Showing papers in "Polymer International in 1992"
TL;DR: In this article, seven experimental criteria for living polymerization are critically reviewed and the experimental criteria of using narrow molecular weight distribution and the formation of block copolymers are illustrated with practical examples and size exclusion chromatography data.
Abstract: Seven experimental criteria for living polymerizations are critically reviewed. The limitations of the use of linear plots of Mn (or X;n) versus conversion and linear plots of the number of polymer chains versus conversion are illustrated by an example of alkyllithium-initiated polymerization of styrene by incremental additions of styrene with deliberate termination (5% per incremental monomer addition). The experimental criteria of using narrow molecular weight distribution and the formation of block copolymers are illustrated with practical examples and size exclusion chromatography data. The use of the terms ‘living polymerization with reversible termination’ and ‘living polymerization with reversible chain transfer’ are proposed.
173 citations
TL;DR: The intrinsic brittle-ductile (craze-yield) behavior of polymers and blends are controlled by two chain parameters: entanglement density ve and characteristic ratio Cx.
Abstract: The intrinsic brittle-ductile (craze-yield) behavior of polymers and blends are controlled by two chain parameters: entanglement density ve and characteristic ratio Cx. These chain parameters can be predicted from chemical structure. Therefore, the intrinsic brittle-ductile behavior of polymers and blends can be controlled by chemical structure using group additivity. The chemical composition and chain structure which can give the ultimate toughness in polymers and blends are discussed.
165 citations
TL;DR: In this paper, the extent of latex coalescence depended upon the chemical nature of the stabiliser employed and at monolayer coverage was not necessarily deleterious to the barrier properties of the films.
Abstract: Poly(butyl methacrylate) films have been prepared from surfactant-free latices which had post-added commonly used latex stabilisers. Water vapour transmission rates were used to study film permeability in relation to morphology, which was also studied by freeze fracture replication transmission electron microscopy. The extent of latex coalescence depended upon the chemical nature of the stabiliser employed and at monolayer coverage was not necessarily deleterious to the barrier properties of the films.
66 citations
TL;DR: In this paper, it is shown that the microstructure of poly(N-isopropylacrylamide) gels is particularly sensitive to these variables, including the number of initiator types and concentration, mold geometry and polymerization time.
Abstract: Properties of poly(N-isopropylacrylamide) gels—equilibrium degree of swelling, shear modulus, effective crosslink density and clarity—depend significantly upon the conditions of synthesis. While it is well known that monomer and crosslinker concentrations affect gel properties, other variables are shown here to have significant effects on the properties of the resulting gels. Initiator type and concentration, synthesis temperature, mold geometry and polymerization time all significantly affect the properties, including the swelling degree. Evidence suggests that the microstructure of these gels is particularly sensitive to these variables.
64 citations
TL;DR: In this article, the formation of both head-to-head and headto-tail alternating monomer structures is explained as the result of cross-proganation of free monomers, whereas anomalous head to head structures are rationalized through the addition of monomer complexes of predicted geometry.
Abstract: Microstructure analysis of styrene copolymers with 2-phenyl-1,1-dicyanoethene, as deduced from high resolution 1 H and 13 C NMR spectroscopy (DEPT, HETCOR, NOESY and JMODXH), demonstrated the formation of both head-to-head and head-to-tail alternating monomer structures. Conventional head-to-tail structures are explained as the result of cross proganation of «free» monomers, whereas anomalous head-to-head structures are rationalized through the addition of monomer complexes of predicted geometry
58 citations
TL;DR: In this paper, the effects of dopants and level of doping on the thermal stability of polypyrrole at 90, 120 and 150°C in dry air and nitrogen was investigated by monitoring the decay of conductivity.
Abstract: The effects of dopants and level of doping on the thermal stability of polypyrrole at 90, 120 and 150°C in dry air and nitrogen was investigated by monitoring the decay of conductivity. Polymer doped with aromatic anions (arylsulphonates) exhibit better stability than polymers doped with and aliphatic anion (dodecyl sulphate). The conductivity decay follows diffusion-controlled kinetics. After an initial decrease in conductivity, polypyrrole doped with p-toluenesulphonate anions maintains a constant conductivity at 150°C in air for at least 4 weeks. Dedoping results in materials of lower conductivity but greater thermal stability
55 citations
TL;DR: In this paper, the reaction properties of the two types of hydroxyl group (aliphatic and phenolic) were assessed from model reactions carried out in the same conditions.
Abstract: Kraft lignin was treated with dicarboxylic aliphatic (sebacoyl) or aromatic (terephthaloyl) acid chlorides in N,N-dimethylacetamide or N-methyl-2-pyrrolidone as solvents in the presence of triethylamine or pyridine as catalysts. The polyester gels obtained were characterized by IR after specific extractions and the chemical incorporation of lignin was proved unambiguously. Their thermal behaviour was determined by DSC and TGA; they are amorphous and stable up to 200°C in a nitrogen atmosphere. The reactivities of the two types of hydroxyl group (aliphatic and phenolic) were assessed from model reactions carried out in the same conditions.
54 citations
TL;DR: In this article, the synthesis of several functionalised aryl cyanate esters bearing reactive allyl groups was presented, and the monomers were purified using preparative HPLC and a range of techniques, including heteronuclear NMR spectroscopy, was employed in their characterisation.
Abstract: The syntheses of several functionalised aryl cyanate esters bearing reactive allyl groups are presented The monomers were purified (to c 98%) using preparative HPLC and a range of techniques, including heteronuclear nuclear magnetic resonance (NMR) spectroscopy, was employed in their characterisation A model functionalised aryl cyanate ester was doped with a variety of additives and the resulting thermal behaviour examined using dynamic differential scanning calorimetry (DSC) Furthermore, the postulated co-reaction of the model functionalised cyanate ester with bis-maleimides was investigated using heteronuclear NMR and dynamic mechanical techniques
52 citations
TL;DR: With homogeneous catalysts on the basis of chiral metallocenes and methylaluminoxane, it has become possible to polymerize cyclic olefins like cyclobutene, cyclopentene, norbornene, or dimethanonaphthalene (DMON).
Abstract: With homogeneous catalysts on the basis of chiral metallocenes and methylaluminoxane it has become possible to polymerize cyclic olefins like cyclobutene, cyclopentene, norbornene, or dimethanonaphthalene (DMON). No ring opening reaction occurs. The crystalline polycycloalkenes show extremely high melting points between 400 and 600°C. Copolymers of DMON with ethene are amorphous. They have molecular weights between 50000 and 150000 and high glass transition points up to 160°C. These copolymers could be used as materials for optical discs and fibers.
46 citations
TL;DR: In this paper, a crossover was observed in the variation of the reduced viscosity, η sp /c, as a function of the concentration, c, for polystyrene solutions in cyclohexane and dioxane.
Abstract: A crossover is observed in the variation of the reduced viscosity, η sp /c, as a function of the concentration, c, for polystyrene solutions in cyclohexane and dioxane. This crossover is attributed to the critical concentration c ** at which the macromolecular coils start to contact. The critical concentration c ** is related to the molecular weight and the intrinsic viscosity of the polystyrene through scaling laws. The values of the Huggins constant determined in the concentration regions below c ** (extremely dilute solutions) confirm the Peterson-Fixman theory
34 citations
TL;DR: In this paper, the non-conjugated diene 1,2-bis(isopropenyl-4-phenyl)-ethane, macrocyclic polyisoprenes were obtained with yields of at least 90% for molecular weights as high as 30 000 mol g−1.
Abstract: Cyclization of α,ω;-dilithiopolyisoprenes has been achieved in hexane solution in the presence of tetrahydrofuran (15% in volume) at −40 to - 50°C. Using as linking agent the non-conjugated diene 1,2-bis(isopropenyl-4-phenyl)-ethane, macrocyclic polyisoprenes could be obtained with yields of at least 90%, even for molecular weights as high as 30 000 mol g−1. With SiCl4 as coupling agent no gelation occurred and yields of about 70% in cyclic dimers, probably bicyclic, have been observed.
These results are compared to those obtained by various authors with α,ω;-dilithiopolystyrenes or α,ω;-disodiopolystyrenes and are attributed mainly to the presence, in the polyisoprene case, of predominant cyclic aggregates even at low organolithium concentration.
TL;DR: In this paper, the preparation, thermal behaviour and ionic transport of thin cast films of PEO-based electrolytes containing monovalent and divalent cations are discussed.
Abstract: The preparation, thermal behaviour and ionic transport of thin cast films of PEO-based electrolytes containing monovalent and divalent cations are discussed. The temperature and composition dependence of conductivity is considered. The possible uses of these polymeric electrolytes in solid-state electrochemical devices such as primary and secondary batteries, electrochromic displays and sensors are discussed
TL;DR: A series of polyurethane block copolymers based on hydroxyterminated polydimethylsiloxane and poly(propylene glycol) soft segments of molecular weights 1818 and 2000, respectively, were synthesized as mentioned in this paper.
Abstract: A series of polyurethane block copolymers based on hydroxy-terminated polydimethylsiloxane and poly(propylene glycol) soft segments of molecular weights 1818 and 2000, respectively, were synthesized The hard segments consisted of 4,4'-diphenylmethane diisocyanate and 1,4-butanediol as the chain extender In mixed-polyols-based copolymers and lower hard-segment content blends, macrophase separation occurred but blends with higher hard-segments contents showed significant reduction in extent of phase separation
TL;DR: In this article, the authors describe the essential features and advantages of semi-batch emulsion polymerization and make suggestions for future work, both experimental and modelling, making use of mathematical models.
Abstract: Essential features and advantages of semi-batch emulsion polymerisation are described. Variations of polymerisation rate, polymer particle number, particle size, copolymer composition and molecular weight distribution are considered and the use of mathematical models is reviewed. Suggestions for future work, both experimental and modelling, are made.
TL;DR: In this article, photosensitive polymers based on pendent chalcone moieties were prepared directly by radical homo-and copolymerization of vinyl-chalcone monomers.
Abstract: Photosensitive polymers based on pendent chalcone moieties were prepared directly by radical homo- and copolymerization of vinyl-chalcone monomers CH 2 =C(CH 3 )COOR (R = PhCH=CHCOPh, PhCOCH=CHPh, PhNO 2 ). The results obtained from the disappearance rates of the C=C bonds indicate in the UV spectra indicate that the photoreactivities of the polymers are largely affected by the position of the chalcone to the polymer backbone and by the concentration of the photosensitizer group
TL;DR: In this paper, acid-catalysed polycondensation of 1,6-hexanediol, 1,8-octanediol and 1,10-decandiol in the 150-190°C temperature range in the presence of H 2 SO 4 or Nafion-H resin was performed.
Abstract: Hydroxy-terminated poly(alkylene oxide)s with molecular weight M n in the range 700-2400 depending on the reaction time and temperature and hydroxy functionality of 2.0 were obtained by acid-catalysed polycondensation of 1,6-hexanediol, 1,8-octanediol and 1,10-decandiol in the 150-190°C temperature range in the presence of H 2 SO 4 or Nafion-H resin.
TL;DR: In this article, aqueous dispersions of polyurethane (PU) ionomers were prepared from hydrogenated diphenylmethane diisocyanate (H12MDI), poly(tetramethylene adipate) glycol (PTAd), bisphenol A propylene oxide ether glycol(LER), and dimethylol propionic acid (DMPA) as potential ionic centres.
Abstract: Aqueous dispersions of polyurethane (PU) ionomers were prepared from hydrogenated diphenylmethane diisocyanate (H12MDI), poly(tetramethylene adipate) glycol (PTAd), bisphenol A propylene oxide ether glycol (LER), and dimethylol propionic acid (DMPA) as potential ionic centres. The urethaneforming reaction was carried out in N-methyl-2-pyrrolidone (NMP) with dibutyltin dilaurate (DBT) as catalyst. The effects of DMPA and bisphenol A polyol on the particle size of the dispersions, and the physical properties of the emulsion cast films were determined. It was found that the particle size decreased with DMPA, and increased with bisphenol A polyol contents. Initial modulus and tensile strength of the emulsion cast films increased, and the elongation at break decreased with DMPA and bisphenol A polyol contents. The results were interpreted in terms of increased interchain Coulombic forces and urethane linkages with DMPA, and increased chain rigidity of PU with bisphenol A polyol incorporation.
TL;DR: In this paper, an erasable memory device is fabricated by the combination of a conducting polymer (poly(3-methylthiophene)) and a solid polymer electrolyte (an ethylene oxide-propylene oxide copolymer crosslinked with a diisocyanate), which is used as a memory channel and the latter as an electrolyte medium.
Abstract: Erasable memory devices are fabricated by the combination of a conducting polymer (poly(3-methylthiophene)) and a solid polymer electrolyte (an ethylene oxide-propylene oxide copolymer crosslinked with a diisocyanate). The former is used as a memory channel and the latter as an electrolyte medium. The channel conductivity can be controlled over 3-4 orders of magnitude by electrochemical doping through a writing electrode. The response time, depending on the writing voltage, is several seconds. The characteristics of the memory device are discussed.
TL;DR: In this article, a new semicrystalline polyimide has been synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 2,2-dimethyl-1,3-(4-aminophenoxy)propane.
Abstract: A new semicrystalline polyimide has been synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 2,2-dimethyl-1,3-(4-aminophenoxy)propane. The polymer has a high glass transition temperature of 230°C and a melting temperature of 325°C. Its overall crystallization rate between 240 and 325°C is quite fast (t1/2<10min) and relatively insensitive to the crystallization temperature. Although the degree of crystallinity obtained is dependent on the crystallization conditions, it can be as high as 50%. The polymer's morphology, which was examined with transmission electron microscopy (TEM), has a randomly stacked, ribbon-like, lamellar texture. Both TEM and polarized light microscopy show that mature spherulites do not develop. The crystal unit cell, which was determined from wide-angle X-ray diffraction measurements on highly oriented films, is monoclinic with a = 0.960nm, b = 0.582nm, c = 2.46nm and γ = 81.1°.
TL;DR: Anionic copolymerization of styrene (M1) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M2) was conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator.
Abstract: Anionic copolymerizations of styrene (M1) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M2) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M;n = 16.1 × 103 g/mol (Mw/Mn = 1.04) and 38.2 × 103g/mol (Mw/Mn = 1.05), and 24 and 38 moles of M2 per macromolecule, respectively, were characterized by size exclusion chromatography, 1H NMR spectroscopy and DSC. The monomer reactivity ratio, r1 = 5.6, was obtained from the copolymer composition at complete consumption of M1, assuming that the rate constant k22 =0,i.e. r2 =0. The polymers exhibited Tg values of 128 and 119°C, respectively, which correspond to an estimated Tg = 217°C for the hypothetical homopolymer of M2.
TL;DR: In this article, a single fiber pull out technique is presented which makes it possible to measure the strength in the interface between fibre and polymer with high precision even if the embedded length of the fibre is short.
Abstract: A single fibre pull out technique is presented which makes it possible to measure the strength in the interface between fibre and polymer with high precision even if the embedded length of the fibre is short. The method allows measurements for all kinds of fibres in thermoplastic or thermosetting polymers. The effect of fibre surface treatment can be investigated ns well as the effect of morphology or internal stresses in the polymer. An analysis of mechanical stress induced during the pull out demonstrates the use and limitation of this method
TL;DR: In this article, traditional and gradient IPNs of various composition have been prepared from cross-linked polyurethane and poly(butyl methacrylate) and the free energy of mixing IPN components has been calculated.
Abstract: Traditional and gradient IPNs of various composition have been prepared from cross-linked polyurethane and poly(butyl methacrylate). For various layers of gradient IPN cut from the surface to the centre the glass transition temperatures and composition have been determined. The sorption of benzene vapour by various layers was measured, and from these data the free energy of mixing IPN components has been calculated.
For all the layer compositions free energies of mixing are positive and dependent on the distance from the sample centre. This effect is thought to be connected not only with composition but with various conditions for phase separation in various layers.
Each layer consists of two phases with their own glass transition temperatures. From these data, using the Fox equation, the composition of each phase for various layers have been calculated and the volume ratio of phase evolved was estimated.
TL;DR: In this article, a CoBr2(PPh3)2 and methylaluminoxane catalyst was used for 1,3-butadiene polymerization and it was found that the polymer produced with the catalyst was composed of approximately 35% cis-1,4- and 65% 1,2-units without stereoregularity.
Abstract: Polymerization of 1,3-butadiene was conducted with a CoBr2(PPh3)2 and methylaluminoxane catalyst. From the spectroscopic analysis of both crude and hydrogenated polymers, it was found that the polymer produced with the catalyst was composed of approximately 35% cis-1,4- and 65% 1,2-units without stereoregularity. Effects of temperature, Al/Co ratio and addition of some Lewis bases on the polymerization were also examined in some detail.
TL;DR: In this article, the authors used hexamethylenediammonium adipate (HMA) particles with a strictly controlled amount of catalyst, either phosphoric acid, sulphuric acid or boric acid.
Abstract: Low reaction rates and distinct transition phenomena from the solid to the melt state restrain solid state polymerisation (SSP) reactions of nylon salts for industrial application. To alleviate these problems, catalysts containing nylon salts are employed. In this study, hexamethylenediammonium adipate (HMA) particles were used containing a strictly controlled amount of catalyst, either phosphoric acid, sulphuric acid or boric acid. The results show considerable acceleration of the reaction rate, especially in the presence of boric acid, while the solid state character of the process is maintained throughout the total course of the reaction. Comparative polymerisation runs were monitored both by end-group and quantitative water determinations of the reacting material to exclude any accumulation of the water of polycondensation within the reacting particles. The results obtained support further the mechanism proposed for the transition solid-melt in SSP runs of nylon salts in the absence of catalysts. In the latter case extended water accumulation is the rule.
TL;DR: In this article, a DSC thermogram showed two separate glass transition temperatures in PVC/PMMA mixtures over the entire composition range; multiphase structures were observed in an optical microscope.
Abstract: A DSC thermogram showed two separate glass transition temperatures in PVC/PMMA mixtures over the entire composition range; multiphase structures were observed in an optical microscope. FTIR spectra indicate that there are no strong specific interactions between these two polymers. The earlier studies on this blend system are briefly reviewed.
TL;DR: Low pressure gas plasma techniques for the fabrication of surfaces designed for compatibility with biological tissue and fluids are investigated in this article, where the surface treatment rendered fluorocarbon polymers wettable by polar liquids, but the wettability decreased with time during storage in air.
Abstract: Low pressure gas plasma techniques for the fabrication of surfaces designed for compatibility with biological tissue and fluids are investigated. Plasma surface treatment rendered fluorocarbon polymers wettable by polar liquids, but the wettability decreased with time during storage in air. Plasma polymerization, on the other hand, allowed the deposition of thin coatings which were more stable with time. STM of plasma polymers, which were coated with a sputtered film of platinum or gald, showed that these coatings were smooth and continuous.
TL;DR: In this article, the nonequalities of the reactivity and the micro-environment of propagating radicals have been found in MMA bulk polymerization, and the decrease of radical reactivity is caused by the trapping of the segments around the propagating radical.
Abstract: The nonequalities of the reactivity and the micro-environment of propagating radicals has been found in MMA bulk polymerization. This nonequal reactivity results from varying rates of diffusion in different micro-surroundings. The decrease of radical reactivity is caused by the trapping of the segments around the propagating radical
TL;DR: In this article, the synthesis of high molecular weight acrylic water-soluble polymers in heterophase water-in-oil polymerizations is discussed and a mechanism has been elucidated which includes elementary reactions in the continuous (organic) and dispersed (aqueous) phases, as well as the interfacial layer.
Abstract: The synthesis of high molecular weight acrylic water-soluble polymers in heterophase water-in-oil polymerizations is discussed. A mechanism has been elucidated which includes elementary reactions in the continuous (organic) and dispersed (aqueous) phases, as well as the interfacial layer. The latter allows for the identification of interfacially active species which can concurrently enhance stability and increase the linear molecular weight of the polymer. Suitable species are found to contain multiple radically active functional groups on either the hydrophilic or hydrophobic moieties.
A one-point light-scattering method is also developed which improves the accuracy in molecular-weight estimation to /pi5%. compared with /pi10% for the conventional dilution procedure. This is demonstrated for high molecular weight polyacrylamides and is found to reduce the sample measurement time fourfold, to 20 min.
TL;DR: In this article, the curing behavior of bis(methacryloxy) derivatives of diglycidyl ether of bisphenol A (vinyl ester resin) containing acrylates (methyl, ethyl and butyl acrylate) as the reactive diluents (40% w/w) were studied by DSC analysis.
Abstract: The curing behavior of bis(methacryloxy) derivatives of diglycidyl ether of bisphenol A (vinyl ester resin) containing acrylates (methyl, ethyl and butyl acrylate) as the reactive diluents (40% w/w) were studied by DSC analysis. Data found in this study indicated that an appreciable curing rate is obtained at lower temperature with increased concentrations of initiator. The acid value, activation energy, Arrhenius factor and specific heat are discussed.
TL;DR: In this paper, the complexation behavior of dithiocarbamate functions supported on polyacrylamides with varying extents (2-20 mol%) of N,N′-methylene-bis-bis acrylamide (NNMBA) crosslinks was investigated.
Abstract: The complexation behaviour of dithiocarbamate functions supported on polyacrylamides with varying extents (2-20 mol%) of N,N′-methylene-bis-acrylamide (NNMBA) crosslinks was investigated. The crosslinked polyacrylamides were prepared by the free radical solution polymerization of the monomers in water at 80°C using potassium persulphate as initiator. The dithiocarbamate ligands were introduced by polymer-analogous reaction involving transamidation with ethylenediamine and dithiocarbamylation with carbon disulphide and alkali. The complexation behaviour of these dithiocarbamate resins with the ligand functions in different macromolecular environments were investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions by a batch equilibration technique. The metal ion intake varied with the extent of the NNMBA-crosslinking. Thus the 8% crosslinked system has the highest complexation capacity. The values for metal ion intake followed the order Hg(II)> Cu(II)> Zn(II)> Ni(II)> Co(II). The time-course of complexation, the possibility of recycling and the swelling characteristics of the uncomplexed and complexed resins were considered, and IR characterization and thermal studies were undertaken. The swelling values of the complexed resins are lower than those of the uncomplexed resins. The thermal stability of dithiocarbamates varied with the extent of NNMBA-crosslinks and with the metal ion.