Rate and molecular weight distribution modeling of syndiospecific styrene polymerization over silica-supported metallocene catalyst

The kinetics of syndiospecific polymerization of styrene over silica-supported Cp^∗Ti(OCH₃)₃/MAO catalyst has been investigated through experimentation and theoretical modeling. At low monomer concentrations, the polymerization rate increases almost linearly with monomer conversion, but the reaction rate becomes independent of monomer concentration at high bulk phase monomer concentrations. A kinetic model that incorporates the monomer partition effect between the solid and the liquid phases has been proposed. The model simulations show that the observed non-linear kinetics can be adequately modeled by the monomer partition model. The polymer molecular weight has also been found to increase with the monomer concentration and the polymer molecular weight distribution (MWD) is quite broad, suggesting that the catalytic behavior deviates from the single site catalytic polymerization model. The MWD broadening is modeled by a two-site kinetic model and a good agreement between the model and the experimental data has been obtained.     

Ethylene polymerization over supported titanium‐magnesium catalysts: Effect of polymerization parameters on the molecular weight distribution of polyethylene

The data on the effects of polymerization duration, cocatalyst, and monomer concentrations upon ethylene polymerization in the absence of hydrogen, and the effect of an additional chain transfer agent (hydrogen) on the molecular weight (MW), molecular weight distribution (MWD), and content of vinyl terminal groups for polyethylene (PE) produced over the supported titanium‐magnesium catalyst (TMC) are obtained. The effects of these parameters on nonuniformity of active sites for different chain transfer reactions are analyzed by deconvolution of the experimental MWD curves into Flory components. It has been shown that the polymer MW grows, the MWD becomes narrower and the content of vinyl terminal groups in PE increases with increasing polymerization duration. It is assumed to occur due to the reduction of the rate of chain transfer with AlEt₃ with increasing polymerization duration. The polydispersity of PE is found to rise with increasing AlEt₃ concentration and decreasing monomer concentration due to the emergence of additional low molecular weight Flory components. The ratios of the individual rate constants of chain transfer with AlEt₃, monomer and hydrogen to the propagation rate constant have been calculated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The glass transition temperature of poly(N-vinyl pyrrolidone) by differential scanning calorimetry

Previously a wide range of values have been reported for the glass transition temperature, T_g, of poly(N-vinyl pyrrolidone), PVP, and it was suggested that lower values are due to variable uptakes of water caused by the hygroscopic nature of the polymer. Now it has been found that there are large variations in T_g, even in carefully dried specimens of PVP. Other factors found to influence T_g are residual monomer and the molecular weight of PVP. Polymers prepared by bulk polymerization, either by γ-irradiation or by heating with 2-azobisisobutyronitrile, have much lower values of T_g than dried ones prepared containing 30% water. The difference is mainly due to depression of T_g by residual monomer which, in the absence of water during polymerization, fails to react completely because of conversion to a glassy state. An unexplained observation is that even when all residual monomer has been removed, polymers prepared by bulk polymerization still have a lower T_g than would be expected from their molecular weight.     

Synthesis of high molecular weight polyacrylamide flocculant by radiation polymerization

The radiation-induced polymerization of acrylamide was studied to prepare a high molecular weight and highly effective polyacrylamide flocculant. Among various solvents, mixtures of water–tert-butyl alcohol and water–acetone were found to be suitable for the synthesis of the high molecular weight polyacrylamide. For polymerization in acetone–water mixtures, the molecular weight of polymer increases with monomer concentration; but at the high concentration, intermolecular imidation of amide groups tends to take place during the polymerization to from crosslinked and water-insoluble polymer. The water-soluble polymer with the largest molecular weight of 6.7 × 10⁶ is produced in the polymerization with monomer concentration of 2.91 moles/1. at 0°C at a dose rate of 6.2 × 10² rad/hr in acetone–water mixture containing 60 vol-% water. The crosslinking of polymer of the formation of water-insoluble polymer could be avoided by the addition of K₂CO₃ or NaOH to raise the pH of the reaction mixture above 6.5. The flocculation effects were evaluated from sedimentation speed of kaolin suspension and transparency of the separated water. The sedimentation speed is proportional to the intrissic viscosity of the polymer in the range of 4 to 23 dl/g. The polymers prepared in this study show much higher sedimentation speed than commercial polyacrylamide flocculants. The transparency of the separated water is higher than 93%, similar to the results with commercial flocculants.     

POLYMERIZATION OF BUTADIENE IN TOLUENE WITH NICKEL(II) STEARATE-DIETHYL ALUMINUM CHLORIDE CATALYST†

A bench-scale batch reactor was used to study the polymerization of butadiene with nickel(II) stearate Et₂AlCl catalyst. In particular, the effects of moisture on polymerization were investigated. The initiation reaction is sensitive to temperature. At 0°C an induction period was observed, but at room temperature initiation can be assumed instantaneous. Water enhances catalytic reactivity, however at water concentrations greater than 10 mmol/L, termination reactions become significant. Maximum conversion is obtained in the 6 to 15 mmol/L range of water. The determining step for the molecular weight of polymer is the chain transfer to monomer. At low H₂O concentration the molecular weight increases with water concentration, however it becomes independent of water concentration at high moisture content. With the help of statistical analysis of the experimental data, a two-active-species model was developed to describe the kinetics of the system and to explain certain polymerization characteristics.     

Polymerization of butadiene with tii4-Al(i-Bu)3 catalyst: Part I: Kinetic study

A kinetic study on the polymerization of butadiene in toluene with TiI₄-Al(i-Bu)₃ catalyst has been carried out in a batch reactor. The effects of catalyst concentration, Al/Ti ratio, initial monomer concentration and temperature on the polymerization rate and the molecular weight distribution were investigated. It was found that the rate of propagation which is first order with respect to monomer concentration is a function of Al/Ti ratio, having a maximum rate at a ratio of 1.5 and decreasing rapidly as ratio increases. The number of active sites which is directly proportional to the concentration of Til₄, is the prime determinant of the molecular weight of the polymer, yet the growth of the living polymer molecules is regulated by the chain transfer reaction to aluminum alkyls. The termination reaction was found significant only at Al/Ti ratio where the catalyst is most reactive.     

Zinc‐based catalyst for the ring‐opening polymerization of cyclic esters

A zinc‐based catalyst zinc bis[bis(trimethylsilyl)amide] was used for the polymerization of cyclic esters including L ‐lactide (L ‐LA) and 2‐methyl‐2‐carboxyl‐propylene carbonate (MBC). The polymerization of L ‐lactide in THF could be carried out successfully under mild conditions in very short time by using the zinc catalyst and alcohols as the initiators. Kinetic study in solution polymerization prooved the polymerization has high monomer conversion degree close to 100% and the molecular weight of the resulting polyester has linear increase with the increase of [M]₀ /[I] (molar ratio of monomer to initiator). Sequential polymerization of L ‐LA and MBC in THF also showed high MBC conversion of 94% with a narrow molecualr weight maintained, indicating a living nature of this polymerization. The zinc catalyst system has also been used for the L ‐LA bulk polymerization with a high monomer conversion. ¹³C NMR indicated the polymer possesses high regioregularity and the minor regioirregular component was owing to the D ‐LA in the monomer inserted into the polymer mainchain during the transesterifcation. Interaction between monomer and zinc catalyst has been found to be a key factor to sustain a homogenous solution during the initiating procedure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modeling of butadiene polymerization using cobalt octoate/DEAC/water catalyst

Two-level fractional factorial designs were employed to study the solution polymerization of butadiene in a batch reactor using cobalt octoate/DEAC/water as catalyst. Conversion and molecular weight data obtained as functions of time were used to develop a kinetic model, and the estimated kinetic parameters were correlated empirically with four operating variables: temperature and concentrations of cobalt octoate, DEAC, and water. The experimental data indicate that at high water concentration a significant amount of oligomers is formed during early stages of polymerization, and the molecular weight of polymer increases with time. Analysis of the data suggests instantaneous initiation, first order propagation with cobalt and monomer, and transfer to monomer. Models which do not take account of the branching are shown to be incapable of fitting data for both M _n and M _w. The catalyst decay seems to follow a first-order mechanism, but the evidence is somewhat inconclusive.     

Ionic graft copolymerization. I. Homopolymerization of β-propiolactone by sodium acetate catalyst

The polymerization of β-propiolactone (βPL) by sodium acetate catalyst has been investigated. The polymerization behavior with monomer purified with calcium chloride was found to be a little different from that previously reported for this monomer. That is, poly-β-propiolactone (PβPL) obtained from βPL dried with CaCl₂ has a higher degree of polymerization than that obtained from conventionally treated βPL, and its infrared spectrum shows type II configuration, which differs from that reported in previous papers. Some chain transfer reaction is observed even for the polymerization of the CaCl₂–dried βPL; however, this is less important in toluene. The electronegativity of the anion or cation in catalyst greatly influences the rate of polymerization.     

Kinetic studies of the chemical polymerization of substituted aniline in aqueous solutions and characterization of the polymer obtained Part 1. 3‐Chloroaniline

Aqueous polymerization of 3‐chloroaniline (mCA) was studied using sodium dichromate as oxidant in the presence of hydrochloric acid. The effect of hydrochloric acid, sodium dichromate and monomer concentration on the polymerization rate, specific viscosity of the obtained polymer and ac conductivity was investigated. The initial and overall reaction rates increase with increasing hydrochloric acid concentration or sodium dichromate concentration, but decrease with increasing monomer concentration. The specific viscosity values (η_sp) increase with increasing hydrochloric acid concentration or monomer concentration, which means that the molecular weight of the polymer samples increases accordingly. On the contrary, the molecular weight decreases with increasing sodium dichromate concentration. The highest ac conductivity value of the obtained polymer was found for 0.0255 mol l⁻¹ of Na₂Cr₂O₇, 0.8 mol l⁻¹ HCl and 0.0956 mol l⁻¹ monomer concentration in the reaction medium. The order of the polymerization reaction with respect to hydrochloric acid, Na₂Cr₂O₇ and monomer concentration was found to be 1.0, 0.9 and 0.75, respectively. The apparent activation energy (E_a) for this polymerization system was found to be 13.674 × 10⁴ mol⁻¹. The obtained poly(3‐chloroaniline) was characterized by UV–visible, IR and ¹H NMR spectroscopy. X‐ray diffraction analysis and electron microscopy studies were carried out. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) results were used to confirm the structure. © 2001 Society of Chemical Industry     

The graft polymerization of acrylamide onto paper preirradiated with high energy electrons

The graft polymerization of acrylamide onto filter paper preirradiated in air with electrons from a 200-keV accelerator has been shown to lead to weight increases of up to 210%. The degree of grafting depends on the radiation dose, the moisture content of the paper, and the time interval between irradiation and grafting, but is independent of the radiation dose rate. The degree of grafting increases with the monomer concentration of the reaction medium, and increases as the grafting temperature is reduced. Irradiations in the presence of O₂ or N₂ and the effect of ferrous ions in the grafting solution indicated that peroxides derived from cellulose do not contribute significantly to the initiation reactions up to 60°C. The results are consistent with the degree of grafting depending primarily on the concentration of trapped radicals present in the paper at the time of copolymerization. The cellulose in the grafted material was degraded and the grafted acrylamide was isolated and its molecular weight measured and compared with a calculated value. The moisture regain characteristics of the grafted material are reported.     

Synthesis and structure of the poly(methyl methacrylate) microlatex

Microemulsion polymerization is a new approach for preparing nanosize polymer materials. In this article, a nanosize poly(methyl methacrylate) (PMMA) was prepared by a novel microemulsion polymerization. The kinetics of the polymerization and the effects of the temperature, the monomer, and emulsifier/water ratio on the polymerization were investigated by means of the conversion, the transmittance, and the refractive index measurements. The structure of the obtained PMMA microlatex was studied through transmission electron microscopy (TEM), nuclear magnetic resonance (¹H‐NMR), and differential scanning calorimetry (DSC). The results show that the polymerization exhibits typical kinetic characteristics of a microemulsion polymerization, i.e., there only exists two rate stages: a stage of increasing rate, and a stage of decreasing rate, and no constant rate stage is observed during the polymerization. The obtained PMMA microparticles are very uniform, regular, and small, being about 17–33 nm in the number‐average diameter. The polymer has higher molecular weight (1.71 × 10⁶ viscosity average molecular weight), higher tacticity (51% syndiotacticity), and higher glass transition temperature (127°C), much different from the commercial PMMA. Experimentally, a stable and transparent PMMA microlatex with higher polymer content (30–40 wt %), lower weight ratio of emulsifier to water (E/W ≤ 0.03) and emulsifier to monomer (E/M ≤ 0.05) as well as smaller particle size (d_p < 40 nm), has been prepared, which is very important for the industrialization of the microemulsion polymerization technique. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2839–2844, 2002     

Effects of water solubility of acrylonitrile on vinylidene chloride/acrylonitrile/styrene suspension polymerization

The water solubility of acrylonitrile (AN) and its effects on vinylidene chloride/acrylonitrile/styrene (VDC/AN/St) suspension copolymerization were investigated in this study. It shows that the VDC/St ratio and the presence of suspending agent have no obvious influences on AN phase partition between the monomer and aqueous phases, whereas the water solubility of AN increases as temperature increases. Polymerization in the aqueous phase occurs extensively with azobis(isobutyronitrile) (AIBN) as initiator, whereas with lauryl peroxide (LPO) as initiator, polymerization in the aqueous phase is negligible. Theoretical analysis and experimental results indicate that transport of the monomer molecule is possible during polymerization. Both VDC and AN transfer from the monomer phase to the aqueous phase when AIBN is used as initiator. AN transfers from the aqueous phase to the monomer phase for the polymerization system initiated by LPO. Sodium nitrite (NaNO₂), but not sodium sulfide (Na₂S), can be used to effectively inhibit polymerization in water and exerts less influence on the polymerization in the monomer phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1431–1438, 2001     

Synthesis,cationic polymerization and curing reaction with epoxy resin of 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane

A new spiro ortho carbonate, 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane was prepared by the reaction of 2‐methoxybenzyl‐1,3‐propanediol with di(n‐butyl)tin oxide, following with carbon disulfide. Its cationic polymerization was carried out in dichloromethane using BF₃‐OEt₂ as catalyst. The [¹H], [¹³C]NMR and IR data as well as elementary analysis of the polymers obtained indicated that it underwent double ring‐opening polymerization. The polymerization mechanism is discussed. The curing reaction of bisphenol A type epoxy resin in the presence of the monomer and a curing agent was investigated. DSC measurements were used to follow the curing process. In the case of boron trifluoride‐o‐phenylenediamine (BF₃‐OPDA) as curing agent, two peaks were found on the DSC curves, one of which was attributed to the polymerization of the epoxy group, and the other to the copolymerization of the monomer with the isolated epoxy groups or homopolymerization. However, when BF₃‐H₂NEt was used as curing agent, only one peak was present. IR measurement of the modified epoxy resin with various weight ratios of epoxy resin/monomer was performed in the presence of BF₃‐H₂NEt as curing agent. The results demonstrate that the conversion of epoxy group increases as the content of monomer increases. The curing process and the structure of the epoxy resin network are discussed. © 2000 Society of Chemical Industry     

在微量水存在下一步法合成羟基聚硅氧烷的动力学特征

以八甲基环四硅氧烷为单体,四甲基氢氧化铵为催化剂,水作封端剂,在较高温度、排氧加压密闭的条件下,一步合成羟基聚硅氧烷。采用重量法测定转化率,根据聚合机理,导得动力学模型:ee[]ln{1}1[]1[]bkBtAA-=---。在此基础上,探讨温度、催化剂、水量等条件对聚合速率及聚合物特性粘数的影响,得到聚合活化能为91.4kJ穖ol-1。研究还发现,反应混合物粘度和聚合物特性粘数随转化率单调递增,这为连续法一步合成羟基硅氧烷创造了条件。     

Poly[N-(2-hydroxypropyl)methacrylamide]. IV. Heterogeneous polymerization

Kinetics of radical heterogeneous polymerization of N-(2-hydroxypropyl)methacrylamide was studied in acetone at 55°C. The values of reaction order with respect to the monomer (1.6) and to the initiator (0.5) indicate a bimolecular termination and degradative transfer during the chain growth. The over-all rate constant of polymerization was found to be 5.6.10-4. Addition of a small amount of a solvent (methanol) to the polymerization mixture led to an increased polymerization rate and increased molecular weight of the resulting polymer, but a higher amount of the solvent brought about a decrease of both characteristics. The Occurence of maxima on the dependences of R_p, as well as M?_w on the monomer concentration was interpreted in terms of the classical Bamford and Jenkins theory.     

Polymerization of Butyl Acrylate using Potassium Peroxy Disulfate as Initiator in the Presence of Phase Transfer Catalyst—A Kinetic Study

The kinetics and mechanism of free radical polymerization of butyl acrylate (BA), using potassium peroxydisulfate (K₂S₂O₈) as initiator in the presence of propiophenonebenzyldimethylammonium chloride (PPBDMAC) as phase transfer catalyst (PTC) has been studied. The reactions were carried out under inert, unstirred conditions and at a constant temperature of 60°C in cyclohexanone/water biphase media. The dependence of the rate of polymerization (R_p) on various experimental conditions such as different concentrations of monomer, initiator, phase transfer catalyst, varying acid and ionic strength, temperature, and volume fraction of aqueous phase were studied. The order with respect to monomer, initiator, and the phase transfer catalyst were found to be 1.5, 0.5, and 0.5, respectively. The rate of polymerization was independent of acid and ionic strength. Based on the results, a mechanism has been proposed for the polymerization reaction.     

Preparation of poly(vinyl acetate) latex with ultrasonic and redox initiation

The high water solubility of vinyl acetate (VAc) monomer increases the need for a good initiator system to speed up the polymerization and remove unreacted monomers. Ultrasonic energy can be used to initiate VAc redox emulsion polymerization in the absence of an inert gas and with sodium dodecyl sulfate as a surfactant. Combining ultrasonic energy and a redox initiator at the ambient temperature leads to a higher conversion and higher rate of polymer production in comparison with just using a redox initiator. Ultrasonic energy plays an important role in synthesizing and controlling the polymer structure. The particle size distribution is an important variable in the formulation of latex paint. Ultrasonic energy has an effect on the particle size distribution and average molecular weight of VAc polymer. The particle size increases with an increase in the monomer conversion for ultrasonic polymerization, whereas the particle size stays constant with the monomer conversion for redox polymerization. An ultrasonic polymer has a broader particle size distribution than a redox polymer. The average molecular weight of poly(vinyl acetate) falls with an increase in the sonication time, whereas it increases with time for a redox polymer. Ultrasonic energy also produces a stable, milky white, opaque latex. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 812–817, 2005     

Kinetics and Mechanism of Potassium Persulphate/L-Serine Initiated Polymerization of Methylmethacrylate

The polymerization kinetics of methyl methacrylate with K₂S₂O₈/L-serine redox system has been investigated volumetrically at 35±0.1°C under nitrogen atmosphere acidic aqueous medium in DMF/H₂O mixture (50% v/v). The rates of polymerization were measured varying concentrations of the monomer, initiator, L-serine as well as temperature; and it was found to increase with increasing of both temperature and concentrations of monomer, initiator, and L-serine. The overall energy of activation (E _a ) has been calculated to be 29.48 kJ/mol from the Arrhenius plot in temperature range 25–50°C. The molecular weight of the polymer was determined by gel permeation chromatography (GPC). Based on kinetic studies and depending on the results obtained, a suitable reaction mechanism has been suggested and the rates of polymerization found to obey the following equation: V _p [methyl methacrylate]^1.09[L-serine]^1.03[K₂S₂O₈]^0.96.     

Associating behaviour of polyacrylamide modified with a new hydrophobic zwitterionic monomer

The nucleophilic ring opening of dicyanoketene ethylene acetal by tertiary amino monomers leads to an hydrophobic zwitterionic monomer [(dimethylammonioethoxy)dicyanoethenolate]propylmethacrylamide (DADPMA) characterized by a very high dipole moment. Hydrophobically modified water soluble polymers have been prepared by classical radical polymerization of acrylamide and DADPMA either in homogeneous medium (water/ethanol mixtures) or in micellar solution (water containing sodium dodecylsulphate (SDS)). The copolymers obtained have a high molecular weight (M _w = 2–5 × 10⁶ g mol^?1) and are water soluble for a content of DADPMA lower than 1% mole/mole. The properties of the copolymers in aqueous solution depend on the synthesis conditions, especially on the ratio ethanol:zwitterionic monomer. © 2001 Society of Chemical Industry