Polymerization of cyclopentadiene initiated by methylaluminoxane

The polymerization of cyclopentadiene (CPD) was effectively initiated by methylaluminoxane (MAO) to generate poly(cyclopentadiene) (polyCPD). The effects on the polymerization of some reaction parameters such as the monomer concentration, the initiator concentration, and solvents were investigated. The conversion of CPD was monitored with gas chromatography to investigate the reaction kinetics. The polymerization rate was proportional to the concentrations of MAO in the first order and of the CPD monomer in the second order, and a reasonable cationic polymerization mechanism was suggested on the basis of the kinetic study. PolyCPD obtained at a low temperature could be dissolved in toluene or chloroform, and this indicated lower cross‐coupling during the polymerization reaction. ¹H NMR and IR analysis of the polymer indicated that there were almost equal amounts of 1,2‐enchainment and 1,4‐enchainment in the polymer chain. The measurement of polyCPD showed its unique properties as a potential candidate for stable wrappings or electronic packaging materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 264–272, 2006     

Photo-induced Living Cationic Copolymerization of Isobutyl Vinyl Ether and Vinyl Ether with Carbazolyl Groups

In this work, a fluorescent monomer 2-（9-carbazolyl） ethyl vinyl ether（CEVE） was synthesized in our lab, and its photo-induced living cationic copolymerization behavior with isobutyl vinyl ether（IBVE） was investigated in detail using diphenyliodonium chloride（DPICl）/2,2-dimethoxy-2-phenylacetophenone（DMPA） and zinc bromide（Zn Br2） initiating system in dichloromethane solution at 5 °C, -5 °C, and -15 °C, respectively. The living nature of this copolymerization system was confirmed by adding fresh comonomer method after the copolymerization almost finished. In addition, the obtained fluorescent copolymer poly（IBVE-co-CEVE） has a low glass transition temperature（Tg）, below -10 °C.     

Synthesis of anilinonaphthoquinone-based nickel complexes and their application for olefin polymerization

A series of anilinonaphthoquinone-based nickel complexes, Ni(C₁₀H₅O₂NAr)(Ph)(PPh₃) (Ar = C₆H₃-2,6-Me (1c); Ar = C₆H₂-2,4,6-Me (2c); Ar = C₆H₃-2,6-Et (3c)), were synthesized and the structures of 1c-3c were confirmed by single crystal X-ray analyses. The anilinonaphthoquinone-ligated nickel complexes activated with B(C₆F₅)₃ showed high activities for ethylene polymerization at 40 °C under atmospheric pressure of ethylene and gave polyethylene with long chain branches and short chain branches. The activity of these systems was decreased by lowering polymerization temperature accompanied by increase in molecular weight. The number of the chain branches was also decreased with lowering polymerization temperature and increasing the bulkiness of the ligand.     

Polymerization of methyl methacrylate by metallocene imido complexes and tris(pentafluorophenyl)alane

The polymerization of methyl methacrylate (MMA) was investigated with tris(pentafluorophenyl)alane [Al(C₆F₅)₃] and four metallocene imido complexes that varied in the complex symmetry/chirality, metal, and R group in the ?NR moiety, as well as a zirconocene enolate preformed from the imido zirconocene and MMA. This study examined four aspects of MMA polymerization: the effects of the metallocene imido complex structure on the polymerization activity and polymer tacticity, the degree of polymerization control, the elementary reactions of the imido complex with Al(C₆F₅)₃ and MMA, and the polymerization kinetics and mechanism. There was no effect of the imido complex symmetry/chirality on the polymerization stereochemistry; the polymerization followed Bernoullian statistics, producing syndiotactic poly(methyl methacrylate)s with moderate (～70% [rr]) to high (～91% [rr]) syndiotacticity, depending on the polymerization temperature. Polymerization control was demonstrated by the number‐average molecular weight, which increased linearly with an increase in the monomer conversion to 100%, and the relatively small and insensitive polydispersity indices (from 1.21 to 1.17) to conversion. The reactions of the zirconocene imido complex with Al(C₆F₅)₃ and MMA produced the parent base‐free imido complex and the [2 + 4] cycloaddition product (i.e., zirconocene enolate), respectively; the latter product reacted with Al(C₆F₅)₃ to generate the active zirconocenium enolaluminate. The MMA polymerization with the metallocene imido complex and the alane proceeded via intermolecular Michael addition of the enolaluminate to the alane‐activated MMA involved in the propagation step. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3132–3142, 2003     

Lactide polymerization co‐initiated by carbohydrate esters and pyranoses

The polymerization of [S]‐lactide was accomplished using an initiating system comprising an alkyl zinc complex and a series of well defined carbohydrate co‐initiators derived from D ‐glucose, D ‐xylose, and 2‐deoxy‐D ‐ribose. The monosaccharide co‐initiators were aldonate esters and pyranoses, they were all prepared in high yield and had only a single alcohol co‐initiating group; the remaining carbohydrate hydroxyl functionalities were protected as acetyl, benzyl ether and isopropylidene acetal groups. The polymerizations were all well controlled, illustrated by the linear increase in poly(S‐lactide) M_n with percentage conversion of lactide, the increase in poly(S‐lactide) M_n with [lactide]₀‐[lactide]_t/[co‐initiator] and the narrow polydispersity indices of the polylactides. Thus, the novel initiating systems were used to produce poly(S‐lactides) end functionalized with a variety of different aldonate ester and pyranose groups and with degrees of polymerization from 10 to 250. The polyesters were fully characterized, including by NMR spectroscopy, size exclusion chromatography (SEC), matrix‐assisted laser deposorption/ionization (MALDI) mass spectrometry and by static water contact angle measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4350–4362, 2008     

Feasibility of Tubular Microreactors for Emulsion Polymerization

The viability of a tubular microreactor for the production of polymer dispersions by emulsion polymerization was investigated. The reactor setup and operational conditions necessary to reach a very stable reactor operation were determined. It was found that stability of pre‐emulsion plays a very important role in achieving steady‐state performance. Further, the flow pattern of the microreactor was characterized, observing that the dispersion model can be used because of the effect of the radial molecular diffusion. Finally, a comparative study of the styrene emulsion polymerization in microreactor and batch laboratory reactor was performed. Similar kinetics and properties were achieved, indicating enough mixing in the microreactor.

     

Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

Studying the Fundamentals of Radical Polymerization Using ESR in Combination with Controlled Radical Polymerization Methods

Electron spin resonance (ESR) spectroscopy can contribute to understanding both the kinetics and mechanism of radical polymerizations. A series of oligo/poly(meth)acrylates were prepared by atom transfer radical polymerization (ATRP) and purified to provide well defined radical precursors. Model radicals, with given chain lengths, were generated by reaction of the terminal halogens with an organotin compound and the radicals were observed by ESR spectroscopy. This combination of ESR with ATRPs ability to prepare well defined radical precursors provided significant new information on the properties of radicals in radical polymerizations. ESR spectra of the model radicals generated from tert-butyl methacrylate precursors, with various chain lengths, showed clear chain length dependent changes and a possibility of differentiating between the chain lengths of observed propagating radicals by ESR. The ESR spectrum of each dimeric, trimeric, tetrameric, and pentameric tert-butyl acrylate model radicals, observed at various temperatures, provided clear experimental evidence of a 1,5-hydrogen shift.     

Homogenous and heterogenous catalytic hydrogenation and isomerization of hex-1-ene by palladium(II) Schiff base complexes

Summary Pd^II complexes of Schiff bases with N₂O₂ donor sets were tested for their catalytic activity towards the reductive hydrogenation of hex-1-ene. During the hydrogenation, trans- and cis-hex-2-ene isomers were formed which generally react more slowly than hex-1-ene, hence the rate of hydrogenation tends to slow down with increasing conversion. The rates of hydrogenation and isomerization were studied in relation to the catalyst structure, time, type of catalysis and amount and nature of solvents. The solubility of H₂ and the polarity of reaction medium play a significant role in the hydrogenation yield and selectivity. Hydrogenation and isomerization are parallel reactions; a mechanism for the isomerization is proposed.     

Thermal Polymerization of Styrene,Part 2 – (Mini)emulsion Polymerization

An experimental and theoretical study on the thermal (spontaneous) polymerization of styrene in compartmentalized systems is presented. Experimental data on thermally polymerized miniemulsions varying temperature and droplet size is provided. This data is used to test a new model approach to describe the thermal polymerization process of a disperse phase. The mathematical model is based on a chemical master equation balancing radical species that are capable of desorption (monomeric radicals) and ones that cannot leave a particle. Reasonable agreement between theory and experiment for the data provided here and for literature data can be achieved. Part 1 of this series is a review on the thermal bulk polymerization of styrene.

     

Modern Analytical Tools essential for Studying Olefin Polymerization

As an alternative to inorganic supports, emulsions and organic carriers were developed for metallocene-catalyzed polyolefin synthesis in the last years. Oil-in-oil emulsions based on a perfluorinated solvent provide the possibility to synthesize polymer particles on the nanometer length scale, while the latex particles consisting of polystyrene with different surface functionalities yield particles on the micrometer range. To obtain a deeper insight to the reaction course of both techniques and to the product morphology and fragmentation behavior of the organic carriers, substantial information concerning the kinetics of these reactions is crucial. Thus, standard analytical methods were combined with real-time video microscopy and laser scanning fluorescence microscopy (LSCFM) of perylene labeled particles for improving these methods for polyolefin synthesis.     

Modeling the Effects of Primary Radicals in Free‐Radical Polymerization

The effects of non‐ideal initiator decomposition, i.e., decomposition into two primary radicals of different reactivity toward the monomer, and of primary radical termination, on the kinetics of steady‐state free‐radical polymerization are considered. Analytical expressions for the exponent n in the power‐law dependence of polymerization rate on initiation rate are derived for these two situations. Theory predicts that n should be below the classical value of 1/2. In the case of non‐ideal initiator decomposition, n decreases with the size of the dimensionless parameter α ≡ (k_tz /k_dz) √r_ink_t, where k_tz is the termination rate coefficient for the reaction of a non‐propagating primary radical with a macroradical, k_dz is the first‐order decomposition rate coefficient of non‐propagating (passive) radicals, r_in is initiation rate, and k_t is the termination rate coefficient of two active radicals. In the case of primary radical termination, n decreases with the size of the dimensionless parameter β ≡ k_t,s r_in^1/2/k_p,s M r_t,l^1/2, where k_t,s is the termination rate coefficients for the reaction of a primary (“short”) radical with a macroradical, k_t,l is the termination rate coefficients of two large radicals, k_p,s is the propagation rate coefficient of primary radicals and M is monomer concentration. As k_t is deduced from coupled parameters such as k_t /k_p, the dependence of k_p on chain length is also briefly discussed. This dependence is particularly pronounced at small chain lengths. Moreover, effects of chain transfer to monomer on n are discussed.     

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     

The Effect of [CuI]/[CuII] Ratio on the Kinetics and Conformation of Polyelectrolyte Brushes by Atom Transfer Radical Polymerization

Summary: The atom transfer radical polymerization of [2‐(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) has been studied under different [Cu^I]/[Cu^II] ratios. The reaction kinetics is followed by ellipsometry and quartz crystal microbalance and it was found that the reaction speed influences the grafting density of the polymer brushes. High [Cu^I]/[Cu^II] ratios, i.e., fast polymerizations, lead to less dense polymer brushes.

Plot of the frequency change of wet brushes on a QCM crystal (Δf) versus the dry thickness of brushes synthesized at different [Cu^I]/[Cu^II] ratios.     

Controlled Radical Ab Initio Emulsion Polymerization of n‐Butyl Acrylate by Reverse Iodine Transfer Polymerization (RITP): Effect of the Hydrolytic Disproportionation of Iodine

Summary: Controlled radical polymerization of n‐butyl acrylate by reverse iodine transfer polymerization (RITP) was achieved in ab initio emulsion polymerization to yield a stable and uncolored latex (particle diameter d_p = 106 nm). Hydrolysis of iodine, I₂, was responsible for an upward deviation from the targeted molecular weight = 10 400 g · mol⁻¹. The iodide concentration [I⁻] was followed by an iodide selective electrode and the amount of efficient iodine (33%) was successfully correlated with the experimental molecular weight = 31 000 g · mol⁻¹. Finally, a simplified mechanism of RITP in ab initio emulsion polymerization taking into account the iodine hydrolysis was proposed.

Evolution of molecular weight and polydispersity index in RITP of BuA in ab initio emulsion.     

Modeling of Nitroxide‐Mediated Semibatch Radical Polymerization

A mechanistic model is developed for high‐temperature (138 °C) styrene semibatch thermally and conventionally initiated FRP, as well as NMP with a two‐component initiating system (tert‐butyl peroxyacetate, 4‐hydroxy‐TEMPO). The model, using kinetic coefficients from literature, provides a good representation of the FRP experimental results. Implementation of a gel effect correlation to represent the change in the diffusion‐controlled termination rate coefficient with conversion improves the fit to the thermally initiated system, but is not required to represent the production of low molecular weight material ( Dalton) by conventionally initiated FRP or NMP. The low initiator efficiency found in NMP is well explained by a reaction network involving combination of free nitroxide with methyl radicals formed from initiator decomposition.

     

Styrene Miniemulsion Polymerization: Incorporation of N-Alkanes

Summary: In this work, the incorporation of alkane hydrocarbons in poly(styrene-co-methacrylic acid) particles via miniemulsion polymerization was investigated. The reactions were performed at 80 °C for 4 hours, using benzoyl peroxide as oil-soluble initiator. The effects of different concentrations of a hydrophilic co-monomer (methacrylic acid) and different types and concentrations of alkanes, namely n-hexadecane, n-octane and n-heptane were evaluated. Miniemulsion stability at room temperature and reaction kinetics were monitored, as well as the particles size and morphology. Results show the viability of encapsulation of alkanes in miniemulsion polymerizations, especially of alkanes with intermediate chain lengths (e.g. n-hexadecane). When short chain alkanes are incorporated the miniemulsions become less stable, due to their lower hydrophobicity. Based on monomer droplet size distribution data, it was determined that the best concentration of hydrophilic co-monomer for the studied system was 1.0 wt%.