Classical Radical Polymerization Research Articles

Effects of Solvent and Monomer on the Kinetics of Radical Generation in Atom Transfer Radical Polymerization

AbstractUnlike classical radical polymerization, the kinetics of atom transfer radical polymerization show significant solvent dependence, possibly arising from solvent effects on the activation step. A kinetic study on the activation of the initiator ethyl α‐bromoisobutyrate by [CuITPMA]+ (TPMA=tris(2‐pyridylmethyl)amine), an initiator/catalyst combination frequently used in ATRP, was carried out in DMSO, DMF, MeCN, anisole, ethyl acetate, and their 50 vol % mixtures with styrene (STY) and methyl methacrylate (MMA). kact values varying about 3 orders of magnitude from 3.14×105 mol−1 dm3 s−1 in DMSO to 9.41×102 mol−1 dm3 s−1 in ethyl acetate were found. These values showed excellent correlation with the solvent polarity/polarizability parameter π*. The effect of MMA or STY depended on polarity compatibility between the monomer and the solvent: After monomer addition, kact decreased considerably in polar solvents, whereas it was almost unaffected in nonpolar solvents.

ВЛИЯНИЕ ДИБЕНЗИЛТРИТИОКАРБОНАТА НА КИНЕТКУ РАДИКАЛЬНОЙ ПОЛИМЕРИЗАЦИИ 5-ВИНИЛТЕТРАЗОЛА

Radical polymerization with reversible chain transfer by the addition-fragmentation mechanism of 5-vinyltetrazole in the presence of dibenzyltrithiocarbonate was carried out. The kinetics of the polymerization was studied by NMR spectroscopy: data on the conversion of the monomer and dibenzyltrithiocarbonate, and the rate of polymerization were obtained and analyzed. A comparison was made with the kinetics of the classical radical polymerization of 5-vinyltetrazole

Immunopharmacological Properties of Methacrylic Acid Polymers as Potential Polymeric Carrier Constituents of Anticancer Drugs.

Cytostatic chemotherapeutics provide a classical means to treat cancer, but conventional treatments have not increased in efficacy in the past years, warranting a search for new approaches to therapy. The aim of the study was, therefore, to obtain methacrylic acid (MAA) (co)polymers and to study their immunopharmacological properties. 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CDSPA) and 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) were used as reversible chain transfer agents. Experiments were carried out in Wistar rats. The MTT assay was used to evaluate the cytotoxic effect of the polymeric systems on peritoneal macrophages. An experimental tumor model was obtained by grafting RMK-1 breast cancer cells. Serum cytokine levels of tumor-bearing rats were analyzed. The chain transfer agents employed in classical radical polymerization substantially reduced the molecular weight of the resulting polymers, but a narrow molecular weight distribution was achieved only with CDSPA and high CPDT concentrations. Toxicity was not observed when incubating peritoneal macrophages with polymeric systems. In tumor-bearing rats, the IL-10 concentration was 1.7 times higher and the IL-17 concentration was less than half that of intact rats. Polymeric systems decreased the IL-10 concentration and normalized the IL-17 concentration in tumor-bearing rats. The maximum effect was observed for a MAA homopolymer with a high molecular weight. The anion-active polymers proposed as carrier constituents are promising for further studies and designs of carrier constituents of drug derivatives.

In Situ Preparation of Polymer Nanocomposites Based on Sols of Surface-Modified Detonation Nanodiamonds by Classical and Controlled Radical Polymerization

The possibility of surface modification of detonation nanodiamonds to give them dispersability in methyl methacrylate is considered. In situ polymer composites are obtained by classical radical polymerization and reversible chain-transfer polymerization based on stable sols of detonation nanodiamonds in a monomer. Evidence that nanodiamonds are dispersed in a polymer matrix up to a size of units of nanometers is given. The effect of detonation nanodiamonds on the molecular weight characteristics and glass transition temperature of poly(methyl metacrylate) obtained in their presence is studied.

Rheological Properties of Acrylonitrile Terpolymer Solutions Synthesized by Different Methods

Series of polyacrylonitrile terpolymers with molecular weights of (7–20) × 104 have been synthesized in dimethylsulfoxide using classical radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the synthesis method on the rheological behavior of dilute and concentrated solutions of the resulting copolymers has been analyzed. No differences have been found in the viscous properties and viscoelastic behavior of the concentrated solutions in the temperature range of 20–80°C. However, viscometry of the dilute solutions made it possible to detect a difference in the interaction between the solvent and macromolecules of the copolymers obtained by these methods. The copolymers differ in the values of the second virial coefficient, which indicates that the interaction of the solvent and polymer is specific to the synthesis method. This phenomenon seems to be caused by different branching of chains in the copolymer and/or its compositional heterogeneity. For dilute solutions, it was possible to construct a single generalized concentration dependence of reduced viscosity in the coordinates of the Martin equation. Transition to the region of concentrated solutions required an introduction of yet another parameter that describes the effective density of the mesh network, namely, the ratio of the current solution concentration to the crossover concentration. This approach made it possible to construct a generalized dependence of viscosity in the entire concentration range of solutions of polyacrylonitrile copolymers.

The Role of a Metallocene Additive in Radically Initiated Polymerization when Solving Direct and Inverse Kinetic Problems

Polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, is considered from the point of view of formal kinetics. Based on the kinetic scheme of the process (which includes the reactions of classical radical polymerization, the reaction of benzoyl peroxide with titanocene dichloride, the reactions of the controlled radical polymerization of organometallic mediated radical polymerization (OMRP) and atom transfer radical polymerization (ATRP), the reaction of the formation of a coordinating active site and the coordinating chain propagation on a mathematical model of the kinetics of the process is created. This model also makes it possible to calculate the molecular-mass characteristics of poly(methyl methacrylate). As a result of the solution of the inverse kinetic problem at a temperature of 343 K, the values of the reaction rate constants of the kinetic scheme are found under which the discrepancy between the calculated models and experimental data is minimal. Using the developed model of the kinetics of the process, a numerical experiment is performed (i.e., a direct kinetic problem is solved). This problem revealed the following regularities of the process. (1) An increase in the initial concentration of titanocene dichloride at a constant initial concentration of benzoyl peroxide leads to an increase in the rate of consumption of benzoyl peroxide but not to an increase in the initial rate of the process compared to classical radical polymerization. (2) With an increase in the initial concentration of titanocene dichloride, the lifetime of the macroradicals at the initial stage of the process is reduced, and hence the molecular weight of the resulting polymethyl methacrylate is less than that of the polymethyl methacrylate obtained in the absence of titanocene dichloride, and it will increase during the process of approaching the final values. (3) During the polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, a smoothing gel effect (as in the case of the polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of ferrocene) does not occur since titanocene dichloride forms stable complexes with methyl methacrylate and, consequently, it participates in reactions consuming macroradicals to a lesser degree than ferrocene.

Electroactive polyacrylates bearing linear conjugated systems based on EDOT moieties

New polyacrylates bearing an electropolymerizable bi or terthiophene group have been synthesized via classical radical polymerization and via RAFT process. Polymerizations can be controlled if thiophene moieties have protected α positions; otherwise polymerization is difficult or impossible. Cross-linked polymers can be obtained after film electropolymerizations on different electrodes (gold, carbon and platinum).

Kinetic scheme and rate constants for methyl methacrylate synthesis occurring via the radical–coordination mechanism

Two kinetic schemes of the bulk radical–coordination polymerization of methyl methacrylate initiated by the benzoyl peroxide–ferrocene system are considered from the standpoint of formal kinetics. The most likely kinetic scheme is the one that includes the reactions characteristic of classical radical polymerization and, additionally, reactions of controlled radical polymerization proceeding via the Organometallic Mediated Radical Polymerization mechanism, a reaction generating a coordination active site, and a chain propagation reaction in the coordination sphere of the metal. The temperature dependences of the rate constants for the reactions of this kinetic scheme at temperatures typical of commercial poly(methyl methacrylate) production (313–353 K) have been determined by solving the inverse kinetic problem.

Synthetic Strategies in Molecular Imprinting.

This chapter introduces the basic principle and the synthetic aspects of molecular imprinting. First, the use of a molecular template to guide the location of functional groups inside molecularly imprinted cavities is explained. Three different mechanisms that ensure a molecular template associates with functional monomers or the imprinted polymers, that is, through reversible covalent, noncovalent, and sacrificial covalent bonds, are then described. The main focus is put on noncovalent molecular imprinting using free radical polymerization. The merits of using classical radical polymerization and more sophisticated, controlled radical polymerization are analyzed. After these synthetic chemistry aspects, the chapter continues to discuss the different polymerization processes that can be used to prepare well-defined polymer monoliths, microspheres, and nanoparticles. New top-down processing techniques that produce micro- and nanopatterns of imprinted polymers are also reviewed. The chapter finishes with a brief introduction to using imprinted polymers as building blocks to construct new functional materials and devices, which we consider as one important direction for further development.

Poly(9-vinyl anthracene peroxide): Synthesis, characterization, degradation and application as macroinitiator for the polymerization of methyl methacrylate

Polymerization of 9-vinyl anthracene (VAn) and molecular oxygen at high pressure in the presence of 2,2′-azobisisobutyronitrile (AIBN) at 50 °C in toluene produces fluorescent poly(9-vinyl anthracene peroxide) (PVAnP). Kinetics studies have been performed at different oxygen pressure to determine the saturation oxygen pressure during the oxidative polymerization of VAn. Elemental analysis, mass spectral fragmentation study, FT-IR and NMR spectroscopy have been used to verify the alternating copolymer structure of PVAnP with repeating peroxy bonds in the copolymer backbone. Highly exothermic thermal degradation of PVAnP has been investigated by differential scanning calorimetry (DSC). Radical polymerization of methyl methacrylate (MMA) has been studied using PVAnP as a macroinitiator at 90 °C in toluene. The rates of MMA polymerizations are determined with respect to the macroinitiator and the monomer. The MMA polymerization follows classical radical polymerization kinetics. Characterization of poly(methyl methacrylate) (PMMA) confirmed presence of fluorescent anthracene moiety at the PMMA chain ends.

Gluconolactone‐derivated polymers: Copolymerization, thermal properties, and their potential use as polymeric surfactants

AbstractStatistical glycopolymers based on gluconolactone have been prepared by classical radical polymerization and followed by 1H NMR in situ. The kinetic behavior of this system in terms of global rate constant has been qualitatively studied. The variation of cumulative feed and copolymer composition with conversion has also been analyzed, showing a diminishment of both as the reaction progresses. The monomer reactivity ratios have been estimated using the Mayo‐Lewis terminal model and extended Kelen–Tüdös equation, being rHEMAG = 1.41 ± 0.06 and rMA = 0.42 ± 0.05. The thermal properties have been examined by differential scanning calorimetry and thermogravimetric analysis. The glass transition and the thermal degradation temperatures of glycopolymers increase as hydrophilic component decreases. In addition, the solution properties of the water‐soluble glycopolymers have been investigated, observing the formation of small micelles. Finally, the potential of these glycopolymers as polymeric surfactants has been proved by the performance of emulsion polymerization of methyl acrylate. The resulting particles are stable and with low polydispersity, decreasing the particle size as the methyl acrylate content increases in the glycopolymer surfactant. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Frontal atom transfer radical polymerization of tri(ethylene glycol) dimethacrylate

Abstract The first frontal atom transfer radical polymerization (FATRP) has been successfully carried out using tri(ethylene glycol) dimethacrylate as a monomer. The effect of the catalyst/initiator ratio has been investigated and related to the front velocity and its maximum temperature. By comparing this new approach with classical radical polymerization routes and with conventional frontal polymerization, it was found that the so-obtained polymer is characterized by higher conversion, shorter reaction times, higher degradation temperature, and does not contain entrapped bubbles.

Associating behaviour of polyacrylamide modified with a new hydrophobic zwitterionic monomer

AbstractThe nucleophilic ring opening of dicyanoketene ethylene acetal by tertiary amino monomers leads to an hydrophobic zwitterionic monomer [(dimethylammonioethoxy)dicyanoethenolate]propylmethacrylamide (DADPMA) characterized by a very high dipole moment. Hydrophobically modified water soluble polymers have been prepared by classical radical polymerization of acrylamide and DADPMA either in homogeneous medium (water/ethanol mixtures) or in micellar solution (water containing sodium dodecylsulphate (SDS)). The copolymers obtained have a high molecular weight (M w = 2–5 × 106 g mol−1) and are water soluble for a content of DADPMA lower than 1% mole/mole. The properties of the copolymers in aqueous solution depend on the synthesis conditions, especially on the ratio ethanol:zwitterionic monomer.© 2001 Society of Chemical Industry

Aqueous electropolymerization of polyacrylamide onto AS‐4 graphite fibers

AbstractConstant current electropolymerization of acrylamide was initiated on the surfaces of AS‐4 graphite fibers. Electropolymerization was performed using an aqueous solution of acrylamide dissolved in dilute sulfuric acid solution. The progress of electropolymerization was followed by measuring the weight of polyacrylamide deposited onto the surfaces of a unit weight of graphite fiber per unit time. The rate of electropolymerization was obtained from the slope of the linear region of the polymer weight gain vs. electropolymerization time curve. The rate of electropolymerization onto AS‐4 graphite fiber surfaces was found to depend on the initial monomer concentration, sulfuric acid concentration, and current density raised to the powers of 1.67, 0.02, 0.54, respectively. Molecular weight measurements on the electropolymerized polyacrylamide were done by solution viscometry. Number average molecular weights of 430,000, 220,000, and 193,000 were obtained for polyacrylamide, electropolymerized at 1 mA/g, 50 mA/g, and 100 mA/g respectively, consistent with classical radical polymerization kinetics.