Increasing Polymerization Time Research Articles

Formation Mechanism of Polyaniline Nanotubes by a Simplified Template‐Free Method

AbstractPANI nanotubes with diameters of 100–150 nm with conductivities of single nanotubes as high as 30.6 S · cm−1 were directly oxidized with APS in the absence of hard templates and acidic dopants. The high conductivity was shown to result from protons produced during the polymerization. The pH decreases with increasing polymerization time, and the morphology changes from hollow spheres to short and long tubes. It is proposed that the micelles formed by the aniline monomer in aqueous solution serve as a soft template for forming hollow spheres at the initial stage. As the polymerization proceeds, these hollow spheres are linearly aggregated and elongated to form short and long tubes.magnified image

Facile Synthesis and Intrinsic Conductivity of Novel Pyrrole Copolymer Nanoparticles with Inherent Self-Stability

Intrinsically self-stabilized nanoparticles of a copolymer from 4-sulfonic diphenylamine (SD) and pyrrole (PY) were facilely synthesized in HCl solution at 10 degrees C by a chemically oxidative polymerization. The critical reaction parameters such as SD/PY ratio, polymerization time, and oxidant species were studied to significantly optimize the polymerization yield, size, conductivity, and solubility of the final copolymer particles. The molecular structure, size, size distribution, and morphology of the particles were analyzed by IR spectroscopy, laser particle-size analysis (LPA), atomic force microscopy, and transmission electron microscopy (TEM). It was found that the polymerization yield of the SD/PY (50/50) copolymers increased dramatically in the initial 2 h of polymerization and then slowly enlarged in the subsequent 22 h. However, the copolymerization yield for the polymerization time of 24 h exhibited a nonlinear dependence on the SD/PY molar ratio, i.e., a maximum at 10/90 and a minimum at 80/20. The number-average diameter, Dn, of the copolymer particles strongly depended on the SD/PY ratio, decreasing rapidly from 6402 to 291 nm as the SD/PY molar ratio changed from 30/70 to 50/50, whereas the polydispersity index, PDI = Dw/Dn (where Dw is the weight-average diameter), surprisingly maintained very small values, decreasing slightly from 1.21 to 1.08. The SD/PY (80/20) copolymer particles prepared with (NH4)2S2O8 as the oxidant had the smallest size of ca. 10 nm by TEM and the lowest Dw/Dn value of 1.03 by LPA, whereas the copolymer particles prepared with FeCl3 as the oxidant exhibited the second smallest size of ca. 20 nm by TEM and the highest conductivity. The conductivity of the SD/PY (50/50) copolymers rose first and then decreased with increasing polymerization time from 10 min to 24 h, exhibiting a maximum (0.217 S/cm) at 12 h. It is of interest that the copolymer particles with SD/PY molar ratios in the range between 50/50 and 80/20 surprisingly exhibited the smallest size, the narrowest size distribution, and the highest conductivity at the same time. In particular, the copolymer nanoparticles exhibited high purity, clean surfaces, good self-stability, high conductivity, and strong chemoresistance that were very important to nanomaterial processibility and application. The obtained copolymers were partially soluble in concentrated H2SO4, demonstrating a new direction for synthesizing a soluble pyrrole copolymer.

Ethylene polymerization catalyzed by TiCl4/MgCl2/MCM-41 catalytic system

Ethylene polymerization was carried out with TiCl4/MgCl2/MCM-41 catalytic system. The morphology of resultant polyethylene was investigated with SEM. It was found that the polyethylene prepared with TiCl4/MgCl2/MCM-41 had fibrous morphology. With increasing polymerization time, the amount of fibers increased. In contrast, the polyethylene prepared with TiCl4/MCM-41 catalytic system only had amorphous morphology. The relations of the morphology and polymerization conditions were explained.

Preparation and characterization of hydroxyapatite/poly(ethylene glutarate) biomaterials

Hydroxyapatite/poly(ethylene glutarate) (HAp/PEG) biomaterial composites were prepared by ring-opening polymerization (ROP) of cyclic oligo(ethylene glutarate) (C-PEG) in porous HAp scaffolds. The HAp/C-PEG precomposites were prepared by immersing the porous HAp scaffolds in the mixture solution of C-PEG and dibutyl tinoxide catalyst overnight and polymerizing at 200 degrees C for 24, 48, and 72 h under vacuum. The successful ROP of C-PEG in the porous HAp scaffolds was corroborated by the signals of hydroxyl end-group of PEG shown in the (1)H NMR spectrum of the ROP-products extracted from the composites. PEG in the composites was present as a thin layer coating on the HAp grains and was evenly distributed throughout the samples. The PEG content was about 13-16 wt % and decreased with increasing polymerization time. Its molecular weight (M(w), weight average) measured by gel permeation chromatography was in the range of 4300-6800 g/mol. Compressive strength of the HAp/PEG composites was significantly increased from 3 MPa of the porous HAp scaffold to 11-15 MPa, depending on the PEG content in the composites. In vitro bioactivity of the HAp/PEG composites was studied by soaking in simulated body fluid (SBF) at 36.5 degrees C for 7-28 days. After prolonged soaking, the HAp nanocrystals precipitated from the SBF solution and formed as a layer of globular aggregates, coated on the composite surfaces. This result suggested that the HAp/PEG composite was a bioactive material.

Effect of 1‐hexene comonomer on polyethylene particle growth and copolymer chemical composition distribution

AbstractAn investigation of the polymer particle growth characteristics and polymer molecular weight and composition distributions in ethylene homopolymerization and ethylene/1‐hexene copolymerization has been carried out with a catalyst comprising a zirconocene and methylaluminoxane immobilized on a silica support. The presence of 1‐hexene leads to higher productivity and easier fragmentation of the support during particle growth. Crystallization analysis fractionation and gel permeation chromatography analysis of ethylene/1‐hexene copolymers prepared at different polymerization times reveals a broadening of the chemical composition distribution with increasing polymerization time as a result of the gradual formation of a relatively high‐molecular‐weight, ethylene‐rich fraction. The results are indicative of significant monomer diffusion effects in both homopolymerization and copolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2883–2890, 2006

Oxidative polymerization of acrylamide in the presence of thioglycolic acid

Abstract Chemical polymerization of acrylamide at room temperature was examined by using thioglycolic acid-cerium (IV) sulfate and thioglycolic acid-KMnO4 redox systems in acid aqueous medium. Water soluble polyacrylamides containing thioglycolic acid end groups were synthesized. The effects of the molar ratio of acrylamide to Ce(IV) nAAm/nCe(IV), the polymerization time, the temperature, the monomer concentration, the molar ratio of cerium (IV) sulfate to thioglycolic acid and the concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. Lower molar ratios of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20 to 70°C resulted in a decrease in the yield but generally resulted in a constant value for the molecular weight of polymer. With increasing polymerization time, the yield and molecular weight of polymer did not change substantially. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions respectively in the polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrophotometry and fluoresce measurements. The amount of Mn(II) incorporated into the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.

Synthesis of unimolecular reversed micelle consisting of a poly(L‐lactide) shell and hyperbranched D‐mannan core

AbstractA novel biodegradable unimolecular reversed micelle consisting of a poly(L‐lactide) (PLA) shell and a hyperbranched D‐mannan (HBM) core, that is, a chestnut‐shaped polymer (PLA–HBM), was synthesized by the polymerization of L‐lactide on HBM with 4‐(dimethylamino)pyridine (DMAP) as the catalyst. The obtained polymers were soluble in dimethyl sulfoxide, tetrahydrofuran, and chloroform but insoluble in H2O. The molecular weights of the PLA chain on PLA–HBM tended to increase with increasing polymerization time. The number of PLA chains on PLA–HBM could be controlled by the ratio of DMAP to the sugar unit in HBM. The obtained copolymer, PLA–HBM, acted as a unimolecular reversed micelle with an encapsulation ability toward the hydrophilic molecule. In addition, the entrapped hydrophilic molecules were slowly released from the core of PLA–HBM, and the release rate was accelerated by the breaking of the PLA chains of the shell when proteinase K as a hydrolase of PLA was used. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 406–413, 2006

Polymerization of propylene with [ t-BuNSiMe 2Ind]TiMe 2–MAO catalyst systems

ansa-Indenylamidodimethyltitanium complex ([ t-BuNSiMe 2Ind]TiMe 2: 1) was synthesized by one-pot reactions starting from the ligand, MeLi and TiCl 4. The structure of 1 was determined by X-ray crystallography and the results obtained revealed that the indenyl ligand coordinate to titanium in an η 4-tendency. Propylene polymerization was conducted with 1 in toluene or heptane as solvent at 0 °C in the presence of dried methylaluminoxane (MAO) or dried modified MAO (MMAO), which was prepared from the toluene solutions of MAO or MMAO by removing free trialkylaluminium contained. Polymerization behavior was investigated from the consumption rate of propylene in a semi-batch system. The dried MAO/toluene system showed the highest activity without any deactivation. The produced polymer in the dried MAO/toluene system had the highest molecular weight and narrowest molecular weight distribution. The number-average molecular weight of the polymer increased almost linearly with increasing polymerization time accompanied by narrowing molecular weight distribution from 1.42 to 1.37 and the number of polymer chains was almost constant. Thus, it was found that quasi-living polymerization of propylene proceeded. The 13C NMR measurement indicated that 1-dried MAO/toluene produced poly(propylene) with isotactic triad of 40%.

Plasma‐graft polymerization of a monomer with double bonds onto the surface of carbon fiber and its adhesion to a vinyl ester resin

AbstractDouble bonds reactive with active radical species were introduced onto the surface of carbon yarn by the plasma‐graft polymerization of adipic acid divinyl ester and ethylene glycol dimethacrylate monomers to increase the adhesive strength in the interface between the carbon yarn and a vinyl ester resin. The degree of grafting increased with increasing polymerization time and polymerization temperature. The degree of grafting depended on both the solvent and the monomer species used in the polymerization, and a high degree was obtained with ethylene glycol dimethacrylate as the conjugated monomer and in a mixture of methyl isobutyrate and water. The grafted yarn, whose surface layer contained double bonds, was reacted with a vinyl ester resin containing benzoyl peroxide and N,N‐dimethylaniline. The pull‐out force of the yarn embedded in the resin increased with increasing degree of grafting. The failure in pulling out the yarn was cohesive. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2415–2419, 2003

Graft Copolymerization of 2‐Acrylamido‐2‐methyl Propane Sulfonic Acid on Dimethyl Sulfoxide Pretreated Poly(Ethylene Terephthalate) Films Using Cerium Ammonium Nitrate as Initiator

In this study, graft polymerization of 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) on poly(ethylene terephthalate) (PET) films using cerium ammonium nitrate (CeAN) as an initiator was investigated. Before the polymerization reaction was carried out, films were swelled in dimethyl sulfoxide (DMSO) at 140°C for 1 h. The effect of polymerization temperature, time, initiator, and monomer concentrations on the graft yield were investigated. It was observed that the graft yield was initially increased with increasing temperature, monomer, and initiator concentrations; and then decreased. Graft yield was found to increase with increasing polymerization time up to 5 h, then remain constant. The effects of monomer and initiator inclusions on the grafting yield were also examined. Optimum conditions for grafting were found to be [AMPS] = 1.0 M, [Ce4+] = 1.5 × 10−2 M, T = 85°C and t = 5 h. The rate of grafting was found to be proportional to the 0.1 and 0.4 powers of monomer and initiator concentrations, respectively. The overall activation energy for the grafting was calculated to be 11.4 kcal mol−1. The effect of grafting on PET film properties such as intrinsic viscosity and water absorption capacity were determined. The grafted PET films were characterized with FTIR spectroscopy and scanning electron microscopy (SEM).

Composition distribution of ethylene or propylene–norbornene copolymers obtained with zirconocene catalysts

AbstractCopolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac‐ethylenebis(indenyl)zirconium dichloride, rac‐dimethylsilylenebis(indenyl)zirconium dichloride (2), rac‐dimethylsilylenebis(2‐methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature‐rising elution fractionation of the copolymers was carried out with cross‐fractionation chromatography with o‐dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2, and the higher‐temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003

Formation of Triangular Polymer Domains in Surfactant Films Adsorbed on Solid Substrate.

An attempt was made to prepare ultrathin polystyrene films in the surfactant film formed on a mica substrate immersed in aqueous solution of tetradecyltrimethylammonium bromide (C14TAB), a cationic surfactant. Formation of polystyrene film was confirmed in the adsorbed C14TAB film on the basis of contact angle and IR spectrum measurements. Examination of the ultrathin film by AFM revealed that triangular polymer domains are formed on the substrate with all triangle sides aligning in the same directions at low concentrations of styrene (up to 43.6 mM). Use of sodium dodecysulfate (SDS) films adsorbed on a mica substrate also gave triangular polystyrene domains, the size of which increased with increasing polymerization time. The observed triangular structure was suggested to be formed under the influence of the hexagonal lattice of mica, independently of the properties of adsorbed surfactant films.

Glycoconjugated Polymer II. Synthesis of Polystyrene-block-poly(4-vinylbenzyl glucoside) and Polystyrene-block-poly(4-vinylbenzyl maltohexaoside) via 2,2,6,6-Tetramethylpiperidine-1-oxyl-Mediated Living Radical Polymerization

The polymerizations of glycoconjugated monomers, i.e., 4-vinylbenzyl glucoside peracetate (1a) and 4-vinylbenzyl maltohexaoside peracetate (1b), were carried out using 2,2,6,6-tetramethylpiperidine-1-oxyl-terminated polystyrene (PS-TEMPO, Mn=8100 and Mw/Mn=1.17) as a macromolecular initiator in xylene at 120°C ([1]/[PS-TEMPO] = 25). The Mn of the product increased from 9900 to 12700 for the polystyrene-block-poly-1a (2a) and from 14200 to 16200 for the polystyrene-block-poly-1b (2b) with the increasing polymerization time, whereas the Mw/Mn values were constant at 1.13–1.21. The deacetylation of 2a and 2b using sodium methoxide in dry-THF provided amphiphilic block copolymers containing glucose and maltohexaose as hydrophilic segments, i.e., polystyrene-block-poly(4-vinylbenzyl glucoside) (3a) and polystyrene-block-poly(4-vinylbenzyl maltohexaoside) (3b). The solution property of the block copolymers 3a and 3b in toluene (a good solvent for polystyrene) and H2O (a good solvent for saccharides) varied depending on the weight fraction of the glucose residues (fg, wt%) in 3, i.e., 3a with an fgs of 4, 10, and 14 wt% formed reversed micelle-like aggregate in toluene, whereas 3a with an fg of 17 wt% and 3b with an fg of 37 and 50 wt% formed micelle-like aggregates in H2O.

Living-Like Polymerization of Propylene with Mixed Metallocene Catalyst Systems

Propylene polymerization was conducted with the Cp2ZrHCl/B(C6F5)3/[tBuNSiMe2Flu]TiMe2 catalyst system with AlOct3 as a scavenger at –50°C. The polymer obtained displayed a bimodal molar mass distribution. It could be confirmed that the polymer with higher M̄n was produced from Zr active sites and the polymer with lower M̄n resulted from Ti active sites. In both fractions, M̄n was increased linearly with increasing polymerization time. The MWD (M̄w/M̄n) values of each fraction were around 1.1. Thus, it could be said that propylene polymerization proceeded in a living manner even with zirconocene active species by using the mixed metallocene system. The living-like polymerization of propylene with Cp2ZrMe2/B(C6F5)3 /Cp*TiCl3 was also demonstrated at –50°C. Under the reaction between carbon monoxide (CO) and this living polypropylene (PP) at –78°C, it could be found that CO was quantitatively incorporated into living PP.

Influence of the polymerization conditions on the impact properties of metallocene‐catalyzed copolymers of ethylene and aryl‐substituted norbornenes with low exo/endo ratios

When testing copolymers of ethylene and aryl-substituted norbornenes with the Charpy impact method it was found that under certain polymerization conditions their impact properties increased with increasing polymerization time. It was also found that this improvement on impact properties was due to increasing exo/endo ratios of the incorporated aryl-substituted norbornene comonomers. This effect is important because impact-resistant copolymers can be made using aryl-substituted norbornene comonomers with low exo/endo ratios, which are more easily synthesized and purified. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1108–1117, 2000

Doxorubicin-loaded poly(butylcyanoacrylate) nanoparticles produced by emulsifier-free emulsion polymerization

ABSTRACT: Doxorubicin-loaded poly(butylcyanoacrylate) (PBCA) nanoparticles (NPs) were prepared by an emulsifier-free emulsion polymerization technique. The pH values of the polymerization medium and the weight ratios of doxorubicin to butylcyanoacrylate had a significant effect on the mean particle size. The particle diameter determined by transmission electron microscopy showed that the nanoparticles were predominantly less than 50 nm. Drug loading and entrapment efficiency increased with increasing pH of the medium. The surface tension of the polymerization media increased with increasing polymerization time and reached a plateau after 4 h. Doxorubicin-loaded PBCA NPs carried a positive charge, and the zeta potential of drug-loaded nanoparticles increased with the increase of the polymerization pH. Molecular weight, analyzed by gel permeation chromatography, showed that the nanoparticles mainly consisted of oligomers of PBCA. The release rate of doxorubicin from nanoparticles in biological phosphate buffer was very slow, with a half-life of 111.43 h. The results indicate that drug-loaded nanoparticles can be prepared by an emulsifier-free emulsion polymerization technique and that the resulting nanoparticles might be suitable for targeting drug delivery vehicles for clinical application. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 517–526, 2000

Influence of the polymerization conditions on the impact properties of metallocene-catalyzed copolymers of ethylene and aryl-substituted norbornenes with low exo/endo ratios

When testing copolymers of ethylene and aryl-substituted norbornenes with the Charpy impact method it was found that under certain polymerization conditions their impact properties increased with increasing polymerization time. It was also found that this improvement on impact properties was due to increasing exo/endo ratios of the incorporated aryl-substituted norbornene comonomers. This effect is important because impact-resistant copolymers can be made using aryl-substituted norbornene comonomers with low exo/endo ratios, which are more easily synthesized and purified. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1108–1117, 2000

Lipase-catalyzed ring-opening polymerization of 3(S)-isopropylmorpholine-2,5-dione

Lipase-catalyzed ring-opening bulk polymerizations of 3(S)-isopropylmorpholine-2,5-dione (IPMD) were investigated. Selected commercial lipases were screened as catalysts for IPMD polymerization at 100°C. Polymerizations catalyzed with lipases PPL, PS, and CR result in IPMD conversions of about 50%, and in molecular weights of the products ranging from 3500 to 17500. Poly(3-isopropylmorpholine-2,5-dione) has a carboxylic acid group at one end and a hydroxyl group at the other end. During the polymerization, racemization of the valine residue takes place. Lipase PPL was selected for further studies. The apparent rate of polymerization increases with PPL concentration and polymerization time. When the PPL concentration is 5 wt.-% and 10 wt.-% with respect to the monomer, a conversion of about 70% is reached after 5 d and 7 d, respectively, while for PPL concentrations of 1 wt.-% and 0.5 wt.-% the conversion is less than 15% even after 11 d. High concentrations of PPL (10 wt.-%) result in high M n values (<4 d); with decreasing concentration of PPL, poly(IPMD) of lower molecular weight is obtained. The highest molecular weight poly(IPMD), M n = 30000, resulted from a polymerization conducted at 130°C. Increasing polymerization time (and conversion) leads for high PPL concentration (10 wt.-%) first to an increase in M n and later to a decrease. The general trends observed by variation of the polymerization temperature are the following: (i) increasing monomer conversion and M n increase with increasing reaction temperature from 100 to 130°C, (ii) increasing reaction temperature leads to a bimodal molecular weight distribution. Water is an important factor that controls not only the conversion but also the molecular weight. With increasing water content, enhanced polymerization rates are achieved while the molecular weight of poly(IPMD) decreases.

Composite Membranes Prepared from Cation Exchange Membranes and Polyaniline and Their Transport Properties in Electrodialysis

A cation exchange membrane was modified with polyaniline by polymerizing aniline with ammonium peroxodisulfate on the membrane surfaces, producing a membrane with polyaniline layers on both surfaces or a membrane with a single polyaniline layer on the surface. The modified membranes, composite membranes, showed sodium ion permselectivity in electrodialysis compared with divalent cations at an optimum polymerization time. The electronic conductivity of dry membranes showed a maximum at the same polymerization time as the time to attain a maximum value of the sodium ion permselectivity. Because emeraldine‐based polyaniline is conductive and has a cationic charge, the sodium ion permselectivity is based on the difference in the electrostatic repulsion forces of the cationic charge on the membrane surface of a desalting side to divalent cations and sodium ions. In fact, the selective permeation of sodium ions appeared only when the layer faced the desalting side of the membrane, and was affected by dissociation of polyaniline. Further oxidized polyaniline, pemigraniline‐based polyaniline, did not affect the permselectivity between cations, and the diffusion coefficient of neutral molecules, urea, increased with increasing polymerization time. Sodium ion permselectivity was maintained with repeated electrodialysis. © 1999 The Electrochemical Society. All rights reserved.

Grafting of Polymers Having Pendant Peroxycarbonate Groups Onto Carbon Black and Postpolymerization of Vinyl Monomers

Postpolymerization of vinyl monomers initiated by pendant peroxycarbonate groups of grafted polymer chains on carbon black (CB) was investigated. The grafting of polymers having pendant peroxycarbonate groups onto CB was achieved by the trapping of polymer radicals formed by the thermal decomposition of copolymers of t-butylperoxy-2-methacryloyloxyethyl-carbonate (HEPO) with vinyl monomers such as vinyl acetate (VAc), styrene (St) and methyl methacrylate (MMA). The copolymers having pendant peroxycarbonate groups were prepared by copolym-erization of HEPO with vinyl monomers using azo initiator under irradiation of UV light at room temperature. The amount of remaining pendant peroxycarbonate groups of the poly(VAc-co-HEPO)-grafted CB obtained from the reaction at 90°C was maximum and decreased above the temperature. Furthermore, the postpolymerization of vinyl monomers, such as St, MMA, and VAc was initiated in the presence of poly(VAc-co-HEPO)-grafted and poly(St-co-HEPO)-grafted CB and the corresponding polymers were postgrafted onto CB to give branched polymer-grafted CB. The percentage of poly(St)-postgrafting (proportion of post-grafted poly(St) to poly(MMA-co-HEPO)-grafted CB used) increased with increasing polymerization time, but became constant at 20% after 4 hours.