Abstract: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(n) 2-ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight M n = 14000 g · mol -1 and a low polydispersity (M w /M n = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi-logarithmic kinetics, which leads to polystyrene with an M n of 13 400 g mol -1 and a low polydispersity index (M w /M n = 1.14). Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right).

Abstract: Phthalimidomethyl trithiocarbonate reversible addition−fragmentation chain transfer (RAFT) agents are effective in imparting living characteristics to radical polymerizations of butyl acrylate (BA)...

Abstract: Ionic liquids based on imidazolium, pyridinium, and alkylammonium salts were investigated as solvents in free radical polymerization of the model monomer n-butyl methacrylate. The properties of the ionic liquids were systematically varied by changing the length of the alkyl substituents on the cations, and by employing different anions such as tetrafluoroborate, hexafluorophosphate, tosylate, triflate, alkyl sulfates and dimethyl phosphate. Results were compared to analogous polymerizations in toluene and in bulk. The solvents have no detectable influence on polymer tacticity. However, the molar masses obtained and the degree of polymerization, respectively, are very sensitive to the choice of the solvent. The degrees of polymerization are significantly higher when polymerizations were carried out in ionic liquids compared to polymerization in toluene, and can even exceed the values obtained by bulk polymerization. Imidazolium salts unsubstituted at C-2 result in an increase in the degree of polymerizatio...

Abstract: Studying the fabrication and composition of semiconductor nanoparticles in polymer matrices has attracted the interest of many scientists because nanoparticle–polymer composites may find applications in high-refractive-index materials, light-emitting diodes, photocatalysts, photovoltaic solar cells, and nonlinear optical devices. Control of the nanoparticle size and size distribution as well as the dispersion homogeneity in the polymer matrix are critical prerequisites for controlling the properties of the composites. However, nanoparticles are prone to aggregation in the polymer because of their high specific surface energies and inherently hydrophilic character. Therefore, it is still a technological challenge to incorporate inorganic nanoparticles into polymer matrices and thus to prepare transparent bulk nanocomposites with high nanoparticle content. Far fewer studies of nanoparticle–polymer bulk materials have been reported than of nanocomposite films. Semiconductor nanoparticles (PbS, CdSe, CdTe) have been introduced into bulk polymer matrices to prepare bulk nanocomposites, although the content of inorganic particles was low (< 5 wt %). In these studies, two main approaches have been developed: in situ formation of nanoparticles in a presynthesized polymer and bulk polymerization of an organic monomer in the presence of premade nanoparticles. The latter provides full synthetic control over both the nanoparticles and the matrices, and is a more effective and practical route for fabricating bulk polymer nanocomposites on a large scale. We have utilized UV radiation curing to prepare transparent ZnS–polymer nanocomposite films with high ZnS contents from a solution mixture of premade ZnS particles and acrylate macromers. This is an effective method for preparing nanocomposite films with nanoparticles dispersed homogeneously horizontally and vertically throughout the entire polymer matrix, but it is unsuitable for preparing thick bulk nanocomposites. In addition, the ZnS nanoparticles obtained by the usual method cannot be redispersed in monomer or solvent because of their incomplete surface modification with organic molecules. The application of c-ray irradiation in the preparation of bulk polymer nanocomposites has remarkable advantages, such as processing under ambient pressure at room temperature and quick polymerization of monomers. These valuable properties can be put to use in the fabrication of nanocomposites with homogeneously dispersed inorganic nanoparticles. In this communication, we report a novel, facile route for the preparation of transparent bulk nanocomposites with high ZnS content via c-ray irradiation initiated polymerization (Fig. 1). Our strategy involves the design and optimization of the nanoparticle surface and polymeric monomer as well as the selection of a suitable polymerization technology. First, we reasoned that the compatibility between nanoparticles and the polymer matrix is a prerequisite for synthesizing a bulk nanocomposite with high nanophase content. So, it is necessary to tailor the corresponding polymer matrix by the decoration of the nanoparticles with organic molecules. Furthermore, it is highly important that the monomer should act as both the ligand and solvent for the inorganic nanoparticles. It has been reported that polar organic solvent molecules, such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), co-ordinate to the surface of ZnS or CdS nanocrystallites and can effectively stabilize them. Thus, it is expected that a monomer with a similar structure to DMF can be selected as both the solvent and ligand for the nanoparticles. Here, we have selected N,N-dimethylacrylamide (DMAA), which can effectively disperse and stabilize ZnS particles, as the monomer. Finally, the c-ray irradiation technique is another crucial factor in the fabrication of a bulk polymer nanocomposite with high particle content. This polymerization method can induce a mild and rapid gelation process for the bulk polymeric system containing a high content of nanoparticles uniformly dispersed inside. We present a simple approach for the large-scale production of mercaptoethanol (ME)-capped ZnS nanoparticles in DMF from Zn(OAc)2 (Ac: acetate) and thiourea. The MEC O M M U N IC A TI O N S

Abstract: Poly(N-vinylpyrrolidone)s (PNVPs) with well-defined macromolecular structure were prepared by organostibine-mediated living radical polymerization. PNVPs with expected number-average molecular weight (Mn = 3000−84 000) and low polydispersity indexes (PDIs = 1.1−1.3) were formed by heating a solution of organostibine mediator and NVP in the presence of AIBN at 60 °C. The polymer structure was analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass and 2H NMR spectroscopies after reduction of the organostibanyl polymer end by tributyltin deuteride. The analyses reveal that, while the addition of AIBN considerably enhances the rate of the polymerization, the effect of azobis(isobutyronitrile) (AIBN)-derived radical to the ω-end structure is negligible. The analyses also reveal the existence of “dead” dormant species due to head-to-head addition followed by the organostibanyl group transfer. However, since the probability of the head-to-head addition is small (0.02−0.10%) compa...

Abstract: Summary: A comprehensive one-dimensional photopolymerization model was utilized to investigate the effect of oxygen on the free-radical photopolymerization kinetics. The spatial profiling aspect of the model provided insight into the heterogeneity of the cure kinetics due to oxygen inhibition, specifically the variance in the concentration profile of monomer and oxygen. Double bond conversion was negligible for the top ten microns of the film due to continuous oxygen diffusion, and increased with increasing depth. Similarly, the oxygen concentration decreased with increasing depth due to the competition between oxygen diffusion time and the polymerization rate. The effect of initiation rate on the extent of oxygen inhibition was investigated for various oxygen concentrations. As the initiation rate increased, the polymerization rate increased, and eventually approached that of a sample in an inert environment. Similarly, as the oxygen concentration was decreased, the polymerization rate increased. The effect of varying the initiation rate on the cure profile in the oxygen-exposed film was also studied. It was found that the unpolymerized tacky layer decreased from 50 µm to 5 µm with a 3 order of magnitude increase in initiation rate. Using the pseudo steady state approximation, the relationship between polymerization rate and initiation rate was derived for films in an oxygen environment. A direct relationship between the polymerization and initiation rate was found for films in air. The polymerization model supported this derivation and found that as the oxygen concentration was decreased, the dependence on initiation rate, or alpha, decreased, reaching the accepted value of 0.5 for alpha in inert environments. Double bond conversion versus film depth and cure time.

Abstract: Ring-opening polymerization of e-caprolactone initiated by titanium n-propoxide Ti(O-n-Pr)4 was compared to the one initiated by titanium phenoxide or Ti(OPh)4. Polymerization was confirmed to proceed via a coordination−insertion mechanism for both initiators after end groups analysis by 1H and 13C NMR (nuclear magnetic resonance) spectroscopy. Bulk polymerization at 100 °C and with a M0/I0 (monomer/initiator ratio) equal to 300 was studied and compared with both initiators. The polymerization with Ti(OPh)4 exhibits a slower kinetic of reaction and the polymer synthesized an higher number-average molecular weight and higher polydispersity than with Ti(OPr)4. These results are consistent with evolution of the average number of active aryloxide groups per initiator ( ) during polymerization for this initiator. Indeed, determined by 1H NMR increases gradually during the polymerization to 2 for around 70% conversion and then decreases at the end of the polymerization and even over the time required for total ...

Abstract: The kinetics of reversible addition−fragmentation chain transfer (RAFT), R-group approach star polymerizations have been studied via a combined experimental and theoretical approach. From the improved understanding herein developed, design criteria have been suggested to aid in future syntheses of RAFT, R-group approach star polymer. The suggested criteria are as follows. To minimize the quantity of linear polymer in the system, it is important to have a high rate of monomer propagation but a small delivery of radicals to the system. Crucial to the prevention of star−star coupling and resulting molecular weight distribution (MWD) broadening is the minimization of radical termination events between star molecules. Noting that the number of termination events is directly correlated to the number of decomposed initiator molecules, this might be achieved via several methods. A slow rate of initiator decomposition, a fast rate of propagation, or use of a rate-retarding RAFT agent can all lead to a reduction in...

Abstract: The free radical homopolymerization of Bis-phenol-A-bis(glycidyl methacrylate) (Bis-GMA), a urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA) induced by a benzoyl perox...

Abstract: Peptide−polymer hybrid nanotubes (PPNT) were prepared by a combination of self-assembling functional cyclic peptides and in-situ surface-initiated atom transfer radical polymerization (ATRP). Cyclic peptides that consist of alternating d- and l-amino acids, carrying ATRP initiators in distinct side chains, were self-assembled into hollow nanotubes that expose all initiation moieties at the outer surface, thereby forming a cyclic peptide initiator nanotube (CP-ini). The CP-ini nanotubes were dispersed in 2-propanol, and a surface-initiated ATRP reaction has been performed using N-isopropylacrylamide (NIPAM) as monomer, tris[2(dimethylamino)ethyl]amine (Me6TREN) as ligand, and additional sacrificial (model) initiator. The molar mass of the resulting PNIPAM can be well controlled by adjusting the polymerization time (i.e., reaction conversion). The solvent-free height of the PNIPAM−PPNT, as measured by statistical analysis of cross sections of atomic force microscopy (AFM) height micrographs, increases with ...

Abstract: The efficiency of 11 cleavable photoinitiators in polymerization reactions was determined in various media, such as oligomer, acrylate, and methacrylate monomers in solution or in poly(methyl methacrylate). It was found that the efficiency of the photoinitiator strongly depends on the polymerized medium. The results are explained and discussed on the basis of the viscosity effect on the rate constants of the processes involved, resulting in good efficiency/reactivity relationships. Quantum yields of initiation were calculated for an acrylate photopolymerization in solution. The efficiency in viscous bulk media is quite well reflected in the dissociation quantum yields of the photoinitiators measured in solution. The role of the other low-viscosity media is also explained. Kinetic treatments were used to examine the influence of the monomer structure on the propagation and termination rate constants of the reaction. These results allowed to shed some light on the influence of the medium on the initiation e...

Abstract: Free radical polymerization of methyl methacrylate (MMA) is initiated upon irradiation at A > 350 nm in CH 2 Cl 2 that contains benzoxazine (P-a) and one of the following photosensitizers: benzophenone (BP), thioxanthone (TX), 2-chlorothioxanthone (CTX), 2-isopropyl thioxanthone (ITX), and camphorquinone (CQ). The postulated mechanism is based on the intermolecular reaction of the excited photosensitizer with the tertiary amino moiety of the ground state P-a and a subsequent hydrogen abstraction reaction. The resulting aminoalkyl radicals initiate the polymerization. The incorporation of P-a groups into polymers is demonstrated by spectroscopic methods. The possibility of deep curing using the described photoinitiating system followed by the thermal ring opening of the incorporated P-a groups is also demonstrated.

Abstract: Schiff base derivatives of the biometals (Zn, Mg, Ca) in the presence of anion initiators have been shown to be very effective catalysts for the ring-opening polymerization of trimethylene carbonate (TMC or 1,3-dioxan-2-one) to poly(TMC) devoid of oxetane linkages The order of catalytic activity as a function of metal was found to be Ca(II) ≫ Mg(II) > Zn(II) Optimization of the calcium system was achieved utilizing a salen ligand with tert-butyl substituents in the 3,5-positions of the phenolate rings and an ethylene backbone for the diimine along with an azide ion initiator These conditions led to a TOF of 1286 h-1 for a melt polymerization carried out at 86 °C Solution studies in tetrachloroethane demonstrated the polymerization reaction to proceed via a mechanism first order in [monomer], [(salen)Ca], and [anion initiator] and to involve TMC ring-opening by way of acyl−oxygen bond cleavage The activation parameters were determined to be ΔH⧧ = 201 kJ/mol and ΔS⧧ = −128 J/(mol K)

Abstract: A highly active and versatile CuBr 2 /N,N,N',N'-tetra[(2-pyridal)methyl]ethylenediamine (CuBr 2 /TPEN)-tertiary amine catalyst system has been developed for atom transfer radical polymerization via activator-generated-by-electron-transfer (AGET ATRP). The catalyst mediates good control of the AGETATRPs of methyl acrylate, methyl methacrylate, and styrene at 1 mol-% catalyst relative to initiator. A mechanism study shows that tertiary amines such as triethylamine reduces the CuBr 2 /TPEN complex to CuBr/TPEN.

Abstract: We use Monte Carlo computer simulation to study the effect of several molecular parameters on controlled/“living” radical polymerization in bulk and on flat substrates. Specifically, we investigate how the molecular weight and molecular weight distribution of grown polymers depend on the initial number of initiators, the initial number of monomers, the initiator activation probability, the initial probability of addition of a new monomer to a growing chain, the probability of terminating two “living” polymers, and the numbers of “living” polymers and their lifetime. Some observations reported here are common to both bulk- and surface-initiated polymerizations. Specifically, we demonstrate that increasing the termination probability and/or decreasing the initial probability of addition of a new monomer to a growing chain broadens the molecular weight distribution. In addition, decreasing the lifetime of the “living” radicals results in polymers with narrower molecular weight distributions. One of the goals...

Abstract: Cinnamoyl chloride was condensed with different glycols to produce five different of hydroxyalkyloxy cinnamate esters. Each cinnamate ester was reacted with polyisobutylene–succinic anhydride adduct to produce five different reactive macromonomers. The synthesized macromonomers were characterized by FTIR and 1 HNMR spectroscopic analyses. These macromonomers were copolymerized with octadecyl acrylate (ODA) at 1, 2 and 4 wt% of trimethylolpropane triacrylate (TPT) crosslinker in presence of benzoyl peroxide as initiator and cobalt octoate as activator. Copolymerization of a cinnamoyloxyethyl methacrylate (CEMA) with octadecyl acrylate (ODA) was prepared by bulk polymerization in presence of ABIN initiator and TPT crosslinker. The crosslinked copolymers were evaluated for oil-absorbency application. The effect of monomer feed composition; crosslinker wt% and type of oil on swelling properties of crosslinked polymers were studied through the oil absorption tests. The network parameters, such as polymer solvent interaction ( χ ), effective crosslink density ( ν e ), equilibrium moduli of elasticity ( G T ), average molecular weight between crosslinks ( M c ) and theoretical crosslink density ( ν t ) were determined and correlated with the structure of the synthesized sorbers. The values of crosslinking efficiency ( β ) and the efficiency of copolymer to form physical crosslinks ( α ) are also computed and discussed.

Abstract: The heteroaromatic thiols (imidazole, oxazole, and thiazole derivatives) were investigated in regard to their abilities to function as co-initiators in free-radical photopolymerizations induced by camphorquinone and isopropylthioxanthone. As shown by the kinetic data, these heteroaromatic thiols are efficient co-initiators with activities comparable to aromatic amines. They quenched the triplet states of isopropylthioxanthone and camphorquinone with rate constants determined to be on the order of 109 and 108 M-1 s-1, respectively. The results suggested that rates of polymerization of a low-viscosity monomer (triethylene glycol dimethacrylate) in an inert atmosphere are dependent on the quantum yields of formation of primary thiyl radicals Φ. However, this effect was also moderated by the reactivities of the thiyl radicals that were generated in the photosensitization stage. The observed activities of the initiator/thiol systems also depended on the possibility of initiator photoreduction by the monomer an...

Abstract: A model for the evaluation of the kinetics and the chain length distribution in living/controlled radical polymerization mediated by reversible addition-fragmentation chain transfer (RAFT) in bulk is presented. Using the free volume theory, the model accounts for the diffusion limitations over both termination and RAFT exchange reactions. Model predictions are compared to experimental results of methyl methacrylate polymerization with cumyl dithiobenzoate as a RAFT agent. It is shown that the polymerization retardation observed in living systems at large conversions is well predicted.

Abstract: Poly(N-isopropylacrylamide) (PNIPAAm)-based microspheres were prepared by precipitation and dispersion polymerization. The effects of several reaction parameters, such as the type and concentration of the crosslinker (N,N′-methylenebisacrylamide or ethylene dimethacrylate), medium polarity, concentration of the monomer and initiator, and polymerization temperature, on the properties were examined. The hydrogel microspheres were characterized in terms of their chemical structure, size and size distribution, and morphological and temperature-induced swelling properties. A decrease in the particle size was observed with increasing polarity of the reaction medium or increasing concentration of poly(N-vinylpyrrolidone) as a stabilizer in the dispersion polymerization. The higher the content was of the crosslinking agent, the lower the swelling ratio was. Too much crosslinker gave unstable dispersions. Although the solvency of the precipitation polymerization mixture controlled the PNIPAAm microsphere size in the range of 0.2–1 μm, a micrometer range was obtained in the Shellvis 50 and Kraton G 1650 stabilized dispersion polymerizations of N-isopropylacrylamide in toluene/heptane. Typically, the particles had fairly narrow size distributions. Copolymerization with the functional glycidyl methacrylate monomer afforded microspheres with reactive oxirane groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 968–982, 2006

Abstract: 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.

Abstract: An investigation of the photoactivated cationic ring-opening frontal polymerizations of a series of alkyl glycidyl ethers was carried out with the aid of a novel technique, optical pyrometry. With this technique, the effects of various experimental parameters, such as the photoinitiator type and concentration, as well as the effects of the monomer structure on the frontal behavior of these monomers were examined. Upon irradiation with UV light, the photopolymerizations of many alkyl glycidyl ethers displayed a prominent induction period at room temperature as the result of the formation of long-lived, relatively stable secondary oxonium ions. The input of only a small amount of thermal activation energy was required to induce the further reaction of these species with the consequent autoaccelerated exothermic ring-opening polymerization. Photoactivated frontal polymerizations were observed for both mono- and polyfunctional alkyl glycidyl ether monomers. The ability of monomers to exhibit frontal behavior was found to be related to their ability to stabilize the secondary oxonium ion intermediates through hydrogen-bonding effects.

Abstract: The present invention relates to a method for preparing an acrylic ester polymer syrup by bulk polymerization, and more particularly, to a method for preparing an acrylic ester polymer syrup, which comprises the steps of: supplying a monomer solution and an initiator solution to a monomer solution reservoir and an initiator solution reservoir, respectively; supplying the monomer solution and the initiator solution to a complete-mixing type continuous reactor, while maintaining the dissolved oxygen in the monomer solution reservoir and the initiator solution reservoir at 0.0001 to 3 ppm, separately or after mixing prior to the supply; and performing bulk polymerization continuously while maintaining the solution mixture supplied to the continuous reactor at 70 to 150 ° C. and 1 to 10 atm, with a mean residence time of 30 to 240 minutes. In accordance with the present invention, an acrylic ester polymer syrup can be obtained with a degree of polymerization of 20 to 70% at a low polymerization temperature, even with a small amount of initiator. Productivity can be improved by reducing reaction time with the use of an initiator having a short half-life and polymerization can be performed very stably and continuously without gelation.

Abstract: The influence of increasing steric demand in the nitroxide moiety of cyclic alkoxyamines derived from side chain modified TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) derivatives on nitroxide-mediated polymerization (NMP) of n-butyl acrylate and styrene is described. Polymerizations at low temperatures (as low as 70 °C) with good control over the molecular weight distribution (polydispersity index, PDI < 1.2) can be achieved using sterically highly demanding nitroxides. Polymerization efficiency increases with the size of the nitroxide substituents. It is shown that in these sterically highly hindered alkoxyamines it is not the rate of homolysis (kd) but the rate of recombination (kc) of the persistent nitroxide with the transient macroradical that is mainly responsible for the enhanced polymerization efficiency (lowering of the reaction time). However, for too bulky nitroxides, the trapping reaction of the nitroxide with the macroradical becomes too slow and uncontrolled NMP is obtained.