bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological basis for the complex melting behaviour of isotactic polystyrene
Authors: Al-Hussein Mahmoud , Strobl Gert 
Published: August 2014

AbstractTemperature-dependent small-angle X-ray scattering spectroscopy of isothermally cold crystallized isotactic polystyrene revealed considerable morphological reorganization during subsequent heating to the melt. Both the crystalline thickness and the long period increased continuously with increasing temperature before the samples finally melted. The temperature dependence of these changes correlated very well with the melting behaviour observed with differential scanning calorimetry. As the temperature increased during a heating scan, the initial lamellae that formed during isothermal crystallization showed only little reorganization until they started to melt. Then, the molten material recrystallized continuously into increasingly thicker lamellae at increasing temperature until they finally melted. As the crystallization temperature approached the final melting temperature of the recrystallized lamellae, the initial lamellae melted without further recrystallization and no morphological changes were seen in this case.
Change of modulus and yielding properties of syndiotactic polypropylene with the glass transition
Authors: Men Yongfeng , Strobl Gert , Wette Patrick 
Published: August 2014

AbstractSemi-crystalline polymers like syndiotactic polypropylene pass during tensile deformation different stages with cross-overs at four critical points. Temperature variation above ambient changes the stresses at the critical points, but leaves the strains constant. Cooling down to the glass transition leads to the following changes: Fracture occurs before the onset of strain hardening. Yield point strain shifts to lower values. Young’s modulus increases by a factor on the order of the inverse of the crystallinity, as can be expected when the amorphous regions also contribute to the transmission of forces.
Simulation of size exclusion chromatography for branched polymers formed by simultaneous long-chain branching and random scission
Authors: Tobita Hidetaka , Kawai Hideki 
Published: August 2014

AbstractIn free-radical olefin polymerization, polymer transfer reactions can lead to chain scission as well as to the formation of long-chain branches. The dimensions of branched polymers so formed are investigated theoretically, by focusing our attention on the effects of scission frequency that is often difficult to determine. Scission reactions decrease the weight-average molecular weight significantly. When the polymer molecules are fractionated by the degree of polymerization (DP), however, the averages of branching density P ρ ̅and the mean-square radius of gyration of polymers with DP = P, <s2>P, are essentially unchanged, as long as the scission frequency is not very large. In a simple relationship between the ratios g and g’ of radii of gyration and hydrodynamic radii, g’ = gb, the value of b may change as a function of DP, and a simplified model function b = A log P + B was used to investigate the elution curve of size exclusion chromatography (SEC). It is shown that, although the molecular weight distribution (MWD) calibrated relative to standard linear polymers in SEC is much narrower than the true MWD, the use of a light scattering photometer to determine the absolute weight-average molecular weight within the elution volume makes the obtained MWD very close to the true one. On the basis of the <s2>P vs. P relationship, the calibrated MWD can be converted reasonably well to the true MWD. This simplified transformation method can be applied without knowing the scission frequency or the DP dependence of b. Once the true MWD is successfully estimated, a reliable parameter for the scission reaction can be determined.
Miscibility in blends of poly(ethylene-co-vinyl nitrate) and poly(vinyl methyl ketone)
Authors: Kondo Masashi , Akiba Isamu , Akiyama Saburo 
Published: August 2014

AbstractThe miscibility and interactions of poly(vinyl nitrate) (PVN) / poly(vinyl methyl ketone) (PVMK) and poly(ethylene-co-vinyl nitrate) (EVN) / PVMK blends were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). PVN/PVMK blends were found to be miscible in the entire composition and temperature range. In addition, the compositional dependence of the glass transition temperature showed a positive deviation from the linear additivity rule, a phenomenon normally associated with compounds having attractive interactions. However, in this case, no attractive interactions between PVN and PVMK were identified by FTIR analyses. On the other hand, EVN/PVMK blends were found to be immiscible for most copolymer compositions, blend compositions and temperature ranges. Furthermore, intramolecular repulsive interactions of EVN were not apparent despite strong contrary expectations. Therefore, the phase behaviour in these blends was explained by a miscibility mechanism different from that of conventional polymer blends containing random copolymers.
Liquid crystalline vinylcyclopropane derivatives bearing cholesteryl side groups: synthesis, characterization and polymerization
Authors: Alupei Valentina , Ritter Helmut 
Published: August 2014

AbstractNew optically active 1,1-disubstituted 2-vinylcyclopropanes ,3a, b were synthesized by esterification of the corresponding 1-ethoxycarbonyl-2-vinylcyclopropane- 1-carboxylic acid 2a,b with cholesterol and characterized by 1H NMR and IR spectroscopy. The liquid crystalline properties of the obtained monomers are reported. The effect of the structure of the 2-vinylcyclopropane monomers on the phase transition of the mesogen was investigated. Radical polymerization of the asymmetrically substituted monomers 3a,b in solution and in bulk resulted in liquidcrystalline polymers with 1,5-opened units, as evidenced by 1H NMR spectroscopy.
Self-organized structures of hydrogen bonded poly(4-vinylphenol) - tertiary amino lipid mixtures
Authors: Akiba Isamu , Sakurai Kazuo 
Published: August 2014

AbstractMesomorphic structures of hydrogen bridged poly(4-vinylphenol) - N,N-dimethyl- n-octadecylamine (PVPh-NDOA) and PVPh - N,N-dioctadecylmethylamine (PVPh-DOMA) mixtures were investigated by means of wide angle X-ray diffraction, small angle X-ray scattering, and IR spectroscopy. Octadecyl chains of the PVPh-NDOA and PVPh-DOMA mixtures showed hexagonal αH and orthorhombic βO packing, respectively. In addition, PVPh-NDOA and PVPh-DOMA formed lamellar structures with periods of 3.5 and 2.5 nm, respectively.
Preparation of cellulose acetate films with controlled porosity
Authors: Estrada Rodolfo-Fabian , Alvarez-Gayosso Carlos , Castaño Victor M. 
Published: August 2014

AbstractPorous polymeric films were obtained by immersing a solution of cellulose acetate and high molecular weight poly(acrylic acid) into an ice-water mixture. The films, the porosity of which can be controlled (reversibly) by immersion into hot water for varying periods of time, were characterized by IR spectroscopy and lowvacuum scanning electron microscopy.
Kinetic parameter estimation using an adiabatic reaction, with validation using NIR spectroscopy, 1 Application to a macrodiol / isocyanate polyurethane formulation
Authors: Dupuy Jérôme , Maazouz Abderahim , Benali Samira 
Published: August 2014

Abstract A kinetic model of the cure of a polyurethane formulation is determined by the evolution of the conversion calculated during adiabatic experiments. The identified kinetic parameters are validated with two different methods: i) by comparing the simulated and measured evolutions of the conversion rates during these adiabatic reactions, ii) by comparing the simulated and measured (using NIR spectroscopy) evolution of the conversion into a mould during a RIM process.
Degradation of chitosan in the presence of poly(vinyl alcohol) and poly(acrylic acid) by a crude enzyme complex from Trichoderma viride
Authors: Paneva Dilyana , Mincheva Rosica , Stoilova Olya , Manolova Nevena , Rashkov Iliya 
Published: August 2014

Abstract The degradation of chitosan in the presence of poly(vinyl alcohol) (PVA) or poly(acrylic acid) (PAA) by a crude enzyme complex from Trichoderma viride was studied. It was found that neither PVA nor PAA suppress chitosan hydrolysis. By varying the experimental conditions, the optimal conditions for chitosan degradation in the presence of PVA (37°C, pH 6) or PAA (37°C, pH 4) were found. The biocontrol agent T. viride was embedded in films of chitosan, PVA, chitosan/PVA and chitosan/PAA. Microbiological tests showed that T. viride retained its ability to develop and reproduce in all studied film types. The obtained results imply that the prepared systems are appropriate carriers of biocontrol agents and might be used as novel agropharmaceuticals.
Convenient synthesis of a surface-active alkoxyamineinitiator from styrene oxide Living/free-radical polymerization of styrene and n-butyl acrylate
Authors: Beyou Emmanuel , Humbert Julien , Chaumont Philippe 
Published: August 2014

Abstract A novel alkoxyamine based on N-tert-butyl-1-diethylphosphono-2,2- dimethylpropyl nitroxide (DEPN) has been designed with a functional group, which promotes the chemisorption of free silanols from silicon surface and organicinorganic hybrid materials by a sol-gel process. This alkoxyamine has been synthesized in high yield from styrene oxide and has been employed for the nitroxide-mediated polymerization of styrene and n-butyl acrylate. The resulting alkoxysilane-containing homo- and copolymer precursors have been shown to have narrow molecular weight distributions.
Polyolefin structural control using phenoxy-imine ligated group 4 transition metal complex catalysts
Authors: Matsukawa Naoto , Ishii Sei-ichi , Furuyama Rieko , Saito Junji , Mitani Makoto , Makio Haruyuki , Tanaka Hidetsugu , Fujita Terunori 
Published: August 2014

Abstract This paper describes the structural control of polyolefins achieved by using group 4 transition metal complex catalysts featuring a pair of phenoxy-imine chelate ligands (named FI catalysts). FI catalysts can produce very low to ultrahigh molecular weight polymers. For example, a Zr-FI catalyst bearing a cycloalkyl group on the imine-nitrogen with methylaluminoxane (MAO) activation is capable of selectively forming vinyl-terminated low molecular weight polyethylenes (Mw < 5000) whereas a Zr-FI catalyst with a triethylsilyl group ortho to the phenoxyoxygen can generate ethylene/propylene amorphous copolymers with ultra-high molecular weights (Mw > 10 000 000) when treated with iBu3Al / Ph3CB(C6F5)4. In addition, a Ti-FI catalyst, possessing an o-phenoxytrimethylsilyl group, with MAO can form highly syndiotactic polypropylenes ([rrrr] = 84%, Tm = 140°C) via a chainend control mechanism. Conversely, upon activation with iBu3Al / Ph3CB(C6F5)4, a Hf-FI catalyst with a tert-butyl group ortho to the phenoxy-oxygen is able to produce high molecular weight isotactic polypropylenes ([mm] = 69%, Tm = 124°C, Mw = 412 000) via a site control mechanism. Therefore, FI catalysts have shown the ability to create various polyolefin architectures by simple variation of the central metal, the ligand structure and the co-catalyst.
Morphology and mechanical properties of transcrystalline isotactic polypropylene
Authors: Nitta Koh-hei , Yamamoto Yoshikazu 
Published: August 2014

Abstract We examined mechanical and morphological properties of fully transcrystalline polypropylene grown from the surface of poly(tetrafluoroethylene) sheets. Comparison of mechanical properties between transcrystalline and spherulitic polypropylenes demonstrated that Young’s modulus is dependent on the crystallinity and independent of the supermolecular structure. On the other hand, the mechanical yielding process was predominantly affected by the supermolecular structure, and the mechanical energy required for yielding of transcrystalline sheets was greater than that of the spherulitic morphology. In addition, it was found that mechanical necking is required for the alignment of lamellae in the stretching direction. This means that the unfolding process of lamellae orienting in the stretching direction is associated with necking and ductility.
Viscometric investigations on the intrinsic viscosity of polyvinylpyrrolidone affected by polymer-polymer interactions in solution
Authors: Al-Azhar Omar Melad 
Published: August 2014

AbstractThe intrinsic viscosity of polyvinylpyrrolidone (PVP) and various added polymers was investigated by the polymer-solvent method. It has been found that both polymer-polymer interactions and the concentration of the added polymer affect the intrinsic viscosity of PVP. In the ‘polymer-solvent’ system poly(methyl methacrylate) + dimethylformamide (PMMA+DMF), the intrinsic viscosity of PVP decreases as the concentration of PMMA increases, showing that the repulsive interaction between PVP and PMMA originates from the contraction of PVP coils in solution due to the intermolecular excluded volume. However, in the polymersolvent systems poly(vinyl chloride) (PVC) + DMF or poly(vinylidene fluoride) (PVDF) + DMF, the attractive interactions between PVP and PVC or PVDF cause an expansion of PVP coils in solution at high concentrations of PVC or PVDF. The polymer-solvent method allows estimating the compatibility of the used polymers.
Synthesis and characterization of poly(ethyl glyoxylate) – a new potentially biodegradable polymer
Authors: Burel Fabrice , Rossignol Laetitia , Pontvianne Pascale , Hartman Jonas , Couesnon Nicole , Bunel Claude 
Published: August 2014

Abstract Poly(ethyl glyoxylate) (PEtG), a new polyacetal, was synthesized via anionic polymerization in CH2Cl2. End-capping was achieved using phenyl isocyanate. Average molecular weights in the range of 9000 - 216 000 were obtained. 1H and 13C NMR characterization highlight the non-stereoregularity of PEtG. The polymer is quasi-atactic and the polymerization almost followed a Bernoulli process. Compared to its homologue poly(methyl glyoxylate), PEtG exhibits enhanced thermal stability (>200°C) and a lower glass transition temperature, Tg. Molecular weight influences Tg, but does not affect thermal stability.
Kinetics of non-isothermal melting and crystallization of gamma-irradiated isotactic polypropylene
Authors: Nedkov Emanuel , Dobreva Tatyana 
Published: August 2014

Abstract The non-isothermal kinetics of melting and crystallization of gamma-irradiated isotactic polypropylene were investigated by differential scanning calorimetry. At constant temperature the melting rate increased with the dose. During the melting, the average lamellar thickness, the free surface energy and the transport energy through the phase boundary reduced with increasing the dose. The crystallization rate decreased with increasing dose at constant temperature. Mixed α-γ spherulites were grown during crystallization. The non-isothermal crystallization rate expressed, in fact, the rate of secondary nucleation of the lamellae in the spherulites and their growth. Raising the irradiation doses led to a decrease of the crystallization temperature. A critical dose of irradiation of about 200 kGy was found, where the dependences of the calculated kinetic parameters underwent an important change. This change could be successfully connected with the effect of radiation annealing and melting.
Monitoring the chemical heterogeneity of metallocenecatalysed copolymers of ethylene and higher 1-olefins using CRYSTAF and SEC-FTIR
Authors: Graef Sven M. , Brüll Robert , Pasch Harald , Wahner Udo M. 
Published: August 2014

Abstract Copolymers of ethylene with 1-decene, 1-tetradecene and 1-octadecene were prepared using the catalyst system racEt[Ind]2ZrCl2/MAO and were analysed with regard to chemical heterogeneity using crystallisation analysis fractionation (CRYSTAF), differential scanning calorimetry (DSC) and size exclusion chromatography coupled to FTIR (SEC-FTIR). The melting and crystallisation temperatures from DSC decrease linearly with increasing amount of comonomer, independently of the nature thereof. The decrease in crystallisation temperature from CRYSTAF of copolymers with higher 1-olefin content indicates a small dependence on the length of the side chain. The chemical heterogeneity of the copolymers as analysed by DSC and CRYSTAF broadens with increasing comonomer concentration.
Effect of SBS compatibilizer on the interphase boundary of polymer blends of polystyrene and natural rubber
Authors: Boyanova Mileta , Mina Mohammed Forhad , Calleja Francisco José Baltá , Fakirov Stoyko 
Published: August 2014

Abstract Microhardness (H) has been used to quantitatively characterize the quality of the interphase boundary of blends of atactic polystyrene (PS) with natural rubber (NR) and the compatibilizer styrene-butadiene-styrene (SBS) block copolymer. Qualitative conclusions are drawn for the same purpose from scanning electron microscopy (SEM) observations on surface indentation. Cast films of neat PS and the blends PS/NR, PS/SBS and PS/NR/SBS were prepared from a common solvent (toluene). While neat PS shows a constant H = 175 MPa, the PS/SBS blend exhibits a gradual decrease starting from H = 130 - 140 MPa at a distance of about 100 μm from the phase boundary up to the final value of 25 MPa. For the PS/NR blend this decrease starts at about 50 μm, reaching the same final value. Owing to the elastic recovery, no indentations on the NR or SBS particles surface can be detected as confirmed by SEM. The compatibilized blend PS/NR/SBS is characterized by the thinnest phase boundary (about 25 μm) and a final H value of 75 MPa which demonstrates that the compatibilizer SBS is distributed just on the phase boundary between PS and NR. Results confirm previous findings in incompatible blends of poly(methyl methacrylate)/NR, highlighting that microindentation is a sensitive tool for studying the breadth and quality of the interphase boundary in compatibilized or non-compatibilized polymer blends and other non-homogeneous materials. This technique allows, in addition, the localization of the compatibilizer in the polymer blends.
Organisation and melting of solution grown truncated lozenge polyethylene single crystals
Authors: Tian Mingwen , Loos Joachim 
Published: August 2014

Abstract Morphological features and the melting behaviour of truncated lozenge crystals have been studied. For the crystals investigated, the heights of the (110) and the (200) sectors were measured to be 14.5 and 12.7 nm, respectively, using atomic force microscopy (AFM) in contact and non-contact mode. Moreover, melting temperatures of 123°C for the (110) sector and of 120°C for the (200) sector have been measured using real-time AFM during annealing experiments. Applying atomic force acoustic microscopy and the n-alkane decoration technique, no difference in the surface fold organisation of (110) and (200) sectors could be detected. For similar stem lengths, variations in stem tilt angle within the sectors might cause the thickness difference observed. However, a very high tilt angle difference above 20° is required. More likely, a shorter stem length within the (200) sector may cause its lower melting temperature.
Effect of polymerization sequence on the electrochemical properties of polypyrrole / poly(3-methylthiophene) bilayers
Authors: Ayoub Samira , Dias Bruna L. , Mascaro Lucia H. , Micaroni Liliana , Gazotti Wilson A. 
Published: August 2014

Abstract The electrochemical and photoelectrochemical characteristics of conducting polymer bilayers composed by polypyrrole, PPy, and poly(3-methylthiophene), PMeT, are described. The bilayers were produced by galvanostatic deposition of the polymers using different charge densities. Scanning electron micrographs indicate that the sequence of polymerization affects the surface morphology of the bilayers and, while PMeT polymerizes into the pores of the PPy film, a PPy film is formed over the PMeT film. Cyclic voltammetry of the bilayers shows the peaks corresponding to PPy and PMeT, regardless of the sequence of deposition; however, the potentials of redox processes are slightly shifted. The sequence of polymer deposition also affects the photoelectrochemical properties of the bilayers. The results show that, for a bilayer with PMeT as inner polymer and PPy as outer polymer, an enhanced photocurrent can be obtained by controlling polymer film thickness.
Frontal atom transfer radical polymerization of tri(ethylene glycol) dimethacrylate
Authors: Bidali Simone , Fiori Stefano , Malucelli Giulio , Mariani Alberto 
Published: August 2014

Abstract The first frontal atom transfer radical polymerization (FATRP) has been successfully carried out using tri(ethylene glycol) dimethacrylate as a monomer. The effect of the catalyst/initiator ratio has been investigated and related to the front velocity and its maximum temperature. By comparing this new approach with classical radical polymerization routes and with conventional frontal polymerization, it was found that the so-obtained polymer is characterized by higher conversion, shorter reaction times, higher degradation temperature, and does not contain entrapped bubbles.
Synthesis and characterisation of propene / higher 1-olefin copolymers with the catalyst system (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2/MAO
Authors: Brüll Robert , Luruli Nyambeni , Pasch Harald , Raubenheimer Helgard G. , Sadiku E. Rotimi , Sanderson Ron , Reenen Albert J. van , Wahner Udo M. 
Published: August 2014

Abstract The melting and crystallization behaviour of random copolymers of propene with 1-butene, 1-pentene and 1-hexene synthesized with the catalyst system (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2/methylaluminoxane (MAO) were investigated by differential scanning calorimetry and crystallization analysis fractionation (CRYSTAF). The melting and crystallization temperatures decreased linearly with increasing comonomer content. The depressions of the melting and crystallization temperatures are strongly dependent on the nature of the monomer and are more pronounced for copolymers of propene with 1-hexene than with 1-butene. In comparison to 1-hexene and 1-butene, the incorporation of 1-pentene leads to an intermediate behaviour. This is in contrast to the behaviour of copolymers of propene with longer chain 1-olefins, where the melting and crystallization temperatures are independent of the comonomer type. The depressant effects of the amount of comonomer incorporated on the melting and the crystallization temperatures are equal.
End-group interchain exchange reaction in polymer blends: evolution of the block weight distribution
Authors: Kudryavtsev Yaroslav V. , Govorun Elena N. 
Published: August 2014

Abstract The kinetics of interchain exchange reactions proceeding via end-group mechanism in homogeneous polymer blends is studied theoretically. A set of kinetic equations describing the evolution of the block weight distribution is derived. It is demonstrated that the process may be divided into a fast and a slow stage. The fast stage is characterized by alteration in the fractions of end sequences of different type. At the same time most of the homopolymer chains transform into copolymer with block weight distribution close to the Flory distribution. In the course of the subsequent slow stage, the distribution shape is preserved, with average block lengths gradually decreasing to the values typical of the completely random copolymer. The copolymer composition is found to change mostly in the course of the fast stage of the process. The possibilities of using kinetic data for the discrimination between end-group and direct interchange mechanisms are discussed.