Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Controlled/“living” atom transfer radical polymerization of methyl methacrylate in the synthesis of triblock copolymers from a poly(oxyethylene) macroinitiator

Atom transfer radical polymerization of methyl methacrylate initiated by a poly(oxyethylene) macroinitiator by the esterification of PEG 1500 with 2-chloro propionyl chloride was synthesized. These polymerization proceeds both in bulk and solution with a quantitative initiation efficiency, leading to A-B-A triblock copolymers. The macroinitiators and their block copolymers were characterized by FT-IR, FT-NMR and GPC analyses. In bulk polymerization, the kinetic study showed that the relationship between ln[M]₀/[M] vs time was linear showing that there is a constant concentration of active species throughout the polymerization and follow the first order kinetics with respect to monomer. Moreover, the experimental molecular weight of the block copolymers increased linearly with the monomer conversion and the polydispersity index remained between 1.3 and 1.5 throughout the polymerization. No formation of homo poly(methyl methacrylate) could also be detected, and all this confirms that the bulk polymerization proceeds in a controlled/“living” manner.     

Polymerization of methyl methacrylate in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization

Four tetradentate nitrogen ligands, viz. dichloro{[N,N^′-diphenyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N^′-dioctyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N^′-dibenzyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N^′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.     

Synthesis of poly(methyl methacrylate) in a pyridine solution by atom transfer radical polymerization

Pyridine was used as a solvent for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The homopolymerizations were carried out with methyl 2‐halopropionate (MeXPr, where X was Cl or Br) as an initiator, copper halide (CuX) as a catalyst, and 2,2′‐bipyridine as a ligand from 80 to 120 °C. The mixed halogen system methyl 2‐bromopropionate/copper chloride was also used. For all the initiator systems used, the polymerization reaction showed linear first‐order rate plots, a linear increase in the number‐average molecular weight with conversion, and relatively low polydispersities. In addition, the dependence of the polymerization rate on the temperature is presented. These data are compared with those obtained in bulk, demonstrating the effectiveness of this solvent for this monomer in ATRP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3443–3450, 2001     

Synthesis of poly(styrene-b-tetrahydrofuran-b-styrene) triblock copolymers by transformation from living cationic into living radical polymerization using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a transforming agent

Synthesis of poly(styrene-b-tetrahydrofuran (THF)-b-styrene) triblock copolymers was performed by transformation from living cationic into living radical polymerization, using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO) as a transforming agent. Sodium 4-oxy-TEMPO, derived from 4-hydroxy-TEMPO, reacted with the living poly(THF), which was prepared by cationic polymerization of THF using trifluoromethanesulfonic acid anhydride as an initiator, resulting in quantitative formation of the poly(THF) with TEMPO at both the chain ends. The resulting polymers were able to serve as a polymeric counter radical for the radical polymerization of styrene by benzoyl peroxide, to give the corresponding triblock copolymer in quantitative efficiency. The polymerization was found to proceed in accordance with a living mechanism, because the conversion of styrene linearly increased over time, and the molar ratio of styrene to THF units in the copolymer also increased as a result of increasing the conversion. The TEM pictures demonstrated that the resulting copolymers promoted microphase segregation. It was found that the films of these copolymers showed contact angles intermediate between those of poly(THF) and of polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2059–2068, 1998     

TEMPO-mediated radical polymerization in the synthesis of poly(methyl methacrylate) macromonomer

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Effect of temperature and solvent on polymer tacticity in the free‐radical polymerization of styrene and methyl methacrylate

The effect of temperature and solvent on polymer tacticity in free‐radical polymerization of styrene and methyl methacrylate was studied by ¹³C and ¹H NMR, respectively. Polystyrene shows a mild syndiotactic tendency (P_m = 0.36 ± 0.02) that is independent of temperature over a wide range (?10 to 120 °C), while poly(methyl methacrylate) shows a stronger syndiotactic tendency (P_m = 0.17 ± 0.01 at 30 °C) that decreases as temperature is increased (P_m = 0.22 ± 0.02 at 80 °C). None of the polymerization solvents studied (bulk, THF, DMF, DMSO, acetonitrile, and acetone) had a significant effect on polymer tacticity in either system. The triad fractions of both polymers showed deviations from the Bernoulli model, implying that the antepenultimate unit affects the propagation reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3351–3358     

The role of excess nitroxide in the SG1 (N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide)-mediated polymerization of methyl methacrylate

Methyl methacrylate (MMA) polymerizations have been conducted in the presence of large excesses of N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl) nitroxide] (SG1) at 110°C. It is demonstrated that such a protocol does not improve control/livingness in the nitroxide mediated polymerization (NMP) of this monomer, instead substantial levels of disproportionation between the nitroxide and propagating radical (PMMA^•) results. The extent of the disproportionation reaction increased with the SG1 concentration, eventually becoming the sole end forming event. Significant disproportionation between SG1 and PMMA^• was also observed at substantially lower temperatures (45°C) in the presence of large excesses of SG1. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2194–2203, 2007     

Atom transfer radical polymerization of methyl acrylate,methyl methacrylate and styrene in the presence of trolamine as a highly effective promoter

Transition metal-mediated atom transfer radical polymerization(ATRP) is a ‘‘living'/controlled radical polymerization. Recently, there has been widely increasing interest in reducing the high costs of catalyst separation and post-polymerization purification in ATRP. In this work, trolamine was found to significantly enhance the catalytical performance of Cu Br/N,N,N0,N0-tetrakis(2-pyridylmethyl) ethylenediamine(Cu Br/TPEN) and Cu Br/tris[2-(dimethylamino) ethylamine](Cu Br/Me6TREN). With the addition of 25-fold molar amount of trolamine relative to Cu Br, the catalyst loadings of Cu Br/TPEN and Cu Br/Me6 TREN were dramatically reduced from a catalyst-to-initiator ratio of 1 to 0.01 and 0.05,respectively. The polymerizations of methyl acrylate, methyl methacrylate and styrene still showed first-order kinetics in the presence of trolamine and produced poly(methyl acrylate), poly(methyl methacrylate) and polystyrene with molecular weights close to theoretical values and low polydispersities. These results indicate that trolamine is a highly effective and versatile promoter for ATRP and is promising for potential industrial application.     

Production of nanoparticles of methyl methacrylate and butyl methacrylate copolymers by microemulsion polymerization in the presence of maleic acid terminated poly(N-acetylethylenimine) macromonomers as cosurfactant

In this study, MMA/BMA copolymer nanoparticles were synthesized in oil-in-water microemulsions that were stabilized by sodium dodecyl sulphate (SDS) and initiated by potassium persulphate KPS. Maleic acid terminated poly(N-acetylethylenimine) (PNAEI) with two different chain lengths was also included in the recipe, as a cosurfactant and a comonomer. FTIR and ¹H-NMR proved incorporation of the macromonomer in the structure. High polymerization yields were achieved upto 98%. The viscosity average molecular weights of the copolymers were in the range of 2.77-5.50 × 10⁵. The glass transition temperatures of these copolymers were between 50.0 and 63.9 °C. The average diameter of nanoparticles were in range of 40-96 nm. It was possible to produce nanoparticles smaller than 100 nm and with narrower size distributions by using much lower concentrations of SDS by including the macromonomers in the microemulsion polymerization recipe.     

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

 To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization. Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles. From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA. Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of hydrogen abstraction is far smaller than that with the sulfate anion radical by 10⁻⁴ times. Received: 26 April 2001 Accepted: 6 September 2001     

Cuso4‐amine redox‐initiated radical polymerization of methyl methacrylate mediated by a CuCl2 complex: Homogeneous reverse ATRP

Kinetic results of CuSO₄/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl₂/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and Cu^ICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2562‐2578     

Enhancing the thermal stability of poly(methyl methacrylate) by removing the chains with weak links in a continuous polymerization

A novel method is proposed to produce PMMA with excellent thermal stability by a continuous process composed of polymerization and devolatilization steps. It is based on the fact that free radical polymerized PMMA is a mixture of polymer chains with different structure, a small fraction of which, containing head-to-head linkages or unsaturated ends, is less thermally stable and the major portion without those defect structures which is much more stable. Our idea is selectively remove the unstable chains from this mixture by pre-decomposing them at suitable temperatures in a continuous process, leaving the stable portion as the final PMMA product. The results showed that during the continuous process, the chains with head-to-head linkages were eliminated by conducting the polymerization at 155 °C, and then the chains with unsaturated ends were removed by devolatilization at 300 °C. The final PMMA was thermally stable up to 313 °C.     

Thermosensitive poly(methyl methacrylate) emulsion prepared in the presence of poly(vinyl alcohol) with a cloud point as a protective colloid

An emulsion of poly(methyl methacrylate) (PMMA) was prepared using poly(vinyl alcohol) (PVA) of low degree of hydrolysis with a cloud point as a protective colloid. The behaviour of an aqueous solution of PVA with 80% degree of hydrolysis was first investigated in terms of the Huggins constant in viscometry. MMA was polymerized using the PVA at 20 °C, where no abnormality in the aqueous PVA was observed. The change in transmittance of the emulsion observed with a UV–vis photometer revealed that in the case of UV light of wavelength 370 nm, the transmittance decreased markedly at around 30 °C with an increase in temperature, and then increased with a decrease in temperature. The thermosensitive property resulted from PVA with a low degree of hydrolysis with a cloud point, at a higher temperature of which the PVA loses solubility in water owing to weakening of the hydrogen bond between PVA molecules and water.     

Thermal‐initiated reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in the presence of oxygen

A novel reversible addition–fragmentation chain transfer polymerization (RAFT) of methyl methacrylate (MMA) in the presence of oxygen was carried out for the first time without added chemical initiators. The polymerization was mediated by 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) or cumyl dithionaphthalenoate (CDN) as RAFT agent. The polymerization demonstrated the features of a living/controlled radical polymerization. The polymerization rate increased with oxygen concentration. Polymers with molecular weight M_n up to 520,000 g/mol, polydispersity M_w/M_n ～1.46 and RAFT efficiency M_n,th/M_n,GPC ～1.026 in the case of CPDN and M_n ～331,500 g/mol, M_w/M_n ～1.35, and M_n,th/M_n,GPC ～1.137 in the case of CDN were obtained. The possible mechanism of the thermal‐initiated RAFT polymerization of MMA in the presence of oxygen was discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3343–3354, 2006     

Multihollow structured poly(methyl methacrylate)/silver nanocomposite microspheres prepared by suspension polymerization in the presence of dual dispersion agents

Poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres with unique multihollow structures were prepared by suspension polymerization in the presence of dual dispersion agents. The addition of a lipophilic emulsifier, polyethylene glycol (30EO) dipolyhydroxystearate (Arlacel P135), not only stabilized water-in-oil (W/O) emulsion, but also converted silver nanoparticles from hydrophilic to lipophilic. When a suspension polymerization dispersion agent, poly(vinyl alcohol), was added to the above W/O emulsion system, a water-in-oil-in-water suspension was formed with silver nanoparticles dispersed in the oil phase. The suspension polymerization was carried out at low temperature with 2,2’-azobis(2,4-dimethylvaleronitrile) as the initiator. When modified silver nanoparticles were added, the rate of polymerization increased slightly. High monomer conversion (about 85%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various hollow structures were synthesized. The PMMA/silver microspheres with multihollow structure showed high antibacterial ability.     

Octafunctional cubic silsesquioxane (CSSQ)/poly(methyl methacrylate) nanocomposites: Synthesis by atom transfer radical polymerization at mild conditions and the influence of CSSQ on nanocomposites

Organic/inorganic hybrid star‐like nanocomposites from two different octafunctional cubic silsesquioxane (CSSQ) nano‐cage cores and poly(methyl methacrylate) (PMMA) were synthesized using atom transfer radical polymerization (ATRP) at mild conditions, in which octafunctional octakis(3‐hydroxypropyldimethylsiloxy)octasilsesquioxane (OHPS) and octa(aminophenyl)silsesquioxane (OAPS) nano‐cages were used as ATRP initiators. The polymerization was carried out at 50 °C in acetonitrile/water mixture. ¹H‐NMR and GPC were employed to characterize the obtained nanocomposites. GPC data revealed that the resulting nanocomposites exhibit unimodal and narrow molecular weight distributions indicating well‐controlled synthesis and well‐defined hybrid nanocomposites with star architecture. The influence of CSSQ nano‐cages on the thermal property of nanocomposites was investigated using differential scanning calorimetry and thermal gravimetric analysis (TGA). It was observed that the nanocomposites exhibit significantly higher glass transition temperature compared with its linear counterpart because of slow relaxation caused by the star‐like architecture. TGA study, however, did not reveal any significant improvement in thermal stability of nanocomposites as compared with linear PMMA. Finally, field emission scanning electron microscopy images of fractured surfaces of nanocomposite sample films showed well dispersed CSSQ nano‐cages in PMMA matrix without phase separation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 766–776, 2008     

The role of protic solvent in asymmetric hydrogenation of methyl levulinate in the presence of a ruthenium-containing catalyst

A comparative study of asymmetric hydrogenation and deuteration of methyl levulinate catalyzed by the Ru^II—(S)-BINAP—HCl system (BINAP is 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) in MeOH and MeOD was carried out. The results obtained suggest an important role of the protic solvent in the formation of catalytically active ruthenium complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 531–533, March, 2007.