Carbon dioxide Cationic polymerization

Mechanisms depending on carbanionic propagating centers for these polymerizations are indicated by various pieces of evidence (1) the nature of the catalysts which are effective, (2) the intense colors that often develop during polymerization, (3) the prompt cessation of sodium-catalyzed polymerization upon the introduction of carbon dioxide and the failure of -butylcatechol to cause inhibition, (4) the conversion of triphenylmethane to triphenylmethylsodium in the zone of polymerization of isoprene under the influence of metallic sodium, (5) the structures of the diene polymers obtained (see Chap. VI), which differ. both from the radical and the cationic polymers, and (6)... 

ROMP reactions have been extensively carried out in water, and the first examples in liquid and scC02 [15] and ionic liquids [16] have been demonstrated. ROMP of norbomene and cyclooctene in scC02 exhibit a similar efficiency to that of chlorinated organic solvents. However, the carbon dioxide based system allows simple and highly convenient work-up of the polymer products. In [bdmim][PF6] (bdmim = 1-butyl-2,3-dimethylimidazolium cation), norbornene has been polymerized using a cationic catalyst as shown in Scheme 10.15. 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

Several fluorinated monomers have been polymerized via homogeneous cationic polymerization in compressed carbon dioxide. For example, vinyl ethers with fluorinated side chains were polymerized in SCCO2 at 40 °C using adventitious water initiation with ethylaluminum dichloride as the Lewis acid coin-... 

Polymerizations in Dense Carbon Dioxide 317 4.S.3.2 Cationic Chain Growth... 

Nearly 500 million pounds of butyl rubber are produced annually in the USA via cationic copolymerization of isobutylene and small amounts of isoprene [134]. The industrial methods for polymerizing isobutylene are plagued by two major drawbacks - the use of toxic chlorinated hydrocarbon solvents and the need to carry out these polymerizations at very low temperatures. Each of these drawbacks may be circumvented through the use of carbon dioxide as the continuous phase for polymerization. 

Dense carbon dioxide represents an excellent alternative reaction medium for a variety of polymerization processes. Numerous studies have confirmed that CO2 is a potential solvent for many chain growth polymerization methods, including free-radical, cationic, and ring-opening metathesis polymerizations. Carbon dioxide has also been demonstrated to be an effective solvent for step-growth polymerization techniques. Advances in the design and synthesis of surfactants for use in CO2 will allow compressed CO2 to be utilized for a wide variety of polymerization systems. These advances may enable carbon dioxide to replace hazardous VOCs and CFCs in many industrial applications, making CO2 an enviromentally responsible solvent of choice for the polymer industry. 

PBOCST is readily synthesized from the polymerization of r-hutoxycarhonyl oxystyrene via radical or cationic polymerization in liquid sulfur dioxide or alternatively by reacting poly(hydroxystyrene) with di-tert-h xty dicarbonate in the presence of a base PBOCST polymers with narrow dispersity have been prepared by living anionic polymerization of 5-tert-butyl(dimethyl)silyloxystyr-ene), followed by desilylation with HCl to form PHOST and protection with di-tert-butyl carbonate PBOCST is very transparent around the 250-nm region of the spectrum (absorbance <0.1/ p,m), thus making it an ideal candidate for DUV 248-nm lithography. 

Cationic Polymeric Hydrogels Responsive to Carbon Dioxide... 

Acrylamide monomer is a white crystal, available commercially as a 50 wt % aqueous solution. Acrylamide monomer can be polymerized to a very-high-molecular-weight (lO -lO g/mole) homopolymer, copolymer, or terpolymer. Polyacrylamide (PAM) is a nonionic polymer. The anionic polyacrylamide species can be obtained from the hydrolysis of the amide (—CONH ) functional group of the homopolymer, or from the copolymerization of acrylamide with an anionic monomer, such as acrylic acid (AA) or 2-acrylamino 2-methyl propane sulfonic acid (AMPS). Acrylamide can be copolymerized with a cationic monomer, such as dimethyl diallylammonium chloride (DMDAAC) or acryloyloxyethyl trimethyl ammonium chloride (AETAC), to form the cationic acrylamide polymer. Acrylamide can simultaneously react with anionic and cationic monomers to form a polyampholyte. The acrylamide homopolymer, copolymers, and terpolymers are synthesized (1-20) by free radicals via solution or emulsion or other polymerization methods. F. A. Adamsky and E. J. Beckman (21) reported the inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. The product classes of acrylamide polymers include liquid, dry, and emulsion. 

Cationic polymerizations are normally conducted at low temperatures to (-10 to -100 °C) in chlorinated hydrocarbon solvents that have sufficient polarity to promote active ion generation. Recently carbocationic polymerization of isobutylene in supercritical carbon dioxide has been reported. It has been demonstrated that at 32.5 C and 120 bar, using an initiator system of 2-chloro-2,4,4 trimethyl pentane / SnCU or TiCU, isobutylene could be polymerized with 30 % conversion and result in a polymer with Mn = 2000 and PDI = 2... 

Some preliminary experiments on cationic dispersion polymerization of isobutylene in supercritical carbon dioxide in the presence of polymeric surfactants has also been reported [32]. 

Ariga, T., Takata, T., Endo, T., 1997. Cationic ring-opening polymerization of cyclic carbonates with alkyl halides to yield polycarbonate without the ether unit by suppression of elimination of carbon dioxide 1. Macromolecules 30, 737—744. 

The photocatalytic activity of Ti02-montmorillonite in the reduction of with oxidation of triethanolamine (261) and the oxidation of several aliphatic alcohols have also been reported (259). The photodegradation of dichloro-methane, which is not readily degraded or hydrolyzed in an aquatic environment, to hydrochloric acid and carbon dioxide using titanium-exchanged montmorillonite, titania-pillared montmorillonite, and titanium-aluminum polymeric cation pillared montmorillonite has been reported (261). 

Polycarbonates have attracted attention in recent years because of their potential use in biomedical applications based on their biodegradability, biocompatibility, low toxicity and good mechanical properties [67]. These polymers can be prepared by the ROP of cyclic carbonate monomers by anionic, cationic, and coordination catalysts. However, lipase-catalyzed polymerization seems to be a feasible alternative to prepare polycarbonates as chemical methods often suffer from partial elimination of carbon dioxide (resulting in ether linkages), require extremely pure monomers and anhydrous conditions. 

Cationic polymerization of MVK is certainly not the method of choice. However, if boron trifluoride etherate was added to a monomer-carbon dioxide mixture in petroleum ether polymerization was observed [298]. Acid-catalyzed polarography of MVK in methanol is also considered to be a cationic polymerization. For the polymer an alternating ketone-ether copolymer structure was suggested [299,300]. The following reaction mechanism is... 

In Chapter 18, Matsuyama and Teramoto report the preparation of new types of cation-exchange membranes by grafting acrylic acid and methacrylic acid to substrates, such as microporous polyethylene, polytetrafluoroethylene, and poly[l-(trimethylsilyl)-l-propyne], by use of a plasma graft polymerization technique. Various monoprotonated amines are immobilized by electrostatic forces in the ion-exchange membranes and used as carriers for carbon dioxide. With these membrane systems carbon dioxide/nitrogen selectivities of greater than 4700 are obtained with high carbon dioxide flux. 

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