Radiation polymerization of methacrylates controlled by a chain transfer catalyst

The effect of γ-radiation dose and chain transfer catalyst on polymerization of methyl methacrylate (MMA) and copolymerization of MMA with hydroxyethyl methacrylate or triethylene glycol dimethacrylate has been investigated. The addition of 5 × 10^?4?10^?3 mol/L of bis[(difluoroboryl) isopropylpyridine dimethylglyoximato]cobalt(II) (Co(II)) makes it possible to produce macromonomers MM _n ⁼⁼ bearing terminal double bonds and having a degree polymerization of n = 2?40 and a polydispersity index of 1.05?1.15. It has been found that the degree polymerization of the macromonomers increases with the increasing γ-radiation dose and monomer conversion through the mechanism of the reversible β-cleavage of the terminal unit: R _k ^? + MM _n ⁼ ? MM _k+1 ⁼ + R _n-1 ^? followed by the living polymerization of both radicals. This reaction may compete with the catalytic chain transfer reaction and have a significant effect on the evolution of the molecular weight characteristics of the macromonomers during the course of MMA (co)polymerization.     

Kinetic theory of self-condensing vinyl polymerization

This review introduces the kinetic theory of self-condensing vinyl polymerization (SCVP), including the SCVP of AB* inimers, the SCVP with non-equal reactivity between A* and B* groups, the SCVP in the presence of a small amount of multifunctional initiators, also the SCVP of both inimers and comonomers. The analytical expressions of various molecular parameters for the resulting hyperbranched polymers, such as the molecular size distribution function, the average molecular weight, the polydispersity index and the degree of branching, are reviewed systematically.     

Isothermal bulk polymerization ofp-alkylaryl methacrylates by DSC

The course and kinetics of free radical polymerization in bulk ofp-alkylphenyl methacrylates with AIBN initiator were studied by DSC, in the temperature range 348–373 K. The enthalpy of polymerization, the residual monomer content, as well as the overall reaction rate constants and the activation energies were determined. The similar values of the overall rate constants indicate that the relatively small alkyl substituents inp-position of the phenyl ring affect the polymerization rate to a very small, if any, extent.

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Zusammenfassung Mittels DSC wurden im Temperaturbereich 348–373 K Reaktionsweg und Kinetik der radikalischen Raumpolymerisation vonp-Alkylphenylmethacrylaten mit AIBN Initiator untersucht. Dabei wurden die Polymerisationsenthalpie, der Monomerrest-gehalt als auch die Geschwindigkeitskonstanten und die Aktivierungsenergien der Gesamt-reaktion bestimmt. Ähnliche Werte für die Gesamtgeschwindigkeitskonstanten weisen darauf hin, daß die relativ kleinen Alkylsubstituenten inp-Stellung des Phenylringes die Polymerisationsgeschwindigkeit nur in sehr kleinem Maße — wenn überhaupt — beeinflussen.

     

Asymmetric polymerization of methacrylates

The syntheses of optically active polymers having helical conformation from bulky methacrylates are reviewed focusing on selected topics. The monomers include triphenylmethyl methacrylate and its analogues. Asymmetric anionic polymerization of the monomers gives isotactic, optically active polymers having a helical structure with excess helicity. The isotactic content and the extent of helical‐sense excess depend on the monomer structure and the reaction conditions. In the case of methacrylates, completely isotactic and single‐handed helical polymers can be produced by asymmetric anionic polymerization (helix‐sense‐selective polymerization). Asymmetric radical polymerization is also possible for this class of monomer. Some of the helical polymers show chiral recognition ability toward a wide range of racemic compounds. Polymers having main‐chain configurational chirality are also discussed.     

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one‐pot procedure. The synthesis involved the use of a monofunctional initiator and the four‐step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm‐first” star polymers; (iii) monomer, to form secondary arms and give “in‐out” star polymers; and, finally (iv) branch unit again, to interconnect the “in‐out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm‐first” and the “in‐out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.     

Synthesis and polymerization of chiral methacrylates bearing a cholesteryl or menthyl group

Chiral methacrylates, that is, cholesteryl (ChMOC) and l‐menthyl (MnMOC) N‐(2‐methacryloyloxyethyl)carbamates, were synthesized from 2‐methacryloyloxyethyl isocyanate and cholesterol and l‐menthol, respectively. Radical polymerizations of ChMOC and MnMOC gave number‐average molecular weights for poly(ChMOC) and poly(MnMOC) of up to 3.74 × 10⁴ and 9.39 × 10⁴, respectively, and the specific rotations ([α]) were −43.1° to −47.7° and −87.6° to −89.0°, respectively. Temperature dependence of the specific optical rotation was observed for poly(ChMOC) but not for poly(MnMOC). The hydrogen bonds based on urethane segments for poly(ChMOC) were stronger than those for poly(MnMOC) according to IR spectra. In addition, the chiroptical properties of poly(ChMOC) were slightly affected by temperature in the presence of trifluoroacetic acid acting as an inhibitor for the formation of hydrogen bonds. Therefore, poly(ChMOC) may have a regular conformation due to hydrogen bonds and interaction between cholesteryl groups. Radical copolymerizations of ChMOC with styrene, methyl methacrylate, N‐cyclohexylmaleimide, and N‐phenylmaleimide were performed with 2,2′‐azobisisobutyronitrile in tetrahydrofuran at 60 °C. Monomer reactivity ratios and Alfrey–Price Q–e were determined. Chiroptical properties of the copolymers were influenced by co‐units. Thermal and X‐ray diffraction analyses were performed for the homopolymers and copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4315–4325, 2000     

Statistical and thermodynamic properties of binary self-condensing vinyl polymerization

The thermodynamic properties of a binary self-condensing vinyl polymerization system consisting of monomers and inimers are investigated by the principle of statistical mechanics.In detail,in terms of two types of canonical partition functions constructed from different viewpoints,the equilibrium free energy,the law of mass action and the size distribution of hyperbranched polymers are obtained.As an application,the specific heat,equation of state and isothermal compressibility concerning the polymerization...     

Mechanistic aspects of group transfer polymerization

The experimental evidence supporting the involvement of enolate anions in group transfer polymerization(GTP) is reviewed. The results of silyl group exchange studies between living silyl ketene acetal-ended oligomers under typical GTP conditions are discussed. It is concluded that the observations of significant amounts of silyl group exchange in the presence of polymerizing monomer are not consistent with the originally proposed “associative mechanism” based on the GTP Criterion which precludes intermolecular silyl group exchange.     

Termination processes in group transfer polymerization

Two major termination processes in the GTP of methacrylates and acrylates have been studied. For methacrylates, intramolecular cyclization is the dominant, if not sole, termination reaction. Both cyclization and O/C-silyl isomerization of the chain end are observed for acrylates. Oligomerization experiments were used to study the relative rates of cyclization and propagation and the influence of temperature, catalyst and dp. Under typical GTP conditions for methacrylates, cyclization is at least two orders of magnitude slower than monomer addition.     

Surface-initiated group transfer polymerization mediated by rare earth metal catalysts

We present the first example of a surface-initiated group transfer polymerization (SI-GTP) mediated by rare earth metal catalysts for polymer brush synthesis. The experimentally facile method allows rapid grafting of polymer brushes with a thickness of >150 nm in <5 min at room temperature. We show the preparation of common poly(methacrylate) brushes and demonstrate that SI-GTP is a versatile route for the preparation of novel polymer brushes. The method gives access to both thermoresponsive and proton-conducting brush layers.     

Molecular architecture control in acrylic polymers by group transfer polymerization

The living polymerization of methacrylates by a repeated silyl Michael addition reaction (GTP)^a operates at room temperature and permits a high degree of molecular architecture control. Chelic, telechelic, block, comb, star, loop, and ladder polymers have been synthesized. For nucleophilic catalysts other than bifluoride, a dissociative mechanism is now proposed.     

Surface active semifluorinated diblock copolymers prepared by group transfer polymerization

Diblock copolymers consisting of poly(methyl methacrylate) and poly(2-perfluorobutylethyl methacrylate) with narrow molecular weight distribution have been synthesized by group transfer polymerization. Different ratios of the PMMA block to the fluorinated block have been prepared. It was found that all polymers are surface active. Critical micelle concentrations are not dependent on the fluorinated block length. Critical surface tensions, extrapolated from Zisman plots and the dispersion force component of the surface energies extrapolated from Girifalco-Good-Fowkes-Young plots were decreasing with increasing length of the fluorinated block.     

Investigation of isothermal bulk polymerization ofo-alkyaryl methacrylates by DSC

The kinetics of the AIBN-initiated free radical bulk polymerization of fiveo-alkylphenyl methacrylates was studied by means of DSC in the temperature range 353–373 K, and the enthalpy of polymerization, the overall reaction rate constant and the activation energy were determined. The results were compared with those published recently on correspondingp-alkylaryl methacrylates. All measured reaction rate constants were found to increase with increasing temperature and to decrease with increasingo-alkyl substituent mass and size. It was shown thato-substituents influence the rates of polymerization to a greater extent thanp-substituents. At about 373 K, all differences in rate, most probably resulting from steric hindrance caused by the alkyl groups, disappear in both series, a phenomenon earlier observed for dimethyl phenyl methacrylates.This work was supported by the Ministry of Science of the Republic of Serbia.     

Stereospecific polymerization of methacrylates by metallocene and related catalysts

Stereospecific—isospecific, syndiospecific, and diastereospecific—polymerizations of methacrylates using group 4 metallocene and related catalysts produce polymethacrylates with controlled stereo‐microstructures. The versatility and stereospecificity of these cat‐ alysts for methyl methacrylate polymerization were demonstrated not only in solution‐phase polymerization, but also in polymerizations on silica surfaces and inside silicate nanogalleries. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3395–3403, 2004     

二元自缩合乙烯基聚合反应体系的统计热力学

应用统计力学原理对二元自缩合乙烯基聚合反应体系(由单体和引发单体组成)的统计热力学特征予以研究.首先从两种不同的角度给出与聚合反应相应的配分函数,据此得到反应体系的平衡自由能、质量作用定律以及超支化高分子的数量分布函数,进而计算了体系的比热和等温压缩系数等热力学量.进一步研究了超支化高分子的空间尺度,给出反应体系k次均方回转半径的递推公式,计算了各种不同溶剂条件下的均方回转半径,指出引发单体分数、反应程度和溶剂效应对超支化高分子空间尺度的影响.     

Reactivity of methacrylates in insertion polymerization

Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O = κ(2)-(P,O)-2-(2-MeOC(6)H(4))(2)PC(6)H(4)SO(3))) affords homopolyethylene free of any methyl methacrylate (MMA)-derived units, even in the presence of substantial concentrations of MMA. In stoichiometric studies, reactive {(P^O)Pd(Me)L} fragments generated by halide abstraction from [({(P^O)Pd(Me)Cl}μ-Na)(2)] insert MMA in a 1,2- as well as 2,1-mode. The 1,2-insertion product forms a stable five-membered chelate by coordination of the carbonyl group. Thermodynamic parameters for MMA insertion are ΔH(++) = 69.0(3.1) kJ mol(-1) and ΔS(++) = -103(10) J mol(-1) K(-1) (total average for 1,2- and 2,1-insertion), in comparison to ΔH(++) = 48.5(3.0) kJ mol(-1) and ΔS(++) = -138(7) J mol(-1) K(-1) for methyl acrylate (MA) insertion. These data agree with an observed at least 10(2)-fold preference for MA incorporation vs MMA incorporation (not detected) under polymerization conditions. Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents. Post-polymerization modification of the latter was exemplified by free-radical thiol addition and by cross-metathesis.     

Anionic polymerization of fluorine-substituted phenyl methacrylates

Synthesis and anionic polymerization of the fluorine-substituted phenyl methacrylates are herein reported.A series of mono-,di-,and multi-substituted fluorophenyl methacrylates H2C=C(CH3)C(O)OC6H4F-4(M1a),H2C=C(CH3)C(O)OC6H4F-3(M1b),H2C=C(CH3)C(O)OC6H3F2-2,4(M2),H2C=C(CH3)C(O)OC6H2F3-2,3,4(M3),H2C=C(CH3)C(O)OC6HF4-2,3,5,6(M4),and H2C=C(CH3)C(O)OC6F5(M5)were synthesized and characterized.Initially,the polymerization was carried out on the monomer M1a by using n Bu Li,t Bu Li,and KH as the respective catalysts;this approach produced the polymers in yields of12%–50%,but with lower molecular weights.Similar results were obtained by using t Bu Li for catalytically polymerizing the other five monomers.By introducing a co-catalyst Me Al(BHT)2,the catalysts Na H,Li H,and t Bu OLi each were tested to polymerize M1a,which gave the polymers in very low yields(3%–7%).Polymer yields of 13%–27%were obtained by each of the catalysts Li Al H4,n Bu Li,Ph Li,and t Bu Li in connection with Me Al(BHT)2,but a better yield(61%)was achieved with KH/Me Al(BHT)2.The KH/Me Al(BHT)2 catalyst system was further employed to polymerize M1b and M2,which afforded respective polymer yields of 12%–63%and 10%–53%,depending on the molar ratios of KH:Me Al(BHT)2 as well as on the monomer concentrations.All of the polymers produced were syndiotactically rich in structure,as indicated by either 1H or 19F NMR data.The polymerization mechanism by the combined catalyst system is proposed.     

Control of a living radical polymerization of methacrylates by light

On-off: A living radical polymerization procedure, which utilizes ppm levels of an iridium-based photoredox catalyst, affords control over chain growth through mediation by visible light (see scheme; P(n) =polymer chain, X=halogen, M=monomer). This process can be activated and deactivated by light, enables control over the molecular weight and molecular weight distributions, and tolerates different functional groups.     

The discovery and commercialization of group transfer polymerization

Group transfer polymerization (GTP) is a fundamentally new method for polymerization of acrylic monomers, discovered at DuPont over 20 years ago. It allows one to make block and other specialized polymer chain architecture at above ambient temperature. The method uses silyl ketene acetals as initiators and requires a nucleophilic catalyst. DuPont uses the process to make dispersing agents for pigmented inks and automobile finishes. The development of GTP from its discovery to introduction of commercial products is presented. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2855–2860, 2000