bluuebunny/crossref_metadata_2025_split huggingface dataset:
γ‐ray polymerization of mesogenic diacrylates in the crystalline, liquid crystalline and liquid state — a kinetic study
Authors: Hohn Wilfried , Tieke Bernd 
Published: April 2003

AbstractA kinetic study of the γ‐ray polymerization of three mesogenic diacrylates, 4,4′‐bis(3‐acryloyloxypropoxy)biphenyl (DAPB), 4,4′‐bis(6‐acryloyloxyhexyloxy)biphenyl (DAHB) and 4,4′‐bis(11‐acryloyloxyundecyloxy)biphenyl (DAUB), is presented. All compounds were studied on their polymerizability in the crystalline state. It was found that they can be completely polymerized though the reaction rates are very different and increase with increasing length of the alkylene spacer unit. Up to moderate conversion, solid‐state polymerization is comparable with that of acrylamide and follows a t2 rate law. DAPB was chosen for a detailed kinetic study of the in‐source and post‐polymerization in the crystalline, liquid crystalline and liquid phase. In‐source polymerization is complete in the various phases though reaction rates and curve shapes of dose vs. conversion curves are very different. Possible origins such as enhanced molecular diffusion at elevated temperatures are discussed. X‐ray studies indicate that a well‐ordered polymer can be obtained from polymerization in a smectic phase, while polymers obtained from a crystaline or melt phase are considerably less ordered. Post‐polymerization was studied as a function of the radiation dose and the temperature of the subsequent annealing process. It was found that the limiting conversion increases with increasing radiation dose and temperature of the annealing process, but the polymerization is always incomplete. Even post‐polymerization in the melt phase does not exceed 55 percent conversion. The post‐polymerization behaviour is comparable with that of acrylamide and can be described by a linear relation between conversion and annealing time t.
Polymerization of olefins with zirconocene catalysts using methylaluminoxane modified with hydroquinone as cocatalyst
Authors: Jin Jizhu , Uozumi Toshiya , Soga Kazuo 
Published: April 2003

AbstractMethylaluminoxane (MAO) was reacted with a small quantity of p‐hydroquinone to obtain a modified MAO insoluble in toluene. Ethylene and propylene homo‐ and copolymerization were conducted with zirconocene using the modified MAO as cocatalyst both in the presence and absence of triisobutylaluminium. It was found that the modified MAO alone cannot activate the zirconocene catalyst, whereas polymers with high molecular weights are obtained when combined with triisobutylaluminium. The catalytic activity is markedly dependent on the mole ratio of p‐hydroquinone to MAO as well as the amount of triisobutyl‐aluminium.
Activation of rac‐ethylenebis(indenyl)zirconium dichloride with a low amount of methylaluminoxane (MAO) for olefin polymerizations
Authors: Coevoet Dorothée , Cramail Henri , Deffieux Alain 
Published: April 2003

AbstractThe homopolymerization of hex‐1‐ene catalyzed by the system rac‐Etlnd2ZrCl2/MAO was investigated in solvents of various polarity (toluene, methylene dichloride and heptane). Polymerization kinetics were monitored by dilatometry. It is shown that reaction proceeds by long‐lived active species rapidly formed and remaining at constant concentration during the whole polymerization. However, the molar masses of the polymer remain controlled by a transfer process. A strong enhancement of the activity is observed in pure CH2Cl2 compared to the one measured in toluene. Besides, the use of CH2Cl2 allows to reduce the amount of methylaluminoxane (MAO) by a factor 20 to reach the plateau of maximum activity, without affecting the isotacticity of the polymer. The increase of activity in CH2Cl2, even for low MAO/Zr ratios, is explained by an easier ionic dissociation of the Zr‐X bond (X = Cl or methyl) yielding the formation of cation‐like active species. A preformation of the catalytic system in minute amount of CH2Cl2 followed by hex‐1‐ene polymerization in heptane or toluene was found to yield also high catalytic activity at a low MAO/Zr ratio. These results suggest that the beneficial effect of methylene dichloride on the formation of the active species is preserved. A tentative explanation is proposed. A first extension of the results obtained with the α‐olefin to ethylene polymerization is also presented.
H2‐D2 exchange reaction with MgCl2‐supported Ziegler catalyst by stopped‐flow method
Authors: Mori Hideharu , Tashino Kunihiko , Terano Minoru 
Published: April 2003

AbstractThe effect of hydrogen on the chain transfer reaction in the initial stage of propene polymerization with MgCl2‐supported Ziegler catalyst was studied through H2‐D2 exchange reaction using the stopped‐flow method. When the exchange reaction was carried out with various catalyst components at room temperature for 5 min, HD was produced only in case of using the catalyst with Al(C2H5)3. In case of the stopped‐flow method (reaction time ca. 0.1 s), the catalyst without pre‐treatment with Al(C2H5)3 showed no activity for the H2‐D2 exchange reaction (no HD produced), while the catalyst with pre‐treatment had exchange activity. As the chain transfer activity of H2 in propene polymerization shows the same tendency, it is evident that chain transfer with H2 occurs via atomic hydrogen generated on the pre‐treated catalyst.
Preparation and polymerization behavior of 2‐[2,2,2‐tris‐(alkoxycarbonyl)ethyl]acrylic ester as a sterically congested monomer
Authors: Yamada Bunichiro , Kobatake Seiya , Konosu Osamu 
Published: April 2003

AbstractMethyl 2‐[2,2,2‐tris(methoxycarbonyl)ethyl]acrylate and methyl 2‐[2,2,2‐tris(ethoxycarbonyl)ethyl]acrylate [M(TE)EA] were synthesized for the first time by the reaction of methyl 2‐(bromomethyl)acrylate with the corresponding tris(alkoxycarbonyl)methane in the presence of triethylamine at room temperature in 90 and 89% yields, respectively. Attempted homopolymerization of these particular acrylates did hardly occur. However, the radical produced by attack of the primary radical from 2,2′‐azo‐2,4,4‐trimethylpentane at the β‐carbon of M(TE)EA was detected via its 5‐line ESR spectrum, and a similar spectrum was observed using tert‐butyl peroxide as initiator. These findings imply that persistency of the adduct radical of M(TE)EA suppresses further propagation to high molecular weight polymer. Steric congestion of the adduct radical was shown by ESR spectral change at different temperatures. Copolymerization of M(TE)EA with methyl methacrylate proceeded at a slow rate and yielded products containing only 1,7–2,7 units of M(TE)EA per polymer chain irrespective of comonomer composition. When the content of M(TE)EA was lower than 10 mol‐% in the monomer mixtures of M(TE)EA with styrene and methyl acrylate, copolymers whose molecular weights decreased with an increase in M(TE)EA content in monomer mixture were obtained. The copolymerization rates were also reduced considerably with increasing content of M(TE)EA in the feed.
Étude de la copolymérisation de monomères acryliques fluorés avec le méthacrylate de morpholinoéthyle
Authors: Guyot Bernard , Boutevin Bernard , Améduri Bruno 
Published: April 2003

AbstractThe copolymerization of 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10‐heptadecafluorodecyl acrylate (AC8), methacrylate (MAC8) and α‐acetoxyacrylate (αAC8) with morpholinoethyl methacrylate (MEMA) is presented. For these three systems, the values of the reactivity ratios (ri) of both comonomers were determined by means of four methods (Jaacks, Macret, Fineman‐Ross and Tidwell‐Mortimer) usually used, and these results were compared. In each case, the copolymer obtained exhibits a structure with a higher content of the fluorinated base unit. A reactivity scale in the radical copolymerization with MEMA is proposed and shows that αAC8 and MAC8 are more reactive than AC8, contrary to their homopolymerization behaviour. An explanation of such a tendency was suggested taking into account the Q‐e scheme of Alfrey and Price of hydrocarbon homologues.
4‐methoxy substituted trityl groups in 6‐O protection of cellulose: Homogeneous synthesis, characterization, detritylation
Authors: Gömez Juan A. Camacho , Erler Ulrich W. , Klemm Dieter O. 
Published: April 2003

AbstractThe reaction of cellulose with methoxy‐substituted triphenylmethyl chlorides under homogeneous conditions in the presence of pyridine was carried out with the aim to develop new protective groups for cellulose simply introducable and completely removable under mild conditions. The obtained cellulose ethers dissolve well in solvents such as N,N‐dimethylformamide, N,N‐dimethylacetamide, dimethyl sulfoxide, 1,4‐dioxane and tetrahydrofuran and show a high 6‐O selectivity. The study proves that the speed of tritylation as well as of detritylation increases in the order unsubstituted trityl/monomethoxytrityl/dimethoxytrityl/trimethoxytrityl. The substituent distribution of the methoxy‐substituted triphenylmethyl ethers of cellulose was determined by means of 13C NMR spectroscopy of the polymers and by high‐performance liquid chromatography after chain‐degradation. Since the methoxy substituted trityl groups were introduced faster and removed easier than the unsubstituted trityl group, they are, therefore, useful tools for a regioselective synthesis of 2,3‐functionalized cellulose derivatives.
Irreversibility of structural changes induced by stretching in poly(vinyl chloride)
Authors: Elicegui Amaia , del Val Juan José , Colmenero Juan , Martínez Gerardo , Millán José Luis , Bellenger Veronique , Verdu Jacques 
Published: April 2003

AbstractIt has been shown that certain structural (X‐ray diffraction) and physical (infrared dichroïsm, α‐relaxation dynamics) characteristics of poly(vinyl chloride) undergo irreversible changes upon sample drawing. This behaviour reveals some non‐equilibrium character of the polymer, even in tetrahydrofuran (THF) solution or in the rubbery state (at, typically, glass transition temperature Tg + 10°C). Two tentative ways of explanation have been proposed. The first one would attribute the cause of this peculiar behaviour to physical crosslinks linked to strong interchain bonding. These bonds would resist to dissolution in THF at room temperature but would be broken during stretching. The second way of explanation involves the presence of a metastable GTTG−TT conformation at the end of an isotactic sequence in an mmr chain segment. Like the above mentioned physical crosslinks, it would be transformed upon mechanical loading but not during dissolution in THF or heating to 90°C. Both hypotheses are not necessarily incompatible: as a matter of fact, GTTG− conformations at the end of the isotactic triads could represent sites of especially high intermolecular interaction, distributed along the polymeric chain.
Molecular dynamics in polystyrene from electron spin resonance (ESR) measurements: comparison between spinprobes and ‐labels attached to the chain ends
Authors: Volkmer Thomas , Wiesner Ulrich , Brombacher Lothar , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe commercially available 15N‐TemponeN‐Tempone: 4‐oxo‐2,2,6,6‐tetramethylpiperidine‐15N‐oxyl; Tempol: 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine ‐15N‐oxyl.
nitroxide radical has been used for the endfunctionalization of anionically polymerized polystyrene. The temperature dependence of molecular motions of the nitroxide radicals in this chain end labeled polystyrene (PS) and a PS/Tempol mixture has been studied using cw‐ESR. Furthermore, these two samples were compared with a mixture of PS with a biradical which has a large molecular volume and is used in its unoxidized form as a polymer additive in commercial products. The temperature dependent spectra were evaluated to give T50G. This allows the volume for reorientation of the radicals and that of a polymer unit to be compared. The temperature dependent spectra were simulated in order to yield the rotational correlation time τR. In contrast to the Tempol probe radical which is highly mobile even at temperatures well below the glass transition temperature (Tg) the spin‐label strongly couples to the α‐process of polystyrene. The biradical exhibits an intermediate mobility and seems to be weakly coupled to the glass transition dynamics. Line shape analysis shows that the motional behavior of the PS/Tempol mixture can adequately be described by the model of isotropic rotational diffusion, whereas for the chain end label significant deviations from this model are observed indicating anisotropic motion due to restrictions imposed by the polymer chain.
Synthesis and characterization of poly(amide‐imide)s containing 1,6‐diamantane moieties in the main chain
Authors: Chern Yaw‐Terng , Chung Wan‐Ho 
Published: April 2003

AbstractA series of new poly(amide‐imide)s were synthesized by direct polycondensation of the 1,6‐bis(trimellitimido)diamantane (1) with various aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) containing lithium chloride. The poly(amide‐imide)s had inherent viscosities of 0.33–1.55 dL/g. The new polycyclic monomer 1 was synthesized from 1,6‐diaminodiamantane with trimellitic anhydride. Dynamic mechanical analysis revealed polymers 3a–c to have main transitions at 385°C, 385°C, and 330°C, respectively. Moreover, these polymers were stable at high temperatures and maintained good mechanical properties (G′ ≈ 108 Pa) up to temperatures close to the main transition well above 350°C. Their 5% weight loss temperatures ranged from 421 to 448°C in nitrogen, and from 417 to 426°C in air. A glass transition of poly(amide‐imide)s 3 was not observed. Poly(amide‐imide)s 3 (except 3e) were soluble in NMP, pyridine, and o‐chlorophenol. Some of the polymers (3a–c) could be cast into flexible films. Their cast films had tensile strengths ranging from 35.5 to 46.9 MPa, elongations at break from 5.8 to 7.5%, and initial moduli from 1.8 to 2.1 GPa.
Synthesis and properties of aromatic polyamides based on 4,4′‐[1,4(1,3 or 1,2)‐phenylenedioxy]dibenzoic acid
Authors: Hsiao Sheng‐Huei , Chang Chih‐Fen 
Published: April 2003

AbstractThree isomeric bis(ether carboxylic acid)s, 4,4′‐[1,2(1,3 or 1,4)‐phenylenedioxy]dibenzoic acid (o‐, m‐, or p‐3) were prepared by nucleophilic substitution reaction of the potassium phenolate of catechol, resorcinol, and hydroquinone, respectively, with p‐fluorobenzonitrile, giving the corresponding bis(ether nitrile)s, followed by alkaline hydrolysis. There series of isomeric polyamides were synthesized by direct polycondensation of the bis(ether carboxylic acid)s with various aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) solution containing dissolved metal salts such as CaCl2 or LiCl using triphenyl phosphite and pyridine as condensing agents. The resultant polyamides had inherent viscosities of 0,52–1,63 dL/g. Most of the polymers were soluble in polar aprotic solvents such as N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide (DMF), NMP, and dimethyl sulfoxide. The catechol‐based polyamides revealed markedly higher solubility than those based on hydroquinone or resorcinol. Transparent, flexible and tough films could be cast from the DMAc or NMP solutions of most of the polyamides. All the casting films were characterized by tensile tests. The glass transition temperatures (Tg's) of most polyamides could be determined with the help of differential scanning calorimetry (DSC) traces, which were recorded in the range of 183–232°C. In general, the polyamides based on catechol had Tg's comparable with the ones of the hydroquinone‐based polyamides and higher Tg's than the corresponding resorcinol‐based ones. Thermogravimetric analysis data of these polymers indicated that all the polyamides were stable up to 400°C in both air and nitrogen atmospheres.
Oligomerization and copolymerization of γ‐butyrolactone — a monomer known as unable to homopolymerize, 1. Copolymerization with ε‐caprolactone
Authors: Duda Andrzej , Penczek Stanislaw , Dubois Philippe , Mecerreyes David , Jérôme Robert 
Published: April 2003

AbstractCopolymerization of γ‐butyrolactone (γBL) with ε‐caprolactone (εCL) initiated with aluminium isopropoxide trimer ([Al(OiPr)3]3, (A3)) is described. Copolymers with molecular weights (Mn) up to 3 · 104 and containing up to 43 mol‐% repeating units derived from γBL are prepared. Their molecular weight is controlled by the concentrations of the consumed comonomers and the starting concentration of initiator {Mn = (86.09 · [γBL]c + 114.14 · [εCL]c)/3[Al(OiPr)3] + 60.10}. 13C NMR and DSC data are indicative of a pseudoperiodic or random copolymer structure.
The preparation of new types of polymerizable vinyl sugars with CC bonds between sugar and double bond
Authors: Wulff Günter , Schmid Jürgen , Venhoff Theodor P. 
Published: April 2003

AbstractThe syntheses of new types of vinyl sugars are described whose vinyl groups are connected with the monosaccharide by a CC bond. Such monomers can be polymerized by radical as well as by anionic initiation. Starting from D‐mannitol, D‐gluconolactone, D‐galactose, and D‐fructose, the isopropylidene‐protected aldehydes (R)‐2,3‐isopropylidene‐D‐glyceraldehyde (3), 2,3;4,5‐di‐O‐isopropylidene‐aldehydo‐D‐arabinose (4), 1,2;3,4‐di‐O‐isopropylidene‐α‐D‐galacto‐hexodialdo‐1,5‐pyranose (5), and 2,3;4,5‐di‐O‐isopropylidene‐β‐D‐arabino‐hexosulo‐2,6‐pyranose (6) were prepared. Grignard reaction of the aldehyde compounds with 4‐vinylphenylmagnesium chloride in tetrahydrofuran (THF) yielded the new styryl monomers of type 1, in each case as a mixture of two diastereoisomers. The corresponding reaction with vinylmagnesium bromide furnished a mixture of two diastereoisomeric allyl alcohol derivatives. Subsequent Swern oxidation (DMSO/(COCl)2) gave the vinyl ketones of type 2. A scale‐up procedure (20 L flask) allowed eight different monomers to be prepared on a 50–200 g scale. Furthermore, the synthesis of the 2,3;4,5‐di‐O‐isopropylidene‐β‐D‐fructopyranose could be considerably improved.
Poly(butylene terephthalate) oligomers containing organosilane end groups
Authors: Boutevin Bernard , Khamlichi Mohammed , Robin Jean‐Jacques 
Published: April 2003

AbstractOligomers with poly(butylene terephthalate) (PBT) containing organosilane extremities were prepared by reacting an α‐allylic oligomer of PBT with silanethiols or with silanes. The α‐allylic oligomer of PBT was synthesized by condensation of allyl alcohol, 1,4‐butanediol and terephthaloyl dichloride. All the oligomers were characterized by means of proton nuclear magnetic resonance, Fourier‐transform infrared spectroscopy, size‐exclusion chromatography, gas chromatography and high‐performance liquid chromatography. Their thermal properties were also investigated.
The Förster radius for energy transfer from naphthalene to anthracene in polyesters with oxyethylene spacers
Authors: Bravo Julio , Mendicuti Francisco , Saiz Enrique , Mattice Wayne L. 
Published: April 2003

AbstractModel compounds for a series of polyesters in which 3,6,9, and 12‐rotatable CH2O and CH2CH2 bonds separate rigid units have been studied using the efficiency of nonradiative singlet energy transfer from naphthalene to anthracene. The model compounds have the structure naph‐CO(OCH2CH2)mOOC‐anth with m of 1–4, where naph and anth denote 2‐naphthyl and 9‐anthranyl groups, respectively. This series of compounds covers a larger range of potential separation of the two chromophores than was possible in an earlier study, in which the flexible spacers consisted of 2–6 methylene units. The nonradiative singlet energy transfer has an efficiency that depends on the solvent viscosity and on m. The theoretical analysis employs a rotational isomeric state model for the conformations of these molecules. The Förster radius for transfer from naphthalene to anthracene in this system is 16 ± 2 Å, and is nearly independent of whether the spacers are constructed from oxyethylene or methylene units.
Polymer bound chromogenic crown ethers for optical ion‐detection devices
Authors: Klok Harm‐Anton , Möller Martin 
Published: April 2003

AbstractThe concept of photoinduced electron transfer has been explored for the development of polymeric transducers for optical ion‐detection devices. For this purpose, a series of N‐(9‐anthrylmethyl)monoaza‐18‐crown‐6 substituted poly(methacrylate)s were prepared, which differ in the chemical nature of the backbone. The fluorescent signaling in these systems is based on disturbances, upon complexation of K⊕, in the competition between de‐excitation pathways of fluorescence and photoinduced electron transfer. The sensitivity and the ultimate enhancement of the fluorescence of these materials upon complexation of K⊕ were found to be strongly influenced by the chemical structure of the polymer backbone.
Local chain motions in a dilute solution of phenolphthalein poly(ether sulfone)
Authors: Wang Jianli , Zhang Jianguo , Li Binyao , Feng Zhiliu 
Published: April 2003

Abstract13C and 1H relaxation times were measured as a function of temperature in two magnetic fields for dilute solutions of phenolphthalein poly(ether sulfone) (PES‐C) in deuterated chloroform. The spin‐lattice relaxation times were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (J. S. model). The phenyl group rotation is treated as a stochastic diffusion by the J. S. model. The restricted butterfly motion of the phenyl group attached to the cardo ring in PES‐C is mentioned but is not discussed in detail in this work. Correlation times for the segmental motion are in the picosecond range which indicates the high flexibility of PES‐C chains. The correlation time for the phenyl group internal rotation is similar to that of the segmental motion. The temperature dependence of these motions is weak. The apparent activation energy of the motions considered is less than 10kJ/mol. The simulating results for PES are also reasonable considering the differences in structure compared with PES‐C. The correlation times and the apparent activation energy obtained using the J. S. model for the main chain motion of PES‐C are the same as those obtained using the damped orientational diffusion model and the conformational jump model.
Modification of poly(L‐lactides) by blending: mechanical and hydrolytic behavior
Authors: Hiljanen‐Vainio Mari , Varpomaa Paula , Seppälä Jukka , Törmälä Pertti 
Published: April 2003

AbstractTwo different poly(L‐lactides) (PLLAb and PLLAa) were blended with poly(ε‐caprolactone) (PCL) and an elastic poly(ε‐caprolactone/L‐lactide) P(CL/L‐LA) copolymer to modify the mechanical properties of PLLA. Blends of both PLLAs with 20 wt.‐% of PCL were prepared. PLLAa was blended with 20 wt.‐% of P(CL/L‐LA) copolymer, and blends of PLLAb and P(CL/L‐LA) copolymer were made with copolymer contents of 5, 10, 20 and 30 wt.‐%. The tensile properties and impact and shear strengths were determined as a measure of the mechanical properties. The hydrolytic behavior of the blends was investigated, and the changes in shear strength as a function of hydrolysis were followed. The structure of the hydrolyzed samples was studied by means of scanning electron microscopy (SEM). The properties of PLLA changed considerably when blended with PCL or P(CL/L‐LA) copolymer. An increasing amount of copolymer in PLLAb decreased tensile modulus and shear strength, but improved the strain and impact strength. In hydrolysis, blends containing PLLAa degraded slower than blends of PLLAb because of the higher initial molar mass and purity of PLLAa. The molar masses of PLLAb blends decreased dramatically, and less than 10% of the initial molar masses and shear strengths were left after 12 weeks in vitro. The morphology of the blends affected the degradation. The blends containing P(CL/L‐LA) copolymer had a porous structure which facilitated water absorption into the blend.