Stereospecific polymerisation

Another important use of BCl is as a Ftiedel-Crafts catalyst ia various polymerisation, alkylation, and acylation reactions, and ia other organic syntheses (see Friedel-Crafts reaction). Examples include conversion of cyclophosphasenes to polymers (81,82) polymerisation of olefins such as ethylene (75,83—88) graft polymerisation of vinyl chloride and isobutylene (89) stereospecific polymerisation of propylene (90) copolymerisation of isobutylene and styrene (91,92), and other unsaturated aromatics with maleic anhydride (93) polymerisation of norhornene (94), butadiene (95) preparation of electrically conducting epoxy resins (96), and polymers containing B and N (97) and selective demethylation of methoxy groups ortho to OH groups (98). 

In general, a catalytic reaction may be named by adding the adjective catalytic to the standard chemical term for the reaction, for example, catalytic hydrogenation (or, if clarity demands, heterogeneous catalytic hydrogenation), catalytic hydrodesulphurisation, catalytic oxidative dehydrogenation, catalytic stereospecific polymerisation. 

Corradini, P., Barone, V., Fusco, R. and Guerra, G. (1983) A possible model of catalytic sites for the stereospecific polymerisation of alpha-olefins Gazzeta Chimica Italiana, 113, 601-607. 

Recent years have seen the implementation of many various elementorganic compounds in economy. Their applications have proved to be extraordinarily wide for stereospecific polymerisation of olefines, for stabilisation of polymer and lubricant materials, as antiknock additives and additives for engine fuels, as antiseptics, pesticides and so on. 

Andreussi, P., Lauretti, E. and Miani, B., in Abstracts of the IUPAC International Symposium on Stereospecific Polymerisation, STEPOL 94, Milan, Italy, 1994, p. 125. 

During the last decade, a variety of new catalysts have been presented for the stereospecific polymerisation of a-olefins, based on non-bridged metallocene or stereorigid ansa-metallocene as the procatalyst and a methylaluminoxane activator [29,30,37,105-107,112-114,116-135], Apart from isotactic [118,119,124, 131,132] and syndiotactic [23,118,124,133] polypropylenes and other poly(a-olefin)s [121], hemiisotactic [112,121,124], isoblock [131,132,134], syndioiso-block (stereocopolymer) [127], stereoblock isotactic [135] and stereoblock isotactic atactic [116,128,129] polypropylenes have been obtained using these new catalysts. 

The same conclusion as in the case of propylene homopolymerisation has been drawn considering IR [396] and NMR [389,395] spectra of ethylene/propylene copolymers obtained with vanadium-based syndiospecific catalysts. The type of propylene insertion depends on the kind of last inserted monomer unit secondary insertion [scheme (40)] occurs more frequently when the last monomeric unit of the growing chain is propylene, while primary propylene insertion [scheme (39)] is more frequent when the last monomeric unit of the growing chain is ethylene [2]. The above explains the microstructure of ethylene/propylene copolymers obtained with vanadium-based Ziegler-Natta catalysts. These copolymers contain both m and r diads when the sequence of propylene units is interrupted by isolated ethylene units i.e. a propylene insertion after an ethylene insertion is substantially non-stereospecific [327,390,397], The existence of a steric interaction between the incoming monomer molecule and the last added monomer unit is also confirmed by the fact that the propagation rate for the secondary insertion of propylene in syndiospecific polymerisation is lower than for primary insertion in non-stereospecific polymerisation [398],... 

Activities of a-olefins in insertion polymerisation with coordination catalysts are generally related to the monomer structure both electronic and steric factors influence the activity of a-olefins in stereospecific polymerisation, but the steric factor primarily influences the rate of polymerisation, which has been especially shown for isospecific polymerisation with heterogeneous catalysts [46, 250],... 

Give the structure and stereochemical designation of all possible poly(a-olefin)s that could, in principle, be obtained by stereospecific polymerisation. Are they all likely to be obtainable in practice (with heterogeneous and homogeneous Ziegler-Natta catalysts) ... 

When a-cyclodextrin-supported Cp TiCl3 is used as the catalyst precursor, [AI(Mc)0]x should be used as an activator in order to obtain a suitable catalyst for the stereospecific polymerisation of styrene (polymerisation syndiospecifi-city ca 93%) with AlMe3 as the activator, a-cyclodextrin-supported Cp TiCl3 had less activity for styrene polymerisation even if a-cyclodextrin was treated with [AI(Mc)0]x prior to supporting Cp TiCl3 [103]. 

Dias, M. L. and Giarrusso, A., Stereospecific Polymerisation of Styrene Monomers with Ni Catalysts, in Proceedings of International Symposium on Synthetic, Structural and Industrial Aspects of Stereospecific Polymerisation, Milan, Italy, 1994, Abstracts, P-71. 

However, no method of polymerisation known before 1954 allowed one to obtain polymers with a high regularity of structure from the most common conjugated dienes. A true breakthrough in the development of conjugated diene rubbers took place after the discovery of stereospecific polymerisation with transition metal-based coordination catalysts. From the late 1950s, a rapid development of industrial production of solution types of polybutadiene by means of polymerisation with Ziegler-Natta catalysts was observed. 

The enantiomorphic catalyst sites control mechanism was found to operate in the stereospecific polymerisation of tiiranes. Sigwalt et al. [79,153] found that... 

A103. P. Sigivalt, Study of the Reaction Mechanism of Homogeneous Phase Stereospecific Polymerisations. CNRS, Paris, 1971. 

The understanding of direct-initation mechanisms. In this context, tire use of metal salts of strong acids has opened a new area of fundamental studies. Indeed, we believe that the chemical insertion of the olefin between the metal cation and the anion following its adsorption on the salt surface closely resembles recent mechanistic proposals put forward by Zambelli and collaborators to rationalise initiation in stereospecific polymerisation (propene with vanadium-based catalysts). We are inclined to conclude that the cationic nature of stereospecific polymerisations of the Ziegler-Natta type is supported by our findings , viz. electrophilic attack by... 

A167. G. Natta and F. Danusso, Stereoregular Polymers and Stereospecific Polymerisation. Pergamon, Oxford, 1967. 871 pp. This contains 170 papers by the Natta school (1954—1959), some unabridged and some as abstracts. 

Elastomer Stereospecific Polymerisation, Adv. in Chem. Series, No. 52, Amer. Chem. Soc., 1966 (includes transition-metal systems). 

Despite tremendous success in the development of scientific fundamentals for stereospecific polymerisation and the commercial production of stereoregular polymers, three key theoretical problems are still under discussion a) the structure of AC b) the mechanism of initiation and chain growth processes and c) the reasons and factors responsible for the stereoregular products of a-olefins and 1,3- diene polymerisation in the presence of Ziegler-Natta catalysts. 

Stereospecific polymerisation of isoprene (2-methyl-butadiene-1,3) in the presence of cis-regulating catalytic Ziegler-Natta systems can be described by the following... 

Figure 3.9 Stereospecific polymerisation of isoprene (2-methyl-butadiene-l,3). The Russian industry has implemented technologies of c/s-l,4-polyisoprene synthesis with Ti-Al Ziegler-Natta catalysts (synthetic c/s-isoprene rubber SKI-3) and neodymium salts-based lanthanide catalysts SKI-5 grade synthetic rubber (TU 2294-051-16810126-96). SKI-3 rubbers contain up to 93 1% of as-1,4 links, while their content in SKI-5 grade rubber is 96 1%...

The AC of stereospecific polymerisation are located on defects of the catalyst s crystalline structure hence, the change of its dispersity (and therefore its specific surface) results in a respective change of the process rate. 

Modified method of the diatomic complexes in molecules , which provides a satisfactory prediction of the valent-bound atoms interaction at the stages of chemical adsorption of catalytic system components and monomer molecules, reactions of initiation and chain growth in a-olefins, and 1,3-dienes stereospecific polymerisation reactions. 

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