Showing papers in "Polymer Bulletin in 2004"

Hydrogels Based on Pullulan Crosslinked with sodium trimetaphosphate (STMP): Rheological study

Abstract: Hydrogels from pullulan crosslinked with sodium trimetaphosphate (STMP) under alkaline condition have been investigated by rheological measurements. The influence of reagents concentration (pullulan, STMP, NaOH) on kinetics of reaction and rheological properties is reported. Increasing concentrations of any reagents lead to an increase of the crosslinking kinetics. Increasing the polymer concentration leads to a “stronger” gel whereas an increase of crosslinking reagent (STMP) evidences a critical concentration above which the rheological properties of the gel do not change anymore. This may be explained by the specificity of the system for which the polymer concentration is high and negative charges appear.

Synthesis and Characterization of 2-(Dimethylamino)ethyl Methacrylate Homopolymers via aqueous RAFT Polymerization and Their Application in Miniemulsion Polymerization

Abstract: Homopolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) have been synthesized directly in aqueous media by reversible addition-fragmentation chain transfer polymerization (RAFT) using 4,4’-azobis(4-cyanopentanoic acid) (V501) as a water-soluble azo initiator and 4-cyanopentanoic acid dithiobenzoate (CPADB) as a chain transfer agent. The resulting polymers were controlled in the range of narrow molecular weight distributions, with \(\bar{M}_{w}/\bar{M}_{n}\) lower than 1.3. Using the produced dithioester-capped DMAEMA homopolymer as a macro chain transfer agent, miniemulsion RAFT polymerization of methyl methacrylate and styrene were carried out, respectively. 1H NMR analysis showed that the diblock copolymer PDMAEMA-b-PMMA in the form of stable latices was obtained as expected.

Synthesis of poly(methylmethacrylate)/montmorillonite nanocomposites via in situ intercalative suspension and emulsion polymerization

Abstract: Na-montmorillonite (MMT) with cation exchange capacity (CEC) of 90 mEq/100g was converted to MMT-CTAB and MMT-CPC forms by the intercalation of Cetyltrimethylammonium bromide (CTAB) and Cetylpyridinium chloride (CPC), respectively. The intercalation of these surfactants onto the basal space of the montmorillonite was evidenced by fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). The intercalation of the CPC expanded the basal space from 12.19 Ao to 21.47 Ao while in case of CTAB it was expanded to 19.35 Ao only. The (MMT-CPC) was subsequently used as a host for the preparation of PMMA nanocomposites via intercalative suspension and emulsion polymerization of methylmethacrylate (MMA) using benzoyl peroxide (BPO) and potassium persulphate (PPS) individually and simultaneously. The use of BPO and PPS together invoked better exfoliation but the yield did not change appreciably in comparison with using either of the initiators alone. Different structures were obtained with the variation of the preparation conditions; exfoliated and intercalated nanocomposites which were characterized by XRD, transmission electron microscope (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The resultant nanocomposites exhibited improved thermal stability relative to the equivalent macrocomposites. No glass transition temperature (Tg) could be detected for the prepared nanocomposites which was assumed to result from the restricted molecular motion of the polymer chains.

Enhancement of the thermal stability, mechanical properties and morphologies of recycled PVC/clay nanocomposites

Abstract: Recycled PVC/clay nanocomposites were prepared by melt mixing of recycled PVCs and modified clays. Characterization of the nanostructure of the nanocomposites was carried out using wide angle X-ray diffraction (WAXD) and transmission electron microscopy(TEM). In case of 10wt.%, the characteristic peak of modified clay was perfectly disappeared, because of aids of plasticizers as co-intercalator. Thermal stability was evaluated from the thermal decomposition behaviors and linear dimension changes by TGA and TMA system. Coefficients of thermal expansion of the nanocomposites were also observed from TMA analysis. Dynamic mechanical properties were evaluated using DMA system. The thermal and mechanical properties of the nanocomposites were improved simultaneously for varied clay loadings, 1,3,5,10wt.%, compared to recycled PVC. Especially, the storage modulus of the nanocomposites with 10wt.% clay loading was increased 11 times compared to that of recycled PVC.

Separation of heavy metal ions by complexation on poly (N-vinyl imidazole) hydrogels

Abstract: Poly (N-vinyl imidazole) (PVIm) hydrogels were prepared by γ-irradiating binary mixtures of N-vinyl imidazole-water in a 60Co-γ source having 4.5 kGy/h dose rate. These hydrogels were characterized with gravimetric and spectrophotometric studies. Hydrogels with equilibrium swelling ratio of 600% in distilled water were used in the metal ion adsorption studies. The effects of pH, equilibration time, and initial metal ion concentration were considered in batch equilibrium study on the chelation of Cu2+, Co2+, Cd2+, and Pb2+ ions. Maximum metal ion adsorption were observed at pH=6.0. It has also been observed that the amount of adsorbed metal ions decreased at lower pHs because of protonation of PVIm ring.

Toughening of Epoxy Composite by Dispersing Polysulfone Particle to Form Morphology Spectrum

Abstract: Fracture toughness of epoxy composite with polysulfone(PSf) particles to form morphology spectrum was investigated. The epoxy resin was based on diglycidyl ether of bisphenol-A(DGEBA type) and diaminodiphenylsulfone(DDS). 1K carbon fabric was used as the reinforcing material. The morphology spectrum which has gradual change of the morphological feature resulting from the concentration gradient of PSf in the composite can be obtained by spreading PSf particles in between the carbon fiber reinforced epoxy prepregs before cure. The relative rate of the dissolution and diffusion of the PSf particle in the epoxy determine the concentration gradient of the PSf. The fracture toughness of the composite with 21 wt % large size particles was 2.2 times higher than that of the unmodified composite. This result was ascribed to the plastic deformation of the continuous PSf rich phase formed inside the swollen PSf particle.

First report of nitroxide mediated polymerization in an ionic liquid

Abstract: Nitroxide-mediated free radical polymerizations (NMP) of styrene (St) and methyl methacrylate (MMA) were carried out in a room temperature ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6). A bimolecular initiation system, benzoyl peroxide (BPO) along with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and a unimolecular initiation system, 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (α-hydrido alkoxyamine, TMPPAH)) were employed. Contrary to the results obtained for atom transfer radical polymerization (ATW) and reversible addition-fragmentation radical transfer polymerization (RAFT) in the same ionic liquid, the molecular weights obtained in NMP were lower with broader polydispersities for a wide range of initiator ratios and temperatures due to the non-living nature of polymerization.

A direct way to determine iPP density nucleation from DSC isothermal measurements

Abstract: In the present work, a large number of growth rate data for α-phase isotactic polypropylene, taken from literature, have been described by the Lauritzen and Hoffmann equation. A general procedure to predict nuclei density by simple DSC measurements is described and applied successfully to a commercial iPP.

Synthesis of Nanocomposites of Metal Nanoparticles Utilizing Miscible Polymers

Abstract: Gold nanoparticles modified with poly(2–methyl–2–oxazoline) have been prepared via chemical reduction of HAuCl4 by NaBH4. The gold nanoparticles were homogeneously dispersed in poly(vinyl chloride) as a polymer matrix by the miscibility between the protecting polymer of the nanoparticle and the polymer matrix. Differential scanning calorimetry and UV–vis absorption measurement clearly showed that the miscibility played an important role for incorporation of the metal nanoparticles in the polymer matrix.

Novel initiating system based on AlCl3 etherate for quasiliving cationic polymerization of styrene

Abstract: Quasiliving cationic polymerization of styrene was obtained in the system 2-phenyl-2-propano-/AlCl3·OBu2/Bu2O in a mixture of 1,2-dichloroethane and n-hexane (55:45 viv) at -15 °C. The molecular weights of the polymers (Mn) increased in direct proportion to the monomer conversion. However, the experimental Mns are essentially higher than theoretical ones, indicating that slow initiation relative to propagation takes place. The molecular weight distributions were broad (Mw/Mn∼2.5), probably due to the slow initiation and slow exchange between reversibly terminated and propagating species.

Nanoporous Crosslinked Polyisoprene from Polyisoprene—Polydimethylsiloxane Block Copolymer

Abstract: The polyisoprene block of a polyisoprene-polydimethylsiloxane (PI-PDMS) diblock copolymer with 0.68 volume fraction of PI was tightly crosslinked with dicumylperoxide. The PDMS part of the obtained glassy material was subsequently quantitatively etched with anhydrous hydrogen fluoride or tetrabutylammonium- fluoride, in this way obtaining a nanoporous material. The fraction of the surviving double bonds was estimated by solid state NMR, while thermal analysis was used to characterize the glass transition temperature of PI as a function of crosslinking degree. Small angle x-ray scattering confirmed the existence of microphase separated cylinders of PDMS in a PI matrix and its conservation in the form of channels in the crosslinked matrix.

Microwave absorption properties of a conductive thermoplastic blend based on polyaniline

Abstract: Conductive thermoplastic blends of polystyrene and polyaniline doped with dodecylbenzene sulfonic acid, DBSA and polystyrene sulfonic acid were prepared in an internal mixer. We used a block copolymer of styrene and butadiene as compatibilizer. Different formulations were tested according to a statistical response surface method. The electrical conductivity and the microwave radiation absorbing properties of the blends were evaluated. The concentration of the compatibilizer and polyaniline and the blend film thickness affect the attenuation properties of the materials.

Investigation of polyethylene-wax blends by CRYSTAF and SEC-FTIR

Abstract: Oxidized wax blends with respectively HDPE, LDPE and LLDPE were investigated using CRYSTAF and SEC–FTIR in order to determine the possibility and extent of co–crystallization of the wax with each of these polyethylenes. CRYSTAF shows very little or no co–crystallization of wax with HDPE and LDPE, while there is a strong indication of co–crystallization in the case of LLDPE. SEC-FTIR analyses show co–elution of wax with LLDPE, indicating some chemical interaction between the oxidized wax and LLDPE.

Encapsulated Zosteric Acid Embedded in Poly[3-hydroxyalkanoate] Coatings—Protection against Biofouling

Abstract: The natural, non-toxic antifouling compound zosteric acid (ZA, p-coumaric acid sulfate) was encapsulated in polystyrene (PS) microcapsules (30 mg ZA /1 g PS) with an efficiency of 30 % via an in-liquid drying process. Electron micrographs showed microcapsules with smooth surfaces and a mean diameter of 200 μm. The FIB method was used to cross-section a microcapsule in order to visualize the inner capsule structure and to localize ZA via element analysis. Coatings of a biocompatible polyester, poly[3-hydroxyalkanoate-co-3-hydroxyalkenoate] (PHAE), were prepared on microscopic slides. These coatings contained dispersed ZA (PHAE/ZA) or ZA-loaded PS microcapsules (PHAE/PS(ZA)). The release of ZA was monitored via conductivy measurements in water and was 4 μgcm-2d-1 for PHAE/ZA and 0.9 μgcm-2d-1 for PHAE/PS(ZA) coatings. To follow the initial steps of biofilm formation, coated slides were exposed to activated sludge and analyzed for cell adhesion with ESEM. ZA was effective during the burst release time of the PHAE/ZA coating, but no significant differences in biofouling were observed after 48 h. This was attributed to the minimal effective release rate of ZA, which is approximately 10 μgcm-2d-1.

Single ion conductive characteristics of poly(organoboron halide)-imidazole complex

Abstract: Poly(organoboron halide)-imidazole complex was prepared by hydroboration polymerization of 1,7-octadiene with monobromoborane-methylsulfide complex and subsequent polymer reaction with 1-methylimidazole and methanol. The ion conductive characteristics of the polymer was evaluated by ac impedance method. The optimized concentration of lithium salt was 100 unitmol% to methoxyboron unit. In the presence of lithium bis(trifluoromethane sulfone) imide (LiTFSI), the polymer complex composed of approximately 50% methoxyboron unit exhibited ionic conductivity of 2.59×1O-5S/cm at 50°C. The lithium ion transference number for this system was calculated to be 0.47, indicating that anions were significantly trapped by Lewis acidic methoxyboron unit.

Gamma Radiation Effects on the Glass Transition Temperature and Mechanical Properties of PMMA/soot nanocomposites

Abstract: Summary Poly(methy1 methacrylate) (PMMA) was produced via free radical polymerization. Polymer samples were sonicated and melt compounded to form 1%, 0.5%, and 0.25% PMMAlsoot samples. Soot containing unpurified carbon nanotubes was provided by NASA Ames Research Center. The composites were compression molded and exposed to ionizing radiation in air from a Cesium-137 source. The PMMAisoot samples were characterized before and after exposure to radiation. Differential Scanning Calorimetry (DSC) was used to determine glass transition temperatures. Mechanical properties of composites were characterized via Dynamic Mechanical Analysis (DMA) and microhardness measurements. The glass transition temperatures from this study, when compared to similar studies conducted by Harmon et. a1 on purified single-wall and multi-wall carbon nanotube composites indicate that soot composites possess lower radiation resistance.

Synthesis, Characterization anc Dopamine Selectivity of 1,4-bis(3-aminopropyl)piperazine - Containing Polyimide

Abstract: A novel polyimide prepared from 1,4-bis(3-aminopropyl) piperazine and pyromellitic dianhydride (PMDA) was characterized by thermal, FTIR, GPC and microanalysis techniques. Thermal properties of the polyimide were evaluated by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetry (TGA). Moreover, platinum electrodes were covered with this polyimide and permeation properties of the resulting polyimide-coated electrodes to dopamine and ascorbic acid were examined by electrochemical method. On the basis of the permselectivity data obtained, it was found that the polyimide-coated electrode exhibited selective permeation for dopamine while blocking ascorbic acid.

Effect of regime of addition of initiator on TEMPO-mediated polymerization of styrene

Abstract: Investigation of the TEMPO-mediated polymerization of styrene at different regimes of addition of AIBN initiator showed that the course of the polymerization could be changed dramatically by a mode of the initiator addition without using any other additives. A very significant acceleration of the polymerization was reached at a specific regime without broadening the polydispersity of the resulting polymer.

Polyester nanocomposite fibers: comparison of their properties with poly(ethylene terephthalate) and poly(trimethylene terephthalate) (II)

Abstract: Two polyester nanocomposites were synthesized, one with poly(ethylene terephthalate) (PET) and the other with poly(trimethylene terephthalate) (PTT), by using organoclay. The in-situ interlayer polymerization method was used to disperse the organoclay in polyesters at different organoclay contents and at different draw ratios to produce monofilaments. The thermal stability and tensile mechanical properties increased with increasing organoclay content at a DR=1 . However, the values of the tensile mechanical properties of the hybrid fibers decreased with increasing DR. The reinforcing effects of the organoclay of the PET hybrid fibers were higher than those of the PTT hybrid fibers.

Ring-opening Polymerization of D,L -Lactide by the Single Component Rare Earth Tris(4- tert -butylphenolate)s

Abstract: Ring-opening polymerization of D,L-lactide (D,L-LA) initiated by single component rare earth tris(4-tert-butylphenolate)s has been carried out for the first time. The influences of rare earth element, solvent, temperature, monomer and initiator concentration as well as reaction time on the polymerization were investigated in detail. The kinetics study indicates that the polymerization rate is first order with respect to monomer concentration and initiator concentration, respectively. The overall activation energy of the ring-opening polymerization is 81.7 kJ.mol-1. The intensity distribution of the various stereosequence resonances in the NMR spectra reveals that transesterification proceeds slowly during the polymerization at the temperatures ≤ 90 oC. DSC data confirm the random distribution of the polymer. Mechanism studies showed that the D,L-lactide monomer inserted into the growing chains with the acyl-oxygen bond cleavage.

Modification of Epoxy by a Liquid Elastomer and Solid Rubber Particles

Abstract: This work covers studies on epoxy resin systems modified with two different rubber phases. The first modification was the use of recycled car tire rubber particles; while in the second one a silicon based liquid elastomer (Tegomer) was mixed with the epoxy resin matrix. In the third method epoxy resin was modified with both solid rubber particles and liquid elastomer together. Mechanical tests showed that these modifications resulted in no significant improvements in the mechanical performance of the epoxy resin system. Fractographic studies indicated that poor interfacial adhesion was occurred between the epoxy matrix and the solid rubber particles, while liquid elastomer resulted in formation of round rubbery domains and some plastic deformation lines in the epoxy matrix. For better improvements interfacial phenomenon will be explored.

Synthesis and characterization of complexes between poly(itaconic acid) and poly(ethylene glycol)

Abstract: Interpolymer complexes of poly(itaconic acid) and poly(ethylene glycol) (PIA/PEG) were prepared by two different procedures: simple mixing of preformed PIA and PEG and by polymerization of itaconic acid on poly(ethylene glycol) as a template. Complex formation was attributed to hydrogen bond formation between the carboxyl group of PIA and the ether group of PEG. The two types of complexes were characterized by viscometric measurements, thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy and adhesive force measurements. The results indicate that complexes prepared by template polymerization have a stronger hydrogen bonding and hence more ordered structure and better mucoadhesive properties.

Investigation of the TiCl 4 reaction order in quasiliving styrene polymerization with 1-phenylethyl chloride/TiCl 4 /Bu 2 O

Abstract: The reaction order with respect to TiCl4 was investigated in the quasiliving polymerization of styrene using a 1-phenylethyl chloride/TiCl4/Bu2O initiating system in mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at -15 °C. It was found out that the reactions order with respect to TiCl4 was closer to 1. A mechanistic scheme to explain the kinetic behavior of quasiliving styrene polymerization in 1-phenylethyl chloride/TiCl4/Bu2O is proposed.

Preparation of Polyacetylenes via Organometallic C-C Coupling Reactions

Abstract: Dehalogenative polycondensation of 1,2-dibromoethylene, trans-1,2-dichloroethylene, and cis-1,2-dichloroethylene with a Ni(0) complex gave a black polymer whose IR spectrum essentially agreed with that of trans-polyacetylene. Suzuki-Miyaura coupling between 1,2-dibromoethylene and vinylene diboronic compounds was applied to synthesis of π-conjugated polymers.

Synthesis and Characterization of a novel star shaped Rod-Coil Block Copolymer

Abstract: A novel star shaped rod-coil block copolymer, tri-armed star poly (e-caprolactone)-b-poly {2,5-bis[(4-methoxyphenyl) oxycabony] styrene} [S-(PCL-b-PMPCS)3], was successfully synthesized via atom transfer radical polymerization in chlorobenzene solution using macro-initiator and CuBr/Sparteine complex as catalyst. The results showed that the number average molecular weigh Mn was increased versus monomer conversion, and that the polydispersities Mw/Mn was quite narrow (<1.35), which were the character of controlled polymerization. The structure of the star shaped blcok copolymers was experimentally confirmed by 1H NMR. The liquid crystalline behavior of them was studied using DSC and POM. The star shaped block copolymer with low molar percentage of PMPCS block could show Tm of PCL. And only those copolymers with long rigid segment PMPCS could form liquid crystalline phase which was quite stable with a high clearing point.

Crystallization and Enthalpy Relaxation of Physically Associating, End-Linked Polymer Networks: Telechelic Pyrene-Labeled Polydimethylsiloxane

Abstract: The effects of physical crosslinking or gelation and molecular weight on the crystallization behavior of polydimethylsiloxane (PDMS) are determined by thermal analysis of telechelic, pyrene-end-labeled PDMS and its precursor, telechelic, amine-end-labeled PDMS. The pyrene-end-labeled PDMS forms physical crosslinks while the amine-end-labeled PDMS does not. The presence of physical crosslinks leads to a major reduction in PDMS crystallinity achieved during a 5 °C/min quench that is a striking function of molecular weight. In going from the amine-end-labeled PDMS to the pyrene-end-labeled PDMS, a 25 kg/mol sample exhibits a reduction in PDMS crystallinity from 59% to 30% while a 4-7 kgimol sample exhibits a reduction in PDMS crystallinity by more than an order of magnitude, from 53% to 2 to 4%, with the latter value depending on the extent of physical crosslinking achieved by the pyrenyl units at the start of the cooling cycle. The PDMS melting temperature is a strong function of physical crosslinking, while the PDMS glass transition temperature is invariant with molecular weight and type of end unit. However, the extent of enthalpy relaxation or physical aging of the PDMS achieved during a brief quench is reduced in the presence of pyrenyl end units and thus physical crosslinking.

2-Ethylhexyl acrylate/4-acryloyloxy benzophenone copolymers as UV-crosslinkable pressure-sensitive adhesives

Abstract: It has been previously shown that copolymer of 2-ethylhexyl acrylate with an 4-acryloyloxy benzophenone can be used as PSA. This paper presents synthesis and application of solvent-based polymer system for the preparation of acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate benzophenone copolymers, having molecular mass in the range of 120 000 to 380 000 Dalton were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength after UV-crosslinking to be useful as PSAs. These copolymers resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Some of the parameters affecting the pressure-sensitive adhesive properties of the copolymer are: amount of the 4-acryloyloxy, molecular mass of the polymeric components, UV-reactivity and such properties like tack, peel adhesion and cohesion.

Comparison of Rheological and Mechanical Behavior of Dynamically and Statically Vulcanized PP/SBS Blends

Abstract: Rheological behavior of dynamically and statically vulcanized blends of isotatic Polypropylene (PP) and 20% wt Styrene-Butadiene-Styrene block copolymer (SBS) was studied with reference to the effect of extrusion conditions, curing agents (sulphur, peroxide) and curing times. All blends showed pseudoplastic behavior. When using sulphur, a slight increase on melt viscosity was observed, showing no differences with vulcanization method or with pre-vulcanization time. With peroxide, melt viscosity changed drastically. Dynamically vulcanized blends with sulphur showed a noticeable rise on elongation at break as well as on toughness while those statically vulcanized showed very low values on these properties.

Synthesis and Optical Properties of Water-Soluble NIR Absorbing Star Polypeptides based on Functional Rylene Dyes

Abstract: In this contribution, the synthesis of two novel amino-functionalized terrylene and quaterrylene diimide derivatives is described. These chromophores have been used as initiators for the ring-opening polymerization of Nɛ-benzyloxycarbonyl-L-lysine N-carboxyanhydride. 4-Arm star polypeptides were obtained with number average chain lengths of 50 and 100 units. Removal of the Nɛ-benzyloxycarbonyl side-chain protective groups afforded unprecedented water-soluble terrylene and quaterrylene based star polypeptides that combined high extinction coefficients in the NIR range with very good chemical and photostability.

Synthesis of heterobifunctional poly(ethy1ene glycol) containing an acryloyl group at one end and an isocyanate group at the other end

Abstract: A New heterobifunctional poly(ethylene glycol) (PEG) having a polymerizable acryloyl group at one end and an isocyanate group at the other end was prepared in three efficient steps from commercially available t-Boc-PEG-NH 2 . The end groups were characterized by 'H NMR and MALDI-TOF-MS spectroscopy. Conjugation of the resulting PEG onto dextran via stable urethane linkage gave the PEG graft polymer with an acryloyl group at the free end of the graft chain.