Average termination rate coefficients in emulsion polymerization: Effect of compartmentalization on free‐radical lifetimes

A method is presented by which the time‐dependent average termination rate coefficient in an emulsion polymerization may be calculated as an appropriate average of the chain‐length‐dependent termination rate coefficients. The method takes advantage of the fact that the overall termination rate is dominated by terminations between rapidly moving short radicals and much slower long ones. This termination rate coefficient is suitable for use in the Smith–Ewart equations describing the compartmentalization of radicals in an emulsion polymerization. Rate data in emulsion polymerizations can be quantitatively interpreted if the kinetics fall into one of two categories: zero–one (showing compartmentalization; intraparticle termination is not rate‐determining) or pseudo‐bulk (no compartmentalization; intraparticle termination is rate‐determining). The new method can be used to interpret rate data for systems falling between these categories and also can be used to find termination rate coefficients from Monte Carlo simulations of termination kinetics. The latter is especially useful for predicting and understanding kinetics in controlled radical polymerizations in disperse media. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1076–1089, 2005     

Batch emulsion copolymerization of 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranose and butyl acrylate: Synthesis and properties of the sugar latices

To obtain new polymer latices based on sugar derivative, batch emulsion copolymerizations of 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and n‐butyl acrylate (BA) were carried out at 70 °C, with potassium persulfate as the initiator. 3‐MDG polymerizes faster than BA because of its higher reactivity ratio, r_(3‐MDG) = 1.94 versus r_(BA) = 0.54. The effect of the initial monomer composition on the polymerization rate and the thermal properties of the end copolymers was investigated. The overall rate of polymerization increases by enhancing the sugar content in the initial monomer composition. The glass‐transition temperature is linearly related to the sugar content in the copolymer. The influence of the type of surfactant showed that the particle size increases by changing from ionic to nonionic surfactant. Furthermore, the effect of the added acrylic acid (AA) on the rheological properties suggests that the sugar latices exhibit different non‐Newtonian flows depending on the pH of the latex and on the AA concentration on the particle surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 788–803, 2003     

Nitroxide‐mediated radical polymerization in miniemulsion: Bimolecular termination in monomer‐free model systems

Bimolecular termination in nitroxide‐mediated radical polymerization in miniemulsion has been investigated through the heating of a polystyrene–2,2,6,6‐tetramethylpiperidinyl‐1‐oxy macroinitiator and its 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy analogue in an aqueous toluene dispersion with sodium dodecyl benzenesulfonate as a surfactant at 125 °C. The level of bimolecular termination by combination, evaluated from the high‐molecular‐weight shoulder, was higher in miniemulsion than in solution and increased with decreasing particle size. Quantitative analysis revealed that these results cannot be rationalized solely by nitroxide partitioning to the aqueous phase. The results are explained by an interface effect, by which nitroxide is adsorbed or located at the aqueous–organic interface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4995–5004, 2007     

Redox initiator systems for emulsion polymerization of acrylates

The performance of different redox initiator couples to initiate the emulsion polymerization of butyl acrylate at low temperature (40–50 °C) was investigated in both batch and seeded semibatch polymerizations. Polymerizations were carried out mimicking industrial conditions, that is, technical grade monomer and no N₂ purging was used during the polymerizations. The redox systems used contained as oxidants persulfates or hydroperoxides and as reducing agents ascorbic acid, formaldehyde sulfoxilate (SFS), tetramethyl ethylene diamine (TMEDA), Bruggolit 6 and 7 (FF6 and FF7), and sodium metabisulfites. Batch experiments showed that for systems using persulfates, the ammonium persulfate (APS)/TMEDA system provided the lower induction period and higher conversion, whereas for the systems with hydroperoxide oxidants, tert‐butyl hydroperoxide (TBHP)/FF7, TBHP/SFS, and H₂O₂/FF7 were the best alternatives. When these selected systems were used in seeded semibatch experiments of BA with allyl methacrylate, it was found that to obtain similar kinetics and microstructure (gel content and crosslinking density) than in case of using a thermal initiator at 80 °C, the polymerization could be run at 40 °C if the reactor was purged with N₂. Alternatively, in absence of N₂ polymerization, temperature should be increased to 50 °C and initiator concentration increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2917–2927, 2009     

Synthesis of polymeric nanocapsules by radical UV‐activated interface‐emulsion polymerization

A new methodology is reported that allows a better control of the synthesis of polymeric core–shell nanocapsules. These nanocapsules were made of biocompatible polymers, obtained from poly(ethylene glycol)diacrylate and poly(ethylene glycol) methyl ether methacrylate, and were used as carrier for curcumin as therapeutic agent. The impact of manufacturing factors (time of sonication, time of UV irradiation, and type of monomer) was investigated in relation to the average size of nanocapsules, their distribution, shape, composition, stability, and their capability to deliver curcumin. We successfully synthesized core–shell nanocapsules in various sizes, ranging from 80 nm to 300 nm, by acting either on the process conditions or on the composition of the monomer mixture. This wide range of sizes makes the method here proposed very promising for the production of nanocarriers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3357–3369     

Frontal free‐radical copolymerization of urethane–acrylates

We report the first synthesis of urethane–acrylate copolymers via free‐radical frontal polymerization. In a typical run, the appropriate amounts of the reactants (urethane–acrylate macromonomer and 2‐hydroxyethyl acrylate) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide. Frontal polymerization was initiated by the heating of the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once it was initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the initiator concentration was investigated. The front temperatures were between 55 and 65 °C, depending on the persulfate concentration. Thermogravimetric analysis indicated that the urethane–acrylate copolymers had higher thermal stability than pure frontally prepared polyurethane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3018–3024, 2006     

First solvent‐free synthesis of poly(N‐methylolacrylamide) via frontal free‐radical polymerization

We report the first synthesis of poly (N‐methylolacrylamide) (PNMA) via free‐radical frontal polymerization (FP) with solid monomers at ambient pressure. The appropriate amounts of reactants (N‐methylolacrylamide) (NMA) and initiator (ammonium persulfate) were mixed together at ambient temperature without solvent. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To suppress the fingers of molten monomer, a small amount of nanosilica was added. We also produced PNMA with dimethyl sulfoxide (DMSO) or N‐methyl‐2‐pyrrolidone, as solvent by FP, to study the macrokinetics in FP of PNMA without fillers. The front velocity and front temperature dependence on the ammonium persulfate and N‐methyl‐2‐pyrrolidone concentration were investigated. The polymer was analyzed by thermogravimetric analysis. Results show that without postpolymerization solvent removal, waste production can be reduced. Solvent‐free FP could be exploited as a means for preparation of PNMA with the potential advantage of higher throughput than solvent‐based methods. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4322–4330, 2007     

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009     

Mechanism and kinetics of the imidazolidinone nitroxide‐mediated free‐radical polymerization of styrene

Styrene radical polymerizations mediated by the imidazolidinone nitroxides 2,5‐bis(spirocyclohexyl)‐3‐methylimidazolidin‐4‐one‐1‐oxyl (NO88Me) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) were investigated. Polymeric alkoxyamine (PS‐NO88Bn)‐initiated systems exhibited controlled/living characteristics at 100–120 °C but not at 80 °C. All systems exhibited rates of polymerization similar to those of thermal polymerization, with the exception of the PS‐NO88Bn system at 80 °C, which polymerized twice as quickly. The dissociation rate constants (k_d) for the PS‐NO88Me and PS‐NO88Bn coupling products were determined by electron spin resonance at 50–100 °C. The equilibrium constants were estimated to be 9.01 × 10^?11 and 6.47 × 10^?11 mol L^?1 at 120 °C for NO88Me and NO88Bn, respectively, resulting in the combination rate constants (k_c) 2.77 × 10⁶ (NO88Me) and 2.07 × 10⁶ L mol^?1 s^?1 (NO88Bn). The similar polymerization results and kinetic parameters for NO88Me and NO88Bn indicated the absence of any 3‐N‐transannular effect by the benzyl substituent relative to the methyl substituent. The values of k_d and k_c were 4–8 and 25–33 times lower, respectively, than the reported values for PS‐TEMPO at 120 °C, indicating that the 2,5‐spirodicyclohexyl rings have a more profound effect on the combination reaction rather than the dissociation reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 327–334, 2003     

Influence of nitroxide structure on the 2,5‐ and 2,6‐spirodicyclohexyl substituted cyclic nitroxide‐mediated free‐radical polymerization of styrene

The 2,6‐spirodicyclohexyl substituted nitroxide, cyclohexane‐1‐spiro‐2′‐(3′,5′‐dioxo‐4′‐benzylpiperazine‐1′‐oxyl)‐6′‐spiro‐1″‐cyclohexane (BODAZ), was investigated as a mediator for controlled/living free‐radical polymerization of styrene. The values of the number‐average molecular weight increased linearly with conversion, but the polydispersities were higher than for the corresponding 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) mediated systems at approximately 2.2 and 1.6 at 100 and 120 °C, respectively. These results were reflected in the rate coefficients obtained by electron spin resonance spectroscopy; at 120 °C, the values of the rate coefficients for polystyrene‐BODAZ alkoxyamine dissociation (k_d), combination of BODAZ and propagating radicals (k_c), and the equilibrium constant (K) were 1.60 × 10^?5 s^?1, 5.19 × 10⁶ M^?1 s^?1, and 3.08 × 10^?12 M, respectively. The value of k_d was approximately one and two orders of magnitude lower, and that of K was approximately 20 and 7 times lower than for the NO88Bn and TEMPO adducts. These results are explained in terms of X‐ray crystal structures of BODAZ and NO88Bn; the six‐membered ring of BODAZ deviates significantly from planarity as compared to the planar five‐membered ring of NO88Bn and possesses a benzyl substituent oriented away from the nitroxyl group leading to a seemingly more exposed oxyl group, which resulted in a higher k_c and a lower k_d than NO88Bn. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3892–3900, 2003     

Cu powder‐catalyzed single electron transfer‐living radical polymerization of acrylonitrile

Single electron transfer‐living radical polymerization (SET‐LRP) has been used as a new technique for the synthesis of polyacrylonitrile (PAN) catalyzed by Cu(0) powder with carbon tetrachloride (CCl₄) as the initiator and hexamethylenetetramine (HMTA) as the ligand in N,N‐dimethylformamide (DMF) or mixed solvent. Well‐controlled polymerization has been achieved as evidenced by a linear increase of molecular weight with respect to monomer conversion as well as narrow molecular weight distribution. Kinetics data of the polymerizations at both ambient temperature and elevated temperature demonstrate living/controlled feature. An increase in the concentration of ligand yields a higher monomer conversion within the same time frame and almost no polymerization occurs in the absence of ligand due to the poor disproportionation reaction of Cu(I). The reaction rate exhibits an increase with the increase of the amount of catalyst Cu(0)/HMTA. Better control on the molecular weight distribution has been produced with the addition of CuCl₂. In the presence of more polar solvent water, it is observed that there is a rapid increase in the polymerization rate. The effect of initiator on the polymerization is also preliminarily investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of poly(4‐vinylpyridine) by reverse atom transfer radical polymerization

Controlled radical polymerization of 4‐vinylpyridine (4VP) was achieved in a 50 vol % 1‐methyl‐2‐pyrrolidone/water solvent mixture using a 2,2′‐azobis(2,4‐dimethylpentanitrile) initiator and a CuCl₂/2,2′‐bipyridine catalyst–ligand complex, for an initial monomer concentration of [M]₀ = 2.32–3.24 M and a temperature range of 70–80 °C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First‐order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number–average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29–1.35 were indicative of controlled radical polymerization. The highest number–average degree of polymerization of 247 (number–average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 °C, [M]₀ = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70–80 °C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5748–5758, 2007     

Kinetic analysis of styrene atom transfer radical polymerization: Extraction of radical‐radical termination rate coefficients

Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical‐radical termination rate coefficients (<k_t>). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical‐radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, <k_t> values of approximately 2 × 10⁸ L mol^?1 s^?1 at 110 °C in 50 vol % anisole were determined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5548–5558, 2004     

Kinetics of surface‐initiated atom transfer radical polymerization

Although atom transfer radical polymerization (ATRP) is often a controlled/living process, the growth rate of polymer films during surface‐initiated ATRP frequently decreases with time. This article investigates the mechanism behind the termination of film growth. Studies of methyl methacrylate and methyl acrylate polymerization with a Cu/tris[2‐(dimethylamino)ethyl]amine catalyst system show a constant but slow growth rate at low catalyst concentrations and rapid growth followed by early termination at higher catalyst concentrations. For a given polymerization time, there is, therefore, an optimum intermediate catalyst concentration for achieving maximum film thickness. Simulations of polymerization that consider activation, deactivation, and termination show trends similar to those of the experimental data, and the addition of Cu(II) to polymerization solutions results in a more constant rate of film growth by decreasing the concentration of radicals on the surface. Taken together, these studies suggest that at high concentrations of radicals, termination of polymerization by radical recombination limits film growth. Interestingly, stirring of polymerization solutions decreases film thickness in some cases, presumably because chain motion facilitates radical recombination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 386–394, 2003     

Ligand‐free Cu(0)‐mediated controlled radical polymerization of methyl methacrylate at ambient temperature

For the first time, ligand‐free Cu(0)‐mediated polymerization of methyl methacrylate (MMA) was realized by the selection of ethyl‐2‐bromo‐2‐phenylacetate as initiator at ambient temperature. The polymerization can reach up to 90% conversion within 5 h with dimethyl sulfoxide (DMSO) as solvent, while keeping manners of the controlled radical polymerization. Extensive investigation of this system revealed that for a well‐controlled Cu(0)‐mediated polymerization of MMA, the initiator should be selected with the structure as alkyl 2‐bromo‐2‐phenylacetate, and the solvent should be DMSO or N,N‐dimethylformamide. The selectivity for solvents indicated a typical single‐electron transfer‐living radical polymerization process. Scanning for other monomers indicated that under equal conditions, the polymerizations of other alkyl (meth)acrylates were uncontrollable. Based on these results, plausible reasons were discussed. The ligand‐free Cu(0)‐mediated polymerization showed its superiority with economical components and needless removal of Cu species from the resultant products. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of polymeric microspheres from a Merrifield resin by surface‐initiated nitroxide‐mediated radical polymerization

Polymeric microspheres were prepared from a Merrifield resin via nitroxide‐mediated radical polymerization. Polystyrene, poly(acetoxystyrene), and poly[styrene‐b‐(methyl methacrylate‐co‐styrene)], poly(acetoxystyrene‐b‐styrene), and poly(styrene‐co‐2‐hydroxyethyl methacrylate) copolymers were demonstrated to graft onto 2,2,6,6‐tetramethyl‐1‐piperidinyloxy nitroxide bound Merrifield resins. The polymerization control was enhanced both on the surface and in solution by the addition of sacrificial nitroxide. The significant increase in the particle diameter (more than a fivefold volume increase for polystyrene brushes) showed that polymer growth was not only on the surface but also within the particles, and this diameter increase could be adjusted through changes in the molecular weight of the polymers. The microspheres were characterized by elemental analysis, IR spectroscopy, particle size analysis, and optical microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2145–2154, 2005     

Synthesis and properties of the polythiourethanes obtained by the cationic ring‐opening polymerization of cyclic thiourethanes

The cationic ring‐opening polymerization of a five‐membered thiourethane [3‐benzyl‐1,3‐oxazolidine‐2‐thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10^?2 L mol^?1 min^?1) was two times larger than that of the six‐membered thiourethane [3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione (BTOT); 6.8 × 10^?3 L mol^?1 min^?1], and the monomer conversion obeyed the first‐order kinetic equation. These observations, along with the successful results in the two‐stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di‐ and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione) [poly(BTOT)] > poly(BTOT₅₄‐b‐BOT₄₆) > poly(3‐benzyl‐1,3‐oxazolidine‐2‐thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT₅₄‐b‐BOT₄₆) > poly(BTOT₅₄‐b‐BOT₄₆‐b‐BTOT₅₀) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795–4803, 2006     

N‐vinylcaprolactam‐based microgels: Effect of the concentration and type of cross‐linker

New microgel particles produced by using N‐vinylcaprolactam (VCL) and poly(ethylene glycol) diacrylate (PEGDA) or N,N′‐methylenbisacrylamide (BA) were synthesized in a batch reactor. The influence of the concentration and type of crosslinker on polymerization kinetics and colloidal characteristics of such temperature‐sensitive particles was studied. The partial and total conversion evolutions of VCL, PEGDA, and BA were determined by quantitative ¹H NMR and the average diameters of microgel particles together with the swelling–deswelling behavior were analyzed by means of photon correlation spectroscopy (PCS). Partial and total conversions, final average diameters at collapsed state, and the swelling–deswelling behavior varied as a function of the type of crosslinker. These results were attributed to the higher solubility and stabilizing ability of PEGDA compared with that of BA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2766–2775, 2008