kim Kyungkon , Park Yongsup , Lee Cheol Eui , Jang Jae Won , Jin Jung‐Il
Published: April 2003

We have found by NEXAFS spectroscopic studies that a PPV derivative (CzEh‐PPV) bearing the carbazole pendants form new intragap states when contacted with calcium metal. Moreover, the polymer exhibited much more balanced mobilities of holes and electrons than PPV and MEH‐PPV. Such characteristics are believed to bring about low turn‐on electric field and improved efficiency for the LED device fabricated with the polymer.