bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal degradation of ethyleneurea formaldehyde polycondensates
Authors: Camino Giovanni , Luda Maria Paola , Costa Luigi , Guaita Marino
Published: April 2003

The mechanism of thermal degradation of the polymer obtained by polycondensation of ethyleneurea with formaldehyde was studied in detail using several techniques. On heating the polymer undergoes crystallisation at about 175°C. Upon melting (at 355°C) further condensation of ethyleneurea with formaldehyde takes place with elimination of water. This process overlaps with the degradation of the polymer which occurs with formation of a complex mixture of volatile products and of a charred residue. The largest fraction of the volatile products of degradation is a low boiling mixture of ethyleneurea with chain fragments containing NH, N‐methyl and unsaturated structures as end groups. A small fraction of gases such as methane, carbon dioxide, carbon monoxide etc. is also evolved. A degradation mechanism is proposed, which accounts for the experimental results.
Systematic investigations on the reactivity of oxazolinium salts
Authors: Nuyken Oskar , Maier Gerhard , Groß Aurelia , Fischer Herbert
Published: April 2003

The termination reaction of the cationic polymerization of 2‐phenyl‐ and 2‐nonyl‐2‐oxazolines was examined by reacting the corresponding model oxazolinium salts having tosylate and trifluoromethansulfonate counterions with various nucleophiles. The reaction was monitored by 1H NMR spectroscopy. Piperidine and KOH react with the oxazolinium salts very fast and quantitatively. In the case of piperidine, the use of a double molar amount of piperidine is necessary to achieve complete conversion. The addition of piperidine, pyridine, 4‐dimethylaminopyridine and morpholine takes place in position 5 of the oxazolinium ring, whereas water and KOH add in position 2. The rate of the termination reaction depends on the electron density of the nucleophile which can be correlated with the pKa value. With CF3SO as counterion the addition of nucleophiles in position 5 is distinctly faster, whereas the addition of water in position 2 is much slower than with TsO− as counterion. The ring‐opening of the nonyl oxazolinium ion is slower than that of the phenyl oxazolinium ion.
Electroconductivity and viscosity of complexes of poly(vinylpyridines) with alkali metal salts in organic solvents
Authors: Bekturganova Gulmira K. , Dzhumadilov Talkybek K. , Bekturov Esen A.
Published: April 2003

The complexation of poly(4‐vinylpyridine) (1), poly(2‐methyl‐5‐vinylpyridine) (2) and poly(2‐vinylpyridine) (3) with bromides, perchlorates and tetraphenylborates of alkali metals in organic solvents was investigated by means of electroconductivity, viscometry and nuclear magnetic resonance spectroscopy. The influence of the nature of the polymer, the low‐molecular‐weight salt and the solvent, salt and polymer concentration as well as the temperature on complexation was studied. The fraction of cations and that of polymer units bound were determined. The compositions of the complexes were found by means of viscometry. It was established that the mechanism of binding of the polymers with alkali metal salts is of the ion‐dipole type.
Synthesis of polyurethanes from saccharide‐derived diols and diisocyanates and their hydrolyzability
Authors: Wilbullucksanakul Sirinat , Hashimoto Kazuhiko , Okada Masahio
Published: April 2003

Polyurethanes with saccharide moieties in their repeating units (8 and 9) were prepared by polyaddition of methyl α‐ and β‐D‐glucofuranosidurono‐6,3‐lactones (3α and 3β, respectively) and 1,4:3,6‐dianhydro‐D‐glucitol (4) with hexamethylene diisocyanate (5a) and methyl (S)‐2,6‐diisocyanatohexanoate (5b), which was derived from L‐lysine, in N,N‐dimethylformamide at 25°C using dibutyltin dilaurate as a catalyst. Their properties were compared with those of the polyurethanes (6 and 7) prepared from D‐glucaro‐1,4:6,3‐dilactone (1) and D‐mannaro‐1,4:6,3‐dilactone (2), respectively, in our previous work. Hydrolyzability of the polyurethanes containing 1, 2, or 3α units in buffer solutions was found to be higher than that of the polyurethanes derived from 3β or 4.
Gas‐phase versus slurry copolymerization of ethylene with 1‐butene over MgCl2‐supported titanium catalysts after prepolymerization
Authors: Wu Qing , Wang Haihua , Lin Shangan
Published: April 2003

Gas‐phase copolymerizations of ethylene with 1‐butene over MgCl2‐supported titanium catalysts after prepolymerization were studied. The activity of a catalyst treated by ethylene/1‐butene prepolymerization “prep‐cat‐2” for the copolymerization is not affected by the monomer composition in the range of 0–10 mol‐% of 1‐butene, but it is higher than that of the homopolymerization of ethylene with a catalyst treated by ethylene prepolymerization “prep‐cat‐1”. Comparative studies of the polymerizations in the gas‐phase and in slurry reactors showed differences in the rate‐time profiles. The higher activities in the early stage and declining kinetics for the gas‐phase polymerizations can be considered to be due to the higher macroparticle diffusivity and to fast deactivation of the active centres which has been confirmed by the determination of the oxidation state of titanium in the catalyst. Data from determinations of monomer reactivity ratios indicated that the gas‐phase process favours the incorporation of 1‐butene into the polymer chains.
Polymorphism and crystal structure identification in poly(aryl ether ketone ketone)s
Authors: Cheng Stephen Z. D. , Ho Rong‐Ming , Hsiao Benjamin S. , Gardner Kenncorwin H.
Published: April 2003

Poly(aryl ether ketone ketone)s (PEKKs) are prepared via a Friedel‐Crafts acylation reaction with diphenyl ether and terephthalic acid (T) and/or isophthalic acid (I). The crystal structure, polymorphism and morphology of three PEKK homopolymers have been investigated using transmission electron microscopy (TEM), electron diffraction (ED) and wide angle X‐ray diffraction (WAXD) experiments. The PEKKs studied consist of either all para‐phenylene linkages [PEKK(T)], one meta‐phenylene linkage [PEKK(I)] or alternating T and I isomers [PEKK(T/I)]. PEKK(T) and PEKK(T/I) show crystalline polymorphism depending upon the crystallization conditions and methods. In PEKK(T) two forms (I and II) can be observed, and their unit cell dimensions and symmetry groups are determined via ED experiments. A possible epitaxial relationship between these two forms is proposed when they coexist. PEKK(I) possesses only one crystal unit cell which belongs to the same category as the form I structure in PEKK(T). The c‐axis dimension of the unit cell has been determined as three phenylenes having a zig‐zag conformation, with the meta‐phenylene lying on the backbone plane. PEKK(T/I) shows a complicated polymorphism. In addition to forms I and II, as in the case of PEKK(T), a possible form III is also observed.
Synthesis and electrochemical behaviour of a polymethacrylate with an azoanthraquinone unit in the side chain
Authors: Leitner Michael Bernhard , Ruhmann Ralf , Springer Jürgen
Published: April 2003

The synthesis of the model compounds 2‐(4‐methoxyphenylazo)anthraquinone (1) and 2‐[4‐(6‐acetoxyhexyloxy)phenylazo]anthraquinone (2), the monomer 2‐[4‐(6‐methacryloyloxyhexyloxy)phenylazo]anthraquinone (3) and the polymethacrylate poly‐3 via radical polymerization of 3 is described. The electrochemical behaviour of poly‐3 is studied by cyclic voltammetry in comparison with 1 and 2. Poly‐3 can be reduced and oxidized reversibly in solution and in thin films in a two‐step redox process. Therefore, poly‐3 is a potential material for a molecular device system using the electrochemical properties.
Amino acid based bioanalogous polymers. Synthesis of novel poly(urethane amide)s based on N,N′‐(trimethylenedioxydicarbonyl)bis(phenylalanine)
Authors: Kartvelishvili Tamara , Kvintradze Akaki , Katsarava Ramaz
Published: April 2003

The feasibility of synthesizing high‐molecular‐weight amino acid based bioanalogous polymers (AABBPs)‐poly(urethane amide)s (PUA) — via polycondensation (PC) of di‐p‐nitrophenyl ester of N,N′‐(trimethylenedioxydicarbonyl)bis(L‐phenylalanine) (3) with diamines or their derivatives under mild conditions in organic solvents was studied for the first time. A regular PUA (ηred = 1,53 dL/g) was obtained by PC of 3 with hexamethylenediamine. A dipeptide (Phe‐Phe) containing regular poly(ester urethane amide) (ηred = 0,58 dL/g) was synthesized by PC of 3 with p‐toluenesulfonic acid salt of bis(L‐phenylalanine) 1,4‐butylene diester. A tripeptide (Phe‐Lys‐Phe) containing PUA (ηred = 0,38 dL/g) with pendent ester groups was prepared via PC of 3 with N,N‐bis(trimethylsilyl)‐L‐lysine methyl ester. These novel AABBPs which may be considered as structural analogs of AB type bioanalogous polymers — conventional poly(amino acids) are of interest in enzymology, immunology, pharmacology, and biotechnology (as materials for biomedical applications).
The synthesis of polymerizable vinyl sugars
Authors: Wulff Günter , Schmid Jürgen , Venhoff Theodor
Published: April 2003

In this feature article we review the synthesis of polymerizable vinyl sugars. Many such syntheses start from isopropylidene‐protected sugars, which still have a free OH‐group. These compounds are then converted to polymerizable monomers by esterification or etherification. Selective reactions at non‐protected sugars, introducing polymerizable groups, can be achieved by enzymatic catalysis. Alternatively, such selective transformations may be accomplished by chemical reaction at the reducing group of the sugar either directly or after transforming the half‐acetal to a more reactive intermediate. Furthermore, results are described on the synthesis of vinyl sugars whose vinyl group is connected with the monosaccharide by a CC bond. Such monomers can be polymerized by radical as well as by anionic initiation. In this case a chemically very stable connection is obtained in the resulting polymers between the sugar moiety and the polymer backbone.
Conductivity, luminescence and vibrational studies of the poly(ethylene glycol) 400 electrolyte based on europium trichloride
Authors: Di Noto Vito , Bettinelli Marco , Furlani Maurizio , Lavina Sandra , Vidali Maurizio
Published: April 2003

Poly(ethylene glycol) 400/(EuCl3)x electrolytic complexes with 0 ≤ x ≤ 0.327 were prepared. The ionic conductivity of these systems was investigated, and the data were satisfactorily well fitted by the empirical Vogel‐Tamman‐Fulcher equation. Two different conductivity regions depending on the electrolytic complexes compositions were observed. The conformation of the poly(ethylene glycol) 400 (PEG 400) in the complexes was investigated by FT‐IR and Raman spectroscopies. These investigations suggest that the PEG 400 chains in PEG 400/(EuCl3)x, present a TGT conformation (T = trans, G = gauche). Moreover, by laser luminescence spectroscopy it was also proved that each Eu3+ ion is coordinated by four oxygen atoms of PEG in a distorted C2v site symmetry.
Photoreactive polyarylenevinylenes: Synthesis, characterization and photochemistry
Authors: Mauermann‐Düll Heike , Böhm Arno , Fiesser Gerold , Müllen Klaus
Published: April 2003

The substitution of every second phenylene subunit in the well‐known poly(p‐phenylenevinylene) (PPV) by o,o′‐bridged biphenyl moieties leads to the novel poly(1,4‐phenylenevinylene‐2,2′‐biphenylylenevinylene) (PPVBV, 5) which can be prepared by palladium‐catalyzed aryl‐olefin coupling (Heck reaction). PPVBV possesses a high solubility in common organic solvents and good filmforming capabilities. It exhibits a thermochemical and photochemical reactivity comparable to that of the monomeric model compound 2,2′‐distyrylbiphenyl (3), which undergoes a [2+2]cycloaddition upon heating or irradiation.
Study of the propagation centre in the anionic polymerization of lactams, 1. Spectroscopic and theoretical study of the activated monomer in dimethyl sulfoxide
Authors: Kříž Jaroslav , Stehlíček Jaroslav , Dybal Jiří , Hauer Jan , Schmidt Pavel
Published: April 2003

Solutions of Li, Na and K salts of 3,3‐dimethyl‐2‐piperidone and ε‐caprolactam in dimethyl sulfoxide‐d6 were studied by 6Li, 7Li, 23Na, 1H and 13C NMR, Raman spectroscopy and MNDO molecular orbital calculations. Using NMR relaxation, the dynamics and equilibrium states of solvation, dissociation and cation exchange were clarified. At concentrations above, 0,1 mol/L, molecular aggregation to a dimer and possibly higher aggregates has been found.
Study of the propagation centre in the anionic polymerization of lactams, 2. Model study of the interaction between an activated monomer and N‐acyllactam in dimethyl sulfoxide
Authors: Kříž Jaroslav , Stehlíček Jaroslav , Dybal Jiří , Hauer Jan
Published: April 2003

Interaction of potassium 3,3‐dimethyl‐2‐piperidone with 1‐benzoyl‐3,3‐dimethyl‐2‐piperidone in DMSO as a model of the complex propagation centre in the anionic polymerization of lactams has been studied by 1H and 13C NMR, infrared spectroscopy, and, for the Li counterion, by MNDO calculations. The reactants were found to form a loose complex which can emerge in various geometries sharing the equivalence and relative motional freedom of both lactam moieties. Types of internal motions in the complex are suggested and their implications for the detailed idea of the propagation mechanism are discussed.
Radicals produced in the photopolymerization of multifunctional monomers, as probes of the polymeric structure
Authors: Selli Elena , Oliva Cesare
Published: April 2003

The EPR spectra of radicals produced during the photoinduced polymerization and cross‐linking of multifunctional acrylic and methacrylic monomers are sensitive to the mobility of the polymeric surroundings. An analysis of the rate of decay of radicals trapped in different environments is reported, with the aim of finding a correlation between the evolution of the EPR spectral shape and the characteristics of the polymeric structure. A dispersive kinetic model was found to be suitable for the interpretation of radical decay results, in terms of a rate parameter (B) and a dispersion parameter (α) which takes into account the disorder of the system. These parameters depend on radical decay temperature and reflect the properties and the mobility of the photopolymerized networks, in relation to the monomer structure and to photopolymerization conditions, such as irradiation time and photoinitiator content.
Copolymerization of propene and higher α‐olefins with the metallocene catalyst Et[Ind]2HfCl2/methylaluminoxane
Authors: Arnold Manfred , Henschke Olaf , Knorr Jana
Published: April 2003

Copolymerizations of propene with higher α‐olefins including 1‐butene, 1‐hexene, 1‐octene, 1‐dodecene and 1‐hexadecene were carried out with an isospecific metallocene catalyst (Et[Ind]2HfCl2/methylaluminoxane) at 30°C in toluene. 13C NMR analysis showed that all products obtained are random copolymers (r1 · r2 ∼ 1). The reactivity of the higher α‐olefins in the copolymerization is surprisingly high and decreases only slightly with increasing length of the olefin. The incorporation rates of the comonomers in this study were found to be much higher than those obtained by the use of heterogeneous Ziegler‐Natta catalysts. Hence, copolymers with every desired composition and α‐olefin homopolymers can be prepared. The molecular weight of the copolymers is reduced with rising comonomer content. Melting points and glass transition temperatures studied by means of differential scanning calorimetry show a decrease with rising comonomer content and increasing length of the α‐olefin.
Photochromism of anils having a long alkyl side chain in polymer matrices
Authors: Yin Ming , Kuwabara Tetsuo , Haramoto Yuichiro , Nanasawa Masato
Published: April 2003

The photochromism of 4‐alkyl‐N‐(4‐methoxysalicylidene)anilines was investigated in amorphous polymer matrices. The absorbance change after irradiation increased with extending the length of the alkyl chain due to the hindrance of conformational change and the stabilization of the colored species by the alkyl side chain. The thermal decay reaction deviates from the first‐order kinetics. The deviation depends not only on the heterogeneity of the polymer matrix but also on the length of the alkyl chain of the anils.
Effect of crown ether on the ionic conductivity of the poly(ethylene oxide)/lithium salt electrolyte
Authors: Mehta Mary Anne , Kaeriyama Kyoji
Published: April 2003

The addition of small amounts of crown ethers was observed to enhance the conductivity of the system PEO20LiCF3SO3 (PEO: poly(ethylene oxide)). Optimum conductivity enhancement was observed for the system PEO20LiCF3SO3(crown ether)0.003 when 12‐crown‐4 and benzo‐12‐crown‐4 were used and for the system PEO20LiCF3SO3(crown ether)0.03 containing the corresponding azacrown ether (cyclen) and thiacrown ether. Maximum conductivity enhancement was observed for PEO20LiCF3SO3(cyclen)0.03. Over the temperature range studied, the conductivity of this system was 1–1.5 orders of magnitude higher than for the system PEO20LiCF3SO3.

The Li+ diffusion coefficient for the system PEO20LiCF3SO3(cyclen)0.03 was determined to be 1.5 · 10−9 cm2 · s−1 at 90°C. This is lower than the values obtained by other workers in the absence of cyclen using pulsed field gradient NMR techniques. The presence of cyclen thus appeared to have the effect of suppressing the Li+ motion. The presence of small quantities of 18‐crown‐6 in PEO8Ca(CF3SO3)2 electrolytes was also associated with a conductivity enhancement. This showed that this effect was not limited to systems containing monovalent cations.
Synthesis, characterization and polymerization of dendrimers with methacrylic end groups
Authors: Moszner Norbert , Völkel Thomas , Rheinberger Volker
Published: April 2003

Dendritic methacrylic crosslinking agents were synthesized by modification of amino functional poly(propyleneimine) dendrimers. On the basis of model reactions, several experimental methods for the introduction of methacrylate end groups were evaluated. In case of the Michael reaction of 2‐(acryloyloxy)ethyl methacrylate (1) the amino‐end groups of the dendrimers of the second, the fourth or the fifth generation add exclusively onto the acrylic double bonds of 1 forming methacrylic end groups in the modified dendrimers. The quantitative and uniform conversion could be proved by NMR spectroscopy. Analogous dendrimer modifications were carried out with mixtures of 1 and other acrylates. The dendrimeric methacrylates of different generations were polymerized in solution and bulk at 80°C with 2.2′‐azoisobutyronitrile as initiator. The polymerization enthalpy of the dendrimeric methacrylates was determined by differential scanning calorimetry and shows that the polymerization of approximately every double bond takes place. The polymerization of methacrylic dendrimers yields crosslinked polymers with glass transition temperatures near or below room temperature.
NMR spectra of polyimides: Interpretation and local chain motion study
Authors: Wang Jianli , Zhang Jianguo , Li Binyao , Ding Mengxian , Feng Zhiliu
Published: April 2003

Three kinds of high‐performance polyimides 1 (poly(ketone‐imide) PKI), 2 (poly(ether‐imide) PEI) and 3 (poly(oxy‐imide) POI) were studied using nuclear magnetic resonance (NMR). The NMR spectra of the polyimides were assigned according to the comprehensive consideration of the substitution effect of different substituting groups, viz. distortionless enhancement by polarization transfer (DEPT), no nuclear Overhauser effect (NNE), analysis of relaxation time, and two‐dimensional correlated spectroscopy (COSY) techniques. The structural units of these three polyimides were determined. Carbon‐13 and proton relaxation times for PEI and PKI were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (JS model) and anisotropic group rotation such as phenyl group rotation and methyl group rotation. Correlation times for the main‐chain motion are in the tens of picosecond range which indicates the high flexibility of polyimide chains. Correlation times for phenyl group and methyl group rotations are more than 1 order of magnitude lower and approximately 1 order of magnitude higher than that of the main chain, respectively.
Radical concentrations, environments, and reactivities during crosslinking polymerizations
Authors: Anseth Kristi S. , Anderson Karin J. , Bowman Christopher N.
Published: April 2003

Radical environments and concentrations during the crosslinking polymerizations of multiethylene glycol dimethacrylates were characterized with electron spin resonance spectroscopy. The relative concentrations of free and trapped radicals were used as a measure of certain structural features in the evolving polymer, especially with respect to microgel formation. The influence of monomer structure and crosslinking density on the polymer structure was studied by examining the radical behavior during the polymerization of diethylene glycol dimethacrylate, poly(ethylene glycol 200) dimethacrylate, and poly(ethylene glycol 600) dimethacrylate. The extent of radical trapping and microgel formation was found to increase with increasing crosslinking density. The influence of the rate of initiation on radical trapping was also investigated, and slower rates of polymerization led to a higher fraction of trapped radicals with respect to the total radical population. Finally, the termination mechanism of radicals was characterized (long‐term and short‐term) and the corresponding kinetic constants quantified.
Infrared analysis on blends of poly(3‐hydroxybutyric acid) and stereoregular poly(vinyl alcohol): influence of tacticity of poly(vinyl alcohol) on crystallization of poly(3‐hydroxybutyric acid)
Authors: Ikejima Tetsuya , Yoshie Naoko , Inoue Yoshio
Published: April 2003

The extens of crystallization of poly(3‐hydroxybutyric acid) (P(3HB)) in blends of P(3HB) with stereoregular poly(vinyl alcohol) (PVA) have been studied by means of infared spectroscopy. The degree of crystallinity of P(3HB) was found to decrease by blending with atactic PVA when PVA was the predominant component of the blend. In P(3HB) blends with highly syndiotactic PVA, a significant suppression of P(3HB) crystallization was observed in a wider range of blend composition than that in P(3HB)/atactic PVA blends. These results are consistant with previous results obtained by means of solid‐state13C nuclear magnetic resonance and differential scanning calorimetry. In blends with highly isotactic PVA, P(3HB) was found to crystallize in the same way as in pure P(3HB).
Copolyesteramides, 9. Random 6‐iminohexanoyl/12‐oxydodecanoyl copolyesteramides
Authors: Goodman Isaac , Rodríguez Maria Teresa
Published: April 2003

Random copolyesteramides composed of NH(CH2)5CO (6A) and O(CH2)11CO (12E) units were prepared by co‐polymerization/condensation of 6‐hexanolactam with 12‐hydroxydodecanoic acid. Lactam elimination during the reactions limited the attainable 6A content to ca. 70 mol‐%. The properties of the materials differ markedly from those of the isomeric O(CH2)5CO/NH(CH2)11CO random copolymers. Those with up to 20 mol‐% 6A units are crystalline and essentially modified 12E polymers. Thereafter, up to ca. 55 mol‐% 6A, the materials were of an intermediate, relatively homogeneous phase character, a discrete polyamide phase appearing incipiently only at still higher 6A contents. The random nature of the copolymers was confirmed by 13C NMR spectroscopy, and IR examination showed the prevalence of amide‐ester hydrogen bonding at lower 6A contents together with a degree of intramolecular sub‐crystalline order in the 12E component over the range from 20–60 mol‐% 6A. It is suggested that the copolymer texture in this range is largely controlled by the preferred conformation of the (CH2)11 units of the ester component. Some properties, including the unit cell parameters, of the little‐known 12E polyester, [poly(12‐oxydodecanoyl)], are reported.
Biodegradable and pH sensitive hydrogels: synthesis by a polymer‐polymer reaction
Authors: Ghandehari Hamidreza , Kopečková Pavla , Yeh Ping‐Yang , Kopeček Jindřich
Published: April 2003

pH sensitive hydrogels containing azoaromatic crosslinks were synthesized by a polymer‐polymer reaction. To minimize cyclization, a three step synthesis was employed. First, a polymeric precursor (P‐ONp) containing side‐chains terminated in reactive p‐nitrophenyl ester groups was synthesized by free radical precipitation copolymerization of N,N‐dimethylacrylamide, acrylic acid, N‐tert‐butylacrylamide, and N‐methacryloylglycylglycine p‐nitrophenyl ester. In the second step, the p‐nitrophenyl ester groups of P‐ONp were converted to NH2 groups (P‐NH2) by a polymer‐analogous reaction with an excess of a diamine, namely N,N′‐(ω‐aminocaproyl)‐4,4′‐diaminoazobenzene. The hydrogel was then prepared in the third step by a polymer‐polymer reaction of P‐ONp with P‐NH2. The linear copolymers were characterized by the content of functional groups and molecular weights. The hydrogels were characterized by equilibrium degree of swelling, modulus of elasticity in compression at pH 7.4, the network structure, and in vitro degradability. The swelling, mechanical properties, and rate of degradation depended on the crosslinking density. Although we were able to restrict cyclization, other side reactions such as unreacted pendent groups and hydrolysis need to be controlled. These hydrogels have potential for colon‐specific drug delivery.
Synthesis and characterization of poly(ether ketone)/poly(ether sulfone) alternating and sequential copolymers by electrophilic reactions
Authors: Finocchiaro Paolo , Montaudo Giorgio , Mertoli Patrizia , Puglisi Concetto , Samperi Filippo
Published: April 2003

The synthesis and NMR characterization of some poly(ether ketone)/poly(ether sulfone) (PEK/PES) alternating copolymers together with a series of sequential homopolymers containing CO, O, S and SO2 bridging groups, all obtained by electrophilic condensation reactions using phosphorus pentoxide/methanesulfonic acid as dehydrating agent, is here reported. Properties of such polymers are compared with those of their model compounds from which it can be inferred that both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, S, CO and SO2 bridges. Differential scanning calorimetry indicates that our polymers are essentially amorphous irrespective of the bridging sequence. From viscosity measurements the molecular weights of these copolymers are judged to be very low.
Phase transitions of hydroxy‐telechelic side‐chain liquid crystalline polyethers and polyurethane networks derived thereof
Authors: Reesink Johannes B. , Picken Stephen J. , Witteveen Arend J. , Mijs Willem J.
Published: April 2003

Hydroxy‐telechelic polymers with side‐chain mesogenic groups have been prepared from epoxy monomers using a BF3/1,6‐hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at temperatures below the clearing temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the clearing temperature, only to reappear after a period of heating above the glass transition temperature.
Low molar mass and oligomeric hexazadienes. Synthesis, thermolysis and photolysis
Authors: Nuyken Oskar , Scherer Cliff , Voit Brigitte
Published: April 2003

Several new low molar mass 1,6‐diarylhexazadiene model compounds and a oligomeric structure, containing hexazadiene units in the main chain, were prepared by N‐N‐coupling of aromatic diazonium salts with hydrazine derivatives. Thermolytic and photolytic decomposition of these labile compounds have been studied in detail. A strong dependence of the decomposition rate on the substitution pattern was observed. Electron donating aromatic substituents as well as methyl groups at N3 and N4 position decrease stability in photolysis and thermolysis. On the other hand electron withdrawing aromatic substituents and acetyl groups at N3 and N4 stabilize the hexazadiene unit. Kinetics analysis showed that in some cases the decomposition reaction may be described by unimolecular one step pathway. Activation energies and rate constants have been evaluated. The oligomeric hexazadiene exhibits a somewhat higher stability towards heat and light compared to the low molar mass model compounds.
Preparation of poly(2‐glucosyloxyethyl methacrylate)‐concanavalin A complex hydrogel and its glucose‐sensitivity
Authors: Miyata Takashi , Jikihara Atsushi , Nakamae Katsuhiko , Hoffman Allan S.
Published: April 2003

A glucose‐sensitive hydrogel was prepared by introducing concanavalin A (Con. A) into poly(2‐glucosyloxyethyl methacrylate) (poly(GEMA)) hydrogel. The decrease in swelling ratio and increase in crosslinking density by introduction of Con. A into the poly(GEMA) hydrogel indicate that the complexation introduces additional crosslinking points. The swelling of the hydrogel increased in the presence of glucose, and the swelling ratio was dependent on the glucose concentration. The glucose sensitivity of the hydrogel is attributable to the dissociation of the complex between poly(GEMA) and Con. A in the presence of glucose. Furthermore, the poly(GEMA)‐Con. A complex hydrogel was responsive to the kind of monosaccharide; its swelling ratio was changed by the presence of glucose or mannose, but not by the presence of galactose. The swelling properties of this hydrogel might be useful for the development of a glucose‐sensitive device.
Effect of tacticity on enzymatic degradability of poly(β‐hydroxybutyrate)
Authors: Timmins Mark R. , Lenz Robert W. , Hocking Philippa J. , Marchessault Robert H. , Fuller R. Clinton
Published: April 2003

Films of synthetic poly(β‐hydroxybutyrate)s (PHB)s ranging from highly isotactic to moderately syndiotactic were cast from each of several polymer fractions isolated from ring‐opening polymerizations of racemic β‐butyrolactone and were subjected to degradation by the extracellular PHB depolymerases of the bacterium Pseudomonas lemoignei and the fungus Aspergillus fumigatus M2A. Films of bacterially produced PHB were also degraded for comparison. Gravimetric determinations of enzymatic degradation were measured relative to control experiments in which no depolymerase was added. Each sample was exposed to the same concentration of enzyme, as determined by the activity of the enzyme solutions towards bacterial PHB powder, and the degradation behavior varied strongly with the tacticity of the samples. Weight loss was greatest for the bacterial polymer, with films being completely degraded by either enzyme in 48 h. The degradation of the synthetic samples by both enzymes followed similar trends, although the fungal depolymerase effected less rapid degradation for all synthetic samples than did the bacterial enzyme. Of the synthetic PHB samples, those of intermediate tacticity (55–60% isotactic diads) exhibited the greatest rate of weight loss, while those most syndiotactic in nature (34–45% isotactic) degraded the most slowly. The observed rates are interpreted in terms of isotactic contents, tacticity sequence distributions, and sample crystallinities.
Photosensitized cationic polymerization using allyl sulfonium salt
Authors: Denizligil Selcuk , Resul Rezan , Yagci Yusuf , Mc Ardle Ciaran , Fouassier Jean‐Pierre
Published: April 2003

The cationic polymerization of cyclic ethers such as cyclohexane oxide (CHO) and vinyl monomers such as butyl vinyl ether (BVE) and N‐vinylcarbazole (NVC) is initiated upon irradiation at λ 380 nm in CH2Cl2 solution containing an allylic sulfonium salt, namely, 2‐ethoxycarbonyl‐2‐propenylthiophenium hexafluoroantimonate (1) (EMT+SbF6−), and one of the following compounds: benzophenone, anthracene, thioxanthone, perylene or phenothiazine. Electron transfer and hydrogen abstraction mechanisms were proposed for the initiation step. Stable cation radicals of phenothiazine were also prepared, and the cationic polymerization of butyl vinyl ether was initiated by these cation radicals.
Synthesis and optical properties of a novel soluble polycarbazolyldiacetylene
Authors: Colombi Claudio , Comoretto Davide , Cuniberti Carla , Musso Gianfranco , Piaggio Paolo , Dellepiane Giovanna , Novi Marino , Dell'Erba Carlo , Bolognesi Alberto
Published: April 2003

A novel soluble polydiacetylene with 3,6‐dialkyl‐substituted carbazolyl side groups (polyDCHD‐S) has been prepared. Its electronic and vibrational properties have been studied in the crystalline state. The results are compared with those of polyDCHD taken as reference. PolyDCHD‐S shows a very high conjugation length like polyDCHD but an increased interchain separation. High non‐linear optical response is then expected; that — together with the processability of the polymer — suggests attractive applications in photonic devices based on thin film technology.
Catalytic polycondensations of bis(trimethylsilyl) p‐xylylene ethers with elimination of hexamethyldisiloxane and their related reactions
Authors: Yokozawa Tsutomu , Nishimori Makoto , Endo Takeshi
Published: April 2003

For establishment of the catalytic polycondensation with elimination of hexamethyldisiloxane, etherification of benzylic trimethylsilyl ethers 2 as a model reaction and polymerization of bis(trimethylsilyl) p‐xylylene ethers

Systematic name: α,α′‐bis(trimethylsiloxy)‐p‐xylenes.

1 were carried out with Lewis acids. Benzyl trimethylsilyl ether (2a) was reacted with 5 mol‐% of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) in dichloromethane at 25°C for 24 h to afford dibenzyl ether (3) in 40% yield. The yield of 3 decreased with time after 24 h because the ether linkage of 3 was cleaved also with Me3SiOTf to generate benzyl cation which underwent Friedel‐Crafts reaction. During the study of catalysts and solvents in this reaction, the reaction of 2a with Me3SiOTf in diethyl ether at 25°C was found to depress considerably the Friedel‐Crafts reaction. Further, the etherification of a secondary benzylic silyl ether, α‐phenethyl trimethylsilyl ether (2b), with Me3SiOTf proceeded rapidly in diethyl ether at 25°C to yield the corresponding dibenzylic ether in good yield. On the basis of the results of the model reaction, the polymerizations of difunctional benzylic silyl ethers, bis(trimethylsilyl) p‐xylylene ether (1a) and α,α′‐dimethyl‐p‐xylylene bis(trimethylsilyl) ether (1b), were carried out with Me3SiOTf in diethyl ether. In the polymerization of 1a, a polyether with low molecular weight (Mn = 2000) was obtained as well as a cross‐linked polymer formed by the Friedel‐Crafts reaction. In the polymerization of 1b, the molecular weight of the polymer increased with time to 9000, then decreased gradually accompanied by the production of cross‐linked polymer after 5 days. The polyether obtained from 1b could not be prepared by the Williamson ether synthesis, because the intramolecular elimination of hydrogen bromide from α,α′‐dimethyl‐p‐xylylene dibromide predominantly took place.
Cryochemical synthesis and structure of metal‐containing poly(p‐xylylenes): system poly(chloro‐p‐xylylene)‐Ag
Authors: Gerasimov Genrikh N. , Sochilin Vladimir A. , Chvalun Sergei N. , Volkova Larisa V. , Kardash Igor Ye.
Published: April 2003

Polymer films with small Ag‐clusters and Ag‐nanocrystals were obtained by the cocondensation of Ag and chloro‐p‐xylylene from the gaseous phase followed by low‐temperature solid‐state polymerization. UV‐Vis spectroscopic data show that the annealing of films at ambient temperature and thereafter at 373 K leads to a sharp rise of the amount of Agnanocrystals by aggregation of small clusters, but the mean size l̄ of the nanocrystals remains practically constant. According to X‐ray data, the lattice of Ag‐nanocrystals is close to that of metallic Ag and l̄ is equal to approximately 50 Å.
Stereoregularity of poly(methacryloyl chloride) and poly(methacrylic salts) prepared by photopolymerization
Authors: Chovino Christian , Gramain Philippe
Published: April 2003

Poly(methacryloyl chloride) (PMACl) and poly(methacrylic tetramethylammonium salts) and poly(methacrylic tetraethyl ammonium salts) (PMAAN+) have been prepared by radical photopolymerization at different temperatures. The obtained molecular weights are independent of the polymerization temperature in the range studied (+24 to −30°C) which is in agreement with a purely photochemical process. The dependence of the tacticity upon temperature was examined by means of NMR spectroscopy. Deviations from Bernoullian statistics were confirmed. PMAAN+ salts prepared in water are highly syndiotactic and a nearly pure syndiotactic structure is obtained at +5°C. This behavior is explained by the repulsive interactions between the carboxylate anions promoting the racemic placement. The tacticity of PMACl is comparable with that of poly(methacryloyl fluoride). The structure is less syndiotactic and much more isotactic than that of poly(methyl methacrylate). This result is interpreted by considering the electron‐withdrawing character of chlorine and fluorine atoms which affects the electronic structure and polarity of the carbonyl group near to the macroradical and competes with the preferential syndiotactic placement observed with α‐substituted acrylates.
Vernetzte globuläre Proteine — eine neue Klasse halbsynthetischer Makromoleküle: Charakterisierung ihrer Struktur in Lösung am Beispiel hyperpolymeren Hämoglobins und Myoglobins mittels Volumenausschluß‐Chromatographie, Viskosimetrie, Osmometrie und Lichtstreuung
Authors: Pötzschke Harald , Barnikol Wolfgang K. R. , Kirste Rudolf G. , Rosenbaum Markus
Published: April 2003

Developing an artificial oxygen carrier for use in humans, we polymerize native haemoglobin and myoglobin, using bifunctional, amino group specific cross‐linkers, to soluble, so‐called hyperpolymers. These polymers, like other polymerized globular proteins, are members of a new class of macromolecues which consist of macromolecular base units. They all have, due to the mechanisms of the chemical reaction, broad distributions of molecular weights. Fractions of hyperpolymers of human haemoglobin were obtained by employing preparative gel‐permeation (size‐exclusion) chromatography. The calibration curve of analytical gel‐permeation chromatography (GPC) for haemoglobin hyperpolymers was determined using mean molecular weights of some fractions, as assessed by osmometric and light scattering measurements. In analogy to native globular proteins, the calibration curve for haemoglobin polymers — within the range of molecular weights considered here, and within the experimental accuracy — is a straight line. All fractions of haemoglobin polymers were further characterized with the aid of calibrated analytical GPC. Mean non‐uniformity was about, 0,6. The dependence of the logarithm of the intrinsic viscosity [η] on the logarithm of the viscosity‐average molecular weightMηof the fractions (the curve in the “structure‐in‐solution diagram”) also is a straight line, which is true for haemoglobin and for myoglobin polymers as well. Its first derivative is the exponentaof the Mark‐Houwink function; for haemoglobin and myoglobin polymers the values are 0,39 and 0,46, respectively. Haemoglobin and myoglobin hyperpolymers, as members of the new class of polymers, both have a characteristic so‐called “structure‐in‐solution diagram”, and a characteristic calibration curve in GPC. The special structure‐in‐solution of the polymer proteins is a novel molecular superstructure. The intrinsic viscosity for native myoglobin was found to be 3,5 mL/g.
Synthesis and characterization of conjugated polymers with imino nitroxide groups
Authors: Saf Robert , Swoboda Petra , Lechner Andreas , Hummel Klaus , Czaputa Rainer
Published: April 2003

Two new conjugated polyradicals with imino nitroxide groups, poly[2‐(3,4‐diethynylphenyl)‐4,4,5,5‐tetramethylimidazolinyl‐1‐oxyl] (3) and poly[2‐(3,5‐diethynylphenyl)‐4,4,5,5‐tetramethylimidazolinyl‐1‐oxyl] (4), were prepared. Spectroscopic methods (IR, UV, ESR, MS) were used for the characterization. The polyradicals were precipitated from pyridine/methylene chloride solution by hexane and investigated magnetically. In the temperature range 78–300 K, polyradical 3 was paramagnetic. The magnetic behavior of polymer 4 pointed to very weak antiferromagnetism. The magnetic properties of 3 and 4 were compared to those of previously described corresponding polymers containing nitronyl nitroxide groups.
Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system
Authors: Cai Xiaoping , Gong Zhi , Wang Fosong , Zhu Xinghao
Published: April 2003

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPri)Cl2‐AlEt3) was examined in a specially designed dilatometer. The rate of polymerization is expressed as Rp ≈ −d[M]/dt = k[Nd]1.40 [M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30°C, 40°C, 45°C and 50°C.
Chromatographic separation and 13C NMR characterization of aromatic diester‐diacids isomers
Authors: Huang Wenxi , Gao Lianxun , Zhang Xin , Xu Jiping , Ding Mengxian
Published: April 2003

Reverse phase high performance liquid chromatography (HPLC) was used to separate and quantify aromatic diester‐diacids isomers which arise from the opening selectivity of anhydride rings towards methanol. 13C NMR spectroscopy was a supplementary tool to characterize the isomer structure. It was found that a meta‐position attack is slightly preferred in pyromellitic dianhydride (PMDA), while the preferred position of an attack in bridged dianhydrides is determined by the chemical nature (donors or acceptors) of the bridged group. The stronger its electron‐withdrawing abilities, the lower the probability of a meta‐position attack.
The effects of physical ageing on conformational changes of poly(ethylene terephthalate) in the glass transition region
Authors: Qian Renyuan , Shen Deyan , Sun Fuge , Wu Liheng
Published: April 2003

In‐situ FTIR studies on the conformational changes of poly(ethylene terephthalate) (PET) films with different thermal histories, i. e., quenched from the melt and sub‐Tg annealed at different temperatures, were carried out while increasing the temperature through the glass transition region. The temperature dependencies of the infra‐red spectra showed that incremental changes of the population of trans conformers in the quenched sample are gradual, while rather abrupt changes occur in the sub‐Tg annealed samples. The magnitude and temperature of the abrupt changes of trans conformers were related with the temperature of sub‐Tg annealing. An energy difference of 28.6 J/g between the trans and gauche conformational states was measured by the infra‐red spectroscopic method. The energy absorbed during the abrupt conformational change represents only part of the energy of the endothermic peak observed by differential scanning calorimetry. The results are explained in terms of the formation of new cohesional entanglements during sub‐Tg annealing.
Dynamic mechanical behavior of poly(ether ether ketone)/poly(ether sulfone) block copolymers
Authors: Cao Junkui , Su Wencheng , Ma Rongtang , Wu Zhongwen , Shibata Mitsuhiro , Takeishi Hiroyuku , Yosomiya Ryutoku
Published: April 2003

Poly(ether ether ketone) (PEEK)/poly(ether sulfone) (PES) block copolymers were synthesized via condensation reaction between fluorine‐terminated PEEK oligomers and hydroxyl‐terminated PES oligomers. The dynamic mechanical behavior of a composite sample prepared by compression molding of a glass fibre cloth and the copolymer was investigated by means of a dynamic viscoelastometer. The β relaxation peak and the α′ relaxation peak were observed in the logarithmic decrement curve of the amorphous block copolymer of PEEK/PES. The glass transition temperature (β relaxation peak) is shifted to higher temperature and approaches a constant value as annealing time and degree of crystallinity increase. The glass transition temperature of the copolymer rises more slowly upon annealing with increasing PES content. The α′ relaxation peak becomes smaller upon annealing, and eventually disappears. The α′ relaxation peaks are related to the motion of molecules upon transition from the non‐crystalline to the crystalline state. The α′ relaxation occurs for the copolymer with a degree of crystallinity of 0 to 3%.
Studies on sequence distribution of aliphatic/aromatic copolyesters by high‐resolution 13C nuclear magnetic resonance spectroscopy for evaluation of biodegradability
Authors: Witt Uwe , Müller Rolf‐Joachim , Deckwer Wolf‐Dieter
Published: April 2003

Copolyesters with different stoichiometric compositions, obtained from 1,4‐butanediol, adipic acid, and terephthalic acid by molten‐state polycondensation, are studied by means of high resolution 13C NMR spectroscopy with respect to copolymer composition and block length distribution. The ratio of aliphatic and aromatic dicarboxylic acids in the polymer, which sensitively influences the biodegradability of the polymers, reflects the initial monomer composition during polycondensation. This indicates that under the conditions applied for polycondensation no loss for example of terephthalic acid due to sublimation occurs. It was found that the aliphatic and aromatic repeating units are randomly distributed within the polymer chain. The experimentally determined average sequence length distribution dependence on stoichiometric copolymer compositions are in accord with ideal polycondensation statistics. In combination with the results of the degradability of aromatic oligomers, predictions about the degradation characteristics of the aliphatic/aromatic copolymers can be made.
Thermodynamics of depolymerization of biotechnological poly[(R)‐3‐hydroxybutyrate] with formation of (R,R,R)‐4,8,12‐trimethyl‐1,5,9‐trioxadodeca‐2,6,10‐trione and of its polymerization with ring‐opening to highly isotactic poly[(R)‐3‐hydroxybutyrate] from 0 to 500 K at standard pressure
Authors: Lebedev Boris V. , Bykova Tat'yana A. , Kiparisova Elena G. , Vasil'yev Valery G.
Published: April 2003

In adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity C of (R,R,R‐4,8,12‐trimethyl‐1,5,9‐trioxadodeca‐2,6,10‐trione a twelve‐membered cyclic trilactone), biotechnological poly[(R)‐3‐hydroxybutyrate] and highly isotactic poly[(R)‐3‐hydroxybutyrate] was studied between 5 K and 500 K; temperatures and enthalpies of melting of the above mentioned substances were measured. In a calorimeter with a static bomb and an isothermal shield the energy of combustion of the same substances was measured. From the results the thermodynamic functions C (T), H0(T) − H0 (0), S0 (T), G0 (T) − H0 (0) were calculated in the range of 0 K to 500 K and thermochemical parameters ΔH, ΔH, ΔS, ΔG were estimated at T = 298,15 K and standard pressure. The thermodynamic parameters of depolymerization of the biotechnological polymer to the 12‐membered trilactone ΔH, ΔS ΔG and of the polymerization of the monomer formed in the highly isotactic poly[(R)‐3‐hydroxybutyrate] ΔH, ΔS, ΔG were calculated for 0 K to 500 K.