Showing papers in "Polymer Bulletin in 2000"

Thermal characteristics of organoclay and their effects upon the formation of polypropylene/organoclay nanocomposites

Abstract: We have examined thermal characteristics of two types of organically modified montmorillonite (OMMT) with different alkylammonium cations and their effects upon the formation of PP nanocomposite, when using a maleic anhydride grafted polypropylene oligomer (maPP) as a compatibilizer. The microstructure of the composite has been characterized by X-ray diffraction (XRD) analysis, transmission electron microscopy and Fourier transform infrared spectroscopy. OMMT showed the decrease of the interlayer spacing at the processing temperature, due to the release of organic ion by thermal decomposition. Thermal characteristics of OMMTs depended greatly on the interlayer structure of OMMT. When the OMMT with small interlayer spacing and less organophilicity was used, PP composite resulted in the only partial exfoliation due to thermal decomposition of the clay layers.

Thermal stability of polyaniline

Abstract: Among conducting polymers with metallic characteristics, polyaniline (PANI) is claimed to have one of the highest environmental stability. From an industrial point of view it would be useful to be able to thermally process this material into useful products using conventional techniques such as extrusion, stretching, rolling, etc., which generally are carried out at elevated temperatures. Somewhat surprisingly, relatively few studies have addressed the thermal stability of PANI, in particular that of the non-protonated emeraldine base form. Therefore, a study of the thermal properties was performed to examine the thermal stability of this material and to identify the optimum processing and maximum application temperatures.

Controlled polymerization of DL-lactide using a Schiff's base al-alkoxide initiator derived from 2-hydroxyacetophenone

Abstract: The kinetics of DL-lactide polymerization was studied in CH2Cl2 at 25°C and in toluene at 70°C with HAPENAlOMe, a new Schiff's base complex derived from 2-hydroxyacetophenone and ethylenediamine. A higher polymerization rate is observed with this initiator as compared to other previously reported Al-alkoxides complexes. The polymerization with HAPENAlOMe is also shown to be a living process in both solvents. Moreover, the polymerization proceeds to quite high conversion without significant occurrence of transesterification reactions as confirmed from 13C NMR and SEC analysis.

ATRP grafting from silica surface to create first and second generation of grafts

Abstract: (11'-Chlorodimethylsilylundecyl)-2-chloro-2-phenylacetate 2 as an atom transfer radical polymerisation (ATRP) initiator was bound covalently to the surface of silica. ATRP grafting of styrene monomer from the silica surface was achieved and the grafts were detached from the solid particles for analysis. It is shown that after polymerisation of a first generation of grafts and work-up of the thus grafted silica the chain ends of the grafts are still active to initiate a second monomer feed to further chain growth.

Equilibrium swelling and mechanical properties of hydrogels of acrylamide and itaconic acid or its esters

Abstract: The equilibrium swelling and the plateau elastic modulus of a family of hydrogels made by the polymerization of acrylamide with itaconic acid or some of its esters were investigated as a function of composition and crosslinking degree to find materials with satisfactory swelling and elastic properties. We show that an appropriate selection of the comonomers and the concentration of the crosslinking agent is very important to produce hydrogels with large swelling capacity and good mechanical attributes. Tailoring of mechanical properties and swelling can also be achieved by this method.

Stirring speed influence study on the microencapsulation process and on the drug release from microcapsules

Abstract: Microparticles in the size range of 20–200 μm, loaded with drug model were prepared by complex coacervation method. The influence of the agitation rate of dispersion on the morphology of particles and on the drug release has been studied. Obtained results show that the relationship found between the Sauter mean diameter of particles and the stirring speed of emulsification is in good agreement with the inertial breakup theory. The paper reports the preliminary results of a work intended to link up the process control parameters of the microencapsulation and the factors controlling the drug release.

Formation of an ordered nanostructure in surfactant- polyelectrolyte complexes formed by interfacial diffusion

Abstract: This paper concerns the obtention of capsules stabilized by a shell formed by an electrostatic complex which also present an ordered nanostructure. The complex involves chitosan as a semi rigid positively charged polyelectrolyte and sodium dodecyl sulphate (SDS) anionic surfactant. The shell consists of a network in which anionic surfactant micelles crosslink the cationic polymer chains.

Uranyl ion adsorptivity of N-vinyl 2-pyrrolidone/acrylonitrile copolymeric hydrogels containing amidoxime groups

Abstract: N-vinyl 2-pyrrolidone (VP) / Acrylonitrile (AN) copolymeric hydrogels were synthesized by using γ-radiation and amidoximated for the purpose of uranyl ion adsorption. Optimum amidoximation time was determined by following the uranyl ion, UO2 2+, adsorption capacity. The adsorption of amidoximated copolymers was studied from different uranyl ion solutions (1000–1850 ppm). The results of all adsorption studies showed that the interaction between UO2 2+ and amidoxime groups comply with Langmuir type isotherm. The adsorption capacity was found as 0.54 g UO2 2+ /g dry amidoximated copolymeric hydrogels. From the stoichiometric calculations, it was found that the bonding between UO2 2+ and amidoxime groups is 1 to 4.

Nickel (salen) / methylaluminoxane catalyzed polymerization of norbornene

Abstract: Nickel (salen) in conjunction with methylaluminoxane (MAO) catalyzes the polymerization of norbornene to poly (2,3-bicyclo [2.2.1] hept-2-ene) [poly (norbornene)]. Methylaluminoxane (MAO) was used as cocatalyst as such (MAO-I) and after distilling off free trimethylaluminium (MAO-II). The catalyst system was very active in chlorobenzene at room temperature. It was also found that MAO-II gave higher activity as compared to MAO-I. The samples of polynorbornene were soluble in 1,2,4-trichlorobenzene. The poly (norbomene)s were characterized by intrinsic viscosity and thermal properties.

Stereocomplex formation in enantiomeric diblock and triblock copolymers of poly (ɛ-caprolactone) and polylactide

Abstract: Enantiomeric diblock and triblock copolymers from caprolactone and lactide with various compositions were synthesized using alcohol/tin octoate as initiator system. Stereocomplexes were formed between pairs of enantiomeric block copolymers and their thermal properties examined. The melting temperatures of the crystalline PCL and PLA phases are depending on the composition of block copolymers. A raise of approximately 55°C of the temperature of PLA phase is observed in the blends as a consequence of stereocomplex formation as well in diblock as in triblock copolymers.

Interaction-structure-property relationships in amorphous polymer blends

Abstract: SummaryMiscibility, structure and property relationships were studied by different techniques forvarious polymer pairs. Four blends of polystyrene (PS), styrene-acrylonitrile copolymer (SAN),polycarbonate (PC) and polyphenylene oxide (PPO) [PS/PPO, PS/PC, PS/SAN and PPO/SAN] were investigated in the entire composition range. Glass transition temperatures weremeasured by DSC, mechanical properties were characterized by tensile test, methanol absorp-tion was determined at 50 °C. The Flory-Huggins interaction parameter ( ) was derived fromHildebrand solubility parameters, and compared to -related quantities calculated from the ex-perimental results. Good correlation was obtained between parameters derived from differentmethods used for the characterization of polymer/polymer interaction.1. IntroductionThe properties of polymer blends are controlled primarily by the microstructure ofthe system, which depends upon the miscibility of the components in the first place. Ther-modinamical miscibility means mixing of the components on molecular level resulting in ahomogeneous structure. The free energy of mixing must be negative for the formation of ahomogeneous system. In contrast to small molecules, the change of entropy is small whenpolymers of high molecular masses are mixed, therefore a large negative enthalpy of mix-ing is required for miscibility. This condition is fulfilled by polymer pairs showing strongspecific interactions. In the case of moderate or weak interactions, a temperature andcomposition dependent miscibility window may exist, as both thermodynamical parameters( H and S) depend on these variables. In the absence of favorable intermolecular inter-actions the solubility parameters of polymers must match in order to find miscible pairs [1].Partial miscibility results in a heterogeneous, two-phase structure, in which only alimited amount of the other component is dissolved in both phases. In such blends the bal-ance of properties may satisfy certain requirements, they are often termed as compatibleblends. The degree of miscibility or compatibility of polymers can be studied by differentmethods [2-6]. A number of theoretical and empirical equations are available for the char-acterization of structure on the basis of property changes. Some of these methods yield theFlory-Huggins interaction parameter ( ) [7] or a number related to it. The goal of thisstudy was comparing parameters and related quantities which were derived from meas-ured properties of blends by various methods.

Preparation and characterization of fully oxidized form of polyaniline

Abstract: The oxidation state of polyaniline (PANI) can be varied from the fully reduced leucoemeraldine base (LEB) to the half oxidized emeraldine base (EB) and to the fully oxidized form pernigraniline base (PNB). In this work, the synthesis and properties of the highest oxidation state of polyaniline, pernigraniline, in the base as well as the corresponding salt form are discussed.

New AB or ABA type block copolymers: atom transfer radical polymerization (ATRP) of methyl methacrylate using iodine-terminated PVDFs as (macro)initiators

Abstract: PMMA homopolymer with CF3(CF2)2CF2- end group was prepared by the ATRP of MMA using CF3(CF2)2CF2-I as an initiator and copper(I) salts/bipy catalysts. This indicated the production of perfluorobutyl radicals by ATRP mechanism and successful polymerization by them. Di- and triblock copolymers were also prepared by the ATRP of MMA using iodine-terminated PVDF as (macro)initiators. The kinetic plots (ln[M]o/[M] vs. time) showed nearly first-order with respect to monomer concentration and the Mn,NMR of block copolymers increased linearly with conversion. However, iodine-terminated PVDF showed low initiator efficiency because propagating rate was much faster than initiating rate

Controlled synthesis of amphiphilic siloxane-siloxane block copolymers with carboxyl functions

Abstract: Poly[2-(carboxymethylthio)ethyl]methylsiloxane-block-polydimethylsiloxane, 1, and poly{[2-(carboxymethylthio)ethyl]methylsiloxane-co-dimethylsiloxane}-block-polydimethylsiloxane, 2, were synthesized by ene-thiol addition of mercaptoacetic acid to respective precopolymers 3 and 4, containing vinyl groups bound to silicon. The precopolymers 3 and 4 were obtained by sequential anionic copolymerization of hexamethylcyclotrisiloxane, D3, with 2,4,6-trimethyl-2,4,6-trivinyl-cyclotrisiloxane, 5, and D3 with 2,4,4,6,6,-pentamethyl-2-vinylcyclotrisiloxane, 6, respectively. The method permits to synthesise the block copolymers with a narrow molecular weight distribution and a high block purity. The ene-thiol addition was performed on free radical route, using AIBN as initiator. The reaction proceeds selectively, leading to the transformation of vinyl groups in the precopolymers into the β-adducts.

Dielectric behavior during sol-gel transition of PEO-PPO-PEO triblock copolymer aqueous solution

Abstract: Thermoreversible sol-gel transition of the PEO-PPO-PEO triblock copolymer(Pluronic F127) aqueous solution was monitored by dielectric behavior measurement. Thermoreversible gelation originates from the micelle formation and micelle volume change due to PEO-water, PPO-water LCST behavior. Micelle volume fraction is the critical parameter that dominates the sol-gel transition behavior of Pluronic aqueous solution. By measuring the dielectric constant of 5-22% Pluronic F127 aqueous solution, critical micelle temperature and micelle volume fraction was obtained. The micelle volume fraction of the gel region exceeded the critical volume fractions of simple cubic packing(0.523). Gelation temperature determined by dielectric measurement agreed well with that determined by the tube tilting method.

Preparation and oil-absorptivity of crosslinked polymers containing stearylmethacrylate, 4-t-butylstyrene, and divinylbenzene

Abstract: The crosslinked polymers, poly(stearylmethacrylate-co-divinylbenzene) [CP(SMA-co-DVB)] and poly(t-butylstyrene-co-divinylbenzene) [CP(tBS-co-DVB)], and CP(SMA-co-DVB)/PtBS IPNs, were prepared by the polymerization of corresponding monomer pairs in the presence of BPO. The structures and thermal properties of CP(SMA-co-DVB), CP(tBS-co-DVB), and the IPN were determined by FT-IR, DSC, and TGA. The oil-absorptivities of CP(SMA-co-DVB) and CP(SMA-co-DVB)/PtBS IPN decreased with increasing concentrations of DVB and tBS, respectively. The highest oil-absorptivities of CP(SMA-co-DVB) and the IPN(PtBS: 25%) were 615 % and 330 %, respectively. The toluene absorptivity of the synthesized polymers decreased in following order: CP(tBS-co-DVB) > CP(SMA-co-DVB) > IPN(PtBS: 25 %) > IPN(PtBS: 50 %) > IPN(PtBS: 75 %) at immersion above 60 min.

Water super absorbents based on copolymers of acrylamide with sodium acrylate

Abstract: Water absorbing materials on the basis of acrylamide copolymers have been investigated. The cross-linking of polymer chains strongly effects the degree of water absorption. The influence of starting composition of polyacrylamide : sodium hydroxide, duration of hydrolysis and irradiation conditions on cross-linking have been determined and optimized technological parameters have been derived. Water super absorbents with the ability to absorb up to 900g water by one gram material have been prepared.

Relationship between the swelling process and the releases of water soluble agrochemicals from radiation crosslinked acrylamide/itaconic acid copolymers

Abstract: An attempt was made in this study to relate the releases of water soluble herbicide (sodium 2,2 dichloropropionate (Dowpon)) and model fertilizers (ammonium nitrate, potassium nitrate and ammonium sulfate) from the cylindrical devices of radiation crosslinked poly(acrylamide/itaconic acid) (AAm/IA) copolymers with the swelling that may effect the release behaviour. AAm/IA copolymers containing agrochemicals are prepared by two different composition of itaconic acid and two different γ-rays doses. The agrochemicals were trapped in the gels by including it in the feed mixture of radiation polymerization. The equilibrium swelling, diffusional exponent, and diffusion and intrinsic diffusion coefficients of the process were obtained. The agrochemical dissolution was determined by conductimetric method. The maximum concentrations of releasing agrochemicals and initial releasing rates were calculated by using of second order kinetics equation. The agrochemical releases appeared to be controlled by swelling. As a result, if AAm/IA hydrogels containing agrochemicals were swelled in water, release of agrochemicals was decreased with the raising of γ-rays doses and itaconic acid quantities in the hydrogel.

Molecularly imprinted polyamide membranes for chiral recognition

Abstract: Molecularly imprinted polymeric membranes were prepared from amorphous poly(hexamethylene terephthalamide/isophthalamide). Membranes imprinted by Z-D-Glu recognize the D-isomer, of which absolute configuration is the same as that of the print molecule, in preference to the corresponding L-isomer, and vice versa. The amino acid preferentially adsorbed by the membrane was also selectively permeated by electrodialysis. An optimum separation factor of 2.0 was reached at the applied potential difference of 2.0 V.

Hyperbranched aromatic epoxies in the design of adhesive materials

Abstract: The use of hyperbranched aromatic epoxy polymer 2 (HARE) as a component in various adhesion experiments has been demonstrated. Two different modes of curing were tested, including a photoinitiated cationic curing process and a polyfunctional amine curing process. These processes gave flexible films that showed good adhesion to nylon, steel, and glass. Furthermore, blends of HARE and the commercial epoxy resin bisphenol F diglycidyl ether (BPFG) were cured with 2-ethyl-4-methylimidazole (EMI) at 150 °C on lap-shear assemblies. These cured assemblies displayed adhesive strengths in the range of 15 MPa over a broad range of HARE/BPFG weight ratios.

Polymer-metal complexes: Synthesis, characterization, and properties of poly(maleic acid) metal complexes with Cu(II), Co(II), Ni(II), and Zn(II)

Abstract: Polymer metal complexes of poly(maleic acid) and Cu(II), Co(II), Ni(II), and Zn(II) were synthesized. Elemental analysis, as well as magnetic, spectral and thermal properties, in addition to electrical conductivities of the chelates were investigated, and possible structures have been assigned to the polychelates. Semi-empirical calculations at the PM3 level were carried out on the geometrical arrangement of the polychelates.

Preparation and characterization of dodecylamine-modified poly(aspartic acid) as a biodegradable water-soluble polymeric material

Abstract: The reaction of poly(succinimide) (PSI) with dodecylamine (DDA) in DMF produced a partially dodecylamine-modified poly(succinimide) (DDA-PSI) When the mole ratio of the DDA units and the succinimide units in PSI (M w = 22,000) varied from 01 to 05 in the feed, the mole fraction of the N-dodecyl aspartamide units in PSI increased from 4 to 46 mol-%, and the M w of DDA-PSI was almost constant at M w =ca 20,000 Sodium DDA-modified poly(aspartate) (DDA-PASP-Na) was obtained in high yield by hydrolysis using NaOH solution DDA-PASP-Na exhibited biodegradability (14 ∼ 21 %) and a high MnO2-dispersion property (103 g-MnO2 / g-polymer)

Crystallization of polydimethylsiloxane end-linked networks

Abstract: End-linked polydimethylsiloxane networks were synthesized, and used to quantify the reduction due to crosslinking of both the extent and thermodynamic stability of the crystalline phase Networks of varying crosslink density were isothermally crystallized at various temperatures The consequent melting points were found to be a linear function of the crystallization temperature, enabling equilibrium melting temperatures to be determined by extrapolation From the dependence of the equilibrium melting point on crosslink density, it was determined that a network junction precludes roughly 8 adjoining chain units from incorporating into the crystal phase This result is consistent with the measured degree of crystallinity suppression in the networks

Temperature sensitive polymers based on 2-(dimethyl maleinimido)-N-ethyl-acrylamide: Copolymers with N-isopropylacrylamide

Abstract: Temperature sensitive polymers with pendant dimethyl maleinimide side groups were prepared by the copolymerization of N-isopropylacrylamide (NIPAAm) with varying amounts of a functional N-substituted acrylamide (2-(dimethyl maleinimido)-N-ethyl-acrylamide, DMIAAm). The polymers were characterized by 1H-NMR, IR, DSC and TGA. Their relative reactivity ratios have been determined. Aqueous solutions of the copolymers showed lower critical solution temperature behaviour (LCST). The phase transition temperatures of the aqueous solutions of these copolymers decreased with increasing comonomer content and disappeared at DMIAAm contents at or above 15.9 mol-%.

Determination of small interactions in polymer composites by means of FTIR and DSC

Abstract: This paper studies polymer composites formed by a polystyrene matrix (PS) and a block copolymer of poly(styrene-butadiene) (SBS). Two series of polymer composites with different compositions have been prepared: the first by extrusion followed by injection and the second by dissolution and evaporation of the solvent from the injected samples. The comparison of the FTIR spectra of the polymer composites with those simulated by addition of the spectra of the component polymers allows the detection of differences attributed to the existence of interactions between both polymers that cause partial miscibility between them. The results obtained are corroborated by differential scanning calorimetry.

Novel π-conjugated organoboron polymers: Poly (ethynylene-phenylene-ethynylene-borane)s

Abstract: Novel poly(ethynylene-phenylene-ethynylene-borane)s were prepared by polycondensation between bifunctional lithium acetylide and aryldimethoxyborane. The polymers obtained are expected as a novel type of organoboron π-conjugated polymers via vacant p-orbital of boron atom. The polymerization between dilithium 2,5-didodecyloxybenzene-1,4-diethynilide and tripyldimethoxyborane [tripyl=2,4,6-triisopropylphenyl] gave the corresponding polymer in 67% yield. From gel permeation chromatographic analysis (THF, PSt standards), the number-average molecular weight of the polymer was found to be 2700. In the UV-vis spectrum of the polymer (in chloroform at room temperature), an absorption maximum was observed at 397 nm. The fluorescence emission spectrum (in chloroform, room temperature, excitation wavelength at 400 nm) showed its γ max at 456 nm in the visible blue region. The polymers obtained were very soluble in common organic solvents such as THF, chloroform and benzene.

Emulsion polymerization of 2-hydroxyethyl methacrylate and partition of monomer between particles and water phase

Abstract: Using sodium dodecyl sulfate (SDS) as the single surfactant 2- hydroxyethyl methacrylate (HEMA, extremely water-soluble) was polymerized at 60°C in aqueous medium to obtain latexes with average particle diameter below 80 nm and the extrapolated kp value was estimated to be 200±20 (L/mol-s). Values of monomer concentration in particles ([M]) used in this calculation were obtained by interpolating the literature available partition data of HEMA between the gel phase (i.e., poly(2-hydroxy-ethyl methacrylate) and the water phase. The [M] values (< 1.00 mol/L) are much lower than those for the sparely-soluble monomer (3 to 4 mol/L), and the [M] values decrease with increasing conversion.

Effects of acrylonitrile content on the properties of clay-dispersed poly(styrene-co-acrylonitrile) copolymer nanocomposite

Abstract: Clay-dispersed nanocomposites have been prepared by simple melt-mixing of two components, i.e. poly(styrene-co-acrylonitrile) copolymers with different contents of acrylonitrile comonomer and two different kinds of organophilic clay (Cloisite® 25A and Cloisite® 30A), with a twin screw extruder. Dispersion behavior of 10-A-thick silicate layers of clay in the nanocomposites was investigated by using an X-ray diffractometer and a transmission electron microscope. It was found that acrylonitrile comonomer incorporated into poly(styrene-co-acrylonitrile) copolymers accelerates intercalation of the copolymers into the galleries of silicate layers modified with an organic intercalant. The faster intercalation of a matrix polymer leads to the better dispersion of silicate layers in the matrix polymer.

Self-aggregates of poly(aspartic acid) grafted with long alkyl chains

Abstract: Biodegradable poly(aspartic acid) (PASP) containing octadecyl chain grafts has been synthesized by thermal polycondensation of aspartic acid, aminolysis by octadecylamine, and followed by hydrolysis of remaining succinimide in polymer backbone. The sonicated suspension formed self-aggregates in aqueous solution. Size exclusion chromatography and dynamic light scattering indicated that self-aggregates became compact and particle size was reduced as increasing the amount of substituted octadecyl chains. In the case of low degree of substitution, self-aggregates assembled loosely due to low hydrophobic interaction. In the concentration range of 0.05–1.0%, the stability of aggregates was maintained due to effective hydrophobic interaction and electrostatic repulsion. Below pH 3.2, macroscopic phase-separation appeared in aqueous solution due to attraction of protonated PASP backbone.

The effect of preparation temperature on the swelling behavior of poly(N-isopropylacrylamide) gels

Abstract: The role of the preparation temperature of poly(N-isopropylacrylamide) (PNIPA) gels on their swelling behavior in water and in aqueous solutions of sodium dodecylbenzenesulfonate was investigated. PNIPA gels were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis) acrylamide in water at fixed monomer and crosslinker concentrations. The equilibrium swelling ratio of the gels increases first slightly up to about 20°C then rapidly with increasing gel preparation temperature. Magnitude of the collapse transition in water at 34°C becomes larger as the gel preparation temperature increases. Calculations indicate a decrease in the effective crosslink density of PNIPA gels with increasing preparation temperature. The gels prepared at temperatures higher then 20°C were heterogeneous consisting of highly crosslinked regions interconnected by the PNIPA chains.