bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the dielectric properties of ferroelectric liquid crystals and related side chain liquid crystalline polymers
Authors: Hsiue Ging‐Ho , Lee Kuang‐Rong , Chen J.‐Hong
Published: April 2003

Broadband dielectric spectroscopy (frequency range 10−1–106 Hz) was used to analyze the frequency and temperature dependence of the molecular dynamics of a series of ferroelectric liquid crystals (FLCs) and polymers which exhibit a chiral smectic C (S) phase in a wide temperature range (about 190°C) including room temperature. Two ferroelectric modes, Goldstone and Soft mode, were observed in the low‐molar‐mass FLCs. Both of these modes were found in the S phase; however, only the soft mode was present in the smectic A (SA) phase. On the other hand, two collective relaxation processes (Soft and Goldstone mode) and four molecular relaxations (δ, α, β and γ‐relaxation) of the side chain liquid crystalline polymer were demonstrated.
The anionic copolymerization of 5‐(N,N‐diisopropylamino)isoprene with styrene
Authors: Petzhold Cesar , Stadler Reimund
Published: April 2003

The anionic copolymerization of 5‐(N,N‐diisopropylamino)isoprene (N,N‐diisopropyl‐2‐vinylallylamine) and styrene initiated with alkyllithium compounds is studied. Copolymers obtained from different compositions are characterized by size‐exclusion chromatography (SEC), differential scanning calorimetry and by 1H NMR and 13 C NMR spectroscopy. Under these conditions the dialkylaminoisoprene, similar to butadiene and isoprene, is more reactive than styrene and is incorporated faster into the polymer backbone. The incomplete conversion of the monomers has been attributed to the formation of intra‐or intermolecular complexes between the Li+ counterion at the chain end and amino groups. Because of the polarity of the aminoisoprene, no tapered copolymer is obtained, contrary to the isoprene/styrene system. The reactivity ratios of the monomers calculated according to Kelen‐Tudos show that the styryl anion reacts preferably with an aminoisoprene monomer, while the aminoisoprenyl anion tends to homopolymerize.
Control of molecular weight and molecular weight distribution in ethylene polymerization with metallocene catalysts
Authors: Han Taek Kyu , Choi Hong Ki , Jeung Dong Wook , Ko Young Soo , Woo Seong Ihl
Published: April 2003

The molecular weight (MW) and the molecular weight distribution (MWD) of polyethylene (PE) prepared with various metallocene catalysts were investigated. The weight‐average molecular weight (Mw) of PE prepared with dicyclopentadienyltitanium dichloride/aluminoxane (Cp2TiCl2/MAO) was about 4,0 · 105, while that of PE obtained with dicyclopentadienylzirconium dichloride/aluminoxane (Cp2ZrCl2/MAO) is about 1,0 · 105. PE of bimodal MWD was obtained with the mixed catalyst Cp2TiCl2/Cp2ZrCl2. Narrow MWD PE was obtained with the mixed catalyst Cp2ZrCl2/Et(ind)2ZrCl2, because each catalyst produced an Mw of 1,0 · 105. However, the change of temperature during the polymerization with the mixture Cp2ZrCl2/Et(ind)2ZrCl2 produced PE with a bimodal MWD and a value of the ratio of weight‐ to number‐average molecular weights of Mw/Mn = 4.
Electrochromic behavior and stability of polyaniline composite films combined with a polycation‐bathophenanthroline‐Fe complex
Authors: Morita Mitsuyuki
Published: April 2003

The electromic behavior of polyaniline‐poly(sodium acrylate) composite films (CPAn‐PAcNa) combined with a polycation bound to the disulfonated bathophenathroline ligand‐Fe complex (QDM‐BPDS‐Fe) was investigated in a LiClO4CH3CN non‐aqueous aprotic solution. The combination was achieved by chemial deposition of CPAn‐PAcNa on QDM‐BPDS‐Fe. When the combined film was prepared with appropriately low quantities of QDM‐BPDS‐Fe, they showed much wider color changes than those of the component materials by overlapping of the electrochromic behavior of CPAn‐PAcNa and QDM‐BPDS‐Fe. However, it was difficult to control their spectral changes individually by a simple operation of polarizing the whole combined films, because the oxidation potential of CPAn‐PAcNa and QDM‐BPDS‐Fe were close to each other. Their electrochemical activity was lowered by the combination. From Fourier‐transform infrared measurements, it was deduced that such a low stability of the component materials in the combined films was caused by formation of an electrochemically inactive complex by electrostatic interaction between the first oxidized state of polyaniline and the sulfonato groups in BPDS.
1H‐13C NMR inverse detection of poly(3‐hexylthiophene): Characterization of the structural defects
Authors: Mucci Adele , Schenetti Luisa
Published: April 2003

NMR inverse detection was applied to the study of regiochemistry of a highly head to tail (HT)‐regioregular poly(3‐hexylthiophene) (PHT). It proved to be a valuable tool in the characterization of polymerization defects not directly revealable or assignable by inspection of the one‐dimensional 13C spectrum. Almost all the 13C chemical shifts of the four configurational triads of PHT were derived by utilizing the aromatic protons, whereas through the α‐protons of the aliphatic chain only carbons belonging to HT‐HT connections were detected, owing to the high regiospecificity of the PHT under study and to the high multiplicity of aliphatic proton signals. The correctness of the model of the interpretation of PHT structure based on the four trimers of 3‐hexylthiophene was confirmed.
Cationic polymerization of isobutylene proceeding by redox initiation
Authors: Marek Miroslav , Pecka Jan , Halaška Vlastimil
Published: April 2003

The cationic polymerization of isobutylene with weak Lewis acids, such as BBr3 and FeBr3, has been studied. These halides are unable to induce individually the polymerization in nonpolar solvents, such as heptane or toluene, or they only initiate the polymerization to low conversions in polar media, such as dichloromethane. The complex compounds, formed by interaction of both Lewis acids, initiate a fast polymerization of isobutylene, which proceeds up to high conversions. The coinitiation effect of HBr in the mixture with BBr3 and FeBr3 was also investigated. The hypothetic formation of efficient initiators and the initiation mechanism of olefin polymerization are discussed on the basis of the ionogenic action of both Lewis acids.
Effects of an interfacial agent on the physico‐chemical characteristics of poly(propylene)/polyamide 6 blends
Authors: Beltrame Piez Luigi , Castelli Antonella , Canauz Michele , Canetti Maurizio , Seves Alberto
Published: April 2003

The present work reports investigations about the structure and the thermal behavior of blends prepared by mixing, at different weight ratios, poly(propylene) (more precisely, a propylene/ethylene random copolymer containing 6% ethylene) with polyamide 6, in the presence of poly(propylene) grafted with 1% of maleic anhydride used as a compatibilizer agent. Blends without the compatibilizer were also prepared and analyzed. The poly(propylene) structural changes in the blends were determined by wide angle X‐ray diffraction (WAXD) measurements. Differential scanning calorimetry, microscopic observations, and mechanical tests supported the occurrence of interfacial reactivity. The compatibilizing effect was confirmed by measuring the decrease of the interfacial tension between poly(propylene) and polyamide 6 due to the presence of the compatibilizer. Such a decrease resulted in improved dispersion and adhesion between the phases. A new material with interesting thermal, structural and mechanical properties was obtained.
Direct evidence of star structure from nuclear magnetic resonance spectroscopy
Authors: Pitsikalis Marinos , Hadjichristidis Nikos , Di Silvestro Giuseppe , Sozzani Piero
Published: April 2003

Until now the characterization of a star‐like structure has been based on an indirect method, i.e. the comparison of the molecular weight of the star polymer and its linear precursor. By preparing well‐defined and narrow‐molecular‐weight‐distribution polybutadiene and polyisoprene stars with up to four arms — using anionic polymerization techniques and the appropriate chlorosilane — and by characterising them by means of 1H and 13C NMR spectroscopy, the key point of the star, which is the core next to the silicon atom, was observed.
Photoinduced electron transfer in porphyrin‐naphthyl pairs covalently and randomly bound to α‐helical poly(L‐lysine)
Authors: Pispisa Basilio , Venanzi Mariano , Palleschi Antonio , D'Alagni Maria
Published: April 2003

The photophysics of protoporphyrin‐naphthyl (P‐N) pairs covalently and randomly bound to the ε‐amino groups of the side‐chains of poly(L‐lysine) (PL) were investigated by steady‐state and time‐resolved fluorescence measurements. The results indicate that quenching of excited naphthalene (λex = 280 nm) chiefly occurs by interconversion to the triplet state when the polymeric matrix is in random coil (pH ≈ 7) and by intramolecular electron transfer from ground‐state porphyrin, P → 1N*, when the polypeptide is in α‐helical conformation (pH ≈ 11), the specific rate constant of the electron transfer being 3,1 · 107 s−1 (25°C). PNPL exhibits very little exciplex fluorescence, whatever the pH, suggesting both a reduced internal Brownian motion of the chromophores, owing to the amide bond in the substituted side‐chains, and a relatively large average interprobe separation distance. This agrees with polarized fluorescence data and with the results of a conformational statistics analysis on the fully ordered PNPL, indicating that the average interchromophoric distance for which the electron transfer has the highest probability to occur is around 12 Å. The computational results allowed us to reproduce the experimental fluorescence decay curves and estimate the parameters governing the electron transfer process. Implications of these findings on the relaxation time of the heli‐xcoil transition in PNPL are briefly discussed.
Thermovolumetric properties versus glass transition temperature of diolic perfluoropoly(oxyethylene‐ran‐oxymethylene) oligomers
Authors: Danusso Ferdinando , Levi Marinella , Gianotti Giuseppe , Turri Stefano
Published: April 2003

The specific volume v from – 20 to 60°C and the glass transition temperature Tg was measured of a homologous series of linear diolic oligomer fractions constituted by a random perfluoro‐poly(oxyethylene‐ran‐oxymethylene) chain of fairly uniform composition and two CH2OH end units, with a degree of polymerization x̄n from 5,4 to 165,9 (M̄n from 400 to 14900). An empirical parabolic v = v(T, wE) equation of state is found as satisfactory, wE being the end copolymeric composition expressed as weight fraction of end units, inversely proportional to M̄n. A predictive bridge is then established between thermovolumetric parameters and Tg, through a highly reliable linear relation vg – Tg between experimental Tg and calculated specific volume at Tg, which leads with measurable parameters to a Tg – wE relation, in very good agreement with experimental results. For the range of M̄n above 1500–2000, simpler relations can also be used to a good approximation, which are discussed in their physical meaning and validity.
Physico‐chemical properties of hyaluronan and its hydrophobic derivatives: a calorimetric and viscometric study
Authors: Geciova Renata , Flaibani Antonella , Delben Franco , Liut Gianfranco , Urbani Ranieri , Cesáro Attilio
Published: April 2003

The physico‐chemical properties of a series of hyaluronan derivatives were studied with the aim of exploring some aspects of the role of electrostatic interactions on the aggregation of these chains in aqueous solution. Experimental data were obtained from calorimetric measurements of the dilution process in water. The data were analysed in terms of the structural charge parameter, ζ, with the polyelectrolyte counterion condensation theory. In addition, intrinsic viscosity data of the hyaluronan derivatives were obtained at several different values of the ionic strength and discussed on the basis of the effect of charge density change upon the elongation properties of the polyelectrolyte chains.
Effect of polyfunctional chain transfer agents on the molecular weight distribution in free‐radical polymerization, 3 Polymerization of methyl methacrylate in the presence of polyfunctional chain transfer agents
Authors: Yuan Cui Ming , Di Silvestro Giuseppe
Published: April 2003

Polymerization of methyl methacrylate was carried out in the presence of polyfunctional chain transfer agents: 1,6‐hexanedithiol, trimethylolpropaneb tris(mercaptoglycolate) and pentaerythritol tetrakis(3‐mercaptopropionate). The theoretical results reported in the preceding papers are completely confirmed: the experimental values of the dispersion index (D = M̄w/M̄n) are 1.62 for f = 2, 1.39 for f = 3 and 1.28 for f = 4. In the case of bifunctional transfer agents the molecular weights calculated are in very good agreement with those obtained by size exclusion chromatography. The formation of star‐shaped macromolecules was confirmed by cleavage of the CSC bonds. The number‐average molecular weight decreases and the dispersion index is approximately equal to 2 after exposure to UV rays. The phenomenon of “pseudo‐living” polymerization in the presence of polyfunctional chain transfer agents is also discussed.
Synthesis of low molecular weight poly(N‐acryloylmorpholine) end‐functionalized with primary amino groups, and its use as macromonomer for the preparation of poly(amidoamines)
Authors: Ushakova Vera , Panarin Evgenji , Ranucci Elisabetta , Bignotti Fabio , Ferruti Paolo
Published: April 2003

Amphiphilic oligomers of poly(N‐acryloylmorpholine) terminated at one end by primary amino groups have been prepared by free radical polymerization of the corresponding monomer, N‐acryloylmorpholine, in the presence of cysteamine (2‐mercaptoethylamine) as chain‐transfer agent. The polymerization reaction was performed in aqueous media at acidic pH, in order to avoid any hydrogen‐transfer addition reaction the the acrylic double bonds by the SH or NH2 groups present in cysteamine. The chain‐transfer constant of cysteamine towards N‐acryloylmorpholine, under the conditions we used, was found to be very close to 1. The aminated poly(N‐acryloylmorpholine) oligomers were found to behave as true macromonomers in polyaddition reactions with a diacrylamide, leading to new poly(amidoamines) carrying poly(N‐acryloylmorpholine) chains as side substituents.
Synthesis, thermal and phase‐conjugate properties of semirigid copolyesters with cyanoazobenzene side‐chains and azoxybenzene units in the main chains
Authors: Sato Moriyuki , Nakagawa Kazuo , Hayakawa Makoto , Mukaida Ken‐ichi , Fujiwara Hirofumi , Tada Yuji
Published: April 2003

Melt polycondensation of a mixture of diethyl 5‐{6‐[4‐(4‐cyanophenylazo)phenoxy]‐hexyloxy}isophthalate and 4,4′‐bis(ethoxycarbonyl)azoxybenzene at various mole ratios with dihydroxyhexamethyleneoxy derivatives of diphenyls in the presence of zinc acetate afforded new combined‐type semi‐rigid copolyesters containing cyanoazobenzene side chains and an azoxybenzene unit in the main chain, which were characterized by FTIR, 1H and 13C NMR spectroscopy and elemental analyses. Differential scanning calorimetry (DSC) measurements and observations in the polarizing microscope demonstrated that some cyanoazobenzene‐rich copolyesters composed of diphenyl ether and benzophenone units form liquid crystalline (LC) phases, but the others have no LC phases in spite of introduction of an azoxybenzene mesogen into the polymer backbone. Most of the copolymers consisting of diphenyl ether and benzophenone units generated simultaneously two types of phase‐conjugate (PC) signals based on photo‐induced anisotropy (PA) and holographic components at high reflectivities by degenerate four‐wave mixing (DFWM) at low pump‐beam powers, which are one of the third‐order non‐linear optical (NLO) properties. This means that these copolyesters can be used not only a phase conjugator, but also as erasable hologram‐recording materials. It is suggested that the presence of the cyanoazobenzene side chains is of importance for the PC signal‐generating process.
New poly(amide‐imide)s syntheses, 14. Preparation and properties of poly(amide‐imide)s based on 3, 3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]‐1‐oxoisoindoline
Authors: Yang Chin‐Ping , Lin Jiun‐Hung
Published: April 2003

An imide ring‐containing dicarboxylic acid, 3,3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]‐1‐oxoisoindoline, was prepared via condensation of 3,3‐bis[4‐(4‐aminophenoxy)phenyl]‐1‐oxoisoindoline and trimellitic anhydride. A series of new aromatic bis(phenoxy)‐1‐oxo‐isoindoline‐containing poly(amide‐imide)s were prepared via direct polycondensation of this diimide‐diacid with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents in N‐methyl‐2‐pyrrolidone (NMP) in the presence of calcium chloride. Most of the resulting polymers are of amorphous nature and readily soluble in polar solvents such as NMP and N,N‐dimethylacetamide. All soluble poly(amide‐imide)s afford transparent, flexible, and tough films. The glass transition temperatures of the polymers are in the range of 267–305°C and show almost no weight loss up to 450°C in nitrogen atmosphere. The properties of 1‐oxoisoindoline containing poly(amide‐imide)s are compared with those of the corresponding analogous poly(amide‐imide)s derived from 3,3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]phthalide.
Characterization of dehydrochlorinated poly(vinylidene chloride) and the shock‐compressed material
Authors: Komatsu Tamikuni , Nomura Masayuki , Kakudate Youzou , Fujiwara Syuzou , Heimann R. B.
Published: April 2003

Dehydrochlorinated poly(vinylidene chloride) proved to be a conjugated polyene‐polyene polymer. Shock compression of the polymer formed a large portion of graphite and trace amounts of diamond and of an unknown carbon. The unknown carbon belongs to the hexagonal crystal system and possesses the cell dimension α0 = 0.338 nm. A comparison with known carbynes was made in terms of the crystalline parameters.
Poly(amide‐imide)s prepared from 4,4′‐[1,4(or 1,3)‐ phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline, trimellitic anhydride, and various aromatic diamines
Authors: Hsiao Sheng‐Huei , Yang Chin‐Ping , Fan Jr‐Chen
Published: April 2003

Two imide ring‐bearing dicarboxylic acids, N,N′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy‐1,4‐phenylene)]diphthalimide‐4‐carboxylic acid (p‐4 and m‐4), were prepared via condensation of 4,4′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline (p‐3 and m‐3) with trimellitic anhydride. Two series of novel poly(amideimide)s were synthesized by the direct polycondensation of the diimide‐diacids p‐4 and m‐4, respectively, with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents. The inherent viscosities of the resultant poly(amide‐imide)s were in the range of 0,43–1,68 dL/g, and most of these polymers were amorphous, as revealed by wideangle X‐ray diffractograms. Almost all the poly(amide‐imide)s were readily soluble in polar aprotic solvents such as N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylacetamide (DMAc), and N,N‐dimethylformamide (DMF), and could be solution‐cast into transparent, flexible, and tough films. These polymers had glass transition temperatures in the range of 200‐267°C and showed no significant decomposition below 450°C, with 10% weight loss being recorded above 485°C in nitrogen or air.
Synthesis of dihydroxy terminated poly(chloroethyl vinyl ether)s by “living” cationic polymerization: evidences for side reactions and their control
Authors: Bennevault Véronique , Larrue Frédéric , Deffieux Alain
Published: April 2003

This paper reports on the synthesis of dihydroxy terminated poly(chloroethyl vinyl ether)s (PCEVE) via bifunctional living cationic polymerization. The bifunctional chain initiator is obtained by reacting malonaldehyde bis(diethyl acetal) with trimethylsilyl iodide (TMSI) to form the corresponding di‐α‐iodo ether derivative. The polymerization of chloroethylvinyl ether is then triggered by ZnCl2. The direct transformation of active ends into aldehyde terminals, as well as their derivatization into hydroxy groups, is described. The synthesis of high molar mass ditelechelics by bifunctional polymerization provides evidence for the occurrence of a monofunctional side initiation. The latter has been attributed to the hydrolysis of TMSI by adventitious water, which leads to the in situ formation of hydrogen iodide. In order to trap hydrogen iodide, the influence of different additives, bulky amines, metals and alkylaluminiums, was investigated. Therefore, in the presence of alkylaluminiums, it is possible to obtain a clean bifunctional polymerization up to relatively high molar mass ditelechelic PCEVE (M̄n = 33000 g/mol, M̄w/M̄n = 1.11).
Investigation of the aggregation phenomenon of polyaniline in dilute solutions
Authors: Liao Yun‐Hsin , Kwei Ti Kang , Levon Kalle
Published: April 2003

Aggregation of polyaniline chains in dilute solutions was observed in N‐methyl‐2‐pyrrolidone by light scattering, gel permeation chromatography, and viscosity measurements. The aggregation resulted in a negative second virial coefficient in light scattering measurements and concave reduced viscosity curves. The driving force for aggregation is assumed to be a combination of hydrogen bounding between the imine and amine groups and the rigidity of backbone, and the aggregation was modeled to occur via side‐on packing of wormlike chains. Polyelectrolyte‐like viscosity behavior was also observed when a small amount of salt was added and the electrostatic interaction in polyelectrolyte polymer based on the Odijk theory was used to explain the role of the salt.
Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 4 NMR and quantum chemical study of the initiation systems containing tert‐butyl 2‐lithioisobutyrate and lithium tert‐butoxide or lithium 3‐methylpentan‐3‐olate
Authors: Kříž Jaroslav , Dybal Jiří , Janata Miroslav , Vlček Petr
Published: April 2003

In contrast to methyl 2‐lithioisobutyrate (I), tert‐butyl 2‐lithioisobutyrate (A) in tetrahydrofuran (THF) appears to have one form only, irrespective of concentration (0,1‐0,8 mol/L) or temperature (203–273 K). According to its relaxation characteristics, this form probably is a tetramer. The results indicate, however, that about 20% of A do not provide well‐developed NMR signals and may be present as a partly organized pseudophase. A is shown to form 2:2 and 1:3 complexes with lithium tert‐butoxide (B) and lithium 3‐methylpentan‐3‐olate (C) in THF in dependence on their mole ratio and partly on storage time. The 7Li, 1H and 13C NMR relaxation behaviour of these complexes support their essentially tetrameric nature. Although intramolecular exchange of Li atoms in a complex appears to be rapid, intermolecular exchange of any of the components is vanishingly slow on the NMR time scale. The complexes of A with either B or C exhibit remarkable stability above 273 K, in contrast to that of A itself. The quantum chemical analysis of the complexes shows that they are held together by a cooperative system of polycentric bonds and electrostatic interactions. Thus they are not easily destroyed by thermal activation but they react readily with monomer. Implications of the results for anionic polymerization of (meth)acrylates are discussed.
Novel blood compatible polyurethanes containing long‐chain alkyl groups and phosphatidylcholine analogues
Authors: Li Yu‐Jun , Matthews Kerr H. , Kodama Makoto , Nakaya Tadao
Published: April 2003

A series of new amphiphilic polyurethanes containing long‐chain alkyl groups as hydrophobic part and phosphatidylcholine analogues as hydrophilic part in the side chains was synthesized and characterized by their IR and 1H NMR spectral data and elemental analyses. The detailed studies for polyurethane 7b show that no evidence of any blood platelet attachment was apparent from the platelet rich plasma (PRP) contact studies and by scanning electron microscopy (SEM) evaluation for the synthesized polyurethane. Moreover, it quickly forms a gel in chloroform, N,N‐dimethylformamide, dimethyl sulfoxide and even to some extent in water. Preliminary studies suggest that these new polyurethanes are very interesting due to their excellent blood compatibilities and prospective importance for biomedical applications.
Saccharide polymers, 1, Synthesis and polymerization of methyl 5‐deoxy‐2,3‐O‐iso‐propylidene‐ß‐D‐erythro‐pent‐4‐enofuranoside
Authors: Yaacoub Emile‐Joseph , Wick Stefan , Buchholz Klaus
Published: April 2003

New “saccharide polymers” were synthesized. For this purpose the synthesis and the polymerization of an unsaturated sugar monomer, methyl 5‐deoxy‐2,3‐O‐isopropylidene‐ß‐D‐erythro‐pent‐4‐enofuranoside, briefly called “exo‐ribene”, is described. All polymers, homo‐and co‐polymers, were synthesized under free radical conditions. The structures and compositions of the soluble “saccharide polymers” were established by elemental analysis, 1H and 13C NMR, and FT‐IR spectroscopy. Some characteristics e. g. molecular weights and optical rotations are reported. Depending on the comonomer reactivity and under optimized chain reaction conditions, saccharide polymers with various sugar content and high molecular weights have been obtained.
Mechanical field orientation of chiral smectic C polymer networks
Authors: Semmler Klaus , Finkelmann Heino
Published: April 2003

Deformation experiments on chiral smectic C elastomers show a significant influence of the layer structure. In contrast to nematic systems a deformation of the smectic polydomain does not lead to a uniform director orientation. Obviously, the smectic layers lock in the polydomain structure in a transient network. Therefore, on experimental time scale, no equilibrium conditions can be achieved during the deformation process in the smectic state. Reducing the influence of the smectic layers by swelling the sample with toluene offers the possibility to prepare samples with uniform director orientation. In these samples the smectic layers are distributed on a cone around the director, preventing ferroelectric properties. Further deformation experiments on these aligned samples show a strong interaction of the layer orientation with the mechanical field in the smectic state. Layers which enclose large angles with the mechanical field realign to layer orientations with small angles to the deformation direction. This orientation behaviour leads to an anisotropic distribution of the layer on the cone causing a non‐centrosymmetric phase structure. This anisotropic alignment can be locked in by chemical crosslinking, leading to a highly transparent non‐centrosymmetric bulk material.
Polymers containing formamidine groups, 5 Formation of a cyclic formamidine trimer by the condensation reaction of 2,6‐diaminopyridine with triethyl orthoformate
Authors: Böhme Frank , Rillich Maik , Komber Hartmut
Published: April 2003

The condensation reactions of the structurally similar monomers 1,3‐phenylenediamine (1a) and 2,6‐diaminopyridine (1b) with triethyl orthoformate have been compared. Whereas the reaction of 1a resulted in an oligomeric polyformamide, a cyclic trimer was obtained almost quantitatively when monomer 1b was used. The structure of the trimer has been discussed with respect to results obtained by NMR and MALDI spectroscopy.
Preparation and characterization of polymides derived from bis(methoxycarbonyl)terephthaloyl chloride by interfacial condensation
Authors: Chern Yaw‐Terng
Published: April 2003

A series of polyimides was synthesized by interfacial condensation of bis(methoxycarbonyl)terephthaloyl choride (1) with aromatic diamines and polycyclic aliphatic diamines. 1 (mixed isomers) was synthesized from pyromellitic dianhydride and contains about 60% para isomers and 40% meta isomer. The poly(amic ester)s 3 had inherent viscosities of 0.85–0.24 dL/g. All the poly(amic ester)s were soluble in NMP, DMAc, DMF, and DMSO, except for the polymer prepared from diamantane‐1,6‐diamine. Through thermal treatment the poly(amic‐ester)s formed imide structures. All the polyimides and poly(amic ester)s were amorphous due to X‐ray diffraction studies. The glass transition temperatures of these polyimides were in the range of 255–340°C, and the 5% weight loss temperatures were between 485 and 640 °C in nitrogen atmosphere. The polyimides (4c and 4d) with polycyclic aliphatic diamines such as adamantane‐1,3‐diamine and diamantane‐1,6‐diamine had good thermal stability, with a temperature of 5% weight loss above 485°C. The polyimides 4c and 4d also had high glass transition temperature of 340°C and 300°C, respectively.
Synthesis of poly(N‐tert‐butylaziridine) macromonomers and graft copolymers with uniform side chains
Authors: Christova Darina C. , Velichkova Rumiana S.
Published: April 2003

Poly(N‐tert‐butylaziridine) (polyTBA) macromonomers with allylamino‐, allyloxy‐ and methacrylate end‐groups were synthesized via deactivation of living polyTBA with appropriate nucleophiles. The macromonomers were copolymerized with N‐vinyl‐2‐pyrrolidone (NVP), 2‐hydroxyethyl methacrylate (HEMA) and isoprene (Is). Two types of graft copolymers were obtained: the first one is constituted of hydrophilic backbone (polyNVP or polyHEMA) and hydrophobic uniform polyTBA side chains. The second type is composed of a flexible hydrophobic polyIs backbone and hard hydrophobic polyTBA side chains which, however, become water swellable after quaternization.
On the chirality of polyvinyl compounds, 19 Influence of double bond position on the asymmetric cyclocopolymerization
Authors: Wulff Günter , Gladow Stefan
Published: April 2003

Cyclocopolymerization of two new monomers, D‐mannitol 3,4‐O‐carbonate 1,2:5,6‐bis‐O‐[(2‐vinylphenyl)boronate] (2) and D‐mannitol 3,4‐O‐carbonate 1,2:5,6‐bis‐O‐[(3‐vinylphenyl)boronate] (3), was investigated. While copolymers of monomer 2, which has the double bond in ortho position, do not show optical activity after splitting off the chiral D‐mannitol template, optically active copolymers were obtained from monomer 3 with its double bond in meta position. The residual optical activity is due to the configuration of the main chain (main chain chirality). With the aid of circular dichroic (CD) spectra and optical rotation measurements the configuration of the (3‐vinylphenyl)boronic acid diads in the copolymer chain could be determined. When methyl methacrylate (MMA) was used as comonomer, the diads possessed (R,R) configuration. The mechanism of cyclopolymerization of monomer 3, which involves a 17‐membered transition state, could be explained by approximating its conformations of lowest energy with semiempirical methods (AM1).
Ductile‐brittle transition behavior of short‐chain branched polyethylenes at 80°C
Authors: Yeh Jen‐taut , Lee Wen‐Shuan
Published: April 2003

A systematic study on the ductile‐brittle transition of short‐chain branched polyethylenes (SBPEs) is reported. The values of threshold stress intensity, the time corresponding to the point of ductile‐brittle transition and the failure time (tf) of samples which failed in ductile and brittle regions were found to increase significantly with increasing branch length of the SBPEs. The fracture kinetics and the morphology at the notched root were distinguished for SBPE samples that failed in ductile and brittle regions. The values of (CC(notch opening displacement at the roof of notch)–BB(the thickness of the craze))/(AA(notch opening displacement at the surface of the specimen)–CC) are less than or equal to about 0.3 for all samples which failed in the brittle region, and these values are only about 20–30% of those of the samples which failed in the ductile region. Finally, an equation was developed to predict tf of SBPEs which failed in the ductile and brittle region in terms of stress intensity, branch length and other material and experimental parameters.
Side‐chain type liquid‐crystalline polyethers, 2 Effects of mesogenic moieties on the thermal properties and their self‐assembly behaviour
Authors: Akiyama Eiichi , Ohtomo Miki , Nagase Yu , Koide Naoyuki
Published: April 2003

A series of polyethers having mesogenic moieties connected to the backbone without flexible spacer in the side‐chain were prepared by ring‐opening polymerization of the corresponding glycidyl ether derivatives containing various mesogens. As the mesogenic side‐chains, tolan and phenylene units with alkoxy or alkoxycarbonyl groups were introduced and compared with biphenyl type mesogens. The polyether with tolan derivative having butoxy group as the side‐chain end exhibited two kinds of highly ordered smectic phases. On the other hand, in the case of biphenyl or tolan as the rigid‐core, introduction of ester group as an end‐group decreased the thermal stability of liquid‐crystalline phase as compared with the case of alkoxy group as the end group. The polyethers with the p‐alkoxyphenyl group in the side‐chain exhibited a smectic A phase which formed a bilayer structure, while no mesophase was observed for those having the p‐alkoxycarbonylphenyl group in the side‐chain. The self‐assembly of bilayer structures, which consist of hydrophilic layer (polyether backbone) and hydrophobic layer (side‐chain), might be responsible for the appearance of liquid‐crystallinity in such polyethers whose mesogen consists only of a simple phenylene ring.
Assignment of finely resolved 13C NMR spectra of polyacrylates
Authors: Kawamura Tokiji , Toshima Naoki , Matsuzaki Kei
Published: April 2003

13C NMR spectra of poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), poly(isopropyl acrylate) (PIPA), poly(butyl acrylate) (PBA), and poly(isobutyl acrylate) (PIBA) with various tacticities were determined. It was found that methine carbon resonances of PIPA split into triad sequences and those of PEA, PBA and PIBA show a mm triad at high field. Methylene carbon spectra of polyacrylates were assigned in terms of hexad sequences using HECTOR (13C‐1H COSY) spectra.
Hydrophilic thermotropic block copolyetheresters with poly(pentamethylene p,p′‐bibenzoate) segments
Authors: Hsiue Lin‐Tee , Ma Chen‐Chi M. , Tsai Hong‐Bing
Published: April 2003

Block copolyetheresters 1 with poly(pentamethylene p,p′‐bibenzoate) segments and poly(ethylene oxide) segments were prepared by melt polycondensation of dimethyl p,p′‐bibenzoate, 1,5‐pentanediol, and poly(ethylene glycol) (PEG) with molecular weights of 400, 1 000, or 2 000. The 1H NMR analysis shows that the feed mole ratio of PEG to dimethyl p,p′‐bibenzoate determines the composition of the block copolyetheresters. The differential scanning calorimetry (DSC) results indicate that some block copolyetheresters exhibit a monotropic smectic liquid‐crystalline phase due to the poly(pentamethylene p,p′‐bibenzoate) segments. The transitions depend on the content and the molecular weight of the PEG. The block copolyetheresters 1 show high water absorption due to the hydrophilic nature of the poly(ethylene oxide) segments. The water absorption increases with increasing PEG content. As the molecular weight of PEG increases, the water absorption increases significantly.
Influence of soluble parts in gelatin/water gels on their network structure in an ultracentrifugal field
Authors: Cölfen Helmut , Borchard Werner
Published: April 2003

If gels are investigated in an analytical ultracentrifuge by means of sedimentation equilibrium experiments, so called soluble parts which are originally not incorporated into the network influence the swelling pressure equilibria of the gels. For gelatin/water, it can be shown that an irreversible process takes place which is dependent on the rotational speed of the experiment. Experimental evidence is given that soluble parts which are partly associated and aggregated to the polymer network can act as a branching and/or crosslinking agent. A model for this process is given. In such a case an application of the results of the swelling theory, e.g. that of Flory and Huggins assuming a constant number of network junctions, cannot be applied anymore. A universal procedure is described how swelling pressure equilibria can be identified, although the crosslinking density is changed. It can be shown that the gradient of the soluble parts, respectively the additional structural changes of the gel by the soluble parts, is reproducible and with it the swelling pressure equilibria. Furthermore the radial distribution of dyed soluble parts inside the gel phase is presented as a function of time during a sedimentation equilibrium run with a gelatin/water gel. It can be shown that the back diffusion process of the soluble parts in the gel is very slow and does not lead to the sedimentation‐diffusion equlibrium of free soluble parts in the considered time interval of 4 months. In combination with the detected fast sedimentation of the soluble component in the gel phase this gives further evidence for the association of the soluble parts to the gel network forming a gradient gel. The predicted formation of the anisotropic gel could be proved by a swelling experiment.
Poly(amido‐amine)s and poly(ester‐amine)s based on aromatic amines containing carboxyl groups
Authors: Loan Do Thi Bich , Rashkov Ilya B. , Panayotov Ivan M.
Published: April 2003

The preparation of poly(amido‐amine)s and poly(ester‐amine)s via polyaddition between aromatic amines containing free or esterified carboxyl groups and compounds with activated double bounds [N,N′‐methylenebis(acrylamide), 1,4‐diacryloylpiperazine and 1,3‐propanediyl diacrylate] is described. The products obtained are typical polyelectrolytes, their solutions exhibiting anomalous viscosity behaviour.
New polymer syntheses, 81 . Poly(3‐oxybenzoate) randomly branched with 3,5‐dihydroxybenzoic acid or 5‐hydroxyisophthalic acid
Authors: Kricheldorf Hans R. , Stöber Olaf , Lübbers Dierk
Published: April 2003

Randomly branched (hyperbranched) Poly(3‐hydroxybenzoate), poly(3‐Hybe), was prepared by polycondensation of silylated 3‐acetoxybenzoic acid with either silylated 3,5‐diacetoxybenzoic acid or bis(trimethylsilyl) 5‐acetoxyisophthalate. The number of branching points was varied by changing the feed ratio of difunctional and trifunctional monomers. 1H NMR and 13C NMR spectroscopy proved the nearly random incorporation of the trifunctional “branching units”. Cocondensations with small amounts of acetylated bisphenol‐P allowed one to control the degree of polymerization (DP) and to determine the DP by 1H NMR spectroscopy. However, analogous copolycondensations with silylated 2‐(4‐tert‐butylphenoxy)terephthalic acid failed. According to GPC measurements, weight‐average molecular weights above 105 were obtained. DSC measurements revealed that the glass transition temperatures (Tg's) vary largely with the degree of branching (DB) and with the nature of the end‐groups. In the case of phenolic OH and acetate end‐groups, the relationship Tg vs. number of branching points passes through a minimum.
A preliminary study of poly(p‐phenylene) based nonlinear optical materials
Authors: Wright Michael E. , Toplikar Edward G. , Lackritz Hilary S. , Subrahmanyan Suchitra
Published: April 2003

This paper describes preliminary work exploring the feasibility of preparing high‐performance nonlinear optical (NLO) materials based on the polyp‐phenylene (PPP) backbone. Three new monomer/NLO‐phores of the general formula: 4‐RSO2C6H4C(4‐XC6H4) (where R = 2,5‐dichlorophenyl; 2a, X = H; 2b, X = OCH3; 2c X = N(CH3)2) were synthesized and then homopolymerized using catalytic nickel and stoichiometric zinc to produce the poly(p‐phenylenes), 3a–c, respectively, as low‐molecular‐weight materials (number‐average molecular weight Mn = 1800–6000). NLO‐phores 2b–c and low‐molecular‐weight oligomers of 3c were dispersed in a poly(methyl methacrylate) (PMMA) host. Spin‐cast films of these guest‐host systems were subjected to corona poling above the glass transition temperature. Tg. Following poling, both monomer NLO‐phore/PMMA guest‐host systems displayed optical nonlinearity with second‐order nonlinear optical susceptibility χ(2) values of 1.7 pm/V and 0.9 pm/V for 2c and 2b, respectively. Both systems exhibited good temporal stability at room temperature, with about 12% loss in second harmonic signal over more than 100h. However, the oligomeric material 3c dispersed in PMMA showed a smaller NLO signal when poled above Tg. Attempts to induce dipolar asymmetry in the homopolymers 3b and 3c were unsuccessful. The observed response during poling and the relaxation of the chromophore orientation following poling, have been discussed in terms of structure and composition of these systems.
Synthesis of polymers containing pseudohalide groups by cationic polymerization, 13. “Living” polymerization of 2‐methylpropene initiated by the system 1,4‐bis(1‐azido‐1‐methylethyl)benzene/BCl3/dimethyl sulfoxide
Authors: Rajabalitabar Berhooz , Nguyen Hung Anh , Cheradame Hervé
Published: April 2003

Polymerizations of 2‐methylpropene (MP) initiated by the system 1,4‐bis(1‐azido‐1‐methylethyl)benzene (DAMEB)/BCl3 in the presence of DMSO were carried out by “all monomer in” (AMI) technique at −70°C in CH2Cl2 solution. FT‐IR, 1H NMR and SEC analyses of polymers (PMP) showed that the Mn versus weight of PMP plot is a straight line without intercept and azide Fn3 and aromatic ring Fϕ functionalities are close to the theoretical values of 2 and 1, respectively. A polymerization of MP initiated by the system α,ω‐diazido‐PMP/BCl3/DMSO led to a final poly(2‐methylpropene) (PMP) with an increase of Mn corresponding to the amount of MP introduced and presenting the same functionalities FN3 and Fϕ as the starting PMP. These results indicate that the polymerization system MP/DAMEB/BCl3/DMSO is a “living” one, because in an acceptably large range of molecular weight (Mn < 50000) the Mayo plot 1/DP versus 1/DP0 is a straight line. The intercept gives ktrM/kp = 4 · 10−5, showing the transfer reaction proceeds at very low rate.
Preparation of ordered and crosslinked films from liquid crystalline p‐vinylphenoxy‐based monomers
Authors: Andersson Henrik , Trollsås Mikael , Gedde Ulf W. , Hult Anders
Published: April 2003

The synthesis of the following monofunctional and bifunctional liquid crystalline p‐vinylphenoxy‐based monomers is described: 4‐methoxyphenyl 4‐[11‐(4‐vinylphenoxy)‐undecyloxy]benzoate (1), 4‐cyanophenyl 4‐[11‐(4‐vinylphenoxy)undecyloxy]benzoate (2) and 3‐(4‐vinylphenoxy)propyl 4‐{4‐[11‐(4‐vinylphenoxy)undecyloxy]benzoyloxy}benzoate (3). Both free radical and cationic polymerization of the monofunctional monomers 1 and 2 yielded side‐chain liquid crystalline polymers exhibiting smectic A mesomorphism. The polymers exhibited high molar masses (Mn = 40000 – 100000 g/mol) and relatively narrow molar mass distributions (Mw/Mn between 1.5 and 3). Ordered thin films were prepared by in‐situ photopolymerization of monomers 1, 2 and 3 oriented in their nematic mesophases. Thin films of a thermally stabilized ordered side‐chain liquid crystalline polymer were prepared by copolymerization of the monofunctional monomer 1 and the bifunctional monomer 3, the latter present in low concentration. The films regained orientation when cooled down from temperatures above the isotropization point (137°C) as evidenced by polarized FT‐Raman measurements.
Structural study of thermotropic liquid crystalline poly(ethyleneiminium) salts alkylated with mesogenic side chains
Authors: Masson Patrick , Gramain Philippe , Guillon Daniel
Published: April 2003

Ionic liquid crystalline polymers were obtained from linear poly(ethyleneimine) (PEI) substituted with 6‐(4‐methoxy‐4′‐biphenyloxy)hexyl bromide or 12‐(4‐methoxy‐4′‐biphenylyloxy)dodecyl bromide, and quaternised with dimethyl sulfate or hydrobromic acid. Their thermotropic polymorphism was studied by means of differential scanning calorimetry (DSC), polarising optical microscopy and X‐ray diffraction. A smectic A mesophase was identified and described from a structural point of view with the help of computer modelling. The completely alkylated and quaternised PEI derivative was shown to form a single layered smectic A structure with pendant groups all on the same side of the polymer backbone in a double row ribbon‐like configuration. The ribbon‐like polymer chains are packed side by side with the polymer backbone parallel to the smectic layers and the mesogenic groups perpendicular to them. For partially alkylated or quaternised PEI derivatives, the layer spacing in the smectic A mesophase is generally different from that of the corresponding molecular length calculated for fully functionalised polymers.
Stereocomplex formation in ABA triblock copolymers of poly(lactide) (A) and poly(ethylene glycol) (B)
Authors: Stevels Willem M. , Ankone Marc J. K. , Dijkstra Pieter J. , Feijén Jan
Published: April 2003

Two series of triblock copolymers of poly(ethylene glycol) (PEG, number‐average molecular weight Mn = 6000) and poly(L‐lactide) (PLLA) or poly(D‐lactide) (PDLA) were prepared by ring‐opening polymerization of lactide initiated by PEG end groups using stannous octoate as a catalyst, either in refluxing toluene or in the melt at 175°C. The weight percentage of PLA in the polymers varied between 15 and 75 wt.‐%. Blends of polymers containing blocks of opposite chirality were prepared by co‐precipitation from homogeneous solutions. The melting temperatures of the crystalline PEG and PLA phases strongly depended on the composition of the polymers. The melting temperature of the PLA phase in the blends was approximately 40°C higher than that of the single block copolymers. Stereocomplex formation between blocks of enantiomeric poly(lactides) in PEG/PLA block copolymers was established for the first time. Water uptake of polymeric films prepared by solution casting was solely determined by the PEG content of the film.
X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) analysis of UV‐exposed polystyrene
Authors: France Richard M. , O'Toole Liam , Short Robert D. , Pollicino Nino
Published: April 2003

The surface photochemistry of polystyrene is shown to exhibit features that distinguish it from the bulk and from the polymer in solution. We report on the use of medium‐ and high‐resolution time‐of‐flight secondary ion mass spectrometry and X‐ray photoelectron spectroscopy in an investigation of the changes that occur as a result of exposure to UV light from a ‘black lamp’ source. The experiment mimics closely the effects of natural sunlight. It is shown that there are substantial changes occurring in the surface molecular structure of polystyrene on irradiation, which correspond to loss of aromaticity, and that these changes precede any uptake of oxygen.
Télomères et cotéloméres d'intérêt biologique et biomédical, 7. Synthèse, évaluations physico‐chimiques et biologiques de télomères amphiphiles de type acryloylamino‐acide
Authors: Polidori Ange , Pucci Bernard , Pavia André A. , Lamaty Gérard , Leydet Alain , Roque Jean Pierre
Published: April 2003

New ionic telomeric surfactants derived from acryloylamino acids were synthesized and their tensioactive properties compared to those of non‐ionic analogs previously reported. We also compared their anti HIV behavior with that of other polymeric polyanionic derivatives. Acryloyl monomers of various amino acids such as glycine, alanine, aspartic, glutamic and γ‐aminobutyric acid were prepared and telomerized in the presence of various alkanes or perfluoroalkanethiols as chain transfer reagents. For a given amino acid, the critical micellar concentration (CMC) was shown to depend upon the nature and the length of the hydrophobic tail and not the size of the hydrophilic head, i.e., the number average degree of polymerization (DPn). None of the telomeric polyanionic derivatives reported herein induced HIV inhibition.