Chain transfer polymerization of methyl methacrylate initiated by organolanthanide complexes

A novel chain transfer polymerization mediated by Cp*₂ Sm(III) species and organic acids is described. The chain transfer polymerization involves the reaction of organic acids such as thiols or ketones with an active bond between samarium(III) and the enolate at a living chain end of poly(methyl methacrylate) (PMMA). This chain transfer reaction resulted in termination of the living chain end and the regeneration of the active initiator which would consist of (C₅Me₅)₂Sm(III) and deprotonated organic acids. The chain transfer polymerization were confirmed by turnover numbers (TON). tert‐Butyl thiol exhibited the chain transfer reactivity effectively to control the molecular weight of PMMA without decreasing of the polymer yield and the stereoregularity. As a result of this chain transfer polymerization, thermal and optical properties of the PMMA obtained were improved by the control of chain end groups or by reducing a large amount of the samarium initiator.     

The influence of molecular interaction on polymerization, 6. GPC study of polymethacrylates obtained in different solvents

Poly(2-naphthyl methacrylate)s (P-2-NM), poly(benzyl methacrylate)s (PBzMA) and poly-(methyl methacrylate)s (PMMA) obtained by radical polymerization initiated with 2,2′-azo-isobutyronitrile (AIBN) in benzene, acetone and acetonitrile were investigated by means of gel permeation chromatography (GPC). The GPC curves of the polymethacrylates containing aromatic rings show lower molecular weights and higher polydispersities than those of PMMA. The polymerization in benzene leads to polymers with higher molecular weights and higher polydispersities than that in acetonitrile. Acetonitrile causes a formation of polymethacrylates with lowest molecular weight distribution. In comparison with the other solvents acetone gives PMMA with lowest molecular weight. Inversely, P-2-NM and PBzMA prepared in acetone are of highest molecular weights. The molecular weight and molecular weight distribution of PMMA is less sensitive to the change of the solvent than those of aromatic methacrylates. The GPC curves indicate similar dependence on the change of the polymerization medium for the copolymers of 2-naphthyl methacrylate (2-NM) with methyl methacrylate (MMA), and of benzyl methacrylate (BzMA) with maleic anhydride (MA) prepared in benzene, carbon tetrachloride, chloroform and acetonitrile. The results are explained assuming various termination and transfer reactions in different solvents. Some correlations established between the GPC curves and the association and dissociation of the monomer molecules in dependence of the dielectric constant of the solvent, previously observed by ¹H NMR, are also discussed.     

Phosphorus functional telomers of vinyl polymers through functional thermal iniferter

The phosphorus-functional iniferter, N,N′-dimethyl-N,N′-bis[2-(N-diethoxyphosphinoyl-N-methylamino)ethyl]thiuram disulfide ( 2 ), was synthesized and characterized. Thermal polymerization of methyl methacrylate (MMA) and styrene in presence of this compound led to the formation of α, ω-phosphorylated PMMA and polystyrene. The kinetics of polymerizations of MMA and styrene using this iniferter was studied at 70°C and the different parameters, related to initiation, chain transfer, and primary radical termination reactions, were evaluated. In the case of styrene the extent of primary radical termination was considerably less and mutual termination reactions were found to be absent. The telomers were analysed for their functionality.     

Radical reactions initiated by chelate complexes of transition metals, 17. Solvent effect on polymerization of methyl methacrylate initiated by copper(II) 2-aminoethanolate

The solvent effect on radical Polymerization of methyl methacrylate initiated by copper(II) 2-aminoethanolate (Cumea) or by the system Cumea-reducing agent (H₂NCH₂CH₂OH, CCl₄) is discussed. In the first case, where the initiating radical is formed from a Cumea-MMA complex, the solvent influences the equilibrium of the complex-forming reaction and thus also the initiation reaction. Further, in this system also primary radical termination and degradative chain transfer are operative. In the initiation by the system Cumea-reducing agent, the non-ideal course of polymerization is due to primary radical termination and degradative chain transfer.     

Polymerization kinetics of HEMA/DEGDMA: using changes in initiation and chain transfer rates to explore the effects of chain-length-dependent termination

The effect of kinetic chain length and chain transfer on the polymerization kinetics and network structure in polymerizations of loosely crosslinked 2-hydroxyethyl methacrylate/di(ethylene glycol) dimethacrylate mixtures was explored. Polymerization behavior of the monomer mixture in the presence and absence of a chain transfer agent was monitored at various initiation rates and chain transfer agent concentration levels. Dependence of the polymerization rate on the initiation rate was found to deviate from the classical square-root relationship because of chain-length-dependent termination. This effect was further confirmed by addition of a chain transfer agent. The presence of a chain transfer agent led to the formation of shorter kinetic chains, which enhanced termination and slowed the polymerization. Investigation of the polymerization kinetics after cessation of irradiation yielded kt/kp[M] values for both systems. Prior to the onset of reaction diffusion-controlled termination, the system that included a chain transfer agent exhibited much higher kt/kp[M] values than the polymerization system without added chain transfer agent. In addition, the onset of reaction diffusion-controlled termination was delayed to higher conversions in the system containing chain transfer agent. The impact of a chain transfer agent on the polymerization behavior and kinetics demonstrates that the chain-length-dependent termination phenomenon is indeed important and must be considered in kinetic modeling of loosely crosslinked systems.     

Die thermische Polymerisation von Methylmethacrylat, 1. Polymerisation in Substanz

Special purification of the monomer and careful preparation of the reaction setup allowed a thorough study of the spontaneous thermal polymerization of methyl methacrylate over a wide range of temperatures (0–140°C). The rates of polymerization are notably lower than the few data previously reported in literature, and the degrees of polymerization slightly higher. The thermal initiation reaction is superimposed by radical production due to the natural ionising radiation (cosmic radiation etc.). This additional initiation becomes significant at temperatures below 60°C. New and more reliable monomer chain transfer constants are given.     

Partitioned polymerization, 2. Simultaneous transfer of monomer and of initiator

The kinetics of the 2,2′-azoisobutyronitrile (AIBN)-initiated emulsion polymerization of methyl methacrylate and butyl methacrylate was studied in the presence or in the absence of 4-stearoyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl radical (STMPO) situated in the oil (monomer) phase. The polymerization was initiated and oligomeric radicals were formed in the aqueous phase to which methyl methacrylate (butyl methacrylate) and AIBN were transferred. Polymerization does not take place in the oil phase because of the inhibitor present. Relatively short inhibition periods of polymerization observed in systems containing STMPO confirm that a small part of STMPO was transferred from the oil to the water phase. The length of the inhibition period in the emulsion polymerization is determined by a competition between the addition reaction of primary radicals with monomer and the termination reaction of primary radicals with STMPO as well as by the rate of STMPO scavenging by oligomer-monomer and polymer-monomer particles. The polymerization system studied belongs to a group of partitioned polymerization systems characterized by simultaneous transfer of monomer and initiator from the oil to the water phase, where the initiation of polymerization takes place.     

CdS–Oleic Acid Quantum Dots as Long‐Wavelength Photoinitiators in Organic Solvent and Preparation of Luminescent,Colloidal CdS/Polymer Nanocomposites

Photoexcitation of luminescent semiconductor quantum dots (QDs) generates an electron–hole pair, which can be utilized for photoinitiation of radical polymerization reactions. Here, oleic acid coated CdS QDs (CdS–OA) are demonstrated as successful photoinitiators in the absence of a protic solvent or a hole scavenger for the first time. This provides photopolymerization of hydrophobic methyl methacrylate in toluene, providing colloidal and strongly luminescent CdS/poly(methacrylic acid) (PMMA) hybrid structures with improved stability of the CdS. Besides, successful photopolymerization of poly(ethylene glycol)diacrylate at different excitation windows (320–480 and 400–500 nm) is demonstrated. This indicates that CdS–OA can act as a long‐wavelength initiator. Electron spin resonance (ESR) studies and control experiments suggest decarboxylation of the oleic acid as the initial source of the free radical. This method represents a unique and very simple way to create luminescent, small, stable, and colloidal QD/polymer hybrids.     

Initiators based on poly(ethylene glycol) for starting heterophase polymerizations: generation of block copolymers and new particle morphologies

Radical heterophase polymerizations with poly(ethylene glycol) radicals lead to the formation of block copolymer particles where the block copolymer architecture and the particle morphology depend on the number of radical per poly(ethylene glycol) chain, the radical termination mode, and the polarity of the monomer, respectively. The thermal decomposition of symmetrical poly(ethylene glycol) azo-initiators following the classical recipes of Heitz results in one radical per poly(ethylene glycol) chain whereas the number of radicals can be adjusted between one or two in the redox system poly(ethylene glycol)/cerium ions. The polymerization of styrene results in latex particles with an almost spherical morphology, consisting of block copolymers, only. In case of a methyl methacrylate polymerization the latex morphology depends on the architecture of the block copolymers formed. Heterophase polymerization with poly(ethylene glycol) azoinitiators in oligo(ethylene glycol) (average molecular weight 200 g · mol⁻¹) instead of in water results in particles with random shape and a strongly indented interface which is explained by the surface tension between polymers and solvent being close to zero.     

Study of radical polymerization by means of ESR, 2. Homogeneous polymerization of methyl methacrylate and vinyl acetate

A very efficient ESR spectrometer was applied to the measurement of the stationary concentration of macroradicals in homogeneous polymerization. From these data the rate constants of chain propagation and chain termination for the polymerizations of methyl methacrylate and vinyl acetate were found in a direct way. Activation energies of these elementary reactions were measured.     

Radical polymerization of vinyl monomers by captodative substituted dimers

Polymerization of vinyl monomers such as styrene, methyl methacrylate, and vinyl acetate was carried out in the presence of the captodative substituted dimers 1 – 6 at 50 to 110°C. It was found that the dimer initiates the radical polymerization of these monomers, even of vinyl acetate. The initiation ability of the dimers depends on the nature of both captive and dative groups as well as the substituent at a remote position. The kinetic study suggests that in the polymerization initiated by the dimers primary-radical termination and chain transfer play a minor role.     

Improvement of fatigue properties of poly(methyl methacrylate) bone cement by means of plasma surface treatment of fillers.

The fatigue properties of poly(methyl methacrylate) (PMMA) bone cement were significantly improved through 13.56-MHz radio frequency plasma treatments on the X-ray opaque powder and on the reinforcing fibers. For the plasma treatments of particle surfaces, a specially designed plasma reactor was used to modify the surfaces of the ZrO2 powder (X-ray opaque filler) and milled carbon fibers (reinforcing filler). The reactor chamber was designed to be rotated continuously to mix the particles during the plasma treatments to obtain uniformly treated particle surfaces. The surface peroxides resulting from the plasma treatments seemed to have a significant effect on the improvement of fatigue properties. The peroxides on the particles may yield free radicals by the reaction with the reducing agent (N,N-dimethyl-p-toluidine) in the bone cement mixture, which can initiate methyl methacrylate (MMA) polymerization. Through this graft polymerization process, the interfacial bond strength between the filler particles and the MMA matrix may be enhanced, resulting in efficient stress transfer from the matrix to the fillers. The best results of the fatigue tests were seen in the reinforced bone cement, which contained surface modified fillers, with hexamethyldisiloxane plasma, and with O2 plasma posttreatment.     

Vinyl polymerization. 221. Polymerization of methyl methacrylate in the presence of cellulose triacetate

A kinetic study on the polymerization of methyl methacrylate (MMA) was made in the presence of cellulose triacetate (CTA) and water. In this case, water was found to be not necessary for the initiation of polymerization. The reaction proceeds by a radical mechanism, and the rate of polymerization can be expressed by the following equation: The overall activation energy for the polymerization was estimated as 7.9 kcal/mole. The grafting efficiency of polymethyl methacrylate (PMMA) to CTA decreased with increase in polymerization temperature. The molecular weight of the extracted PMMA decreased also slightly with increase in polymerization temperature and was independent on the concentration of CTA. These results suggest that the molecular weight of PMMA is mainly affected by the transfer of growing radical to monomer molecule.     

Chain End‐Functionalized Polymer Brushes with Switchable Fluorescence Response

Herein is described the switchable fluorescence response of poly(methyl methacrylate) (PMMA) brushes. Chain end fluorescein labeled PMMA brushes are prepared by combining surface‐initiated atom transfer radical polymerization (SI‐ATRP) with a copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) click reaction. Successful attachment of fluorescein is confirmed by measuring fluorescence of the as‐prepared films. Utilizing co‐solvency of PMMA in isopropanol‐water mixtures, responsive behavior of the end‐functionalized brushes is demonstrated by measuring the changes in fluorescence intensity between the swollen and collapsed states.     

Lithium alkylnickelate and alkylpalladate bimetallic “ate” complexes as initiators for anionic polymerization of methyl methacrylate

Anionic-coordinative polymerization of methyl methacrylate (MMA) was carried out in the presence of new bimetallic initiators based on lithium alkylnickelates and alkylpalladates in tetrahydrofuran, at ?78°C. Well-defined poly(methyl methacrylate), PMMA, with molecular weights increasing linearly with conversion and relatively narrow polydispersities (M?_w/M?_n = 1,26 to 1,4) were prepared by initiation with some of the “ate” complexes. In the presence of lithium “ate” Ni-based complexes, PMMA with enhanced syndiotacticity [(rr) = 73 to 75%] was formed.     

Kinetics of radical polymerization of methyl methacrylate initiated with dimethyl 2,2′-azodiisobutyrate

The kinetics of free-radical bulk polymerization of methyl methacrylate with dimethyl 2,2′-azodiisobutyrate as an initiator was investigated at 40, 60, and 80°C. Non-ideal polymerization behaviour was observed when the initiator concentration was varied by a factor of more than one thousand. This departure from classical polymerization kinetics is discussed in terms of primary radical termination and a chain length dependent termination rate constant, with the structural similarity of both primary and polymeric radicals facilitating the treatment very much. The kinetic analysis indicates that in the polymerization of methyl methacrylate the termination rate constant is a function of the degree of polymerization of the involved macroradicals.     

Rapid Synthesis of Poly(methyl methacrylate) Particles with High Molecular Weight by Soap‐Free Emulsion Polymerization Using Water‐in‐Oil Slug Flow

A flow process for the production of poly(methyl methacrylate) (PMMA) particles is proposed by soap‐free emulsion polymerization using a water‐in‐oil (W/O) slug flow in a microreactor. Thin oil films generated around the dispersed aqueous phase of the W/O slug prevent the prepared particles from adhesion to the microchannel wall, enabling the continuous production of PMMA particles without clogging. The effects of the linear flow rate of the slug flow and the addition of ethanol in the dispersed aqueous phase on the polymerization are evaluated. It is found that increasing the linear flow rate of the slug flow or the addition of ethanol in the dispersed aqueous phase results in PMMA particles with high molecular weight (≈1500 kg mol^?1) in 20 min reaction time. It is believed that this process would be a promising way to prepare polymer particles with high molecular weight in a short reaction time.     

Suspension polymerization of 2-hydroxyethyl methacrylate in the presence of polymeric diluents: a novel route to spherical highly porous beads for biomedical applications

Spherical, highly porous beads of poly(2-hydroxyethyl methacrylate) (PHEMA) cross-linked with ethylene glycol dimethacrylate (EGDM) were prepared by suspension polymerization of HEMA in concentrated NaCl solutions in presence of toluene, poly(methyl methacrylate) (PMMA) in toluene, and poly(tetramethylene glycol) (PTMG). Magnesium hydroxide prepared in situ in the dispersion medium gave the best stabilization effect for the monomer droplets. In the presence of PTMG, beads having nearly 1.0 mm in diameter could be prepared, while toluene alone as the diluent produced beads of very small size. Removal of PMMA or PTMG from the beads after polymerization using suitable solvents gave rise to highly porous PHEMA microspsheres. Polymerization in the presence of PTMG produced microspsheres with better spherical geometry as compared to those generated in the presence of PMMA. The effect of various factors such as NaCl concentration, concentration of Mg(OH)2, and the concentration of PMMA or PTMG in the monomer phase on the stability of the suspension and the particle size distribution was investigated.     

Photoresponsive Azopolyester–PMMA Block Copolymers Obtained by Combination of ATRP,Polycondensation, and “Click” Chemistry

Novel azobenzene‐containing block copolymers (BCs) with a polyester block bearing azobenzene moieties in the side chain and a poly (methyl methacrylate) (PMMA) block have been synthesized by the combination of atom transfer radical polymerization (ATRP), polycondensation, and “click” chemistry. Two azide‐terminated polyesters with different molecular weight (obtained by polycondensation) were coupled to an alkyne‐functionalized PMMA (obtained by ATRP). Blends of the BC with the highest azo content (wt%) and an azopolyester homopolymer were also prepared. All these compounds were investigated by polarized light optical microscopy (POM), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Polarized light‐induced anisotropy was studied by birefringence and dichroism measurements.     

Benzil/triethylamine combination as photoinitiator for methyl methacrylate polymerization

Photopolymerization of methyl methacrylate (MMA) in bulk and in solution was studied using the combination benzil (BZL)/triethylamine (TEA) as photoinitiator. The initiation was found to occur through photoreduction of the ketone in presence of an amine via exciplex formation. A kinetic study of the polymerization showed that both carbonyl groups of benzil are involved in exciplex interaction, resulting in diradical formation. An analysis of the initiator dependent termination process revealed that primary radical termination is predominant in the particular system compared to the degradative initiator transfer. A kinetic scheme was designed to account for the various wastage reactions occurring in the polymerization system.