Kinetic study of aqueous polymerization of methyl methacrylate initiated by Ce(IV)-maltose redox system

Polymerization of methyl methacrylate initiated by ceric ammonium nitrate-maltose has been investigated in aqueous nitric acid under nitrogen in the temperature range 20.5-35°C. The dependence of the initial rate of polymerization and the initial rate of ceric ion consumption on maltose, Ce(IV), and monomer concentrations has been determined. The reaction orders were found to depend on ceric ion concentration. At a moderately high Ce(IV) concentration (1 × 10^?3mol litre^?1) the orders were 1/2 and 3/2 with respect to maltose and monomer concentration, respectively, and independent of Ce(IV) concentration. But at a low Ce(IV) concentration (4 × 10^?4mol litre^?1) the orders with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The effect of temperature was also examined. The average molecular weight, as determined by size-exclusion chromacography, was found to depend on maltose, Ce(IV), and monomer concentrations, as well as on temperature.     

Aqueous polymerization of methyl methacrylate initiated by the redox system Ce(IV)—D-glucose. I: General features and kinetics

The polymerization of methyl methacrylate initiated by the ceric ammonium nitrate-D-glucose redox system has been studied in aqueous nitric acid under nitrogen in the temperature range 20-5 to 35°C. The initial rate of polymerization was determined gravimetrically whereas the initial rate of ceric ion disappearance was determined by titration of ceric ion. The relationships between conversion and D-glucose, Ce(IV), and monomer concentrations were determined. The dependence of the rates on D-glucose, Ce(IV), and monomer concentrations was evaluated. The effect of temperature was also examined.     

悬浮聚合法制取不同分子量级别的聚甲基丙烯酸甲酯

采用粉状MgCO3 作为分散剂 ,悬浮聚合制取了分子量从 2 4× 10 4 ～ 2 5 4× 10 4 的聚甲基丙烯酸甲酯。考察了温度、引发剂种类和浓度、分子量调节剂、转化率对聚合物分子量的影响规律 ,用粘度法测量了聚合物聚甲基丙烯酸甲酯 (PMMA)的分子量。结果表明 :温度的升高、引发剂浓度的增大、分子量调节剂的加入都会导致分子量的减小 ,随着转化率的提高 ,聚合物的分子量增大。在同等条件下 ,引发剂过氧化苯甲酰 (BPO)聚合所得的分子量较偶氮二异丁腈 (AIBN)高。通过实验 ,得到了满足作者需求的分子量 (96× 10 4 ～ 10 0× 10 4 )的聚合物的聚合条件为 :分散剂MgCO3 用量 1% ,单体∶水相 =1∶2 5 (质量比 ) ,引发剂BPO浓度 0 5 % ,反应温度 70℃ ,反应时间 3h。     

Kinetic and molecular weight control for methyl methacrylate semibatch polymerization. II. Open control

The gel effect will bring a violent increase of conversion for methyl methacrylate (MMA) polymerization in a short time. It will be very dangerous for the reactor, as it causes an increase of molecular weight and broadens the molecular weight distribution. To unify the kinetics, molecular weight, and its distribution, on the basis of the mathematical models for semibatch polymerization of MMA, three controlled objectives that are the heat load distribution index, the change in molecular weight, and molecular weight distribution index are presented. Three materials (monomer, solvent, and chain transfer agent) and their flow rate and feeding mode are analyzed for the open control of kinetics, molecular weight, and its distribution. The optimum flow rate and mode are obtained. The heat load distribution index and molecular weight distribution index are even less than 2.0 and 2.2, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4399–4405, 2006     

Kinetic and molecular weight control for methyl methacrylate semi‐batch polymerization. I. Modelling

There are gel, glass, and cage effects in the methyl methacrylate (MMA) bulk polymerization. These effects will cause the propagation and termination rate constants and initiator efficiency change during the polymerization process, and make the kinetics and molecular weight more complex. A violent increase of conversion will bring a large amount of reaction heat evolved in a short time, and will promote temperature increase if the heat cannot be removed in time. Molecular weight of polymer will raise ten times at the same time. So, the temperature of polymerization system, kinetics of polymerization, and molecular weight and its distribution of polymer cannot be controlled. To control and unify them, the semibatch polymerization method is preferably selected. Furthermore, the kinetic and molecular weight models for MMA semibatch polymerization with the participation of chain transfer agent and new materials addition flow rate are presented. Using the presented models, the effects of temperature, initiator concentration and type, monomer or solvent concentration, and chain transfer agent concentration and type on the kinetics, and molecular weight and its distribution are simulated in this article. Experimental data of kinetics and molecular weight obtained from the published literature are compared with the simulation results to examine the presented models. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2838–2846, 2006     

Aqueous polymerization of acrylamide initiated by Ce(IV)-thiomalic acid redox system

Summary The use of a Ce (IV)-thiomalic acid (Ce⁴⁺-TMA) redox system as an initiator in the polymerization of acrylamide (M) in an aqueous medium has been investigated. The Ce⁴⁺ forms a 11 complex with TMA, decomposing through free radical mechanism in an acid medium. From 5 to 15% conversion the rate equation is where Rp is the rate of polymerization and x is 0.5 or 1.0 depending upon the concentration of monomer. The overall energy of activation has been calculated to be 9.12 k cal. deg^–1 mol^–1(38.12 kJ/mol) in the investigated range of temperature (25°–40°C) the degree of polymerization (P) of the polymer is directly proportional to [M]. The number of average molecular weight of the polymer remains unaffected at lower concentration of Ce⁴⁺ and is found to decrease at higher concentrations.In this investigation the kinetics and mechanism of the Ce(IV)-thiomalic acid (TMA) redox system to initiate the polymerization of acrylamide has been studied.Acrylamide (E. Merck) was purified by usual methods. Thiomalic acid and eerie ammonium sulfate were used without purification. All solutions were p repared in twice distilled water.The polymerization procedure adopted was similar to the one used by MISRA et al. [3, 4]. The polymerization was followed by quantitative estimation of the double bonds in acrylamide as described [8]. A small variable induction period was observed perhaps due tothe residual oxygen in the thiol solution. Curves were plotted after eliminating the induction period.The average molecular weights of the p olymers were determined by viscosity measurements at 30°C in an aqueous medium using the relationship of DAINTON et al. [2]. Where []=intrinsic viscosity of the polymer solution and ¯Mn=molecular weight of the sample.     

Effects of reaction conditions on poly(methyl methacrylate) polymerized by living radical polymerization with iniferter

Living radical polymerization of methyl methacrylate (MMA) through the use of benzyl diethyl dithiocarbamate (BDC) was studied. The aim was to investigate the role of the concentration, BDC‐to‐MMA mol ratio, and reaction time upon the molecular weight, polydispersity, and conversion of the product. It was found that the molecular weight and the conversion increase with increase of the concentration at the expense of low polydispersity. The reaction time also played a significant role, especially at a relatively long reaction time where molecular weight, polydispersity, and conversion increased with increasing reaction time. In terms of the mol ratio effect, it was found that there was a critical mol ratio for maximum conversion. The results indicate that the kinetics of polymerization of MMA through the use of a BDC inifeter is different from that in the presence of a conventional initiator. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 938–944, 2000     

The grafting of methyl methacrylate onto ultrahigh molecular weight polyethylene fiber by plasma and UV treatment

In this study, ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with a gas plasma of argon for 5 min. The plasma-treated UHMWPE fibers were put into a methyl methacrylate solution with n-hexane or chloroform as the solvent and irradiated with a UV lamp. The UV irradiation time was changed. The surface topography that had a significant change on the fiber was seen by scanning electron microscopy. Infrared spectra (IR) and electron spectroscopy for chemical analysis (ESCA) were also studied to probe the surface atomic chemistry and to identify the functional groups and their relative changes with treatment conditions. The grafting content was estimated by the titration of esterfication method. It was found that the grafting amount for the system with chloroform as the solvent is larger than that for the system with n-hexane as the solvent. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:365–371, 1997     

Effect of Co and V complexes on polymerization of methyl methacrylate initiated by AlEt2Br‐TEMPO catalyst

2,2,6,6‐Tetramethyl piperidinoxy (TEMPO) activated with diethyl aluminum bromide was employed as an initiator system for methyl methacrylate polymerization. Effect of addition of Co(acac)₃ and VO(acac)₂ complexes to the initiators system on methyl methacrylate polymerization were studied in benzene solvent. Various reaction parameters such as Al/TEMPO, monomer concentration, reaction temperature and time applied to the polymerization were investigated. The polymer yields, molecular weight and molecular weight distributions can be controlled with the addition of Co(acac)₃ to the initiator system. PMMA's of molecular weight distributions, as low as 1.10 was obtained under relatively mild conditions, in the temperature range 40–60°C in benzene solvent. However, Co and V complexes did not influence the micro structure of the PMMA's formed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of poly(methyl methacrylate) grafted sago starch using potassium persulfate as redox initiator

In this article, the graft copolymerization of methyl methacrylate (MMA) onto sago starch (AGU) was carried out in aqueous medium using potassium persulfate (PPS) under nitrogen gas atmosphere. The maximum percentage of grafting achieved was 90% under optimized conditions of reaction temperature, monomer, PPS, AGU, and reaction period corresponding to 50°C, 47 mmol, 1.82 mmol, 6.17 × 10^?3 mol L^?1, and 1.5 h, respectively. The grafting of MMA onto sago starch was confirmed by the differences in infrared spectroscopy. The viscosity measurement and the average molecular weight determination were estimated using Huggin's and Mark Houwink's equations, respectively. This material may have application as a biodegradable plastic. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1891–1897, 2004     

Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10⁻³ and 32.48 × 10⁻³ mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 777–793, 1999     

Graft polymerization of methyl methacrylate onto radiation‐peroxidized ultrahigh molecular weight polyethylene in the presence of metallic salt and acid

Using a radiation peroxide grafting technique, a ultrahigh molecular weight polyethylene (UHMWPE) stored at room temperature for 10 days after irradiation in air was graft copolymerized with methyl methacrylate (MMA) in the presence of metallic salt and acid. The MMA‐grafted UHMWPE samples were analyzed by measuring Fourier transform infrared spectroscopy in attenuated total reflectance (FTIR–ATR) and by electron spectroscopy for chemical analysis (ESCA). The 1,1‐diphenyl‐2‐picrylhydrzyl (DPPH) technique was utilized to evaluate the concentration of peroxide formed in the peroxidized UHMWPE samples by counting the quantity of DPPH consumed from the reaction of peroxide radicals with DPPH. It was shown that the inclusion of an FeSO₄ ·7H₂O and sulfuric acid in MMA grafting solutions was extremely beneficial and led to a most unusual synergistic effect in the radiation‐peroxidized grafting. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 659–666, 1999     

Aqueous polymerization of methyl methacrylate initiated by redox pair: Ce(IV)–Azo compounds with methylol functional groups and synthesis of copolymers

Hydroxyl functional azo compounds have been used as reducing agents in redox polymerization of methyl methacrylate (MMA) in conjuction with ceric ammonium nitrate (which acts as an oxidizing agent in aqueous nitric acid at 20°C). Kinetic measurements were followed by gravimetric method, at lower conversions, not exceeding 10% conversion. The dependence of rate of polymerization and average molecular weight, which was determined by gel permeation chromatography (GPC), on azo, Ce(IV), and MMA concentrations, respectively, were investigated. The homopolymers, which contain thermo-and photolabile azo groups, were utilized with different comonomers to give block or graft copolymers depending on termination mechanism of homopolymerization. © 1994 John Wiley & Sons, Inc.     

A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate)

The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers.     

Graft polymerization of vinyl acetate onto granular starch: Comparison on the potassium persulfate and ceric ammonium nitrate initiated system

This work was undertaken to discuss in depth the vital differences in the morphological development during synthesis, and properties of starch‐g‐poly‐(vinyl acetate) copolymers using two different initiators, potassium persulfate (KPS) and ceric ammonium nitrate (CAN). KPS‐initiated system gave relatively low values of grafting ratio and grafting efficiency, indicating a great tendency for the formation of poly(vinyl acetate) homopolymer (PVAc). Yet, higher values were seen for the CAN‐initiated system. Transmission electron microscope observations indicated a relatively broad distribution of latex particles for the KPS‐initiated system. The surface potential of latex particles was about ?3.5 mV, which turned out to be insufficient to maintain stability of latex particles. On the other hand, a uniform particle size distribution was found for the CAN‐initiated system, as the surface potential of latex particles was 21.5 mV. Moreover, radicals on starch molecules were generated directly through a redox reaction with positively charged ceric ion. The hydrophobic PVAc chains were thus grafted on starch, resulting in an amphiphilic graft copolymer, which provides a sufficient stabilization degree as a role of surfactant to render a relatively uniform distribution of latex particles. The synthesized starch‐g‐poly(vinyl acetate) copolymers were further converted to starch‐g‐poly(vinyl alcohol) through saponification, which were subjected to evaluations regarding the biodegradation and cell culture capability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3017–3027, 2006     

Synthesis of poly(methyl methacrylate) nanoparticles initiated by azobisisobutyronitrile using a differential microemulsion polymerization technique

Nanosized poly(methyl methacrylate) (PMMA) particles with a high molecular weight of 10⁶ g mol^?1 and a polydispersity index of about 1–2 were synthesized, for which 2,2′‐azobisisobutyronitrile was used as the initiator and a differential microemulsion polymerization technique was employed. The kinetics of the polymerization, the glass transition temperature, tacticity, the particle size distribution, and the morphology of the nanosized PMMA synthesized were investigated. The dependence of the number of the polymer particles (N_p) and the number of the micelles (N_m) on the concentration of the surfactant was discussed. The molecular weight distribution was found to be nearly constant over the polymerization time, which was attributed to the significance of micellar polymerization. The resultant nanosized PMMA has a rich syndiotactic configuration (53–57% rr triads) with a glass transition temperature of about 125°C. A beneficial operation condition was discovered where the conversion reached a maximum at a high monomer‐to‐water ratio. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Block copolymerization of poly(diethylene glycol phthalic anhydride) and methyl methacrylate initiated by potassium diperiodatonickelate(IV)

Block copolymers of methyl methacrylate (MMA) and poly(diethylene glycol Phthalic Anhydride) (PPAG) was synthesized using a novel redox system—potassium diperiodatonickelate(IV) [DPN]/PPAG system in an alkaline medium. Block copolymers with high percentage of blocking were obtained, which indicated that DPN/PPAG redox system was an efficient initiator for this blocking. Effects of different factors on the blocking parameters were examined. The overall activation energy of this blocking was calculated to be 55.12 kJ/mol. The structure of the block copolymer was determined by infrared, X‐ray diffraction, and scanning electron microscope (SEM). A mechanism is proposed to explain the generation of radicals and the initiation of block copolymerization. The block copolymer was used as the compatibilizer in blends of PMMA and Nylon6. The SEM photographs show that the block copolymer greatly improved the compatibility of the blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1312–1317, 2006     

Controlled radical polymerization catalyzed by CuCl/BDE complex in water medium. II. Polymerization of methyl methacrylate and formation of PMMA with bimodal molecular weight distribution

The emulsion polymerization of MMA was explored for the BDE/CuCl coordinated catalyst. The M_n of PMMA linearly increased both with increasing the monomer conversion and the proceeding polymerization time, which means that the MMA polymerized in “living”/controlled characters with zero order kinetics under BDE/CuCl‐catalyzed emulsion conditions. The apparent polymerization rate constants of MMA were k = 0.765 mol/min, k = 0.760 mol/min at 80°C, while k = 0.228 mol/min at 50°C, respectively. Slight differences of polymerization results were obtained when emulsifier lauryl phosphate (ADP) and Polyoxyethylene nonyl phenyl ether (OP‐10) were adapted in the polymerization. Based on the “coordinated radical cage” mechanism proposed particularly to the BDE/CuCl catalyzed polymerization, reversible equilibrium between common free radical and the coordinated “living” species should exist in this system. Increasing the amount of catalyst must affect the fast equilibrium between those two species, thus, also affecting the relative content in the emulsion circumstance. Therefore, PMMA, with bimodal molecular weight distribution, was achieved through this approach. The formation of PMMA with bimodal distribution was affected by concentration of catalyst and polymerization temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3076–3081, 2002; DOI 10.1002/app.2336     

Graft copolymerization of methyl methacrylate onto biomedical polyvinyl chloride initiated by Ce(IV)–glucose redox system

Graft copolymerization of methyl methacrylate onto PVC was carried out using Ce(IV)–glucose redox system in aqueous sulfuric acid medium under nitrogen atmosphere. To find out the optimum conditions for grafting, effects of concentrations of metal ion, glucose, monomer, and acid on the percentage of grafting was studied. The graft yield was found to be influenced by reaction time, temperature, and amount of PVC. An appreciably high graft yield could be achieved with the present system. On the basis of the results from the present study, a plausible reaction mechanism has been proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2105–2111, 2005     

Influence of molecular weight on the fracture of poly(methyl methacrylate) (PMMA)

A model is proposed to explain the dependence of fracture parameters on the molecular weight of glassy polymers. The model assumes that the fracture event occurs in two stages; the first involves the orientation of polymer chain segments between entanglement points and the second, the fracture itself. A value has been calculated, (～0.6J m^?2), for the fracture surface energy corresponding to the lower critical molecular weight between entanglements, M=M_e. Allowing for the simplifying assumptions made in its derivation, this value is in good agreement with that found experimentally. It is proposed that, after the chain segments between entanglements crossing a plane have been fully extended, two possible mechanisms are involved; chain ‘pull-out’ up to a maximum governed by the time scale of the local fracture event, or chain scission. Using the concept of a reptating chain it is proposed that above M ～2 M_e there is a relationship between the fracture energy (γ) and the molecular weight of the form γ∝ ∝M² up to a critical value of M, above which γ is constant. It has been shown that there is some agreement with experimental relationships determined independently.