Catalysis, cationic

Chemical Modification of Polystyrenes in the Presence of Cationic Catalysis and Their Industrial Applications... 

When the physical modification method is used, PS is modified by mechanical stirring with various synthetic rubbers such as polybutadiene, polybutadiene styrene, polyisopropene, polychloropropene, polybutadiene styrene-acrylonitrile copolymers. In the chemical modification, PS is modified with polyfunctional modificators in the presence of cationic catalysis. 

The chemical modification of PS with epichlorohydrin (EC), maleic anhydride (MA), acetic anhydride (AA), butadiene, and isoprene in the presence of cationic catalysis such as AICI3, FeCU, BF3 0(C2H5)2, ZnCb, TiCL, and SnCU, have been extensively studied under various conditions for the last 15 years. We have also studied their kinetics, physico-mechanical, thermal, and dielec-... 

In the chemical modification of PS with MA, AA, EC, butadiene, and isoprene using cationic catalysis caused either destruction of macromolecules or the binding of functional groups to the aromatic ring. 

In general, physico-mechanical properties of polymers depend on the molecular weight. However, the physico-mechanical properties of PSs decreased in the presence of cationic catalysis, but increased in the case of the binding of functional groups to the aromatic ring in spite of the destruction of PS. Therefore, new properties such as adhesion and photosensitive capability increase... 

When the molecular weight of PS was decreased from 5.0 x 10 to (3.0-4.05) x 10, the abovementioned properties were also decreased in the presence of cationic catalysis after the destruction of PS. These predicted properties are related to the nature and the quantity of functional groups. 

Initially the LP-DE effect was ascribed to the high internal pressure generated by the solubilization of the salt in diethyl ether [34]. Today the acceleration is explained in terms of Lewis-acid catalysis by the lithium cation [35]. The contribution of both factors (internal pressure and lithium cation catalysis) has also been invoked [36]. 

Isobutene is one of the very small number of aliphatic hydrocarbons which form linear high polymers by cationic catalysis (see Section 5). The reason for this is that only in these few among the lower aliphatic olefins is there found the right balance of those factors which determine the path of a cationic polymerisation. For the formation of linear high polymers it is necessary that the propagation reaction should be much faster than all alternative reactions of the growing end of the chain and for any appreciable numbers of chains to be formed at all, the initiation must be fast. ... 

The aliphatic mono-olefins present a particularly complicated picture at first sight. Only a few of them will give high polymers by cationic catalysis most of these are either 1,1-disubstituted ethylenes, or ethylenes with a single branched substituent, such as 3-methylbutene-1 and vinylcyclohexane. The reasons why ethylene, propene, and the n-butenes do not give high polymers have been set out in detail [71]. Briefly, the ions derivable directly from all of these are either primary or secondary, e.g.,... 

Special interest attaches to the cyclic aliphatic hydrocarbons. Cyclopropane can be converted to oligomers by cationic catalysis [75, 76], and these appear to be essentially linear but whether they are really different from the polypropenes formed under the same conditions from propene is not yet settled. The initiation most probably involves formation of a non-classical cyclopropyl ion [77], as in alkylations with cyclopropane [78],... 

Improvements Relating to Polymeric Substances (graft polymers by cationic catalysis), P.H. Plesch, inventor National Research Development Corporation, assignee BP 31652,1955. 

PIB (structure 5.57) was initially synthesized in the 1920s. It is one of the few examples of the use of cationic catalysis to produce commercial-scale polymers. Low-molecular weight (about 5000 Da) PIB can be produced at room temperature, but large chains (over 1,000,000 Da) are made at low temperatures where transfer reactions are suppressed. 

Finally, the absence of catalysis by such highly charged ions as Co(NH3)6+3 indicates that the cation catalysis noted here is due to an interaction of a specific short-range character—that is, a chelate—and not to a purely electrostatic interaction. 

Tsou, Magee and Malatesta (39) showed the effect of catalyst ratios on steric control m the polymerization of styrene with alkyllithium and titanium tetrachloride. These authors have shown that the isotactic polymer was produced when the butyllithium to titanium ratio was kept within the limits of 3.0 to 1.75. Outside of this critical range, amorphous polymers were produced. In the discussion of this paper, Friedlander (40) pointed out the cationic nature of the low-lithium-to-titanium-ratio-catalysts which also produced considerable rearrangement of the phenyl groups. Above 2.70 lithium to titanium ratio, an anionic type polymerization set in, which produced atactic polymer. At low ratios cationic catalysis also produced atactic polymer. Tsou and co-workers concluded that crystallinity of the catalyst is not important for steric order in the polymer. 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

The reaction engineering aspects of these polymerizations are similar. Excellent heat transfer makes them suitable for vinyl addition polymerizations. Free radical catalysis is mostly used, but cationic catalysis is used for non-aqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads, is directly suitable for some applications (e.g., paints, gel-permeation chromatography beads, expanded polystyrene). Most of these polymerizations are run in the batch mode, but continuous emulsion polymerization is common. 

The above catalysts are believed to operate by a coordinated cationic mechanism. A general discussion of coordinated cationic catalysis is given in section V/5/c. 

Figure 2. Copolymerization of styrene and methyl methacrylate A Anionic catalysis B Radical catalysis C Cationic catalysis 0 Radical catalyst, this work O AlEti.sCh.s, this work Radical catalyst plus AlEti.sCh.s...

Thus, in Table 7.2 the polymerisation rate constants of PO and EO in anionic and in cationic catalysis are compared. 

Table 7.2 The comparative rate constants of PO and EO polymerisation in anionic and cationic catalysis [54] ...

Thus, PO is approximately 7500-8000 times more reactive in cationic catalysis than in anionic catalysis, at 30 °C and around 20-25 times more reactive in cationic catalysis, at 30 °C, than PO anionic polymerisation at 120 °C. It was observed that in cationic polymerisation, EO is around 50 times less reactive than PO, at 30 °C. However, in anionic catalysis there is a reversed order EO is around 2-3 times more reactive than PO. 

This very high PO polymerisation rate in cationic catalysis, at lower temperatures, is extremely attractive from the technological point of view. 

For low MW oligomers, (e.g., polyether triols initiated by glycerol with a MW of 600-1000 daltons), the cationic catalysis is used successfully especially in the synthesis of the starters/ precursors for coordinative polymerisation with dimetallic catalysts (DMC) (see Chapter 5). 

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