bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crosslinking of ethylene‐vinyl alcohol copolymers via polymeranalogous reactions
Authors: Fedtke Manfred , Henning Kerstin 
Published: March 2011

AbstractA practical model for polymeranalogous reactions is ethylene‐vinyl alcohol copolymer with a controllable amount of hydroxylic groups. The reaction of the hydroxyl groups with various compounds leads to further functionalized polymers. The functional groups introduced are useful for modification or crosslinking reactions. The modification of ethylene‐vinyl alcohol copolymers with carboxylic anhydrides and hydroxy carboxylic acids is the main subject of this investigation. The crosslinking reaction of these products with bifunctional epoxies was followed by means of viscosimetric measurements. The dependence of the reaction behaviour on the structure of the functionalized polymers used is discussed.
New additives in glass reinforced polyolefins
Authors: Severini Febo , Pegoraro Mario , Ricca Giuliana , Di Landro Luca 
Published: March 2011

AbstractPoly(butyl acrylate)‐g‐poly(4‐vinylpyridine) graft copolymer and polypropylene modified with maleic anhydride or poly(maleic anhydride) have been prepared and characterised. These products have been tested as coupling agents in glass reinforced polyolefins. The adhesion of glass fiber or glass filler to polyolefin has been evaluated by “Single fiber composite” method or studying the volume variation under tensile strength. The results indicate that all the prepared additives improve the adhesion between olefin matrix and glass filler or fiber.
The influence of oxygen on radiation crosslinking and degradation of polymers at low irradiation doses
Authors: Babić Dragan 
Published: March 2011

AbstractThe influence of oxygen on radiation cross‐linking and scission at low doses has been followed in order to explain anomalous drop of molecular weight found in polyethylene at low irradiation doses. The G ‐ values and yields of crosslinking and scission estimated on the basis of molecular weight measurements (by GPC) are much higher than those obtained through gel content determinations at higher doses. The possible explanations of such a peculiar behavior are suggested and discussed. The influence of oxygen, even when present in the form of air absorbed in the sample, was found to be an important factor of scission process in irradiated polymer.
Structure and rheological properties of PVC melts
Authors: Lyngaae‐Jørgensen J. 
Published: March 2011

AbstractThe Theological properties of PVC compounds reflect the state of the flow units. The steady state structure which may be found in PVC melts is predicted to depend on the interaction of stresses in simple flow and temperatures for transition from rubberlike solid to liquid state and transition from a liquid state containing crystallite aggregates to a liquid state without crystallite aggregates, called the gel destruction temperature Td and the dynamic melting temperature Tdynm, respectively. The model predictions for Td and Tdynm are compared with experimental data.
13C and 1H NMR analysis of structural defects in PVC: Application to the production of defects at various polymerization stages
Authors: Llauro‐Darricades Marie‐France , Bensemra Naima , Guyot Alain , Petiaud Roger 
Published: March 2011

AbstractHigh resolution 1H and 13C NMR data were obtained on PVC and PVC reduced with Bu3SnH. The reduction is never complete and CH2Cl groups preferentially remain. It causes almost complete formation of cyclopentane structures from both internal and chain end unsaturation. 1H NMR gives total unsaturation as well as chain end unsaturation except if there are interferences with initiator residues; in that case, its combination with 13 C NMR of reduced PVC gives the chain end unsaturation. By the last method short branches and long ends are determined. Residual primary chlorine in all kinds of branches (methyl, ethyl, butyl, long ends) is taken into account. Long end contents are to be corrected (factor around 1.5), due to incomplete relaxation in standard analysis conditions. 1H NMR of reduced PVC can be used to get the total non‐reduced structures, both ‐CH2Cl and ‐CHCl‐. PVC was prepared by suspension or solution (trichlorobenzene) polymerization at 55° C, using dicetyl peroxydicarbonate as an initiator. The initiator residue content is higher in suspension PVC at very low conversion, and then levels off at a low value; in solution polymerization, it chiefly depends on the monomer/initiator ratio. At low conversion, more chain end and less short branches are present in suspension polymerization. Otherwise, only the butyl branch content shows a definite trend to increase with conversion. In solution polymerization, the number of defects is chiefly dependent on the initial monomer concentration; it is generally much higher than in suspension, except for the chloromethyl branches where both processes give about the same results.
Rubber elasticity of branched polyethylenes
Authors: Klein P. G. , Brereton M. G. , Rasburn J. , Ward I. M. 
Published: March 2011

AbstractTwo grades of ethylene/1‐hexene copolymer, containing about 0.4 and 1.3 butyl branches per 1000 carbons, were subjected to electron beam irradiation in vacuum and in an acetylene atmosphere. The resulting networks were characterized by gel fraction determination and melt elasticity behaviour. The rubber elastic force‐extension data were analysed in terms of the Edwards‐Vilgis slip‐link model. This theory provided good fits to the experimental data, and the calculated parameters agreed well with the gel fraction determinations. The results indicate that an increase in branch concentration causes an increased susceptibility to chain scission.Irradiation in acetylene is shown to enhance greatly the crosslinking process, without affecting the chain scission, leading to a more perfect network.
Mechanochemical energy conversion of neutral polymer gels
Authors: Horkay Ferenc , Zrinyi Miklós 
Published: March 2011

AbstractMechanochemical energy conversion exhibited by water‐swollen poly(vinyl alcohol) gels has been studied. The effective mechanical work produced as well as the chemical energy converted were measured simultaneously. It is shown theoretically and experimentally that the mechanical work developed during the swelling of the mechanochemical system increases with increase of the external load (m), the degree of cross‐linking (DC) and the deswelling ratio (ϕ/ϕe, i.e. the ratio of the volume fraction of network polymer (ϕ) to that of the same gel in equilibrium with pure diluent (ϕe)). The chemical energy converted was found to be practically independent of m. The efficiency of energy conversion increased with increase of m and DC, and significantly decreased with increase of ϕ/ϕe. Comparison is made between theoretical predictions and experimental findings.
Mechanism and kinetics of the radical polymerization of acrylamide in inverse micelles
Authors: Candau Françoise 
Published: March 2011

AbstractA kinetic study of the photoinitiated polymerization of acrylamide in oil/AOT/H2O reverse micelles has been investigated. Determinations of the dependence of the rates of polymerization and the molecular weights of the polymers on initiator and monomer concentrations, as well as the relative light intensity and the identity of the oil employed were performed. Rates of polymerization were measured by dilatometry, and polymer molecular weights were determined by viscometry. The polymerization was shown to be first order in monomer concentration, and the order of the termination step of the polymerization depended strongly upon the oil employed. When the oil was benzene, termination occurred by a biradical process. When benzene was replaced by toluene, a monoradical termination was shown to occur, suggesting that a degradative chain transfer to toluene is occurring in this case. The similarities and differences of polymerization in conventional emulsions and in micelles are discussed on the basis of these results.
Synthesis of block copolymers by heterogeneously initiated emulsion polymerization
Authors: Chrástová V. , Citovický P. , Pristačová J. 
Published: March 2011

AbstractThe contribution refers to the possibility of using emulsion polymerization of styrene, initiated by a heterogeneous initiator Chydroperoxide of isotactic powdered polypropylene) in the presence of a complex type activator, for the synthesis of block copolymers. Vinylmonomers with various water‐solutibility, i.e. methyl methacrylate (MMA), acrylonitrile (AN) and maleic anhydride (MA), were utilized as comonomers of styrene. It was found that at the used conditions, the composition of block copolymers PS‐b‐P(S/AN) and PS‐b‐PCS/MA) can be varied by the time of polymerization of the first or second comonomer. The block copolymers were characterized by their molecular weight, and their thermal stability was also investigated.
Polymer networks via cationic ring‐opening polymerization
Authors: Goethals Eric J. , van Meirvenne Dirk , Trossaert Geert , Deveux Robert 
Published: March 2011

AbstractThree methods for the formation of polymer networks from bifunctionally growing polymers obtained by cationic ring‐opening polymerization are described. The first method is based on the irreversible inter‐molecular termination reaction of thietane polymerizations. Starting from bifunctionally living poly(THF) a new kind of polymer structure consisting of ABA block copolymers with cross‐linked A‐segments is obtained. The second method is the direct coupling of active species with primary amines or ammonia. The third method consists in transformation of the living end groups of poly(THF) into triethoxysilane end groups, followed by cross‐linking by addition of water and a trace of acid.
Catalyzed silicon‐mediated living polymerizations, structure control, catalyst design and mechanisms
Authors: Sogah D. Y. , Hertler W. R. , Dicker I. B. , Depra P. A. , Butera J. R. 
Published: March 2011

AbstractGroup transfer polymerization (GTP) and the related Aldol‐GTP are new types of living polymerization mediated by silicon for precise control of polymer structure. The two processes are regenerative in that the reactions are accompanied by transfer of silyl group from living end to the incoming monomer and vice versa to produce a reactive functional group as the living end. The reaction can be carried out on solid supports, such as crosslinked polystyrene. Even though the reactions are normally catalyzed, they can be carried out at high pressures without the use of any catalyst. They operate above room temperature, thus enabling one to control molecular weight, polydispersity and monomer sequence under industrially significant conditions. The scope of catalysis is broadened to cover oxyanions.
Recent developments in living carbocationic polymerization of alkenes
Authors: Kennedy Joseph P. 
Published: March 2011

AbstractThe recent discovery of living cationic polymerization of alkenes has been followed up in three areas: 1) Demonstration of the validity of the DPn = [Mo]/[Io] relationship and the synthesis of high molecular weight polyisobutylenes Mn_>100 000) of narrow molecular weight distribution (Mw/Mn ≈︁1.1) 2) Discovery of electrophilic quenching and the use of this method for the preparation of allyl‐telechelic polyisobutylenes by quenching with trimethylallylsilane and 3) Synthesis of novel linear and three‐arm star radial thermoplastic elastomers comprising rubbery polyisobutylene central sequences connected to glassy polystyrene or a polystyrene derivative (i.e., p‐methylstyrene, p‐tert‐butylstyrene, indene) outer sequences. Some physical‐mechanical properties of these materials have been investigated.
Design and initiators of living cationic polymerization of vinyl monomers
Authors: Sawamoto Mitsuo , Higashimura Toshinobu 
Published: March 2011

AbstractThis paper discusses recent developments in living cationic polymerization of vinyl monomers, specifically focusing on (a) new initiating systems, (b) kinetics and mechanism, and (c) controlled polymer synthesis. The new initiating systems were based on nucleophilic stabilization of the growing carbocations, either by counteranions (as in phosphate/ZnI2 and Me3SiI/ZnI2 systems) or by added Lewis bases (as 2,6‐dimethylpyridine for EtAlCl2). The kinetic study included the determination of the lifetime of living cationic polymers. The controlled polymer synthesis by living cationic processes led to not only end‐ and pendant‐functionalized polymers of narrow molecular weight distributions but also star‐shaped polymers and sequence‐regulated vinyl ether oligomers with functional groups.
Kinetics of polymerization by activated monomer mechanism
Authors: Biedron Tadeusz , Szymanski Ryszard , Kubisa Przemyslaw , Penczek Stanislaw 
Published: March 2011

AbstractPolymerization of cyclic ethers by activated monomer mechanism involves consecutive additions of protonated monomer molecules to the growing macromolecules fitted with hydroxyl groups at their ends. For oxirane itself and symmetrically substituted oxiranes there is only one kind of hydroxyl groups and one, unique way of ring‐opening. Unsymmetrically substituted oxiranes provide however two sites of attack and two different hydroxyls, resulting from these ring‐openings.Kinetics of polymerization of epichlorohydrin (chloromethyloxirane) has been studied and all four rate constants determined, namely rate constants of the primary and secondary alcoholate chain ends with a protonated monomer, opening in result of the attack on substituted or unsubstituted carbon atom. These rate constants are (in mol−1·1·s−1 at 25°C, in CH2Cl2 solvent): k11 = 0.055, k12 = = 0.41, k22 = 0.135, and k21 = 0.0011 (e.g. k12 is the rate of reaction of the primary alcohol producing the secondary alcohol). Thus, polymerization proceeds almost exclusively on the secondary alcoholate groups, reproducing themselves (k22).
Anionic and pseudoanionic polymerization of lactones ‐ a comparison
Authors: Kricheldorf Hans R. , Kreiser‐Saunders Ingrid , Scharnagl Nico 
Published: March 2011

AbstractPolymerization via anionic mechanisms or insertion mechanisms (pseudoanionic mechanisms) are compared for β‐lactones and L‐lactide. The following aspects are discussed: initiation and deprotonation of β‐lactones, back‐biting degradation, stereosequences of poly(β‐D,L‐butyrolactone), racemization of L‐lactide, systematic variation of endgroups including synthesis of macromers.
Eval membranes for blood dialysis
Authors: Chen Leo‐Wang , Young Tai Horng 
Published: March 2011

AbstractBoth dry‐ and wet‐process were employed for preparing membrane of ethylene‐vinylalcohol copolymer (EVAL) for blood dialysis.Asymmetric and symmetric, dense or porous membranes were prepared by the dry‐process. The relationship between the structure of membranes and the experimental variables is explained by using a solubility curve model. This model predicts the membrane structure successfully under various conditions, including the change of temperature of the environment, the solvent system and the temperature of polymer solution. For wet‐processes, the casting solutions were coagulated in a precipitation bath (water). Three different structures were obtained: finger type, sponge type and particle‐bonded type. The cloud point experiment and the polymer segment motion help to understand and control the membrane structure. Some properties of the EVAL membrane for blood dialysis are shown. It is comparable with or better than the commercialized one. This study may prove useful in determing the controlling parameters for the preparation of membranes from other polymers.
Synthesis and evaluation of polyamine graft and block copolymers as novel biomaterials for cell separation
Authors: Tsuruta Teiji 
Published: March 2011

AbstractGraft copolymer (HA) composed of 2‐hydroxyethyl methacrylate (HEMA) and a polyamine exhibits unique biospecific behavior at the interface with living cells. In the present paper, the writer will discuss on four topics : (i) effective separation of rat lymphocyte subpopulations by using HA copolymer; (ii) surface analysis of HA copolymers by ESCA and streaming potential measurements; (iii) a hybrid field flow fractionation/adhesion chromatography technique; and (iv) specific cellular recognition of poly(HEMA)‐graft‐quaternized polyamine copolymer (HQA)
Proton spin diffusion as a tool for characterizing polymer blends
Authors: VanderHart D. L. 
Published: March 2011

AbstractProton spin diffusion studies for characterizing minimum domain dimensions have been carried out on three blends: a 40/60 blend of nylon 6,6 with the aromatic rigid rod polymer poly(benzo[a,d]dithiazol‐2,6‐diyl‐1,4‐phenylene), PBZT, a 47/53 blend of an amorphous nylon with PBZT, and a 50/50 blend of a polyetherimide (PEI) and a polybenzimidazole (PBI). Polarization gradients necessary for these experiments were generated using both chemical shift differences (via multiple pulse techniques) and linewidth differences. Polarization readout techniques included proton lineshape deconvolution, multiple pulse proton lineshapes and 13C CPMAS spectra utilizing short CP times. The two nylon/PBZT blends are expected to phase separate from thermodynamic arguments; however, kinetic considerations, more than thermodynamics, determine domain size. In the 40/60 blend, the minimum domain dimensions of each of the nylon and the PBZT phases were about 4 nm with some scattered larger crystals of nylon. In the 47/53 blend, mixing in some regions indicated domain dimensions similar to the 40/60 blend. In contrast to the 40/60 blend, however, the 47/53 blend was still far from internal spin polarization equilibrium after spin diffusion times of 140 ms. The implication is that the sample‐average composition is not found over dimensions like 40 nm; the problem is that the possible morphological explanations are manifold. By investigating the proton rotating frame relaxation, T1p, the possibility that some of the PBZT domains are isolated from the nylon, in a spin diffusion sense, was eliminated. It is more likely that about half of the nylon protons are isolated by spin diffusion from the PBZT protons on a 140 ms timescale. The PEI/PBI blend is a compatible blend of two aromatic polymers where mixing on a molecular scale is expected. We were interested in a measurement of the lower limit of domain size using proton spin diffusion. This lower limit turned out to be about 2.5 nm based on low temperature T1p measurements as opposed to room temperature multiple pulse methods. The latter measurements monitored the disappearance of a polarization gradient between the PEI methyl protons and all the remaining protons. The superiority of the T1p measurements over the multiple pulse method for establishing the smaller minimum domain dimension is not a general result and reasons are discussed. Finally, some general remarks about characterizing polymer blends by solid state NMR, particularly blends which have undergone spinodal phase separation, are included.
1H spin‐lattice relaxation and observation of interfacial material in solid polyethylenes
Authors: Packer K. J. , Poplett I.J.F. , Taylor M. J. , Vickers M. E. , Whittaker A. K. , Williams K.P.J. 
Published: March 2011

AbstractThe 1H NMR laboratory‐ and rotating‐frame (LF,RF) spin‐lattice relaxation (SLR) behaviour in solid polyethylenes is reviewed in light of the two region spin diffusion coupled model. Highly crystalline high‐density materials show single T1 values indicative of the fast diffusion limit whilst RFSLR is close to the slow diffusion limit, allowing direct determination of the dimensions of the crystalline and disordered regions. The LFSLR and RFSLR of the HDPE's suggest the existence of an interfacial material which the SLR behaviour includes as part of the crystalline region in contrast to XRD and DSC. 13C CPMAS measurements of 1H RFSLR in a LLDPE provide an additional insight into this problem. The 1H RFSLR is best represented by a superposition of two exponentials, measured by either 1H or 13C NMR. The 1H RFSLR, measured at different chemical shifts in the 13C NMR spectrum, provides direct evidence of the interfacial material. The possible use of spin‐locking at angles other than 90° in the rotating frame to scale the spin diffusion rates is reviewed and its possible utility for LLDPE materials explored.
NMR investigations of polymer electrets
Authors: Geschke Dieter , Holstein Peter 
Published: March 2011

Abstract1H NMR investigations were performed on thin films of poly(vinylidene fluoride) (PVDF) and polyamide 11 (PA 11). The variation of the angle between the static magnetic Bo‐field and preferred directions given by drawing and poling leads to characteristic dependences of T20ff, which can be discussed in terms of Legendre polynomials of the orientational distribution functions of crystallographic c‐ and b‐axis. A good c‐axis alignment can be realized by uniaxial drawing. The tendency for b‐axis to orient towards the direction of the applied electric field via the orientation of the electric dipoles is evident. The b‐axis alignment can be “switched” periodically.
Relaxation spectrometry in solid polymers based on NMR and EPR measurements
Authors: Kashiwabara Hisatsugu , Shimada Shigetaka , Hori Yasurō 
Published: March 2011

AbstractWide distribution of relaxation times is taken into consideration in determination of the activation energy of the molecular motion associated with the motional narrowings of line widths of magnetic resonance spectra. The molecular motion of rotational vibration around the chain axis of polyethylene in urea‐polyethylene inclusion complex is examined. Relaxation spectra can be obtained from the data of the motional narrowings of EPR and NMR by assuming the activation energy as a parameter. Also, the representative relaxation times corresponding to EPR and NMR observations can be estimated. These relaxation times give us an activation energy since EPR and NMR observations correspond to different time constants of observations. The activation energy estimated from the data of the representative correlation times is identical with the activation energy obtained as a parameter in determination of the identical relaxation spectrum from the data of motional narrowings of EPR and NMR observations.
The measurement of diffusion and flow in polymer solutions using dynamic NMR microscopy
Authors: Xia Y , Callaghan P T 
Published: March 2011

AbstractThe new method of dynamic NMR microscopy has been used to obtain velocity and diffusion maps for polymer solutions in capillary flow. In particular we observe power law shear‐thinning behaviour in poly(ethylene oxide) (PEO) solutions in the semi‐dilute regime but without slip at the walls. Some evidence is apparent for enhanced solvent diffusion along the shear axis in region of high shear.
ESR and ESE studies on polymer semiconductors of weakly doped poly(tetrathiafulvalene)
Authors: Roth H.‐Klaus , Brunner Winfried , Völkel Georg , Schrödner Mario , Gruber Harald 
Published: March 2011

AbstractIn the studied poly(tetrathiafulvalenes), PTTF, the TTF units are linked via phenyl groups or via tetrahydroanthracene bridges. The PTTF are doped with oxygen and with iodine respectively. The electrical conductivity strongly depends on temperature as it is typical of semiconducting materials.The existence of various types of paramagnetic centres is confirmed by ESR saturation experiments, by spectra simulation and by electron spin echo (ESE) measurements in the temperature region of 2 K to 400 K. At room temperature the doped PTTF have a dc conductivity between 10−9 Scm−1 and 10−4 Scm−1.Relations between the concentration of various radicals and the electrical conductivity of the polymers are discussed by means of a model based on mobile and immobile radicals, polarons and bipolarons. There are experimental indications for temperature‐dependent formation and break‐up of bipolarons which are discussed in the paper.