Free Radical Bulk Polymerization Research Articles

Bulk and suspension polymerization of styrene in the presence of n‐pentane. An evaluation of monofunctional and bifunctional initiation

AbstractThe plasticizing effect of n‐pentane on the rate of bulk free radical polymerization of styrene and molecular weight distribution development has been modeled on the basis of the free volume theory for both monofunctional and bifunctional initiation. A strong decrease in the reaction rate in the late stages of the polymerization, due to the displacement of the onset of the gel effect, has been observed for both types of initiation. This decrease in the polymerization rate limited the terminal conversion to values well below 100% for mono‐functional initiation. However, in bifunctionally initiated polymerization, terminal conversions close to 100% were obtained in spite of the decrease in reaction rate. Contrary to what was expected, the molecular weight distribution obtained at terminal conversion was almost completely insensitive to these changes in polymerization rate. This phenomenon is explained in terms of limited transfer to monomer reactions when n‐pentane is present in the system. In suspension polymerization, the limiting conversion and plasticizing effects of n‐pentane in monofunctionally initiated systems, caused enhanced coalescence leading to suspension set‐up. In bifunctionally initiated systems this enhanced coalescence was completely overcome by the short duration of the particle growth stage, owing to high polymerization rates, and stable suspensions were achieved. For these systems the particle size distributions obtained were similar to that of suspension polystyrene without n‐pentane. © 1993 John Wiley & Sons, Inc.

Free-radical polymerization of lauryl methacrylate by differential scanning calorimetry: Part 1. Enthalpy of polymerization

The free-radical bulk polymerization of lauryl methacrylate (LMA) in the presence of 2,2'-azobisisobutyronitrile (AIBN) has been studied by differential scanning calorimetry (DSC) in dynamic and isothermal modes. The measured heats of reaction Δ H, increased with the concentration of the initiator. The enthalpy of polymerization in the presence of a large excess of AIBN was obtained by extrapolation. At low concentrations of AIBN, a constant heat of polymerization of LMA (−41.7kJ mol −1) was obtained after correcting for both the incomplete conversion to polymer and the decomposition enthalpy of AIBN.

Radiolysis of poly(phenyl methacrylate)

Powdered poly (phenyl methacrylate), synthesized by free-radical bulk polymerization, has been irradiated to doses, between 200 kGy and 600 kGy, of cobalt-60 γ-rays under an argon atmosphere. A G (scission) value of 1·8 has been calculated from the changes in number-average molecular weight as determined by gel permeation chromatography. Energies of activation for the decomposition of irradiated polymers have been calculated from the results of thermogravimetric experiments.

E.s.r. study on permeation of oxygen in crosslinked polymers

Polymeric networks of methyl methacrylate (MMA)/ethylene glycol dimethacrylate (EGDMA) with various EGDMA levels were synthesized via bulk free-radical polymerization using an AIBN initiator and a programmed temperature rise. The trapped radicals in the polymer network were used to investigate the permeation of oxygen by electron spin resonance (e.s.r.). The decay rates of radical concentration in the temperature range, 110 to 180°C were used to estimate the permeability coefficients of oxygen. It was found that the permeability coefficient reached a peak value at about 70 wt% EGDMA, indicating that porosity of the network increased with EGDMA content reaching a maximum at 70 wt% EGDMA. The glass transition temperature ( T g) of poly(EGDMA) obtained using the oxygen permeability data was estimated to be 144°C, and the permeation activation energies below and above T g were 7.3 kJ mol −1 and 58.3 kJ mol −1, respectively.

Selective radical ring-opening polymerization of α-cyclopropylstyrene

Bulk free radical polymerization of unsubstituted as well as 4-chloro and 4-methoxy-α-cyclopropylstyrene yields the polymer [CH 2 C(Ph)=ChCH 2 CH 2 ] n by 1,5-ring-opening polymerization

Kinetics of free radical styrene polymerization with the symmetrical bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy) hexane

The kinetics of bulk free radical polymerization of sytrene is studied with the symmetrical bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane. The initiator, monomers and live polymers undergo complex initiation, propagation, chain transfer and chain termination reactions due to the presence of two labile peroxide groups of equal thermal stabilities in the initiator. The effects of reaction temperature and initiator concentration on the polymerization rate and polymer molecular weight properties have been investigated. It is shown that the composition of a polymerizing mixture is influenced by the initiator concentration and reaction temperature. The apparent initiator efficiency factor was found to decrease as the initiator concentration increased. A detailed kinetic model is also presented and used to analyse the fate of peroxide groups during the course of polymerization.

A kinetic investigation of butyl acrylate polymerization

AbstractAn experimental investigation of the kinetics of the bulk free radical polymerization of butyl acrylate initiated with 2,2′‐azobisisobutyronitrile (AIBN) was conducted at 50° and 60°C using two initiator concentrations. Conversion levels were measured by gravimetry and were independently confirmed using replicate runs. The experiments, conducted in glass ampoules, were performed over the full conversion range. A mathematical model for process simulation purposes was developed. The model was able to predict conversion at the two temperatures and initiator concentrations, thus providing a better understanding of the butyl acrylate homopolymerization kinetics.

Heat effects for free-radical polymerization in glass ampoule reactors

Herein is reported an experimental study to evaluate the level of temperature control during bulk free-radical polymerization of methyl methacrylate/ethylene glycol dimethacrylate in ampoule reactors of various sizes at various temperatures, initiator levels and for two heat transfer fluids (water and silicone oil). This monomer system was chosen because of the pronounced autoacceleration in polymerization rate that it experiences. Five ampoule diameters (3, 4, 5, 7 and 10 mm outside diameter, Pyrex glass), four temperatures (60, 70, 80 and 90°C) and five initiator levels (0.1, 0.3, 0.5, 1.0 and 2.5 wt% 2,2′-azobisisobutyronitrile) were investigated. Polymerization conditions and reactor size under which near-isothermal polymerizations during autoacceleration may be followed using glass ampoule reactors are presented.

Mössbauer studies of acrylonitrile/alkyl methacrylate copolymers doped with ferric chloride

Acrylonitrile/methyl methacrylate (A/M), acrylonitrile/ethyl methacrylate (A/E) and acrylonitrile/n-butyl methacrylate (A/B) copolymers containing ferric chloride were prepared by free radical bulk polymerization. TGA studies show that the addition of ferric chloride increases the thermal stability of these copolymers. Mossbauer studies of the copolymers showed the presence of Fe3+ species only. Mossbauer spectra of the copolymer heated at 200°C, 350°C and 500°C did not show a reduction of the Fe3+ species, and α-Fe2O3 was the final product formed.

Kinetics of Crosslinking Vinyl Polymerization

Abstract Bulk free-radical polymerization of a reaction mixture containing monovinyl and divinyl monomers is strongly affected by the gel effect. A model based on diffusion-controlled mechanisms is developed to describe the curing kinetics. At very high conversion the propagation reaction becomes diffusion limited and this can be used to explain the often observed limiting conversion. Experimental data available in the literature are used to assess the proposed model. Reasonable agreement between the model predictions and conversion-vs-time data is observed.

Radical trapping and termination in free-radical polymerization of methyl methacrylate

Post-effect measurements of radical concentrations for bulk free-radical polymerization of MMA with AIBN initiated by UV were made. Number-average termination rate constants decrease dramatically in the post-effect period at high conversions in disagreement with the concept of termination by propagation-diffusion that was expected to be dominant. It is found that there exist two radical populations in the reacting mass, free radicals and trapped radicals, which have very different reactivities in both propagation and termination reactions

Radical concentrations in free radical copolymerization of MMA/EGDMA

Radical concentration histories for the bulk free radical copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) initiated with 0.3 wt% 2,2'-azobis(2-methyl-propionitrile) (AIBN) at 70°C over the entire composition range were measured with an on-line electron spin resonance spectrometer. Radical concentrations of 10 −7−10 −3moll −1 were observed. At high EGDMA levels, the radical concentration increases monotonously from the onset of polymerization. Even in the glassy state, the radical concentrations continue to increase significantly. Once high concentrations of radicals which are chemically bound to the crosslinked network form, they are stable to temperature increases above the glass transition temperature. These stable radicals can propagate with a newly added monomer to the swollen gel. For low EGDMA levels (<25wt%) there exist four stages of radical concentration change with reaction time (monomer conversion): (1) the radical concentration remains relatively constant for low monomer conversions; (2) at some intermediate conversion there is a dramatic rise; (3) after reaching a peak concentration there is a small decrease; (4) the concentration then increases gradually and levels off. The dramatic rise in the second stage is in agreement with the hypothesis that the autoacceleration of reaction rate in a free radical polymerization is due to an increase in the radical concentration. An analysis of the radical concentration rise rates reveals that the use of the quasi-stationary state hypothesis (QSSH) at high levels of crosslinking is not valid. These radical concentration measurements coupled with the corresponding conversion rate data give a direct estimate of the propagation constant ( K p). The propagation constant was found to fall slightly at low conversions, but to fall dramatically at some high conversion where the conversion rate approaches zero. This explains why the polymerization rate of a bulk free radical polymerization run at T< T gp (the glass transition temperature of the polymer) falls to almost zero even though appreciable monomer and initiator still exist in the reacting mass. The fall in K p is in turn due to a radical trapping effect, i.e. the radical centres are surrounded by a solid environment consisting of polymeric segments. Using the assumption that bimolecular termination at high conversions is controlled by ‘propagation diffusion’, with K t∝ K p[M], the initiation efficiency ( f) and the termination rate constant ( K t) were also calculated from the data. The initiation efficiency was found to fall almost simultaneously with the propagation rate constant.

Thermal properties of copolymers of alkyl methacrylates with triallyl cyanurate

AbstractThe homo‐ and copolymers of triallyl cyanurate and methyl methacrylate, ethyl methacrylate, propyl methacrylate, n‐butyl methacrylate, and cyclohexyl methacrylate were synthesized by free radical bulk polymerization using benzoyl peroxide as the initiator. The thermal properties of the polymers have been studied. The influence of the triallyl cyanurate content on the thermal behaviour of the copolymers has been investigated.

Some properties of copolymers of alkyl acrylates and styrene with N‐tolylmaleimide

AbstractCopolymers of methyl acrylate, ethyl acrylate and styrene with N‐tolylmaleimide having different compositions were synthesized by free radical bulk and solution polymerization. Some of their properties, e.g. chemical resistance, thermal strength, density, shrinkage on polymerization, and refractive index, were studied. The influence of the content of N‐tolylmaleimide in the copolymers on their properties is discussed.

Kinetics of bulk free-radical polymerization of methyl methacrylate using potassium peroxydisulfate with 18-crown-6 as phase-transfer catalyst

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of bulk free-radical polymerization of methyl methacrylate using potassium peroxydisulfate with 18-crown-6 as phase-transfer catalystK. Y. Choi and C. Y. LeeCite this: Ind. Eng. Chem. Res. 1987, 26, 10, 2079–2086Publication Date (Print):October 1, 1987Publication History Published online1 May 2002Published inissue 1 October 1987https://doi.org/10.1021/ie00070a025RIGHTS & PERMISSIONSArticle Views463Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (878 KB) Get e-Alerts Get e-Alerts

Free-radical bulk polymerization kinetics of 1-vinyl-imidazole at total conversion by DTA

The free-radical polymerization of 1-vinyl-imidazole at total conversion in the temperature range 363 to 433 K has been studied by differential thermal calorimetry (DTA). From the experimental data the kinetic order has been calculated and a change in the order has been found in the temperature interval 363–393 K. At higher temperatures the kinetic order remains constant. In order to explain this change we have proposed a kinetic scheme. Finally, the activation energy, E A, and the pre-exponential factor, A, are calculated using the Arrhenius equation.

Kinetics of free radical polymerization of ortho‐ and para‐alkylaryl esters of methacrylic acid

AbstractThe kinetics of free radical polymerization in bulk of alkylphenyl methacrylates with ethyl‐,isopropyl and tert‐butyl groups in the ortho‐ and para‐positions of the phenyl ring with dilauroyl peroxide as initiator were investigated. For comparison and completion of the investigation, ortho‐ and para‐tolyl methacrylates were reinvestigated with this particular initiator. Most of the results obtained do not obey classical kinetics of polymerization. The results were treated according to the concept of degradative chain transfer and it was concluded that this mechanism is responsible for the non‐ideality. The ortho‐substitution with increasing size of the substituents decreases the overall rate of polymerization and strengthens chain transfer to monomer.

Rheokinetics of free-radical polymerization

The authors elaborate theoretical concepts and obtain mathematical relations describing the increase in viscosity of reactive masses during bulk free-radical polymerization. The results obtained are confirmed experimentally for free-radical polymerization of alkyl methacrylates and styrene.

The dynamic behavior of continuous polymerization reactors—II Nonisothermal solution homopolymerization and copolymerization in a CSTR

The possible types of dynamic behavior have been determined for a CSTR in which bulk or solution free radical polymerization is carried out. To illustrate the methodology, the expected behavior of reactors for vinyl acetate or methylmethacrylate homopolymerization and vinyl acetate-methylmethacrylate copolymerization has been explicitly determined. The monomer feed ratios, solvent concentrations, and reactor cooling capacity which allow multiple steady states and limit cycles have been carefully mapped.

Mechanismus der photopolymerisation des styrols, 3. Zur kinetik der photo‐elementarprozesse

AbstractThe photoinduced free radical bulk polymerization of styrene (M)—in the absence of any sensitizer or free radical initiator—was investigated at different intensities, Ja, and at different wavelengths, λe, of the exciting light (λe = 313 nm, 335 nm; 25°C). The polymer conversion was followed dilatometrically in optical cells and the photo‐oligomers which are built up simultaneously in the polymerizing system —cis‐1,2‐diphenylcyclobutane (c‐CB), trans‐1,2‐diphenylcyclobutane (tr‐CB), 1‐phenyl‐1,2,3,4‐tetrahydronaphthalene (1‐PhT), 2‐phenyl‐1,2,3,4‐tetrahydronaphthalene (2‐PhT), 1‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T1) and 2‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T2),—were quantitatively analyzed by GLC. The quantum yields were found to be φc‐CB = 0,10, φtr‐CB = 0,02, Φ1‐PhT = 0,0084, Φ2‐PhT = 3,7.10−3, ΦT = 5,0.10−4, respectively, and from the experimentally observed dependence of the rate of polymerization, VP, on the square root of the light intensity, Ja, the apparent quantum yield of the formation of radicals can be calculated to be ΦS = 5,6.10−4. On the basis on the proposed structure of the photointermediates, I, which had been previously confirmed by 1H NMR spectroscopy in enriched systems, the kinetic treatment of the photostationary state gives a complete data set of mean values of partial quantum yields, φ, concerning all the photo‐elementary processes of I under polymerizing conditions: φS = 2,56.10−3, φT = 2,3.10−3, φPhT = 5,5.10−2 and φ2M = 0,94 (retro‐Diels‐Alder decomposition).