Kinetics and mechanism of emulsion copolymerization. IV. Kinetic modeling of emulsion copolymerization of styrene and methyl methacrylate

Based on the micellar nucleation theory, a mathematical kinetic model for an unseeded emulsion copolymerization system is developed, where the radicals with and without electric charge are discriminated from each other in view of the role in the particle nucleation process. In order to demonstrate the validity and utility of this kinetic model, the experiments of the unseeded emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA) are carried out varying the initial initiator (potassium persulfate) and emulsifier (sodium lauryl sulfate) concentrations and the monomer composition in the initial monomer feed, and various kinetic features observed are compared with the model predictions. It is concluded from this comparison that in this system, almost all the polymer particles are generated by the charged radicals stemming from the initiator, and further that this mathematical kinetic model can provide a satisfactory explanation of the various kinetic features observed.     

Radiochemical study of the radical copolymerization of styrene and methyl methacrylate

The rates of initiation for the copolymerization of styrene and methyl methacrylate at 50°, in different reaction media (bulk, acetone, dimethylformamide and dioxane) have been determined by using the isotopic labelling technique (¹⁴C - azobisisobutyronitrile). For all mixtures, except dioxane, the experimental data do not support the linear interpolation of the initiation rates, which is usually adopted in literature. In the whole range of monomer feed compositions, any modification of the reaction medium causes a relevant change of the initiation rate, so that the overall pattern is markedly modified. The strongest solvent effect is given by dioxane, which reduces the initiation rates for all monomer mixtures.The radioactive tracer method also enables the determination of the modes of termination, which occur almost exclusively by combination for monomer feed compositions up to about 70 molar % of methyl methacrylate. The $\text{P}\text{?}{}_{\mathrm{w}}\text{P}\text{?}{}_{\mathrm{n}}$ ratios obtained by g.p.c. confirm the general trend of the termination mechanisms as a function of monomer mixture and reaction medium.     

Effect of solvent on the termination step for the radical copolymerization of methyl methacrylate and styrene

The kinetics of the radical copolymerization of methyl methacrylate and styrene in benzene, chlorobenzene and benzonitrile has been investigated gravimetrically. The copolymerization termination step is analysed on the basis of the chemically controlled model, the diffusion-controlled model and the combined physical and chemical model, taking into account the corresponding reactivity ratios and the homopolymerization parameters in the three solvents used. The values obtained for the termination step parameters suggest that the termination step might be controlled by the viscosity of the reaction medium, but the sequence distribution and the stereochemical configuration of the polymer chains must also be considered.     

Kinetics of ylide-initiated radical copolymerization of 4-vinylpyridine and methyl methacrylate

The ylide-initiated radical copolymerization of 4-vinylpyridine (4-VP) with methyl methacrylate (MMA) at 60°C using carbon tetrachloride as inert solvent yields non-alternating copolymers. The kinetic parameters, average rate of polymerization (R_p) and orders of reaction with respect to monomers and initiator, have been evaluated and the kinetic equation is found to be R_pα[ylide]^0.94 [MMA]^1.0 [4-VP]^1.5. The values of the energy of activation and k_p²/k_t are 48 kJ mol^?1 and 6.6 × 10^?5 litre mol^?1s^?1, respectively. The copolymers have been characterized by IR and NMR spectroscopy.     

Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

Effect of aqueous comonomer solubility on the surfactant-free emulsion copolymerization of methyl methacrylate

Surfactant-free emulsion copolymerization was used to prepare methyl methacrylate-hydroxyethyl methacrylate (MMA-HEA) and methyl methacrylate-hydroxypropyl methacrylate (MMA-HPMA) latex particles. Also, glycidyl methacrylate (GMA) was grafted onto the surface of the preformed MMA-HPMA latex particles by seeded surfactant-free emulsion copolymerization. The copolymerization reactions were conducted at 75 °C using a water-soluble initiator, potassium persulfate (KPS). The morphologies of copolymer latex particles were observed using Scanning electron microscopy (SEM). The influence of different reactions parameters (the MMA saturation concentration (Sr), the KPS concentration and the aqueous solubility of the comonomers (HEA or HPMA)) on the particles average diameter and particles size dispersity was investigated. The experimental results showed that the increase of initiator concentration induces in all investigated cases the increase of particles average diameter, while the presence of HEA or HPMA as comonomers in the copolymerization reaction of MMA (1,000% Sr) lead to a decrease of particles average diameter. At small KPS concentration the latex is monodisperse, the increase of the initiator concentration leading to the formation of polydisperse latex. In the case of grafting reaction of GMA onto the monodisperse preformed MMA-HEA latex particles, although the average diameter of the final particles doubles the latex remains quasi-monodisperse.     

MMA/N-对甲苯基马来酰亚胺乳液共聚的研究

通过乳液共聚得到N－对甲苯基马来酰亚胺（NPTMI），甲基丙烯酸甲酯（MMA）的二元共聚物，用扭辫分析，热重分析和维卡软化点测定仪研究了不同NPTMI含量对共聚物热性能的影响，以及共聚物的力学性能，流变性能，研究结果表明，共聚物初始分解温度（Tini)，失重50％时的温度，玻璃化转变温度（Tg)及维卡软化点（TViout)都随NPTMI的含量增加而提高，当NPTMI含量为15％时，Tg提高14．1℃，Tini提高23．2℃，TVicut提高8．9℃，工聚物熔体呈假塑性流体，同时共聚物熔体非牛顿指数随NPTMI含量的增加而增大。     

Atom transfer radical copolymerization of glycidyl methacrylate and methyl methacrylate

Glycidyl methacrylate (GMA) and methyl methacrylate (MMA) copolymers were synthesized by atom transfer radical polymerization (ATRP). The effect of different molar fractions of GMA, ranging from 0.28 to 1.0, on the polymer polydispersity index (weight‐average molecular weight/number‐average molecular weight) as the indicator of a controlled process was investigated at 70°C, with ethyl 2‐bromoisobutyrate as an initiator and 4,4′‐dinonyl‐2,2′‐bipyridyne (dNbpy)/CuBr as a catalyst system in anisole. The monomer reactivity ratios (r values) were obtained by the application of the conventional linearization Fineman–Ross method (r_GMA = 1.24 ± 0.02 and r_MMA = 0.85 ± 0.03) and by the Mayo–Lewis method (r_GMA = 1.19 ± 0.04 and r_MMA = 0.86 ± 0.03). The molecular weights and polydispersities of the copolymers exhibited a linear increase with GMA content. The copolymer compositions were determined by ¹H‐NMR and showed a domination of syndiotactic structures. The glass‐transition temperatures (T_g) of the copolymers analyzed by differential scanning calorimetry (DSC) decreased in the range 105–65°C with increasing GMA units. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate

The concentration of sodium lauryl sulfate (SLS) in the initial reactor charge is the most important parameter in determining the particle size of a semibatch emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The number of particles formed is proportional to the concentration of SLS to the 0.5–1.2 power and it is proportional to the concentration of the nonyl phenol–40 mol ethylene oxide adduct to the 0.014–0.72 power. The number of particles is almost independent of the concentration of the initiator. The solubility of monomer in water has an important effect on the nucleation mechanism according to the literature. However, the ratio of MMA to BA does not show any significant effect on the latex particle size in our laboratory. The particle size also increases with increasing ionic strength or agitation speed. Experimental data of particle-size distribution and molecular weight distribution support the coagulative nucleation mechanism when the concentration of SLS is way below its critical micelle concentration (CMC). © 1995 John Wiley & Sons, Inc.     

Study on soapless emulsion copolymerization methyl methacrylate and n-butyl acrylate

The soapless emulsion copolymerization of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) at four levels of monomer feed composition (f₁₀) was studied. Conversion (X), average particle diameter (D_p), molecular weight distribution (MWD), surface charge density, and glass transition temperature (T_g) of the copolymer as a function of reaction time (t) were measured. The copolymers obtained even at low conversion, except for the run of (f₁₀) = 90 wt. percent MMA, exhibit two T_gs in their DSC thermograms. Phase separation is found to occur in the latex particles during polymerization. The heterogeneous distribution of monomers in particles, in which a relatively rich MMA region exists in the shell and a relatively rich n-BuA region exists in the core of the particles, is assumed to arise from phase separation. The average copolymer composition and the fraction of the two domains are estimated. The polymerizatrion course and particle size growth follow the linear X vs. t² and D_p^3/2 vs. t relationships, respectively. Although the coagulation of particles happens after around 30 percent conversion, the polymerization behaviors, except for increasing rates, are not affected.     

Synthesis of monodisperse styrene/methyl methacrylate/acrylic acid latex using surfactant‐free emulsion copolymerization in air

Monodisperse styrene/methyl methacrylate/acrylic acid (St/MMA/AA) copolymer microspheres have been prepared with surfactant‐free emulsion polymerization in air. The presence of oxygen in the system not only caused an induction period but also decreased the average particle size (D_p). However increasing AA concentration ([AA]) gave a reduction in the induction period. The FTIR and NMR analysis of the latex copolymer confirmed that the correlation of the copolymer compositions with the feed compositions was much better at the lower [AA] than at the higher levels. The AA contents of the copolymers obtained in air were much lower than those of the copolymers obtained under N₂ protection. Decreasing [AA] led to decrease in the copolymer molecular weight and broadening of the molecular weight distribution, but the particle size distribution (δ/D_p) was unaffected. In addition, the average particle diameter (D_p) was proportional to [AA]^–0.255, and increasing comonomers feed content caused linear increase of D_p, and a monodisperse sample with final solids contents up to 34.2 wt % was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization by tin-specific size exclusion chromatography of the free radical copolymerization of tributyltin methacrylate and methyl methacrylate

Copolymers of tributyltin methacrylate (TBTM) and methyl methacrylate (MMA) comprise an important class of biocidal slow-release organometallic polymers (OMPs). Little is known of the kinetics and mechanism of copolymerization. TBTM and MMA were copolymerized in the presence of a free radical initiator (benzoyl peroxide) at 80.1°C. Aliquots, taken at preselected intervals from 0 to 1440 min, were fractionated by size exclusion chromatography (SEC) coupled with ultraviolet (UV) and tin-specific graphite furnace atomic absorption (GFAA) detectors. A UV absorbance observed at 254 nm was associated with low-molecular-weight species, decreasing in concentration continuously with time of reaction. Tin-specific GFAA indicated a decrease in low-molecular-weight species (ca. 350 daltons) with concurrent increases in high-molecular-weight species (ca. 40,000 daltons). The fraction of high molecular-weight increased as a linear function of the logarithm of the time of reaction. SEC–UV–GFAA thus provides a tool of major importance for characterizing the time dependence and continuity of the process by which monomers of TBTM are converted to a useful bioactive slow-release coating material.     

Accumulation and desorption of free radicals in emulsion copolymerization

The emulsion copolymerization of styrene with acrylonitrile, seeded on a polybutadiene support and initiated either potassium persulfate or γ-rays has been studied. The original technique of support activation consists of two steps: the start of the copolymerization in the presence of a small fraction of monomers, followed by the addition of the rest of monomers, which leads to a great increase in the reaction rate. The experimental data provide evidence for a new mechanism that takes into account the desorption–reentry of the free oligoradicals into another particle, their transfer to the polybutadiene support, which results in the accumulation of trapped free radicals. As a consequence of free radicals' accumulation, the overall copolymerization rate increases. The accumulation as well as the desorption processes place this type of copolymerization far from Smith–Ewart theory case II.     

Radiation-induced copolymerization of vinylphosphonic dichloride with methyl methacrylate and styrene

The γ-ray-induced copolymerization of vinylphosphonic dichloride (VPDC) with methyl methacrylate (MMA) and styrene (St) was studied at 25°C (liquid phase) and ?78°C (Solid phase). The reaction mechanisms are discussed. The reactivity ratios for the copolymerization of the VPDC–MMA system were determined as follows: The difference between the reactivity between the liquid-phase (25°C) and solid-phase (?78°C) copolymerization is mainly attributable to the r₂ value. The behavior of the liquid-phase copolymerization of the VPDC–St system was anomalous, the r₁ value being negative in the range from 0 to 80 mole-% of VPDC monomer. In the solid-phase (?78°C) copolymerization for the VPDC–St system, the reactivity ratios r₁ and r₂ were 0.097 and 1.6, respectively. The rate of copolymerization (R_p) at 25°C, for both the VPDC–MMA and VPDC–St systems, passes a maximum point at a certain monomer concentration, suggesting that the composition of copolymer is considerably affected by R_p. This phenomenon was interpreted by the assumption that an energy transfer reaction from VPDC monomer to the other vinyl compound can easily occur.     

Solvent effect on the emulsion copolymerization of methyl methacrylate and lauryl methacrylate in aqueous media

Aqueous emulsion homo- and copolymerization of lauryl methacrylate (LMA), a highly hydrophobic, almost water-insoluble monomer, is quite challenging. Due to the addition of ethanol to the aqueous phase the solvency for LMA is increased and it is possible to successfully produce LMA-methyl methacrylate (MMA) copolymer particles. The incorporation of LMA is confirmed by ¹H NMR spectroscopy. Coagulation at higher ethanol content in the continuous phase could be avoided by polymeric steric stabilizers such as poly(vinyl pyrrolidone) or poly(vinyl alcohol). The conversion–time curves exhibit, independent of the stabilizer, an initially high rate where predominantly MMA is polymerized and a second period with slower rate dominated by LMA consumption as proven by ¹H NMR spectroscopy and DSC data. The morphology of the copolymer particles changes with increasing ethanol content from solid sphere - like to porous. For medium PVP - stabilizer concentrations the particles possess a single pore and appear almost bowl-shaped. The large difference between the hydrodynamic and the hard sphere particle diameter indicates a high degree of swelling of the copolymer particles with the water–ethanol mixture of the continuous phase.     

Modelling of free radical polymerization of styrene and methyl methacrylate by a tetrafunctional initiator

A mathematical model for free radical polymerizations initiated by tetrafunctional initiators is described in detail with comparisons to experimental results. Reactions involving the fate/efficiency of functional groups are properly accounted for, while in the past, kinetic models for difunctional initiators found in the literature have ignored this. Free volume theory is used to describe the diffusion-controlled regime. Based on model predictions, multi-radical concentrations were estimated to be several orders of magnitude smaller than mono-radical concentrations. Through various case studies, the model was able to demonstrate that the concentration and chain length of various polymer structures (i.e., linear, star or coupled stars) depend upon monomer type and reaction conditions. The model was found to be useful in explaining experimentally observed differences in the behaviour of a tetrafunctional initiator with styrene compared to methyl methacrylate (MMA). In both cases, higher reaction rates could be obtained when switching from a mono- to a tetrafunctional initiator; however, the influence on molecular weight was found to vary between the two systems. Work with styrene showed similar trends as with difunctional initiators, where the tetrafunctional initiator maintained similar molecular weights compared to a monofunctional initiator. Yet, for MMA, replacing the monofunctional initiator with its tetrafunctional counterpart decreased the molecular weight.     

Vinyl-functionalized gold nanoparticles as artificial monomers for the free radical copolymerization with methyl methacrylate

Vinyl-functionalized gold nanoparticles (AuNP) were prepared by surface polymerization of vinyl-functionalized ligands induced by carboxy-functionalized radical initiators followed by vinyl-transformation of the carboxy-group. These AuNP were regarded as artificial molecules as they were used as comonomers for the free radical copolymerization with methyl methacrylate (MMA). Successful copolymerization was proven by gel permeation chromatography (GPC) and by thermogravimetrical analysis (TGA). Further analysis of the novel hybrid material was carried out by transmission electron microscopy (TEM) and by atomic force microscopy (AFM) to proof the presence of AuNP and their arrangement.     

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1 W cm⁻² and then it was found to decrease with a further increase to 33.80 W cm⁻². The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40 nm.     

Block copolymers obtained by free radical mechanism. II. Butyl acrylate and methyl methacrylate

Block copolymers were synthesized using methyl methacrylate and butyl acrylate as the monomers and a multifunctional initiator, di-t-butyl 4,4'-azobis(4-cyanoperoxyvalerate). The polymerizations for the formation of the block copolymers were carried out in two stages. First the poly(methyl methacrylate) polymeric initiator was synthesized and isolated. In the second stage, the thermallyactivated azo group in the polymer backbone initiated the polymerization of butyl acrylate. Upon termination by combination a tri-block results. Selective solvent fractionation was used to separate the block from the homopolymers.