Rate Of Homopolymerization Research Articles

Epoxy prepolymers cured with boron trifluoride‐amine complexes, 3. Polymerization mechanism of a prepolymer containing epoxy groups

AbstractThe reaction of a diepoxy prepolymer (2) initiated by the BF3‐complex of 4‐chloroaniline (3), solubilized in poly(ethylene oxide) (PEO) of molecular weight 300, was studied. An initial induction period was observed, followed by a pseudo‐stationary stage with decreasing reaction rate due to gelation. In the pseudo‐stationary stage, the homopolymerization rate is given by the expression: Rp = k[2]1 · [3]·−0,55 · [PEO]·0,57. In addition to 2, we also used a Novolac prepolymer 4. Different networks were prepared and analyzed by thermal and mechanical techniques, and their water‐absorption rates were measured.

Grafting of methyl methacrylate onto guar gum by hydrogen peroxide initiation

AbstractGraft copolymerization of methyl methacrylate (MMA) onto guar gum (GG) in aqueous slurry has been carried out using hydrogen peroxide (H2O2) as initiator. The copolymers were characterized by infrared spectroscopy. The grafting parameters like percent grafting, grafting efficiency, percent add‐on, and the grafting frequency were determined, and the effect of reaction time, concentration of initiator, and [GG]/[MMA] ratios on the grafting parameters have been discussed. The decrease in % add‐on at increasing concentration of H2O2 indicated enhancement in the rate of homopolymerization of methyl methacrylate.

Propene polymerization with MgCl2 supported Ziegler catalysts: Activation by hydrogen and ethylene

AbstractComplementary experiments confirm the recent findings that the rate of propene polymerization is temporary enhanced if a small amount of ethylene is introduced during the polymerization, normalizing after consumption of ethylene by copolymerization. In addition, the study of the sequence distribution of propene monomeric units in the copolymerization carried out under various conditions revealed that the activation by ethylene does not involve the propagation steps, but the re‐initiation after deactivation. A similar temporary activation effect was observed after the addition of small amounts of hydrogen. In this case, however, hydrogen is not consumed. Thus, the deactivation observed after the initial rate enhancement is due to another reason. The deactivation could be shown to be reversible after removal of the adsorbed hydrogen when either ethylene or hydrogen was added again to allow re‐initiation of the polymerization. One of the important reasons of the continuous decrease of the propene homopolymerization rate may be due to the fact, that, after a transfer step, the re‐initiation of polymerization does not take place spontaneously. Small amounts of ethylene or hydrogen allow the reinitiation to take place, at least for some kind of active sites.

Cationic polymerization and copolymerization of lactams and lactam derivatives

AbstractLactams and lactam derivatives may be polymerized by various types of processes, but only the cationic mechanisms provide suitable pathways for the polymerization of all types of lactam monomers. Therefore, the cationic polymerization is predestinated for the synthesis of their copolymers. Random copolymers can be obtained even if the rates of homopolymerization of comonomers differ by several orders of magnitude, either by transacylation of block copolymers, or in a new process designated as polymerization with transient chemical activation. This process is operative e.g. in the copolymerization of an unsubstituted and an N‐acylated lactam. It implies N‐acylation of the unsubstituted lactam by the polymer of the N‐acylated one, followed by the incorporation of the activated monomer and subsequent deacylation of the incorporated monomer unit.

Grafting of poly(glycidyl methacrylate) onto alginic acid

Grafting of poly(glycidyl methacrylate) (PGMA) onto alginic acid was carried out using ceric ammonium nitrate as initiator, using various concentrations of monomer and initiator, and various temperatures and times. Percentage grafting, grafting efficiency and rates of polymerization, graft copolymerization and homopolymerization were evaluated in all cases. Infrared spectra for pure alginic acid, poly(glycidyl methacrylate) and the alginic acid-poly(glycidyl methacrylate) were taken to establish the occurrence of grafting. Differential scanning calorimetry was carried out for alginic acid, poly(glycidyl methacrylate), the graft copolymer and the physical mixture to establish evidence for grafting.

Contribution à l'étude cinétique du greffage du polyéthylène, en suspension dans l'eau, par l'acide acrylique

The radical grafting, in water suspension, of a polar monomer (acrylic acid) onto a non-polar polymer (low density polyethylene) was studied in the presence of t-butyl peroctoate. A preliminary study of the homopolymerization of acrylic acid was carried out under the experimental conditions used for the grafting and with: [A] 0 = 0.0025 and 0.0050 mol 1 −1 and [M] 0 = 0.125, 0.75 and 1.25 mol 1 −1. It is shown that the initial rate of polymerization is second order in monomer. The grafting experiments were carried out with [A] 0 = 0.0025 and [M] 0 0.125, 0.75 and 1.25 mol 1 −1. For each experiment, the contents of grafted, homopolymerized and non-polymerized acrylic acid were determined separately. The initial rates of grafting and homopolymerization were determined as well as the orders in monomer. Several preliminary treatments of polyethylene led to a significant increase of the grafting efficiency.

Engineering plastics from lignin. I. Synthesis of hydroxypropyl lignin

Hydroxypropylation of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several ligninlike model compounds and with kraft lignin. While the PO homopolymerization rate increased rapidly at temperatures above 85°C, and was too fast to be determined accurately at 180°C, the addition of model compounds and lignin was found to delay homopolymerization in relation to the presence of ionizable functional groups. The observations are consistent with a reaction mechanism involving first order kinetics with regard to each alkoxide and PO concentrations. Where the reaction rates toward PO increase with increasing pKa values, the reaction sequence proceeds in the order of declining basicity. Thus lignins with high acidity were found to be subject to greater degrees of modification than those with more neutral character. This explains the earlier observed beneficial effect of lignin carboxylation on the properties of lignin–PO reaction mixtures.

Graft copolymerization of 2-hydroxyethyl methacrylate and methyl methacrylate onto hide powder

Graft copolymerization of 2-hydroxyethyl methacrylate(HEMA) and mixtures of HEMA with methyl methacrylate (MMA) onto hide powder was attempted using ceric ammonium nitrate as initiator, with a view to optimize the conditions for graft copolymerization. Percent grafting and grafting efficiency were calculated for various variables such as monomer concentration, initator concentration and mole ratio of HEMA to MMA. R p, R g and R h (rates of polymerization, grafting and homopolymerization respectively) were also evaluated. It was observed that R p increased linearly with increasing concentration of MMA except at very low concentrations of the monomer. An explanation is given for the effect of variables on extent of grafting and grafting efficiency.

Synthesis of casein‐g‐poly(vinyl acetate)

AbstractCasein‐g‐poly(vinyl acetate) was synthesized using potassium persulfate as initiator. Changes in monomer concentration, initiator concentration, backbone concentration, and temperature were effected. The rate of total conversion of monomer, the rate of homopolymerization and graft copolymerization, the grafting efficiency and the percentage of grafting were calculated. The grafting results were discussed in the light of grafting efficiency and percentage of grafting. They were found to be lower in the case of casein‐g‐poly(vinyl acetate) when compared to those of casein‐g‐poly(butyl acrylate).

Copolymerization of N‐carboxy Nϵ‐carbobenzoxy L‐lysine anhydride with N‐carboxy β‐benzyl L‐aspartate anhydride in acetonitrile

AbstractCopolymerization of N‐carboxy Nϵ‐carbobenzoxy L‐lysine anydride with N‐carboxy β‐benzyl L‐aspartate anhydride was initiated with n‐butylamine in acetonitrile. The copolymerization proceeded almost homogeneously except for the initial stage, when the proportion of N‐carboxy anhydride (NCA) in the polymerization mixture varied from 25 to 75 mol %. This was due to the fact that the copolypeptides formed were soluble or highly swollen in the solvent, in contrast to the homopolymerization of NCAs such as Nϵ‐carbobenzoxy L‐lysine NCA and β‐benzyl L‐aspartate NCA in acetonitrile, which proceeds heterogeneously. The compositions of the copolymers obtained were, within experimental error, the same as their monomer feed compositions. The initial rates of copolymerization were almost the same as the rate of homopolymerization of β‐benzyl L‐aspartate NCA, which propagates with a nonhelical polypeptide, but were slower than the rate of homopolymerization of Nϵ‐carbobenzoxy L‐lysine NCA, which propagates with a helical polypeptide.

The polymerizations of N-methyl-N-phenyl-2-aminoethyl methacrylate and 4-dimethylaminostyrene initiated with carboxylic acids

By using the copolymerizations of N-methyl-N-phenyl-2-aminoethyl methacrylate (I) and 4-dimethylaminostyrene (II) with styrene initiated with 2,2′-azoisobutyronitrile (AIBN) and with CCl 3COOH, the copolymerization parameters and Alfrey-Price copolymerization constants e and Q were determined for I and II. The only product of polymerizations initiated with CCl 3COOH and CH 3COOH in mixtures of II with vinyl monomers was a homopolymer of II. The order of homopolymerization of II in benzene initiated with CCl 3COOH at 50° was 0.99 with respect to [II] and 1.10 with respect to [CCl 3COOH]; the temperature dependence of homopolymerization in the range 25–40° was 63 ± 5 kJ mol −1. The rate of homopolymerization of II in solution in C 6H 6 at 50° was virtually unaffected by inhibitors. In the polymerization initiated with carboxylic acids, the radical character of propagation centres was proved for I, but not for II.

Emulsion polymerization and copolymerization of vinyl benzoate

AbstractEmulsion polymerization of vinyl benzoate and its copolymerization with vinyl acetate or styrene are described. The effect of the potassium persulfate initiator, and the sodium lauryl sulfate emulsifier concentration on the rate of vinyl benzote homopolymerization and the molecular weight of the polymers was determined. In copolymerization with vinyl benzoate, both comonomers, vinyl acetate and styrene, decrease the initial polymerization rate. With increasing amounts of styrene in the comonomer mixture the polymerization rate increases but with vinyl acetate an opposite effect is observed. Reactivity ratios of copolymerizations were determined. For the vinyl benzoate [M1]‐styrene [M2] comonomer system a r1 = 0.03 and a r2 = 29.58 and for vinyl benzoate [M1]‐vinyl acetate [M2], a r1 = 1.93 and a r2 = 0.20 was obtained. From the vinyl benzoate‐styrene reactivity ratios the Qe parameters were calculated.

Graft polymerization of methyl methacrylate onto nylon 6 using pentavalent vanadium as initiator

AbstractPentavalent vanadium ion (Vv)‐induced graft polymerization of methyl methacrylate onto nylon 6 was investigated under a variety of conditions. Increasing the Vv‐concentration up to 2 mmol/l was accompanied by an enhancement in grafting; the latter was not affected by further increase in Vv‐concentration. Unlike grafting, the homopolymer and total conversion tended to increase by increasing Vv concentration. The graft yield enhanced significantly when the MMA‐concentration was increased up to 3% further increase in MMA‐concentration had no effect on grafting. Raising the polymerization temperature from 50° up to 70°C caused a significant increase in the rates of grafting, homopolymerization and total conversion. Using a solvent‐water mixture as medium for polymerization affected considerably the magnitude of grafting. While using methyl alcohol, ethyl alcohol and acetone at any ratio in the solvent‐water mixture resulted in decreased grafting, using an isopropyl alcohol‐water mixture up to a ratio of 25 : 75 gave rise to increased grafting.

Model simulation studies of complex free radical reactions: The graft copolymerization of styrene and acrylonitrile onto ethylene‐propylene‐isopropylidendicyclopentadiene terpolymer

AbstractA kinetic analysis without steady approximation of the graft copolymerization of styrene‐acrylonitrile onto ethylene‐ propylene‐isopropylidendicyclopentadiene terpolymer (EP‐IPDCP) is described. Some of the kinetic constants were experimentally determined. The grafting process is interpreted mainly in terms of the attack on EP‐IPDCP by benzoyloxy radicals; phenyl radicals play a minor negative role by enhancing the rate of homopolymerization. A major contribution to the grafting yield is made by the propagation steps in graft polymerization and by crossed termination between grafted and ungrafted chains; of minor importance are the cross terminations between ungrafted growing chains and rubber radicals. The ole played by the solvent (benzene) and by saturated and unsaturated units in the EP‐IPDCP chains is analyzed. Diffusion effects caused by the poor solvent compatibility of grafted and ungrafted chains were taken into account by allowing the termination and propagation rate constants to change in a controlled way during the reaction. The trapping of EP‐IPDCP units caused by the aggregation of polymer particles seems to be indispensable to explain the decreasing trend of the grafting efficiency curve. Other information of interest pertains to the distribution of initiating radicals among the various competing reactions in the process and to the data of concentrations versus reaction time for reactants, products, and free radical intermediates. The results of a sensitivity analysis and the rate constants used in the calculations are given.

Cationic polymerization of dimethyl‐1,3‐butadienes

AbstractThe cationic polymerizations of dimethyl‐1,3‐butadienes with various catalysts in methylene chloride and toluene have been investigated. The activity of catalysts decreased in the order WCl6 > AcClO4 > SnCl4·TCA > BF3OEt2. The homopolymerization rate of dimethyl‐1,3‐butadienes with WCl6, AcClO4, and SnCl4·TCA decreased in the order 1,3‐dimethyl‐1,3‐butadiene > 2,3‐dimethyl‐1,3‐butadiene > 1,2‐dimethyl‐1,3‐butadiene > 2,4‐hexadiene. The polymers prepared with WCl6, SnCl4.TCA, and BF3OEt2 were rubberlike polymers or white powders, whereas those prepared with AcClO4 were oily oligomers. The 1,4‐propagation increased in the order 1,2‐dimethyl‐1,3‐butadiene < 1,3‐dimethyl‐1,3‐butadiene < 2,3‐dimethyl‐1,3‐butadiene < 2,4‐hexadiene. This order may indicate that the steric effect of methyl group determine primarily the microstructure of the polymer. The relative reactivity of dimethyl‐1,3‐butadienes toward a styryl cation decreased in the order 1,3‐dimethyl‐1,3‐butadiene > 1,2‐dimethyl‐1,3‐butadiene > 2,3‐dimethyl‐1,3‐butadiene > 2,4‐hexadiene. This order may be explained in terms of the stability of the resulting allylic cation.

Graft polymerization of 2‐methyl‐5‐vinyl pyridine on poly(ethylene terephthalate) fibres using H2O2 as initiator

AbstractGraft polymerization of 2‐methyl‐5‐vinyl pyridine (MVP) on unstretched poly(ethylene terephthalate) fibers (PET) using H2O2 as initiator was investigated under different conditions. The extents and rates of grafting, homopolymer and total conversion depended upon concentration of the initiator and the monomer as well as on the polymerization temparature. The extent and rate of grafting decreased as the H2O2 concentration increased from 6.82x10−2 to 27.29x10−2 mol · 1−1. The same holds for the extents and rates of homopolymerization and total conversion. Whereas the extents and rates of grafting and total conversion increased significantly by increasing the MVP concentration from 0.162 to 0.648 mol.1−1. Raising the polymerization temperature from 65 to 95°C was also accompanied by a significant enhancement in the extents and rates of grafting and total conversion. Stretching the PET fibres prior to grafting reduced appreciably the susceptibility of the fibres towards grafting, being dependent on the magnitude of stretching.

Effect of pH on the reactivity ratios in aqueous solution copolymerization of acrylic acid and N‐vinylpyrrolidone

AbstractAcrylic acid (AA) and N‐vinylpyrrolidone (NVP) were copolymerized in aqueous solution at 30°C in the pH range 4–9 and the monomer reactivity ratios (r1 for AA and r2 for NVP) were determined as a function of pH from the high conversion data by using both the differential (YBR) and the integrated copolymerization equations. The value of r1 decreased from 5.2 at pH 4 to a minimum of 1.3 at pH 5 and then increased to 8.1, 6.6, and 7.2 at pH 7, 8, and 9, respectively. Addition of 1M NaCl at pH 6.5 restored the r1 nearly to that at pH 4, the predominantly un‐ionized acid. The r2 values for NVP were nearly zero at all pH values except at pH 5. The variation of the reactivity ratios with pH was examined in terms of the electrostatic interactions between the ionized monomer molecules, the rate of homopolymerization of acrylic acid, and the cation binding to the poly(acrylic acid) molecules. The r2 values for NVP compared favorably with the literature values reported in bulk and organic solvent systems, although r1 values are much higher.

Radical copolymerization of ethylene with unsaturated organosilicon monomers under pressure

The rate of copolymerization of ethylene with the organosilicon monomers CH 2 = =CHSiR 3 (m), where R represents the alkoxy or the OSi(CH 3) 3 group, is about the same as the rate of homopolymerization of ethylene over a wide range of composition of the monomer mixture. With a low concentration of m in the reaction mixture, the conversion of m is approximately the same as that of ethylene when R is an alkyl, alkoxyl or (OSi (CH 3) 3 group; the conversion is considerably greater than that of ethylene when R is a phenyl or phenoxy group or Cl. As the concentration of m increases, the density of the copolymers increases when R is a phenyl or alkoxy group, and decreases when R is an alkyl or a OSi (CH 3) 3 group. The capacity of the copolymers to crosslink with vinylalkoxysilanes decreases as the length of the alkyl group is increased. Thermooxidative degredation of the high molecular crosslinked copolymers occurs at a slower rate, as compared with polyethylene.

Kinetic features of the oxidative polymerization of oligo-ester acrylates

Kinetic features of the polymerization of oligo-ester acrylates in thin films in air are analysed on the basis of double bond expenditure and the consumption of oxygen. The relative roles played by reactions of homopolymerization and copolymerization with oxygen have been determined up to the gel point and in the three dimensional polymerization. Before the onset of gelation anomalously high rates of homopolymerization were observed. To explain this it is thought that oligo-ester acrylates may be regarded as being highly associated liquids. Three dimensional polymerization in thin films of OEA in air proceeds mainly as homopolymerization.

Synthesis and Polymerization of Methylvinylthiosilanes

Methylvinylthiosilanes, (CH3)4−nSi(SCH=CH2)n (n=1—3), were first synthesized by the reaction of the corresponding methylchlorosilanes and vinylthiomagnesium bromide.All these vinylthiosilanes were found polymerizable by a radical initiator. The radical polymerization of di- and trivinylthiosilanes seemed to involve cyclopolymerization. The rate of radical homopolymerization was found to be almost independent of the number of the vinylthio group.There was no significant difference between trimethylvinylthiosilane and vinylthiocarbon compounds in radical copolymerizability. The cationic polymerization did not give high-molecular-weight products.A radical homopolymer of trimethylvinylthiosilane was converted into poly(vinyl-mercaptan) by methanolysis.