Benzoyl Peroxide Initiator Research Articles

Radical cotelomerization of ethylene and propylene with CCl4

1. We have examined the radical cotelomerization of ethylene and propylene with CCl4 at 90°C with benzoyl peroxide initiation. Among the reaction products we identified two cotelomers with two monomer units, CCl3CH2CH(CH3)CH2CH2Cl, CCl3CH2CH2CH2CHClCH3, and three cotelomers with three monomer units, CCl3CH2CH(CH3)CH2CH2CH2CH2Cl, CCl3CH2CH2CHzCH2CH2CHClCH3, and CCl3CH2CH(CH3)CH2CH2CH2CHClCH3. 2. The influence of the polar factors persists throughout all stages of the cotelomerization of CCl4, with ethylene and propylene, two monomers that differ less in polar properties than the monomer pairs examined earlier.

Effect of inititiator on the molecular weight distribution in dispersion polymerization of styrene

AbstractDispersion polymerization of styrene in the particle size range of 10 μ with lauroyl peroxide as initiator results in a double‐peak molecular weight (MW) distribution. The high‐MW fraction was due to emulsion polymerization. The same phenomenon also exists in AIBN and benzoyl peroxide initiation, although it is less obvious. The kinetics of the reaction for dispersion polymerization was dependent on the concentration of the dispersing agent and the nature of the initiator.

Particle nucleation in emulsion polymerization. IV. Nucleation in monomer droplets

AbstractNucleation in finely dispersed monomer emulsions in competition with homogeneous and micellar mechanism was studied. The emulsions were prepared with a high‐pressure homogenizer under varying homogenizing conditions and made stable by the addition of hexadecane to the monomer. Sodium dodecyl sulfate was used as emulsifer. The number of particles in latexes polymerized with potassium persulfate and benzoyl peroxide initiators was measured and plotted as a function of the free emulsifier concentrations. With persulfate initiator the particle number achieved a minimum in the transition region between droplet and water phase–micellar nucleation mechanisms. With very fine emulsions Smith–Ewart case II kinetics with n = 0.5 applied. The reaction rate, which differed from conventional emulsion polymerizations, decreased with time up to the point at which n began to increase. In these runs the particle size distribution became nearly monodisperse.

Grafting onto polyformaldehyde fibers

Acrylic acid (AA), acrylonitrile (AN), and acrylamide (AM) were grafted onto polyformaldehyde (PF) fibers employing γ-ray irradiation as well as benzoyl peroxide initiation. The nature of the graft copolymer obtained from a given monomer was dependent on the type of method used for the grafting reactions. This was reflected in the various characteristics of the grafted PF fibers such as moisture regain and dyeability to disperse, direct, basic, and acid dyes. The extent of grafting was dependent on time, concentration of the initiator, concentration of monomer, and irradiation dose. The grafting reaction with all the three monomers and both methods of grafting studied followed first-order kinetics. The rate constant values for grafting with AA, AN, and AM were 0.493, 0.576, and 0.420 hr−1, respectively for the irradiation method and 0.385, 0.385, and 0.346 hr−1, respectively, for the benzoyl peroxide initiation technique. The increase in the moisture regain was directly proportional to the amount of graft in the fiber. Acrylic acid grafted PF fibers were rendered hydrophilic to the highest extent (7.9% M.R. for 42% graft), while AM-grafted fibers were rendered so to the lowest extent (7.23% M.R. for 76.5% graft). Considerable improvement in dyeability of PF fibers was observed as a result of grafting. In general, dyeability was proportional to the amount of graft introduced in the fibers. The AA-grafted PF fibers gave a six-to sevenfold increase in disperse dye content when the irradiation method was followed and a four-to fivefold improvement when the chemical method was used during the grafting reaction. The AA-grafted and AM-grafted PF fibers show considerable affinity toward direct cotton dyes. The two substrates could also be dyed with fiber-reactive dyes in deep fast shades, the AM-grafted PF fibers giving deeper shades as a result of higher reactivity imparted to the substrate by the NH2 group of the graft copolymer. The AA- and AN-grafted PF fibers could be dyed in intense deep shades with cationic dyes. Similarly, AM-grafted substrates gave bright deep shades with acid dyes. Infrared studies, used to analyze the grafted PF fibers, indicated the presence of COOH, CN, and NH2 groups introduced in the fiber structure as a result of grafting with AA, AN, and AM.

Several features of the radical cotelomerization of ethylene and vinyl chloride with CCl4

1. The radical cotelomerization of ethylene and vinyl chloride with CCl4, (9°C, benzoyl peroxide initiator) results in the formation of homotelomers of ethylene with CCl4 and of vinyl chloride with CCl4 as well as the cotelomers. 2. The structural isomers of the cotelomer containing two monomer units, viz., CCl3-CH2CHClCH2CH2Cl and CCl3CH2CH2CH2CHCl2, form in a 3∶1 ratio. We found the following cotelomers with three monomer units: CCl3CH2CHClCH2CH2CH2CH2Cl and CCl3CH2CH2CH2CHClCH2CH2Cl. 3. The composition, structure, and distribution of the cotelomers are evidence of the sensitivity of the cotelomerization process to polar effects both in the growth stage and in the chain-transfer step with CCl4.

Kinetics of two‐phase bulk polymerization. II. The influence of dissolved polymer

AbstractThe effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high‐precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions increased with the amount of dissolved polybutadiene and with its molecular weight and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Surprisingly, analogous rate reductions were observed when polystyrene were substituted for the polybutadienes, except that at high polystyrene concentrations, the expected autoacceleration was observed. These rate reductions showed no correlation with the viscosity of the reaction mass, nor did the dissolved polymer affect initiator efficiency. At a given level of a particular dissolved polybutadiene, rate reductions were diminished by increasing levels of each initiator, and by adding a chain‐transfer agent. Good quantitative agreement was obtained with the number‐average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain‐transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated by North and Reed whereby the dissolved polymer makes the reaction mass a “poorer” solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.

The kinetics of two‐phase bulk polymerization. I. Monomer and initiator distribution

AbstractRubber‐reinforced thermoplastics are produced commercially by dissolving a rubber in the monomer of a glassy polymer and commencing polymerization with a free‐radical initiator. Beyond a few per cent conversion, the incompatibility of the two polymers causes a phase separation, with each phase containing one nearly pure polymer. Subsequent polymerization occurs in each phase. The heterogeneous nature of the reaction can influence both the kinetics of the reaction and the amount of grafting in the product. The fact that only monomer which polymerizes in the rubber phase can possibly graft establishes an upper limit to the amount of grafting and hence influences the mechanical properties of the product. It is shown theoretically how unequal partitioning of monomer and initiator between the phases can influence the extent of grafting, and can also explain the kinetic rate reductions which have been observed in such systems. The distributions of monomer and benzoyl peroxide and azobisisobutyronitrile initiators between the phases have been determined experimentally for a styrene–polystyrene–polybutadiene system. They cannot account for the rate reduction observed in such systems.

The terpolymerization of methyl methacrylate, methyl acrylate and maleic anhydride

AbstractMeasurements of the compositions of terpolymers of methyl methacrylate, methyl acrylate and maleic anhydride prepared with benzoyl peroxide initiator from various monomer feeds indicate that the reactivity of methyl methacrylate towards a maleic anhydride ended radical is approximately four times greater than that of methyl acrylate. Although proton magnetic resonance measurements suggest that complexes are formed between methyl methacrylate and maleic anhydride, and methyl acrylate and maleic anhydride, there is no evidence that these complexes affect the kinetics of the polymerization reactions.

Competitive growth of polystyrene latex particles: Theory and experiment

AbstractThe results of the competitive growth of monodisperse polystyrene latex particles reported earlier by Vanderhoff et al. are reconciled with the predictions of more recent particle‐growth theories. In these experiments, monomer was polymerized in a seed latex comprised of a mixture of two monodisperse latexes so that the particles of different size competed with one another for the available monomer and free radicals. The results were expressed in terms of the equation dV/dt = kDc, where V is the particle volume, D the diameter, and k and c constants. The value of c is zero for emulsion polymerizations obeying Smith‐Ewart Case II kinetics and 3 for polymerizations in homogeneous phase. Experimentally, for water‐soluble persulfate initiator, the value of c was 2.5 for particle sizes larger than about 1500 Å and decreased toward zero as the particle size was decreased below 1500 Å; for oil‐soluble benzoyl peroxide initiator, it was 2.5 until the larger particles reached the critical size needed to sustain two growing radicals (about 13,000 Å), after which it increased to 3. The present work uses more recent particle‐growth theories to demonstrate that these experimental values of 2.5 and 3 are consistent with the theoretical predictions for water‐soluble and oil‐soluble initiators, respectively.

GRAFT-POLYMERIZATION OF ACRYLIC ACID ONTO POLYETHYLENE TEREPHTHALATE FIBERS BY INITIATOR

This research has been done with the object of modifying the hydrophobic property of the polyethylene terephthalate (PET) fiber. Acrylic acid was graftpolymerized with benzoyl peroxide (BPO) initiator onto the commercial PET fibers pretreated with benzyl alcohol.Since original commercial PET fiber has a poor graftreactivity, the fibers were pretreated with benzyl alcohol (150°C, 1 hr) as the swelling agent to increase its reactivity.The graft-polymerization was carried out in aqueous solutions of various compositions containing BPO as the initiator, polyoxyethylene nonylphenylether (nonionic surfactant) as the penetrating agent, and acetic acid, dimethyl formamide, Na-acetate, Na-acrylate or pyridine as the pH modifier of the reaction medium. The presence of 1_??_3% of nonionic surfactant in the reaction medium increased the grafting per cent of acrylic acid onto the fiber up to 2_??_4 times. The presence of pH modifier in the reaction medium affected the grafting. When the graft amounts were plotted against pH they had the maximum at 2.5_??_3.0 for various compositions of the reaction media.Ca salt of graft copolymer was isolated from dichloroacetic acid solution of the fiber by precipitation and extraction. Infrared spectra of the Ca salt of graft copolymer showed absorption at 1570cm-1 for carboxyl anion, and 1110cm-1 and 875cm-1 for phenyl group.

Polymerization of vinyl chloride by the AlEt 3/benzoyl-peroxide/Lewis-base system and the role of the Lewis base in initiation

Kinetics of polymerization of vinyl chloride under the influence of the AlEt 3 benzoyl-peroxide initiation system in the presence of the complexing agents allyl acetate, dibutyl ether and pyridine have been studied. It follows from the kinetic dependences established (which were confirmed by infra-red and nuclear magnetic resonance spectroscopies) that the role of polar agents, irrespective of their complexing ability, is to reduce the initial concentration of aluminium alkyl. Free-radical formation proper occurs by the interaction of the uncomplexed form of AlEt 3 with peroxide. The process as a whole has S N1 kinetics. When the polar monomer vinyl acetate is used as a complexing agent, the complexed form of AlEt 3 participates in the initiation. A suggestion is put forward concerning the possibility of the occurrence of a quite different mechanism of interaction between the components of the initiation system in the presence of polar monomers.

Chemical structures of surface‐oxidized and grafted polyethylene: Adsorption and wetting studies

AbstractSurfaces of thin low‐density polyethylene films are chemically modified either by oxidation or by grafting with maleic acid. The oxidation is performed at constant tempera‐ture by sulfuric acid and potassium chlorate mixtures of variable compositions. Grafting was carried out at constant temperature and time in the solution of maleic anhydride in acetic anhydride in the presence of benzoyl peroxide initiator. Isotherms of calcium adsorption at these surfaces have been established by the use of the radioactive tracer technique. The chemical composition (number of obtained polar sites) of these modified polyethylene surfaces is thus determined. The measurements were conducted at different pH and salt concentrations. Wettability of the modified surfaces is determined by contact angle measurements. It was found that the wettability of these films is directly related to the chemical composition of their surfaces.

Absorption spectrum of gamma-irradiated poly(methylmethacrylate) within the range 245 to 450mμ

The absorption spectrum of poly(methylmethacrylate) irradiated with γ-rays at room and liquid nitrogen temperatures has been studied within the range 245 to 450 mμ. The materials used varied considerably in nature and concentration of initiator and chain-transfer agent additives. Most of the samples irradiated at liquid nitrogen temperature showed peak absorption wavelengths very close to those noted after room-temperature irradiation; a minority group showed shorter peak wavelengths, which shifted to the room-temperature values when subsequently warmed to room temperature. A marked dependence of spectral behaviour on both initiator and chain-transfer agent content was noted, indicating that most of the absorbing species originate in the additives; on the other hand, an absorption peak around 252 mμ was found in several samples independent of their additive content, and also independent of the temperature of irradiation. As a strong absorption peaking close to this wavelength was observed in radiation polymerized poly(methylmethacrylate), it is postulated that the species giving rise to this particular absorption is formed on methylmethacrylate monomer residue in the polymer. Evidence is presented to show that the absorbing species are not radicals. It is possible that they are ionic in nature, probably cations. It is postulated that the absorbing species formed on the monomer residue is a carbanion C̈HCHCH which, with appropriate electron pairing, would not give rise to an e.s.r. signal. Of the materials polymerized with the help of additives, those containing fairly large concentrations of mercaptan compounds as chain-transfer agents showed a slowly decaying absorption peaking around 252 mμ at liquid nitrogen temperature and 255 mμ at room temperature; the species giving rise to this absorption is to be distinguished from that formed on monomer residue. Materials containing benzoyl peroxide initiator showed peak absorption values around 280 and 290 mμ, independent of temperature.

Investigation of fast‐setting acrylic adhesives for bonding attachments to human tooth surfaces

AbstractSome of the problems encountered in adhesive bonding of plastic attachments to human tooth surfaces were investigated. Acrylic adhesives based on poly(methyl methacrylate)–methyl methacrylate monomer mixtures with benzoyl peroxide initiation and N,N‐dimethylaniline acceleration were utilized. Both homopolymers and copolymers were investigated. Recently extracted upper central incisors were employed in the bonding experiments. Bond strengths were improved by pretreating the tooth surfaces with mineral acids such as H3PO4. Surface wetting by the liquid adhesive was shown to be improved by the acid treatment. The molecular weight of polymer or copolymer employed in the liquid adhesive had an important effect on bond strengths. The optimum molecular weight for obtaining maximum bond strengths was around 20,000 g./mole. Water immersion of the bonded specimens at 37°C. for periods up to 6 weeks had a deleterious effect on bond strengths. Nevertheless, it was shown that some of the adhesives formed reasonably strong bonds for periods exceeding 6 months even with water immersion.

Monomer Reactivity Ratios for the Copolymerization of Styrene with Pure Meta-and Pure Para-Divinylbenzenes

Abstract Reactivity ratios for the copolymerization of styrene (r 1) meta-divinylben-zene (r 2–m) and with para-divinylbenzene (r 2–p) have been redetermined under different reaction conditions and with different radioactivity assay techniques. The copolymers were prepared at two conversion levels [0.55 to 3.7% and 2.7 to 7.5% and at 80° (rather than 100°)] with benzoyl peroxide (in place of τ-butylhydroperoxide) initiator. The ionization chamber-vibrating reed electrometer radioactivity assay technique developed for other copolymerization studies was used in place of the direct counting technique previously used for the styrene/divinylbenzene systems. The new values are r 1 = 0.605/r 2-m = 0.88: r 1 = 0.77/r 2-p = 2.08 at 0.55 to 3.7% conversion and r 1 = 1.27; r 2–m = 1.08 at 2.7 to 7.5% conversion. These are not in close agreement with previous values partly because of the difference in conditions of copolymerization (temperature, per cent conversion, initiator) and in the improved analytical precision...

Kinetics of polymerization of vinyl benzoate

AbstractVinyl benzoate was polymerized in bulk as well as in solution, using benzoyl peroxide and azobisisobutyronitrile initiator at a temperature of 79.6°C. The overall rate of polymerization was found to be proportional to the concentration of the monomer and to the square root of the initiator concentration. Polymerization progressed to a normal extent, except that it increased with conversion, probably because of transfer with polymer. The value of the transfer constants with the monomer, initiator, and some solvents are reported.

Reactions of unsaturated and macromolecular compounds Communication 9. Copolymerization of isopropyl vinyl ether with methyl acrylate

1. Reaction proceeds between methyl acrylate and isopropyl vinyl ether in presence of the initiators benzoyl peroxide and 2,2′-azobis[2-methylpropionitrile] with formation of copolymers. 2. As the concentration of isopropyl vinyl ether in the reaction medium increases, the yield of copolymer falls, but the proportion of isopropyl vinyl ether units in the copolymer increases. 3. Copolymers prepared in presence of 2,2′-azobis[2-methylpropionitrile] contain a somewhat higher proportion of isopropyl vinyl ether units than copolymers prepared in presence of benzoyl peroxide. 4. In spite of the use of a very great excess of isopropyl vinyl ether in the reaction mixture, it was not found possible to raise the content of vinyl ether units in the copolymer to above 50%.

On the mechanism of polymerization retardation by aromatic nitro compounds

AbstractIn vinyl polymerization retarded by aromatic nitro compounds, the growing chain reacts with the retarder to form stabilized products. The locus of radical attack has been reported as taking place at an aromatic carbon or at a nitro‐group oxygen. A direct experimental test has been devised to permit a choice between these alternatives. Rates of racemization of optically active nitrobiphenyl derivatives used as retarders in polymerizing systems have been compared with rates in nonpolymerizing monomer. These compounds were found to racemize more rapidly in the presence of polymerizing methyl methacrylate or vinyl acetate. Benzoyl peroxide initiator was not responsible for the considerable difference in racemization rate. The results support the view that primary attack of the growing chain is upon the nitro group and not at an aromatic carbon atom.

Rates of termination in polymerizations initiated by benzoyl peroxide and by ammonium persulfate

AbstractPolymerizations of styrene have been carried out in solution using as initiators benzoyl peroxide or ammonium persulfate. It has been shown that the ammonium persulfate initiated polymerizations proceed at a faster rate and produce polymers of higher molecular weight than those initiated by benzoyl peroxide, although all the conditions for polymerization remained identical in both cases. This behavior is explained in terms of a reduced rate of termination. It is suggested tentatively that the reduction in the rate of termination may be due to the mutual electrostatic repulsion of the chains caused by the presence of electrically charged end groups arising from initiation by the sulfate ion radical. Calculations are presented showing the essential conditions that have to be fulfilled to make the explanation tenable.

Polyvinyl chloroacetate

AbstractSeries of bulk and solution polymerizations of vinyl chloroacetate have shown that the properties of the polymer vary widely with variation in polymerization conditions. The highest viscosity polymer, intrinsic viscosity polymer, intrinsic viscosity of 1.32, is prepared by bulk polymerization with 0.028% benzoyl peroxide initiator at 70°C. At polymerization temperatures sdover 70°C. and at catalyst concentrations over 0.14%, the polymer is discolored, insoluble, or has relatively poor aging characteristics. Polymerization in an equal volume of methyl isobutyl ketone at 80°C. and with 0.013% benzoyl peroxide gave 93% yield of polymer of intrinsic viscosity 0.15. In nitrobenzene, toluence, trichloroethylene, or ethyl acetate, only traces of polymer are obtained. In carbon tetrachloride, unstable telomers are produced.