Synthesis of chitosan‐modified poly(methyl methacrylate) by emulsion polymerization

Emulsion polymerization of methyl methacrylate (MMA) in the presence of chitosan was studied and a reaction mechanism was proposed. It was proved in the companion article that potassium persulfate (KPS) free radicals can degrade chitosan chains into chain free radicals. Therefore, it is possible to produce a chitosan copolymer when the monomer and the KPS initiator are added into the chitosan solution. According to the proposed mechanism, concentrations of different species such as the initiator, total free radicals, and degraded chitosan chain were calculated with the reaction time. All the results agreed with the experimental observation. The results showed that the polymerization rate varied with 0.83‐ and 0.82‐order of the total free‐radical concentration and chitosan repeating unit concentration, respectively. It was also verified that chitosan played multiple roles in the reaction system. If the monomer was added into the chitosan solution before the addition of KPS, chitosan served mainly as a surfactant. Consequently, the polymer particle number was increased with the chitosan addition and so was the polymerization rate. However, if the monomer was added into the solution where the chitosan was already degraded by KPS, the polymerization rate was decreased with the predegradation time of chitosan. In both cases, the final polymer particles consisted of the poly(methyl methacrylate) (PMMA) homopolymer and the chitosan‐PMMA copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3047–3056, 2002     

Study on bulk polymerization of methyl methacrylate initiated by low intensity ultrasonic irradiation

Methyl methacrylate (MMA) was polymerized in bulk solutions using low intensity ultrasonic radiation of 0.25 W/cm². The polymerization occurred after 1 h of irradiation time was applied. The polymerization rate was greatly accelerated either by increasing the amount of poly (methyl methacrylate) (PMMA) granular added into the system or by elongating the irradiation time. However, it was found that the reaction rate increased with the decreasing of the ultrasonic frequencies when the exposure time of the polymerization under the irradiation was less than 3 h. Experimental results verified that the polymerization was initiated by free radicals, which were mainly generated from the degradation of PMMA macromolecular chains, the friction between the polymer macromolecular chains and the solvent monomer. These findings were obviously different from those obtained when high intensity ultrasonic irradiation was used. The polymers fabricated in this study by using ultrasound irradiation have a narrower molecular weight distribution compared to those obtained from the polymerizations induced by the conventional initiators. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Photoinitiierte Polymerisation mit Dialkoxythiocarbonyldisulfiden – eine Polymerisationsreaktion mit Primärradikalabbruch

Photoinitiated Polymerization with Dialkoxy Thiocarbonyl Disulfides – a Polymerization Reaction with Primary Radical Termination The photoinduced free radical polymerization of methyl methacrylate (MMA) and some other vinyl monomers using dialkoxy thiocarbonyl disulfides ( 1 – 4 ) as photoinitiators was studied. The photolysis of these initiators leads to cleavage of the S S bond, which was determined by spin trapping experiments with phenyl tert-butyl nitrone. No evidence was found for a further thermal decomposition of the primary alkoxy thiocarbonyl sulfide radicals (R·) at room temperature. In the absence of scavengers the primary radicals react back exclusively to the initial compounds, due to a strong cage effect. By means of UV spectroscopic measurements and in the presence of MMA the quantum yields of the initiator decomposition were detected to be 0.8. The polymerization of acrylic and methacrylic derivatives can be initiated by the R·, contrary to the situation with fumarates and maleates. The mechanism of MMA polymerization depends on the light intensity absorbed by the initiators. At high intensities the combination of primary and polymer radicals terminates the chain reaction. This follows from the measured monomer exponent of α = 2, the light intensity exponent of β = 0,2 and the number of thiocarbonyl end groups of 2 in the polymers isolated. Contrary to this, in the low intensity region the experimental data obey the ideal kinetic equation. Kinetic modelling gives evidence for an interaction of the monomer with the cage radicals.     

Analysis of ultrasonically induced free radicals in the emulsion polymerization system by GC–MS

A specially designed gas chromatography–mass spectrometry (GC–MS) analytical method has been developed and applied to identify the source of free radicals that served as initiators in a new ultrasonically induced emulsion polymerization system with monomer methyl mathacrylate (MMA), surfactant sodium dodecylsulfate (SDS) and water. The results showed the radicals came from the dissociation of SDS under ultrasonic irradiation. A quantitative determination procedure has been also developed and utilized to investigate the effects of the polymerization parameters, such as the surfactant concentration, the acoustic intensity of ultrasound, and the argon flow rate on the concentration of the generated free radicals in the emulsion system under ultrasonic irradiation. The results were helpful to understand the mechanism and kinetics of the system. © 1994 John Wiley & Sons, Inc.     

Ultrasonically initiated free radical‐catalyzed emulsion polymerization of methyl methacrylate (i)

The emulsion polymerization of methyl methacrylate initiated by ultrasound has been studied at ambient temperature using sodium lauryl sulfate as the surfactant. The investigation includes the: (1) nature and source of the free radical for the initiation process; (2) effects of different types of cavitation; and (3) dependence of the polymerization rate, polymer particle number generated, and the polymer molecular weight on acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration. It was found that the polymerization could be initiated by ultrasound in the emulsion systems containing methyl methacrylate, water, and sodium lauryl sulfate at ambient temperature in the absence of a conventional initiator. The source of the free radical for the initiation process was found to come from the degradation of the sodium lauryl sulfate, presumably in the aqueous phase. The weight average molecular weight of the poly(methyl methacrylate) obtained varied from 2,500,000 to 3,500,000 g mol⁻¹, and the conversion for polymerization was up to 70%. Deviations from the Smith–Ewart kinetics were observed. The polymerization rate was found to be proportional to the acoustic intensity to the 0.98 power; to the argon gas flow rate to the 0.086 power; to the surfactant concentration to the 0.08 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 0.58 power, with the 0.139M–0.243M surfactant concentration range. The polymerization rate was found to increase with increasing initial monomer concentration up to a point where it became independent of initial monomer concentration. The polymer particle number generated per milliliter of water was found to be proportional to the acoustic intensity to the 1.23 power; to the argon gas flow rate to the 0.16 power; to the surfactant concentration to the 0.3 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 1.87 power, with the 0.139M–0.243M surfactant concentration range. The polymer weight average molecular weight was found to be proportional to the acoustic intensity to the 0.21 power, and to the argon gas flow rate to the 0.02 power. It was found to be inversely proportional to the surfactant concentration to the 0.12 and 0.34 power, with the 0.035M–0.139M and the 0.139M–0.243M surfactant concentration ranges, respectively. The polymer yield and polymerization rate were found to be much larger than those obtained from an ultrasonically initiated bulk polymerization method. The polymerization rates obtained at ambient temperature were found to be similar to or higher than those obtained from the conventional higher temperature thermal emulsion polymerization method. This investigation demonstrated the capability of ultrasound to both initiate and accelerate polymerization in the emulsion system, and to do this at a lower temperature that could offer substantial energy savings. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 797–825, 1999     

Novel Sm(PPh2)2 initiator for the synthesis of poly(ε-caprolactone) with linear and star-shaped structures§

Summary Photolysis of tetrasubstituted bi(phosphine sulfides) at 254 nm yields disubstituted thiophosphinyl radicals that initiate the polymerization of methyl methacrylate. The phosphorus-containing chain ends of the polymers produced in these polymerizations were easily measured and characterized using ³¹P-NMR spectroscopy. These measurements showed that thiophosphinyl radical additions to methyl methacrylate are regiospecific. The yields obtained in bi(phosphine sulfide)-initiated MMA polymerizations compare favorably with yields obtained using a commercially available photoinitiator, Lucirin TPO, but the reaction times required are considerably longer. The molecular weights of PMMA samples obtained from bi(phosphine sulfide)-initiated polymerizations are lower than those of TPO-initiated samples, due to the ability of bi(phosphine sulfides) to also act as chain transfer agents. Received: 16 November 2001/Revised version: 11 February 2002/ Accepted: 12 February 2002     

One‐step,one‐pot photoinitiation of free radical and free radical promoted cationic polymerizations

We describe here a novel approach to photoinitiate free radical and cationic polymerizations concurrently, involving the use of benzoin in conjunction with an onium salt such as diphenyl iodonium or N‐alkoxy pyridinium salt. On photolysis, benzoyl radicals formed from the decomposition of benzoin initiate free radical polymerization of methyl methacrylate. The hydroxy benzyl radicals formed concomitantly are readily oxidized to the corresponding cation by the onium salt to initiate cationic polymerization of cyclohexene oxide in the same system. Evidence for two independent polymerizations was obtained from studies involving gel permeation chromatography, extractions, and infrared and proton nuclear magnetic resonance analysis of the polymers. The effect of the type of the onium salt on each polymerization was also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2389–2395, 2002     

Redox polymerization: Kinetics of polymerization of acrylonitrile initiated by the system 2,2′-thiodiethanol/trichloroaquobipyridylmanganese(III) in dilute sulfuric acid

The kinetics of polymerization of acrylonitrile and methyl methacrylate initiated by the redox system 2,2′-thiodiethanol/trichloroaquobipyridylmanganese(III) have been investigated in the temperature range 20–35°C in dilute sulfuric acid. The oxidation of the substrate in the absence of monomer has also been studied. A third-order reaction involving the complex, the substrate, and H⁺ leads to the production of primary radicals which initiate polymerization of the monomers. The primary radicals are more reactive towards methyl methacrylate than towards acrylonitrile. The termination of polymerization with both monomers is by mutual interaction between the growing radicals. A suitable kinetic scheme has been proposed, and the rate constants evaluated.     

Experimental study of emulsion polymerization with crosslinking

Herein is reported the results of an extensive experimental investigation of the kinetics of emulsion polymerization as affected by crosslinking in the polymer particles. The model monomer system, methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA), was chosen for this study due to its earlier comprehensive investigation in bulk polymerization. Standard recipes with sodium dodecylsulfate (SDS) as anionic emulsifier and potassium persulfate (KPS) as initiator were used for the batch emulsion polymerizations. Results, which clearly show the effect of crosslinking on the kinetics, are discussed in detail. These include swellability of polymer particles by monomer; polymer particle nucleation rates, below and above the critical micelle concentration (CMC); average number of radicals per particle; and gel-sol levels. It was found advantageous to use electron spin resonance (ESR) to follow radical concentrations during crosslinking in polymer particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 935–957, 1997     

Mechanochemical copolymerization of methyl methacrylate and styrene initiated by the grinding of quartz

The copolymerization of methyl methacrylate and styrene mechanochemically initiated by the grinding of quartz in the monomer mixture was investigated by using a vibrating ball mill. The effect of the grinding of quartz on the copolymerization was investigated by characterizing both the polymer formed and the ground quartz. The copolymerization proceeds apparently from the quartz grindings and was closely related to the total surface area of the ground quartz. The molecular weight distributions of the copolymers formed were unimodal as found in a homopolymer of only methyl methacrylate. It was clear from the composition analysis of the copolymer that the mechanochemical copolymerization of methyl methacrylate and styrene proceeded with a radical polymerization mechanism because of radicals on the quartz surface produced by the grinding. The monomer reactivity ratios obtained by the Fineman‐Ross method suggested that the copolymers formed were alternating copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2011–2017, 2002; DOI 10.1002/app.10544     

Mechanistic aspects of sonochemical copolymerization of butyl acrylate and methyl methacrylate

This paper attempts to get a physical insight into the sonochemical emulsion copolymerization using butyl acrylate (BA) and methyl methacrylate (MMA) as model monomers at low to moderate ultrasound intensity. The principal physical mechanism underlying beneficial effects of ultrasound on emulsion polymerization system is cavitation, which affects the system in both chemical (i.e. generation of radicals that can initiate/propagate polymerization process) as well as physical (i.e. emulsification of reaction mixture) way. By taking dual approach of coupling experiments with simulations of cavitation bubble dynamics, we have tried to justify the trends in experiments results. The role of cavitation in the present study is found to be only physical. Quite interestingly, the chemical effect of cavitation is found to have no role to play. Reactivity ratios of both monomers for applied experimental conditions have been found to be less than 1, which hints at moderately alternating behavior of copolymerization. Theoretically calculated copolymer composition using the reactivity ratios of copolymers matched well with experimental values. The copolymer composition for all monomer feed ratios is rich in MMA, due to higher reactivity of MMA than BA. The molecular weight of the copolymer reduced with greater fraction of MMA in the reaction mixture. This effect is attributed to nature of termination of the BA (i.e., combination) and MMA (i.e., disproportionation) monomer radicals.     

Synthesis of block copolymers by using polysilanes

Poly(methyl phenyl silane) was used to photoinitiate the polymerization of methyl methacrylate. Poly(methyl methacrylate) (PMMA), obtained this way, contains remaining polysilane chains. Photolysis of this PMMA in the presence of vinyl monomers such as styrene makes it possible to prepare block copolymers. Such PMMA prepolymers were also used to induce the polymerization of cyclohexene oxide through formation of PMMA-attached silyl radicals and subsequent oxidation to the corresponding ions in the presence of N-ethoxy-2-methylpyridinium hexafluorophosphate resulting in the formation of a block copolymer.     

Radiation-induced solid-state polymerization in binary systems. V. Polymerization in binary systems containing long chain compounds

Radiation-induced solid-state polymerization in binary systems containing long-chain compounds has been investigated. Butyl stearate–methyl methacrylate and stearyl alcohol–methyl methacrylate systems have been studied in detail. In these systems insource polymerization does not occur but a remarkable post-polymerization takes place on warming after irradiation at low temperature. The limiting conversion characteristics of this post-polymerization depend greatly on the nature and the concentration of the long-chain compounds. The post-polymerization is observed to be more marked in the butyl stearate–methyl methacrylate system than in the stearyl alcohol–methyl methacrylate system, and it increases with increasing concentration of the long-chain component. An optimum warming rate and warming temperature exists for the maximum saturated conversion. Irradiation in air causes some decrease of conversion compared to irradiation in vacuo. The possible mechanism is that monomer diffuses into the crystals of the long-chain compound after melting at the eutectic temperature. The polymerization may be initiated by trapped radicals of the long-chain compound and carried out in the crystal of the long-chain compound with a smaller possibility of termination. In binary systems containing long-chain compounds, lowering of the melting point is slight, and the eutectic composition exists at the richer composition of monomer, so almost all the long-chain substance remains as excess crystals, which are suitable for holding trapped radicals. The crystal lattices of long-chain compounds may be softer than those of compounds of small molecular size. This fact is favorable for monomer diffusion. This explains why such a post-polymerization takes place only in systems containing long-chain molecules.     

The effect of the amine structure on photoinitiated free radical polymerization of methyl methacrylate using bisketocoumarin dye

Photoinitiation of the polymerization of methyl methacrylate by the bis-diethylaminocoumarin dye (BKC) in the presence of various amines was studied in order to determine the efficient amine that leads to the formation of the initiating radicals. RT-FTIR studies were also performed for multifunctional methacrylate. According to photoinduced polymerization and RT-FIR studies, N-methyldiethanol amine was the more efficient H-donor compared with the others.     

Photoactive epichlorohydrin, 2. Photoinitiated free-radical and promoted cationic polymerization by using polyepichlorohydrin with benzoin terminal groups

The photoinitiated free-radical polymerization of methyl methacrylate (MMA) and the radical-promoted cationic polymerization of cyclohexene oxide (CHO) in the presence of low-molecular-weight polyepichlorohydrin terminated with groups containing benzoin derivatives were studied. Benzoin-terminated polyepichlorohydrin was prepared by Activated Monomer (AM) polymerization. Upon photolysis. polymer-bound alkoxy benzyl radicals were generated, initiating the radical polymerization of MMA. In the case of radical-promoted cationic polymerization of CHO, the cationic initiating species were formed by the oxidation of photochemically generated polymeric radicals by N-ethoxy-2-methylpyridinium hexafluorophosphate.     

ESR and kinetic study of a novel polymerizable photoinitiator comprising the structure of N‐phenylmaleimide and benzophenone for photopolymerization

A novel polymerizable photoinitiator, 4‐[(4‐maleimido)phenoxy]benzophenone (MPBP) comprising the structure of N‐phenylmaleimide and benzophenone was used for the photopolymerization with N,N‐dimethylaminoethyl methacrylate (DMAEMA) as coinitiator. The ESR spectrum of this photoredox system was studied and compared with BP/DMAEMA; the results showed the same signals of them and verified that N‐phenylmaleimide does not generate radicals. The kinetics for photopolymerization of methyl methacrylate (MMA) using such system was studied by dilatometer. It was found that the polymerization rate was proportional to the 0.3172th power of the MPBP concentration, the 0.7669th power and the 0.1765th power of MMA concentration and DMAEMA concentration respectively; the overall apparent activation energy obtained was 31.88 kJ/mol. The polymerization kinetics of 1,6‐hexanediol diacrylate (HDDA) initiated by such system was studied by photo‐DSC. It showed that the increase in the MPBP concentration, light intensity, and temperature leads to increased polymerization rate and final conversion. The apparent activation energy was 11.25 kJ/mol. This polymerizable photoredox system was significantly favorable for reducing the migration of active species but owning high efficiency. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2347–2354, 2006     

Unexpected effect of the monomer concentration on the rate of a radical polymerization

The radical polymerization of vinyl monomers is usually initiated by physical and chemical means. After an increasing polymerization rate, R_p, at low monomer concentrations, some reactive systems show an unexpected minimum for R_p at high enough monomer concentrations. The radical polymerization of methyl methacrylate (MMA) initiated by the redox system D -glucose–ceric ion at varying MMA concentration is discussed. The peculiar behaviour of R_p is explained by the presence of two circumstances: the initiation rate from D -glucose radicals does not depend on MMA concentration when most of the D -glucose radicals formed react by adding to monomer, and the radical chains initiated by D -glucose radicals undergo mutual termination with a portion of the radical chains initiated by monomer radicals. Some information about the nature of the polymer end-groups is reached from the mechanistic approach.     

Radical polymerization of methyl methacrylate with methyl 2,2-dimethyl-3,3-diphenyl-3-cyanopropionate as a thermal iniferter

Summary To clarify the mechanism of living radical polymerization of methyl methacrylate (MMA) with tetraphenylsuccinodinitrile (TPSN) as a thermal iniferter, a model compound for the end group of the poly(MMA) produced, methyl 2,2-dimethyl-3,3-diphenyl-3-cyanopropionate (2), was synthesized and found to initiate a living radical polymerization of MMA, indicating that the hexa-substituted C-C bond in 2 dissociated into radicals. The poly(MMA) thus obtained further initiated the radical polymerization of styrene (St) to give a block copolymer.     

Modeling of a Buss‐Kneader as a polymerization reactor for acrylates. Part II: Methyl methacrylate based resins

The Buss‐Kneader has proven to be a suitable reactor for the polymerization of acrylates. In this second part, the polymerization of methyl methacrylate and the ter‐polymerization of methyl methacrylate (MMA), hydroxyethyl methacrylate and n‐butylmethacrylate is carried out in a pilot Buss‐Kneader. The reactor had to be pressurized up to about 10 bars to avoid evaporation of MMA. Instabilities in output rate and temperature profiles were observed as a result of fluctuating die pressures. Because of good mixing there may be no diffusion limitation for radicals. As a result, even at high conversions, no gel effect was observed.     

Thermal degradation of poly(methyl methacrylate) at 50°C to 125°C

Small but significant numbers of chain scissions occur in a commercial poly(methyl methacrylate) sheet exposed to temperatures between 50 and 125°C. The scission rate is initially high and then levels off to a constant rate. The short-time rate of chain scissions is temperature dependent, while the long-time rate of chain scissions appears to be temperature independent. Four possible sources of random chain scission initiation were considered: (1) the presence of unreacted initiators of polymerization, (2) free radicals generated from additives in the commercial film, (3) weak links in the polymer chain, and (4) free radicals generated from the thermal decomposition of an oxidation product of methyl methacrylate (MMA) monomer. The source most consistent with our results is the one involving free radicals generated from the oxidation product of MMA monomer.