Titanium tetrachloride polymerization initiator

Plesh (188) treated polyvinyl chloride and vinyl chloride-vinylidene chloride copolymers with aluminium chloride or titanium tetrachloride for initiating the carbonium polymerization of styrene. As expected (218)... 

THE can form potentially explosive peroxides upon long exposure to air. THE may react violently with strong oxidizers and reacts vigorously with bromine and titanium tetrachloride. Polymerization can occur in the presence of cationic initiators such as certain Lewis acids and strong protic acids. 

Blin et al. determined the transfer and termination constants for the cationic polymerization of 1-and 2-vinylnaphthalenes and 3-vinylphenanthrene in methylene chloride and titanium tetrachloride as initiator [340]. For each monomer these constants increased with increasing temperature. Their values were significantly larger than those of styrene at the same conditions. This is supposed to be a consequence of the existence of highly reactive aromatic sites, which permit Friedel-Crafts attacks by the growing chain. 

Cationic polymerization with Lewis acids yields resinous homopolymers containing cycHc stmctures and reduced unsaturation (58—60). Polymerization with triethyl aluminum and titanium tetrachloride gave a product thought to have a cycHc ladder stmcture (61). Anionic polymeriza tion with lithium metal initiators gave a low yield of a mbbery product. The material had good freeze resistance compared with conventional polychloroprene (62). 

Note added in proof. Marek and Chmelir [40b, c] found that the polymerization of isobutene in heptane by aluminium bromide is greatly accelerated by addition of titanium tetrachloride. They suggested that the polymerization by aluminium bromide only is initiated by a cation such as AlBr2+ which adds to the isobutene and which is formed by self-dissociation of the catalyst. The enhancement of the rate by titanium tetrachloride they attribute to an increase in the concentration of ions by the reaction... 

The action of water in the titanium tetrachloride catalyzed polymerization is paradoxical, since water at —60 to —80° was present only in the solid phase its solubility in hexane at these temperatures is in the order of 10-10 moles per liter (Plesch et al., 83). It was found to be essential that the water be present as an extremely fine dispersion such as might result from the rapid bubbling of moist air through the liquid at the low temperature. Addition of liquid water which formed lumps of ice in the reaction mixture did not initiate polymerization. It may be concluded that a fine dispersion is necessary in order that reaction with titanium tetrachloride can occur and a chain reaction is initiated ... 

It can be seen that both the solvent and the catalyst affect the structure of the polymer produced. For example, the structure of the polyisoprene differs strongly with the alkali metal, even when used in the same solvent medium. Experiments with a typical organometallic complex catalyst, consisting of trialkyl-aluminum and titanium tetrachloride, show that the same initiator can lead to quite different structures in the products of polymerization of isoprene and of butadiene. 

Several catalysts and initiator systems have been tested for the polymerization of GlcAnBzl3, including the following Lewis acids boron trifluoride and its etherate, phosphorus pentafluoride, titanium tetrachloride, and antimony pentachloride and pentafluoride. Several cationic initiators have also been used, including (triphenylmethyl) antimony hexachloride, 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl hexa-fluorophosphate, acetyl hexafluorophosphate, pentamethylbenzyl hexa-fluorophosphate (most of which were generated in situ), and triethyl-... 

Another type of ionic species was proposed by Uelzmann (92). Uelzmann suggested that from trialkylaluminum and titanium tetrachloride, TiClg)+ and (R3A1C1) caused cationic initiation on the titanium followed by an anionic propagation on the aluminum ion. Bestian and co-workers (70) proposed similar cationic intermediates which propagate by anionic shifts. These steps are the opposite of the anionic initiation and cationic propagation proposed in this review for the butene-1 polymerization. 

Just about the same time Japanese workers (107) polymerized this dialdehyde with boron trifluoride etherate, p-toluene sulfonic acid, and titanium tetrachloride as well as with aluminum triethyl-water catalyst systems. Completely insoluble products were obtained with the cationic catalysts, whereas partially soluble materials were isolated with the latter initiator. On the basis of infrared evidence, the above structure was assigned to the soluble product. In spite of the fact that ether linkages were found by infrared analysis in the cationic product, the authors concluded that its structure was different from that of the soluble polymer obtained with organometallic catalyst. The structure of the soluble fraction was assumed to be ... 

Even when conditions are scrupulously controlled, the kinetics of cationic polymerization are rarely simple. Water is highly reactive towards organic cations and if present as initiator, any excess will terminate polymer chains. Excess water may also destroy the coinitiator in some cases, or compete successfully with monomer for the initiator-coinitiator complex (see later). The kinetic influence of water is thus complicated. In some systems, the initial rate of polymerization increases with concentration of water at low concentrations and becomes independent as this concentration increases. Such behavior has been reported for the polymerization of isobutene in dichloromethane initiated by titanium tetrachloride and water [21]. In other systems, the initial rate of polymerization may rise to a maximum and then decline with increasing concentrations of water. Such behavior has been observed in the SnCl4/H20 initiated polymerization of styrene in carbon tetrachloride [22]. 

Moreover, the absence of unsaturations in the resulting polymers clearly indicated the absence of chain transfer reactions. Similar living polymerization characteristics were reported for cationic isobutene polymerizations initiated with cumyl methyl ethers (Scheme 8.6) with BCI3 as activator [29, 30] as well as with cumyl ethers and cumyl esters as initiators together with titanium tetrachloride as activator [31],... 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

Although the exact mechanism of the polymerization of olefins by Ziegler-Natta catalysis is not delineated with the precision that would satisfy every one, it is possible to write a reasonable mechanism [1,2]. The first of these is a monometallic mechanism. The following mechanism is for a TiCl3/AlEt3 combination. We have seen above that titanium tetrachloride has been initially used in the polymerization of ethylene. It has been subsequently found that TiCls is better than TiCLj. 

---