Low Monomer Concentration Research Articles

Chelating polymer granules prepared by radiation-induced homopolymerization. I?Kinetic study of radiation polymerization process

Chelating polymer granules containing amidoxime chelating groups were synthesized by radiation-induced homopolymerization of acrylonitrile monomer. The chemical reactive intermediate polyacrylonitrile was treated with hydroxylamine solution to convert the chemical active cyano groups into the amidoxime groups. Kinetic study of the effects of monomer concentration, radiation dose, dose rate, and temperature on the polymerization process was investigated. It was found that at low monomer concentration, the rate of polymerization is roughly independent on the initial monomer concentration, while at high monomer concentration, 35–65%, a marked acceleration on the rate was observed. The order of the dependence of the initial rate of polymerization on the dose rate is 0.77, which deviates from the classical square-root law due to the precipitation of the formed polymer. The conversion percent and molecular weight of the produced polymer are inversely proportional to dose rate at constant radiation dose. The activation energy was found to be 2.7 kcal/mol, and the rate constant of initiation is independent of temperature. The effect of type of solvent on the polymerization was studied. DMF solvent of the closest solubility parameter to the solubility parameter of polyacrylonitrile is the best solvent for the polymerization process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1405–1412, 2000

Synthesis of porphyrin-PPV copolymers for application in LEDs

A new series of soluble porphyrin-containing copolymers have been synthesized via the Gilch methodology [1], for use in light-emitting devices (LEDs). These materials consist of random copolymers of 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene (MEH-PPV) and a porphyrin-substituted phenylene vinylene. Low concentrations of porphyrin monomers were used in order to improve solubility, and help prevent aggregation (and consequent fluorescence quenching) of the porphyrin units. Emission is red-shifted from that expected in dialkoxy-PPVs such as MEH-PPV owing to an efficient exciton transfer to the fluorescent porphyrin unit.

Kinetics and reaction mechanism of template polymerization investigated by conductimetric measurements. 2. Radical polymerization of sodium methacrylate in the presence of poly(allylamine) hydrochloride

The polymerization of sodium methacrylate in water was investigated using conductimetry and dilatometry. Conductimetry was shown to be a reliable tool for the determination of the kinetic parameters of the blank polymerization (order of reaction with respect to monomer and initiator, activation energy). The conductimetric investigation of template polymerization of the acrylic monomer onto poly(allylamine) hydrochloride at low monomer concentration indicates that the reaction proceeds by a ‘zip’ mechanism. © 1999 Society of Chemical Industry

Horizontal chevron domain formation and smectic layer reorientation in SmC* liquid crystals stabilized by polymer networks

The influence of a polymer network, stabilizing an initial texture of horizontal chevron geometry, on the in-plane smectic C* layer reorientation process is studied for different applied electric field conditions. As expected, the reorientation of smectic layers is strongly slowed down and eventually suppressed by the network, even at rather low monomer concentrations. Polymer network formation in a uniformly reoriented smectic layer state reveals that the network acts in two ways: first it gives a biased elastic torque counteracting a field of such symmetry as to cause a change from the templated layer direction; second it introduces an increased effective viscosity counteracting the reorientation in both directions. The behaviour of samples stabilized by two different kinds of polymer networks, created in between the smectic layers (intra-layer) and across them (inter-layer), is then investigated and discussed.

Phase separation in free-radical crosslinking copolymerization: formation of heterogeneous polymer networks

A model combining both the thermodynamic and kinetic aspects of free-radical crosslinking copolymerization (FCC) is presented to predict the formation conditions and the properties of heterogeneous (porous) networks. The model involves thermodynamic equations describing the phase equilibria between the network and separated phases during FCC of vinyl/divinyl monomers and kinetic equations giving the concentration of reacting species and the polymer properties as a function of the monomer conversion. Calculation results are presented for styrene/ m-divinylbenzene (S/ m-DVB) copolymerization system in the presence of inert diluents. S/ m-DVB copolymerization system at a high m-DVB concentration, or, at a low monomer concentration phase separates at the gel point and results in the formation of a microgel solution. The calculation results also show that the heterogeneity in S/ m-DVB copolymer networks increases on increasing DVB or diluent concentration, or, on decreasing the solvating power of the diluent, in accord with the experimental data published previously. The model also predicts correctly the equilibrium volume swelling ratio of heterogeneous networks in solvents.

Functionalization of polyolefins and elastomers with an oxazoline compound

The aim of this work was to graft ricinoloxazoline maleinate (OXA) onto polyethylene (PE), and onto an ethylene propylene copolymer (E/P) and styrene ethylene/butylene styrene copolymer (SEBS), by melt free radical grafting in a twin-screw midiextruder. A study was made of the effects of the initial monomer and peroxide concentrations and of temperature on the degree of grafting, on the amount of residual monomer, and on the molecular weight. The initial monomer and peroxide concentrations were 1.5–9.0 wt % and 0.15–0.90 wt %, respectively. The grafting yield was found to increase with the initial monomer and peroxide concentrations. Grafting yields up to 2.1 wt % for PE, 2.3 wt % for E/P and 2.7 wt % for SEBS were achieved. The degree of grafting also varied considerably with the temperature. E/P and SEBS decomposed with low initial monomer and peroxide concentrations, but crosslinked with raising the initial concentrations. Polyethylene crosslinked even with low initial concentrations, but with a suitable choice of peroxide grafted polyethylene could be produced with good grafting yields and without gel formation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 877–885, 1999

Functionalization of polyolefins and elastomers with an oxazoline compound

The aim of this work was to graft ricinoloxazoline maleinate (OXA) onto polyethylene (PE), and onto an ethylene propylene copolymer (E/P) and styrene ethylene/butylene styrene copolymer (SEBS), by melt free radical grafting in a twin-screw midiextruder. A study was made of the effects of the initial monomer and peroxide concentrations and of temperature on the degree of grafting, on the amount of residual monomer, and on the molecular weight. The initial monomer and peroxide concentrations were 1.5–9.0 wt % and 0.15–0.90 wt %, respectively. The grafting yield was found to increase with the initial monomer and peroxide concentrations. Grafting yields up to 2.1 wt % for PE, 2.3 wt % for E/P and 2.7 wt % for SEBS were achieved. The degree of grafting also varied considerably with the temperature. E/P and SEBS decomposed with low initial monomer and peroxide concentrations, but crosslinked with raising the initial concentrations. Polyethylene crosslinked even with low initial concentrations, but with a suitable choice of peroxide grafted polyethylene could be produced with good grafting yields and without gel formation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 877–885, 1999

Studies on poly(diphenylamine) synthesized electrochemically in nonaqueous media

Poly(diphenylamine) has been synthesized electrochemically under galvanostatic condition in nonaqueous acetonitrile media at different monomer concentrations. The UV–Vis spectra reveals the selective formation of conducting phase ∼840 nm at a low monomer concentration of 0.05 M. An increase in monomer concentration to 0.1 and 0.4 M leads to a loss in selectivity in the formation of conducting phase (especially at a higher time interval). The characteristics observed in the IR absorption spectra are in accordance with those obtained in the UV–Vis spectra. Morphology of the films exhibit a change over from fibrillar to granular type on going from a monomer concentration of 0.05 to 0.4 M. The effect of monomer concentration on the redox properties of diphenyl amine and poly(diphenylamine) are investigated using a cyclic voltammetric technique. On comparing the two sets of cyclic voltammograms, a shift in peak potential is observed. From the thermal analysis it is found that the loss in second step is greater at lower monomer concentration due to predominant formation of conducting phase.

Chain transfer reactions in propylene polymerization with zirconocene catalysts

The chemical structures of end groups of medium-low molecular weight atactic and isotactic polypropylenes (a-PP and i-PP), produced with zirconocene/methylalumoxane catalysts, have been analyzed and used to infer the chain-transfer reaction mechanisms, which are then correlated with the zirconocene ligand structure and the polymerization conditions. For the chiral, isospecific ansa-zirconocenes such as rac-[ethylenebis(1-indenyl)]ZrCl2/methylalumoxane (1/MAO) and rac-[ethylenebis(4,7-dimethyl-1-indenyl)]ZrCl2/methylalumoxane (2/MAO) catalysts, i-PP molecular weight is dependent on the regiospecificity of the catalyst, as shown by the presence of cis-2-butenyl end groups, formed by chain transfer to the monomer after a secondary propylene insertion. At low monomer concentration, chain-transfer with 2/MAO shifts from predominant transfer to the monomer after a secondary propylene insertion to β-methyl (allyl end groups) and β-hydrogen transfers after a primary insertion (2-propenyl, or vinylidene, end group). Ansa-bis(3-R-indenyl)ZrCl2 (ansa = CH2CH2, Me2Si, Me2C; R = Me, t-Bu, Me3Si) catalysts, which are highly regiospecific, produce polypropylenes with chain transfer via both β-hydrogen transfer after a primary insertion and β-methyl transfer. For example, rac-Me2C(3-t-Bu-Ind)2ZrCl2 (4) exhibits the highest selectivity for β-methyl transfer so far observed in an isospecific zirconocene. As for 2/MAO, the rate of β-methyl transfer in 4/MAO increases by lowering [propylene].

Cationic Polymerization of 1,3-Pentadiene Initiated by Aluminum Chloride: Determination of the Various Side Reactions

The polymerization of 1,3-pentadiene initiated by AlCl3 was investigated in a nonpolar medium at room temperature. It was shown that, besides propagation, the system undergoes various side reactions such as cross-linking, cyclization, double bond isomerization, .... An examination of the various possible structures of the polymer showed that the comparison of the 1H and 13C quantitative NMR spectroscopies allows the determination of the relative importance of cyclization and double bond isomerization. It is shown that some of these side reactions can be kept under control: for instance cross-linking could be avoided at low monomer concentration, while cyclization could be strongly decreased at high monomer concentration and by catalyst sublimation. Double bond isomerization was eliminated in the presence of a transfer agent such as methyl-2-butene-2.

Simulation Study to Model Extremely Slow Reaggregation Processes in Micelle Solutions

Photon correlation measurements on the dodecylpyridinium iodide/water system as nuclei had shown that large micelles are formed after a temperature jump from 80 to 25 °C. The micellar radius exhibits relaxation characteristics with extremely long relaxation times, reaching values up to several hours. Proceeding from a thermodynamic approach of the size distribution of aggregates, model calculations have been performed in which the nonlinearized rate equations of the underlying isodesmic reaction scheme have been used to describe the micelle kinetics. The results of these calculations give valuable indications of the mechanism behind the extremely slow relaxation. In the solutions under consideration, the nucleation of a sufficient number of micellar aggregates obviously is hindered by the extremely unfavorable equilibrium concentration of intermediates of submicellar size. This leads to a strongly deviating nonequilibrium distribution with an excess of extra large micelles during thermal equilibrium. Establishing the final equilibrium is then a very slow process, due to the low monomer concentration, which is maintained by the presence of the extra large micelles. Our model is also capable to verify the slow and fast relaxation process as predicted by the linearized Aniansson−Wall model. It also shows up the ultrafast process of oligomer formation as studied recently by broadband ultrasonic spectrometry.

One-step electrochemical process for the formation of poly( N-methylpyrrole) coatings on steel in different media

Poly ( N-methylpyrrole) coatings have been successfully formed on steel by a one-step electrochemical process in different media. Electropolymerization was performed in aqueous medium with low monomer concentration and in a mixed aqueous/organic media with higher monomer concentrations. Ethanol (EtOH) and N,N-dimethylformamide (DMF) were chosen as the organic components of the mixed solvents and oxalic acid was used as the electrolyte. The effect of process parameters on the formation of poly( N-methylpyrrole) was systematically investigated. The composition and morphology of the coatings were also studied by elemental analysis, FT-IR and scanning electron microscopy (SEM). Our results reveal that the formation and properties of poly ( N-methylpyrrole) coatings were all dependent on the solvent composition and other process parameters. The amount of poly( N-methylpyrrole) formed on steel increased with time and applied current for all the solvent-electrolyte systems. For the electropolymerization performed in distilled water-oxalic acid solution, the amount of polymer coatings formed decreased with increased electrolyte concentration. In contrast, the amount of polymer coatings formed on steel in distilled water:ethanol (1:1)-oxalic acid and distilled water:DMF (1:1)-oxalic acid systems, increased with increasing electrolyte concentration. By controlling the electrochemical parameters, smooth, uniform and strongly adherent coatings could be formed onto steel substrates.

Extremely Slow Reaggregation Processes in Micelle Solutions. A Dynamic Light Scattering Study

Photon correlation measurements were performed on the dodecylpyridinium iodide/water system to yield the mean radius of micelles as a function of the time interval after a change in the temperature from 80 to 25 °C. Depending on the purification procedure applied to the sample, large aggregates, probably with dust particles as nuclei, may be formed after the temperature jump. Simultaneously, large micelles are also formed, the radius of which may reach four times the equilibrium value of the system. The micellar radius exhibits relaxation characteristics with extremely long relaxation times, reaching values up to several hours. Obviously, the nucleation of a sufficient number of micellar aggregates is hindered by the extremely unfavorable equilibrium concentration of submicellar-size intermediates. This leads to a strongly deviating nonequilibrium distribution with an excess of extra large micelles during the thermal equilibrium. Establishing the final equilibrium is then a very slow process, due to the low monomer concentration, which is maintained by the presence of the extra large micelles.

Polymerization of polymer/ferroelectric liquid crystal composites formed with branched liquid crystalline bismethacrylates

Polymerization and phase behaviour of a branched liquid crystalline bismethacrylate in a ferroelectric liquid crystal (FLC) were characterized. Addition of the monomer increases the temperature range of the smectic A phase, and, at relatively low concentrations of monomer, the temperature range increases to more than 10 times that observed in the neat FLC. Other phases such as the smectic C* phase are no longer exhibited as the monomer interferes with the inherent tilt of the FLC molecules. After polymerization, the polymer network phase separates and the phase transition temperatures return to values close to those of the FLC. The monomer also shows a high degree of orientational order before polymerization, which is retained to a large extent after polymerization. The order in the polymer network results in considerable birefringence at temperatures well above the clearing point of the pure FLC. This behaviour is induced by the order of the polymer network and interactions of the FLC molecules with the network which prevent a fraction of the FLC molecules from exhibiting typical phase behaviour. In the formation of the branched liquid crystalline bismethacrylates/FLC composites, a steady increase is observed in the polymerization rate as the polymerization temperature increases and the order of the FLC phase decreases, a behaviour significantly different from that observed in other monomer/FLC mixtures for which the polymerization rate increases as the order of the FLC phase increases. Additionally, at appropriate polymerization temperatures around the clearing point, polymerization driven endothermic phase transitions may be observed.

Electrochemical synthesis of intrinsically conducting polymers of 3-alkylpyrroles

In the present work the electrochemical polymerization of pyrrole (Py) derivatives has been performed in order to identify the conditions for obtaining intrinsically conducting polymers, checking film morphology and conductivity. The study mainly concerns 3-alkylsubstituted pyrroles with different chain lengths (3-hexylpyrrole (3HP), 3-decylpyrrole (3DP), 3-hexadecylpyrrole (3HDP)). In the case of 3DP (0.01 M) various experimental conditions have been adopted: different solvents (propylene carbonate, acetonitrile), different counterions (ClO 4 −, BF 4 −, NO 3 −, PF 6 −, TsO −) with the same cation Bu 4N + and different current densities (0.05, 0.1, 0.2, 0.4 mA cm −2) in the case of BF 4 − in propylene carbonate. Porous and elastic films are obtained when the substituent alkyl side chain is longer and the supporting electrolytes are ClO 4 −, BF 4 −, PF 6 −; with these last electrolytes the best conductivity is also obtained (0.1–0.8 S cm −1 for poly(3-decylpyrrole), P3DP). P3DP(TsO) and P3DP(NO 3), aside from the type of solvent, show poor mechanical properties and low electrical conductivity (10 −3 and 10 −6 S cm −1 for P3DP(TsO) and P3DP(NO 3), respectively). The conductivity decreases as the alkyl side chain becomes longer. When the polymerization is performed at low monomer concentration (of the order of 0.001 M), the surface properties of P3DP(ClO 4) are very poor and the conductivity is only 10 −3 S cm −1. The obtained polymers have also been electrochemically characterized through cyclic voltammetry. The voltammetric evolution observed during cycling is studied under different experimental parameters (counterion type, solvent nature and electrochemical cycling). The cyclic voltammetry change, regarding the gradual shift to negative potentials of the redox process on P3DP with ClO 4 −, BF 4 − and PF 6 − as counterions, seems to be ascribed to a gradual deprotonation process. Analysing the voltammetric profile change from the point of view of a deprotonation process, it can be concluded that this process is speeded up by the basic character of the solvent (propylene carbonate) and in the presence of a basic counterion (tosylate) this is almost complete and immediate. P3DPNO 3, although conductive (10 −6 S cm −1), can be switched from the oxidized form to the reduced one only a few times in acetonitrile and never in propylene carbonate, showing the difficulty of the polymer in being reduced and oxidized several times.

Polymerization of N-vinylcarbazole by rhenium carbonyl compounds

The polymerization of N-vinylcarbazole by rhenium carbonyl compounds such as Re2(CO)10 and Re(CO)5X (X = Br, Cl, I) has been carried out photochemically at 355 nm (bulk) and thermally at 25 and 70°C in dichloromethane. The effects of the catalyst structure, the concentrations, the solvent's polarity, and the ligand's structure were examined. Polymerization proceeds very rapidly at low monomer and catalyst concentrations. The molecular weight of the resulting polymer was determined by viscosity.

Aromatic polymers obtained by precipitation polycondensation. 6. Morphology of polyketone particles

AbstractSyntheses of aromatic polyketones in the form of particles were performed using a very small monomer concentration (0.05 mol/1) by the precipitation polycondensation method. Some of these particles present highly ordered elongated needle‐like structures (whiskers) particularly for the all‐para polyketone samples. The use of isophthaloyl instead of terephthaloyl for the same low monomer concentration produces, in addition to the globular particles, bundles of ribbon‐like structures. The average size of the needle‐like particles is 1−5 μm in width and 150−250 μm in length. The factors controlling the morphology texture and size of the whiskers and ribbons are shown to be the polymer structure and the reaction conditions. Formation mechanisms are discussed.

Aromatic polymers obtained by precipitation polycondensation, 2. Synthesis of poly(ether ketone ether ketone ketone) (PEKEKK)

AbstractA high molecular weight, linear aromatic poly(ether ketone ether ketone ketone) (PEKEKK) has been synthesized by electrophilic Friedel‐Crafts acylation condensation of 1,4‐diphenoxybenzophenone with terephthaloyl chloride. The syntheses were performed as precipitation polycondensations, and the polyketones were obtained in particle form. The viscosity (molecular weight), shape and size of these particles were found to be strongly dependent on the reaction conditions. For low monomer concentration, highly ordered needle‐like particles were also obtained. The chemical structure of the polymers obtained was confirmed by 1H and 13C NMR spectroscopy, and para‐substitution in aryl fragments of the main chain was identified. Analysis of the expanded 1H NMR spectra for the ring proton resonances reveals defect meta‐ and ortho‐structures. The amount and isomer ratio of these defect structures depend on the monomer concentration used.

Preparation of Copolymer Particles of Styrene withN-Vinylimidazole–Metal Complexes

The preparation of fine copolymer particles ofN-vinylimidazole–metal complexes with styrene by emulsifier-free emulsion polymerization was investigated. Monodisperse spherical particles were formed in low concentrations of monomers. Significant amounts of Co and Ni were introduced into the copolymer particles. The amounts of Co incorporated into the particles are higher than those of Ni.

Polymerization of methacrylic acid esters with the aged system of lanthanum versatate and p‐chlorobenzenediazonium tetrafluoroborate

AbstractThe aged system of lanthanum versatate (1) and p‐chlorobenzenediazonium tetrafluoroborate (2) was found to initiate effectively the radical polymerization of acrylic monomers including alkyl methacrylates, butyl acrylate and acrylonitrile, although its initiating activity is lower than that of the non‐aged system. The polymerization of methyl methacrylate (3) with the aged 1/2 system was studied kinetically in acetone. The initial polymerization rate (Rp) is expressed by Rp = Kċ[aged 1/2]0.80 ċ [3]1.1 at 50°C. The overall activation energy of the polymerization is 59.0 kJ ċ mol−1. The molecular weight of the resulting poly(3) formed in the early stage increases with increasing conversion. The polymerization system involves a persistent radical showing a four‐line EPR spectrum with a g‐value of 2.004. A three‐line spectrum due to the nitroxyl radical was also observed at lower monomer concentrations. The total concentration of persistent radicals was found to correspond well to the instantaneous polymerization rate. The copolymerization of styrene (M1) and 3 (M2) with the aged initiator system was examined at 50°C in acetone. r1 and r2 are 0.19 and 0.47, respectively. The former is considerably smaller than that (0.52) reported for the conventional radical polymerization.