Showing papers in "Polymer Bulletin in 1994"
TL;DR: In this article, a mixture of isotactic polypropylene, PP and atactic polystyrene (PS) was used to study the nucleation mechanism of immiscible melt mixed blends of a crystallisable polyolefin (isotactic PP) and PS in a wide composition range.
Abstract: Immiscible melt mixed blends of a crystallisable polyolefin (isotactic polypropylene, PP) and atactic polystyrene (PS) were prepared in a wide composition range. It was found that when PP is the major component in the blend its crystallisation behaviour is not affected by blending it with PS. However if PP is the minor component, it will be dispersed in the immiscible PS matrix, hence the nucleation mechanism changes from predominantly heterogeneous to predominantly homogeneous as long as the size of the dispersed PP droplets is below a critical value (of the order of 1–2 μm).
109 citations
TL;DR: In this article, a two-level fractional factorial design was used to assess the influence of selected experimental variables with respect to intermolecular transesterification, whose extent in the resulting high molecular weight poly(D,L-lactide)s (PLA50) was investigated by13C NMR.
Abstract: Racemic lactide (D,L-lactide) was bulk-polymerized comparatively using stannous octoate and zinc metal as initiators. A two-level fractional factorial design was used to assess the influence of selected experimental variables with respect to intermolecular transesterification, whose extent in the resulting high molecular weight poly(D,L-lactide)s (PLA50) was investigated by13C NMR. Five variables, namely polymerization temperature, monomer-to-initiator ratio, polymerization time, nature of the initiator and monomer degassing-time, were found significant and were ranked according to their average effect on transesterification. A significant interaction of polymerization temperature and polymerization time was also detected. Zinc led to lower stereoregularity than stannous octoate.
90 citations
TL;DR: In this paper, a new ethylene polymerization catalysts based on half-sandwich imido complexes of the Group 5 metals and bis(imido) complexes of Group 6 metals are described.
Abstract: New ethylene polymerization catalysts based on half-sandwich imido complexes of the Group 5 metals and bis(imido) complexes of the Group 6 metals are described.
80 citations
TL;DR: In this article, the water soluble poly(γ-glutamic acid) (γ-PGA) was synthetized by bacteria and a series of new, less water soluble α-esters were prepared by repeated esterification.
Abstract: The water soluble poly(γ-glutamic acid) (γ-PGA) was synthetized by bacteria. A series of new, less water soluble α-esters were prepared by repeated esterification. The characterization of the resulted polymers was performed by 200 MHz 1H and 75.4 MHz 13C NMR spectroscopy.
55 citations
TL;DR: In this paper, the thermal properties of hyperbranched polymers were studied with differential scanning calorimetry and three relaxation transitions were found in 5G-OH: α, the glass-rubber transition and two subglass processes denoted β and γ with an activation energy of 96±2kJ mol-1.
Abstract: Dielectric permittivity and loss have been measured over the frequency range 10-2 Hz-10 kHz between 100 K and 350 K for samples of 50/50 mixtures of each of two hyperbranched polyesters, one five-generation hydroxy functional (5G-OH) and one threegeneration alkyl-terminated polymer (3G), with dielectrically inactive linear polyethylene. The thermal transitions of the hyperbranched polymers were studied with differential scanning calorimetry. Three relaxation transitions were found in 5G-OH: α, the glass-rubber transition and two subglass processes denoted β and γ showing Arrhenius temperature dependence both with an activation energy of 96±2kJ mol-1. The low temperature process could be assigned to motions of the terminal hydroxyl groups whereas β is due to reorientation of the ester groups. Sample 3G showed only a glass transition and one subglass process being assigned to reorientation of the ester groups. The high activation energy (202 kJ mol-1) of this process indicates that the ester groups are highly constrained in this polymer.
52 citations
TL;DR: In this article, the authors applied liquid chromatography of polymers under limiting conditions of their solubility to poly(methyl methacrylate)s differing in their tacticity, and found that less soluble syndiotactic poly (methyl, methacylate) moved along the column together with the zone of its initial solvent.
Abstract: The unconventional liquid chromatography of polymers under limiting conditions of their solubility was applied to poly(methyl methacrylate)s differing in their tacticity. The polymers were dissolved in thermodynamically good solvents and injected into an appropriate size exclusion chromatographic (SEC) column flushed with matched, moderately strong nonsolvents. The set of (limiting) conditions was found under which less soluble syndiotactic poly(methyl, methacrylate) moved along the column together with the zone of its initial solvent while better soluble isotactic poly(methyl methacrylate) was eluted according to the SEC mechanism. This indicates the potential of liquid chromatography under limiting conditions to characterize the tacticity of poly(methyl methacrylate)s.
51 citations
TL;DR: In this article, the mixture of poly(ether imide) (PEI) and poly(ethylene terephthalate) (PET) was studied by differential scanning calorimetry (DSC), indicating that the blends are miscible in the amorphous region.
Abstract: Miscibility of blends of poly(ether imide) (PEI) and poly(ethylene terephthalate) (PET) were studied by differential scanning calorimetry (DSC). Single and composition-dependent Tg's are observed over the entire composition range, indicating that the blends are miscible in the amorphous region. The overall crystallization rate of PET in the blends decreased with increasing the PEI content. The interaction energy density B, which was calculated from the melting point depression of the blends using Nishi-Wang equation, was-5.5 cal/cm3.
51 citations
TL;DR: In this paper, the influence of several additives (liquid reactive rubbers or core-shell particles-CSR) on thermal and mechanical properties of an epoxy network based on diglycidyl ether of bisphenol-A (DGEBA) and dicy (DDA) is studied.
Abstract: The influence of several additives (liquid reactive rubbers or core-shell particles-CSR) is studied on thermal and mechanical properties of an epoxy network based on diglycidyl ether of bisphenol-A (DGEBA) and dicy (DDA). Using high speed stirring, without any solvent, a good dispersion of the CSR is achieved. It is shown that the glass transition temperature (Tg)of the networks decreases when liquid rubbers are added but remains constant with the addition of CSR. It is demonstrated that every kind of particles favors the shear yielding of the networks, and well fit a modified Von Mises criterion. The fracture energies increase with the addition of rubbers, especially for the rubber with the higher acrylonitrile content. The same toughening effect is obtained with CSR if compared to the lower acrylonitrile content of liquid reactive rubbers but without any decrease in Tg of the epoxy network.
50 citations
TL;DR: In this paper, reaction of succinic anhydride of the elastomer with the amine-endgroups of polyamide-6 enhanced PA-6 dispersion and proved to be the key to unusual property synergisms.
Abstract: Reactive blending of 70 vol.-% polypropylene (PP) and 30 vol.-% polyamide-6 (PA-6) was performed in the presence of various amounts of succinic-anhydride-functional elastomers which are immiscible with both blend components. Characteristic morphological feature of the resulting multiphase polymer blends was a continuous polypropylene matrix containing dispersed core/shell microparticles with rigid polyamide-6 core and soft elastomer shell. Accumulation of the elastomer component at the polypropylene/polyamide-6 interface and reaction of the succinic anhydride of the elastomer with the amine-endgroups of PA-6 enhanced PA-6 dispersion and proved to be the key to unusual property synergisms. In contrast to the conventional soft maleicanhydride-grafted EPM elastomer (EPM-g-MAH), the stiffer maleic-anhydride-grafted poly[styrene-b-(ethene-co-butene-1)-b-styrene] (SEBS-g-MAH) was much more efficient as blend compatibilizer and gave PP/PA-6 blends with greatly improved strength and toughness without sacrificing stiffness.
48 citations
TL;DR: In this paper, the effects of operation parameters on the surface composition and hydrophilicity of HDPE powder have been determined and the contact angle has been correlated with the composite parameter as: θ=90−6.64×10-3.
Abstract: A plasma surface treatment of HDPE has been carried out in a fluidized bed. The effects of operation parameters on the surface composition and hydrophilicity have been determined. The oxygen functionalities are formed at the outermost layer of HDPE powder. The hydrophobic surface of HDPE powder has been transformed to hydrophilic surface by the oxygen-plasma treatment in a fluidized bed. The contact angle of the plasma treated HDPE powder decreases linearly with radio frequency (rf) power but increases with O2 flow rate. Also, the angle decreases with increasing the composite parameter as the total plasma energy down to 6,000 [(W/FM)t]. The contact angle has been correlated with the composite parameter as: θ=90−6.64×10-3 [(W/FM)t].
44 citations
TL;DR: In this paper, a new family of ligands (dual σ-π ligand) was proposed to promote living anionic polymerization of methacrylic and acrylic esters, including a number of primary alkyl acrylates.
Abstract: A new family of ligands (dual σ-π ligand), i.e. chelating lithium alkoxides, Li-O-(CH2-CH2O)nCH3, is shown to be very effective in promoting the living anionic polymerization of methacrylic and acrylic esters, including a number of primary alkyl acrylates such as n-butyl acrylate and 2-ethylhexylacrylate.
TL;DR: The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship.
Abstract: The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.
TL;DR: The influence of binary mixtures of alcohols with different diluents on the porous structure of styrene-divinylbenzene (Sty-DVB) copolymers was investigated in this paper.
Abstract: The influence of binary mixtures of alcohols with different diluents on the porous structure of styrene-divinylbenzene (Sty-DVB) copolymers was investigated. Two series of binary mixtures were tested: one with isoamyl alcohol (i-AmA) and another with benzyl alcohol (BA). For systems containing i-AmA, the hydrogen bonds between alcohol and polar solvent molecules exert strong precipitating effects. Copolymers prepared with polar solvent/i-AmA presented higher porosities than copolymers obtained in presence of nonpolar solvent/i-AmA. Binary mixtures with i-AmA produced more porous and rigid networks than with BA.
TL;DR: In this paper, a ruthenium catalyzed regioselective copolymerization reaction between acetophenone and α,ω-dienes such as divinyltetramethyldisiloxane and divinyldimethylsilane was reported.
Abstract: This paper reports a novel ruthenium catalyzed regioselective copolymerization reaction between acetophenone and α,ω-dienes such as divinyltetramethyldisiloxane and divinyldimethylsilane which leads respectively to copoly(3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene/2-acetyl-1,3-phenylene) and copoly(3,3-dimethyl-3-sila-1,5-pentanylene/2-acetyl-1,3-phenylene). This reaction involves the ruthenium catalyzed insertion of the carbon-carbon double bonds of α,ω-dienes into the aromatic C−H bondsortho to the acetyl group of acetophenone. Similar ruthenium catalyzed reactions between acetophenone and alkenes to yield monomericortho alkyl substituted acetophenones have been recently reported.1
TL;DR: In this paper, a Monte-Carlo simulation procedure of kinetically controlled structure growth including network formation determined by generalized Smoluchowski equations was described, where the random number generator selects a certain reaction event characterized by its rate out of all possible events at four decision levels, reaction mechanism, types of reacting groups, selection of molecule and its reaction partner.
Abstract: A Monte-Carlo simulation procedure of kinetically controlled structure growth including network formation determined by generalized Smoluchowski equations was described. In addition to intermolecular reactions affected by possible time and space long-range correlations, cyclization or degradation reactions can be considered. The kernel of these reactions can be a function of not only the numbers and types of the reactive groups but also of the composition and structure of the molecule. The random number generator selects a certain reaction event characterized by its rate out of all possible events at four decision levels, (1) reaction mechanism, (2) types of reacting groups, (3) selection of molecule and (4) its reaction partner
TL;DR: In this article, an attempt is made to extend the model of Leibler for the emulsifying activity and interfacial properties of A-b-B diblock copolymers.
Abstract: An attempt is made to extend the model of Leibler for the emulsifying activity and interfacial properties of A-b-B diblock copolymers in incompatible blends of the homopolymers A and B-which are identical with the respective copolymer components- to enthalpically interacting C-b-D diblock copolymers, the block C being thermodynamically compatible with A and D with B. Due to the attractive enthalpic interaction the A/C-b-D/B compatibilized blends are promising for optimum phase adhesion (bold types for thermodynamically compatible partners). Thus, the extended model for a plane interfacial layer includes the enthalpic interaction of the compatible polymer pairs beside the entropic effects. The approach starts with the equillibrium supposition, not taking into consideration enthalpy driven migration effects of the block copolymer from the bulk to the interface, The model confirms a dominant role of the enthalpic interaction between blocks of the diblock copolymer and the respective homopolymers to the compatibilization of incompatible blend components. It is applicable also for blends compatibilized with block copolymers of unfavourable repulsive type interaction, A/C-b-D/B, and for blend systems with mixed type interactions, e. g. A/C-b-B/B or A/C-b-D/B.
TL;DR: In this paper, the influence of crystallinity of the matrix, type of rubber and chain architecture on the impact resistance of the resulting materials was investigated and a poly(l-lactide-co-e-caprolactone) rubber semi-crystalline poly(Lactide)s could be impact modified to a greater extent than amorphous noncrystallizable lactide matrices, and linear and star-shaped block copolymers which yield supertough materials that do not break in Izod notched impact testing.
Abstract: Semi-crystalline and amorphous copolymers of lactide and glycolide were rubber modified with degradable rubbers based on e-caprolactone. The influence of crystallinity of the matrix, type of rubber and chain architecture on the impact resistance of the resulting materials was investigated. With a poly(l-lactide-co-e-caprolactone) rubber semi-crystalline poly(lactide)s could be impact modified to a greater extent than amorphous non-crystallizable lactide matrices. Poly(trimethylene carbonate-co-e-caprolactone) was used in blends and linear and star-shaped block copolymers which yield supertough materials that do not break in Izod notched impact testing. Rubber content appears critical around 20 weight percent, where a sharp transition is observed.
TL;DR: In this article, a mixture of benzene and cyclohexane was used for pervaporation processes and the coordination of the feed with cobalt in the membrane played a major role in the separation of the mixture.
Abstract: Chelate poly(vinyl alcohol)/poly(allyl amine) blend membrane was prepared and used for the separation of benzene/cyclohexane mixture by pervaporation processes. The coordination of benzene in the feed with cobalt in the membrane plays a major role in the separation of the mixture. Chelate poly(vinyl alcohol)/poly(allyl amine) blend membrane showed a preferential sorption toward benzene and was found to be more effective for permeating benzene in the benzene/cyclohexane mixture than an original Schiff base poly(vinyl alcohol)/poly(allyl amine) membrane.
TL;DR: In this article, commercial samples of hydroxyl terminated polybutadienes (HTPB) were analyzed by 1H and 13C NMR spectroscopy, in regard to their end groups.
Abstract: Commercial samples of hydroxyl terminated polybutadienes (HTPB) were analysed by 1H and 13C NMR spectroscopy, in regard to hydroxylated end groups. The results were discussed and compared with those reported so far.
TL;DR: In this article, a heterotactic polymerization of methyl methacrylate (MMA) withtert-butyllithium (t-C4H9Li) in toluene in the presence of aluminum alkoxides such as ethoxide, tert-butoxide and 2,6-di-tert butylphenoxide, were examined at various Al/Li ratios.
Abstract: Polymerization of methyl methacrylate (MMA) withtert-butyllithium (t-C4H9Li) in toluene in the presence of aluminum alkoxides such as ethoxide,tert-butoxide and 2,6-di-tert-butylphenoxide, were examined at various Al/Li ratios. In the cases of ethoxide andtert-butoxide, predominantly isotactic polymers with broad molecular weight distribution were obtained. Combinations oft-C4H9Li and bis(2,6-ditert-butylphenoxy)methylaluminum [MeAl(ODBP)2] were found to be an efficient initiating system for heterotactic polymerization of MMA, which gives PMMA rich in heterotactic triads up to 68% with narrow molecular weight distribution (Mw/Mn=1.09−1.17). End group analysis by1H NMR indicated thatt-C4H9Li initiates the polymerization and MeAl(ODBP)2 works as a stereospecific modifier. From stereosequence analysis of the heterotactic PMMA by13C NMR, it was found that the calculated pentad fractions from the first-order Markovian statistics (Pm/r=0.742, Pr/m=0.627) fitted the observed ones better than those from Bernoullian statistics. The glass transition temperature of the heterotactic PMMA was 13°C lower than that of syndiotactic PMMA, and the intrinsic viscosity in tetrahydrofuran was close to that of isotactic PMMA with a similar molecular weight but higher than that of syndiotactic PMMA.
TL;DR: In this article, polymerizable surfactants derived from maleic anhydride have been synthesized and the hydrophilic part is obtained by a controlled ethylene oxide polymerization according to a new heterogeneous catalytic process.
Abstract: Polymerizable surfactants derived from maleic anhydride have been synthesized. The hydrophilic part is obtained by a controlled ethylene oxide polymerization according to a new heterogeneous catalytic process. Some maleates derivatives have been obtained and fully characterized by 1H and 13C NMR. Their cmc were also measured. Some of them have been engaged in styrene emulsion polymerization in which monodisperse latex particles have been produced.
TL;DR: In this article, a Monte-Carlo simulation procedure of kinetically controlled structure growth including network formation determined by generalized Smoluchowski equations was described, where the random number generator selects a certain reaction event characterized by its rate out of all possible events at four decision levels, reaction mechanism, types of reacting groups, selection of molecule and its reaction partner.
Abstract: A Monte-Carlo simulation procedure of kinetically controlled structure growth including network formation determined by generalized Smoluchowski equations was described. In addition to intermolecular reactions affected by possible time and space long-range correlations, cyclization or degradation reactions can be considered. The kernel of these reactions can be a function of not only the numbers and types of the reactive groups but also of the composition and structure of the molecule. The random number generator selects a certain reaction event characterized by its rate out of all possible events at four decision levels, (1) reaction mechanism, (2) types of reacting groups, (3) selection of molecule and (4) its reaction partner.
TL;DR: In this paper, the HI/ZnI2 system was used to produce living polyvinyl ethers bearing a fluoroalkyl group, which is free from chain transfer and termination reactions.
Abstract: Cationic polymerization of 1H,1H,2H,2H perfluorooctyl vinyl ether (CH2=CH-O-C2H4-C6F13), initiated by the HI/ZnI2 system in 1,1,2 trichloro trifluoro ethane at-30°C, leads to living polyvinyl ethers bearing a fluoroalkyl group. Results indicate that the polymerization is indeed free from chain transfer and termination reactions and that polyethers of controlled molecular weight and a narrow molecular weight distribution can be made available.
TL;DR: In this paper, a poly(ethylene oxide) with a primary amino group at one end and a hydroxyl group at the other terminus were synthesized with new sila-protected amino functionality initiator, potassium N-[2,2,5, 5,5-tetramethyl-1-aza-2-5-disilacyclopentyl)-ethyl amide.
Abstract: Well-defined poly(ethylene oxide)s with a primary amino group at one end and a hydroxyl group at the other terminus were synthesized with new sila-protected amino functionality initiator, potassium N-[2-(2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentyl)-ethyl]methyl amide [1b]. 1b initiated an anionic polymerization of ethylene oxide (EO) to form a polymer (PEO) without any side reactions such as a cleavage reaction of protective group and a chain transfer reaction. The molecular weights of the PEO determined from GPC and MALDI TOF-MS spectrometry agreed well with those from end group analysis using 1H and 13C NMR and TLC and also with the expected value from EO/initiator ratio. From these results, it was concluded that the polymers thus obtained had a primary amino group at one end and a hydroxy group at the other end and can be regarded as hetrobifunctional PEO.
TL;DR: In this article, the tensile strength of poly(3-hydroxybutyrate) and copolymer was investigated by measuring Young's modulus and molar mass after different periods of thermal treatment at temperatures slightly above their melting temperatures.
Abstract: Microbially produced poly(3-hydroxybutyrate) (P(3HB)) and a copolymer were investigated by measuring tensile strength, Young's modulus and molar mass after different periods of thermal treatment at temperatures slightly above their melting temperatures in order to describe the changes of molecular and mechanical properties. The tensile strength turns out to be strongly influenced by time and temperature of heat treatment. After a heat treatment for 10 min at 190 °C the tensile strength drops to 30% of its initial value.
TL;DR: In this paper, the effects of the solvating power of pure diluents on the porous structure and swelling properties of styrene-divinylbenzene copolymers were investigated.
Abstract: The effects of the solvating power of pure diluents on the porous structure and swelling properties of styrene-divinylbenzene (Sty-DVB) copolymers were investigated. The Hildebrand solubility parameter (δ) and the three-dimensional solubility parameter (δ T ) were used to predict the diluent-polymer affinity. In a general way, δ T was a better predictor than δ. It was found that the accessibility of polymer surfaces depends not only on the fixed pore volume but also on the elasticity of internuclear chains
TL;DR: In this article, a commercial hydroxyl terminated polybutadiene (HTPB) produced by Brazilian technology is characterized with respect to molecular weight, functionallty, microstructure and hydroxy group types.
Abstract: Liquiflex is a commercial hydroxyl terminated polybutadiene (HTPB) produced by Brazilian technology. It was characterized with respect to molecular weight, functionallty, microstructure and hydroxyl group types. The results were compared with those obtained for R45M and R45TH Atochem products. A mechanistic approach for the polymerization reaction is presented
TL;DR: In this paper, the structures, conductivities and heat resistant properties of poly(naphthalene) films obtained from the described medium composed many parallel arranged polymer layers were also studied.
Abstract: Poly(naphthalene) (PN) has been deposited on a platinum electrode by direct oxidation of naphthalene in BF3-ethyl ether solution containing 5×10-3 mol/l water. Experimental results demonstrated that the PN films obtained from the described medium composed many parallel arranged polymer layers. The structures, conductivities and heat resistant properties of the PN products were also studied.
TL;DR: In this article, a photo-initiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO2.
Abstract: Methacrylic acid was photopolymerised using CdS and composite, CdS/HgS and CdS/TiO2, colloidal semiconductor particles as initiators. The previously proposed photoinitiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO2. The effect of pH on the course of the polymerisation was investigated and is discussed.
TL;DR: In this article, the β transition of a poly(vinyl chloride) after either nucleophilic substitution to various extents or plasticization with distinct amounts of diocytl phthalate has been measured by Dynamical Mechanical Thermal Analysis.
Abstract: The β transition of a poly(vinyl chloride) after either nucleophilic substitution to various extents or plasticization with distinct amounts of diocytl phthalate has been measured by Dynamical Mechanical Thermal Analysis. Both sets of experiments are shown to result in similar loss of β transition. The results are argued in the light of prior work on the substitution mechanism determining role of the mmr chain segments at the end of isotactic sequences. They strongly suggest the mmr structures to interact specifically with plasticizer thereby becoming stiffer (antiplasticization).