Cyclopentadiene, cationic polymerization

Cationic polymerization of thiiranes CMT (9-(thiiran-2-ylmethyl)-9//-carbazole) 217 and PMT (10-(thiiran-2ylmethyl)-1077-phenothiazine) 218 was studied by a Lithuanian group <2002JPH63>. Initiators were di-(/-butylphenyl)iodonium tetrafluoroborate (BPIT), diphenyliodonium tetrafluoroborate, cyclopropyldiphenylsulfonium tetrafluoroborate, and ( 7 -2,4-cyclopentadien-1 -yl) [1,2,3,4,5,6- )-( 1 -methylethyl)benzene]-iron(- -)-hexafluorophosphate(—1). The influences of temperature and initiator concentration on the polymerization rate and the conversion limit were determined. The values of initiator exponent and activation energy for the photopolymerization of CMT and PMT initiated with BPIT in 1,2-dichloroethane was established. 

Polymerization Catalysed by Acids and Bases. Carbonium ions and carbanions respectively are carriers of the chain transfer in cationic and anionic polymerizations respectively. Ionic polymerization mechanism was exploited for the synthesis of polymeric stabilizers in comparison with the free-radical polymerization only exceptionally. The cationic process was used for the synthesis of copolymers of 2,6-di-tert-butyl-4-vinylphenol with cyclopentadiene and/or for terpolymers with cyclopentadiene and isobutylene [109]. System SnCWEtsAlCla was used as an initiator. Poly(lO-vinylphenothiazin) was prepared by means of catalysis with titanium chlorides [110]. Polymers of 4-[a-(2-hydroxy-3,5-dimethylphenyl)ethyl]-vinylbenzene [111] and 3-allyl-2-hydroxyacetophenone [112] were also prepared under conditions of cationic polymerization. 

A series of low-molecular-weight resins from natural products or industrial side products is known as cumarone-indene-like resins, since these resins have similar physical properties to the actual cumarone-indene resins. For example, cyclopentadiene from the petroleum process dimerizes easily to what is known as dicyclopentadiene (lUPAC 4,7-methylene-4,7,8,9-tetrahydroindene). Dicyclopentadiene cationically polymerizes to polymers with different monomeric units. The commercially available polymers soften at 100-120°C and become insoluble as surface films on further heating. 

When a difunctional trityl ion salt was used to initiate the living cationic polymerization of cyclopentadiene, block copolymers were formed through charge neutralization with living anionic ct-MS. By varying the functionality of the a-MS polymers, controlled block sequences were generated in the copolymers. 

The cationic polymerization of cyclopentadiene is catalyzed by tin-tetrachloride/ trichloroacetic acid/boron trifluoride [402-407]. The polymers that are partially insoluble in hydrocarbons feature 40 to 60% 1,2-structures next to trans-, 4 portions [Structures (60) and (61)]. With Ti(OC4H9)Cl3, soluble high-molecular-weight polycyclopentadiene is formed. Due to H-atoms in allyl and tertiary positions of the chain, the polymer is extremely sensitive to oxidation. This can be overcome by chlorination of the double bonds [408,409]. 

The cationic polymerization of 1,3-dimethylcyclopentadiene can be initiated by boron trifluoride/diethyl ether/tin(IV) chloride, titanium(IV) chloride, and triethylalumi-num/titanium(IV) chloride [410]. The poly (1,3-dimethylcyclopentadienes) that are obtained at — 78 °C are easily soluble with identical portions of 1,4 and 1,2 structures [411]. Under the same conditions, 1-methyl- and 2-methylcyclopentadienes are polymerized to powdery polymers [412]. The same applies to ally Icy clopentadiene and allylmethylcyclopentadiene. The polymerization proceeds exclusively via the C-C double bond in the cyclopentadiene ring with increasing portions of 1,4-structures in the polymers for monomers with growing steric hindrance. 

Recently, Spange et al. (19,20) have successfully achieved cationic graft polymerizations of vinyl ethers, vinyl furan, and cyclopentadiene onto silica, initiated by a stable ion pair formed from silanol and aiylmethyl halide, such as di(p-methoxy-phenyl)methyl chloride. The grafting of the polymer onto silica is proposed to take place via the propagation based on olefin insertion to a cation center being in a rapid equilibrium with the ion pair, as shown in Scheme 12.1.3. 

Pillinger, M., Goncalves, I. S., Lopes, A. D., Ferreira, R, Rocha, J., Zhang, G. F., Schafer, M., Nuyken, O. and Kuhn, F. E. Mesoporous silica grafted with multiply bonded dimolybdenum cations XAFS analysis and catalytic activity in cyclopentadiene polymerization, Phys. Chem. Chem. Phys., 2002, 4, 696-702. 

First, suitable monomers are required for radiation-induced polymerization proceeding by a cationic mechanism. Isobutylene, vinyl ethers, cyclopentadiene and p-pinene polymerize only by a cationic mechanism, whereas a-methyl styrene polymerizes by both cationic and anionic mechanisms. Second, it is necessary to use the conditions of the existence of ions M+ (M—>M+ + e) and the stabilization of secondary electrons capable of neutralizing M+. This is achieved (a) by carrying out polymerization at low temperatures when the lifetime of ions increases and the activity of free radicals drastically decrease, and (b) by using electron-accepting solvents or additives. 

K10 montmorillonites exchanged with different cations, dried at 120°C or calcined at 550°C, are used as catalysts in Diels-Alder reactions of methyl and (-)-menthyl acrylates with cyclopentadiene. In general, calcined clays give rise to better conversions and selectivities. Zr(IV) and specially Ti(IV) clays display the best catalytic activities. However, the best asymmetric induction is achieved with Cr(lll) and Ca(ll) calcined clays. Clays containing easily reducible cations behave differently due to the cyclopentadiene polymerization via radical cations. 

Except for Ce(IV)-K10 montmorillonite, this abnormal behaviour disappears when calcined clays are used as catalysts. Given that calcination eliminates internal water and, consequently, most of Bronsted acid sites [5], it can be concluded that Bronsted acidity greatly favours the polymerization of the diene. However, in the case of Ce(IV) clay there must be an additional mechanism for diene polymerization. It has been reported [6] that the formation of radical cations accelerates this iateral reaction. In fact, EPR spectra of Ce(IV)-clays in the presence of cyclopentadiene show a narrow signal at g = 2.004 0.002 which could be characteristic of organic radicals. 

Cu(ll), Fe(lll) and Ce(IV) calcined clays behave differently. When Fe(lll) or Ce(IV) clays are used as catalysts, both selectivities decrease with increasing conversions, which is particularly noticeable with Ce(IV) clay. With Cu(ll) clay the reaction stops at low conversions. This behaviour can again be attributed to the polymerization of cyclopentadiene. Given that calcination eliminates most of Brensted acid sites, a cation radical mechanism must be invoked for the extensive diene polymerization. Ce(IV), Fe(lll) and Cu(ll) are the most easily reducible cations of those used and their EPR spectra in the presence of cyclopentadiene show the above-mentioned signal of organic radicals. 

Preparations of macro-initiators or telechelic polymers by cationic methods have been executed primarily by polymerizing isobutylene in the presence of a co-initiator that also functions as a chain transfer agent. A typical reaction sequence is shown in Scheme 1, outlining the synthesis of difunctional polyisobutylene (PIB), which is then used to initiate the polymerization of a-methyl styrene (ffi-MS) to produce an A-B-A type block copolymer. By similar methods, polyisobutylenes with phenol, phenyl, cyclopentadiene, and olefin termini have been synthesized. 

In 1988 Reetz et al. introduced the concept of metal-free polymerization of acrylates, methacrylates and acrylonitrile [224,225]. Metal-free initiators are salts consisting of a carbanion (A ) having R4N as cationic counterions. They are synthesized by the reaction of neutral CH or NH-acidic compounds such as malonic acid esters, nitriles, sulfones, nitro-alkanes, cyclopentadiene, fluorene derivates, carbazoles and succinimide. Water is removed azeotropically using toluene. 

Kinetic investigation on the polymerization of cyclopentadiene in the presence of cationic initiators such as BF3, TiCl4, or TiCl3 (0 -Bu) pointed out a correlation of the reaction rate with monomer and initiator concentrations [187]. The initial rate was... 

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