High molecular weight 1-alkenes

Liquid-Phase Oxidation of High Molecular Weight 1-Alkenes... 

It was found that if the content of the hydrocarbons extracted by supercritical 2-methyl-butane were analyzed, no hydrocarbons other than C12 alkene (two isomers) were detected. It is clear that C12 alkene, derived from oligomerization reactions, deposited onto catalytic sites and deactivated the catalyst. More specifically, high molecular weight alkenes such as C12, which have high electron density, might combine strongly with Lewis acid sites inside... 

Other Systems. - The commercial application of Rh hydroformylation catalysts is currently limited to alkenes of relatively low molecular weights where the product can be removed by distillation. Similar constraints apply to SLPC systems and for chemically immobilized systems low activites can be expected for high molecular weight alkenes because of problems connected with reactant diffusion. A number of publications have appeared over the past five years which address this problem. 

In the second step, reaction 7.3.3.4, the alkenes undergo cross-metathesis and generate ethylene and/or a mixture of alkenes of higher molecular weight. The precatalyst used here is 7.35. Finally, in reaction 7.3.3.5, the high-molecular-weight alkene(s) and/or ethylene are hydrogenated. The precatalyst here is the same iridium pincer complex of reaction 7.3.3.3. 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

In their polymerization, many individual alkene molecules combine to give a high molecular weight product Among the methods for alkene polymerization cationic polymerization coordination polymerization and free radical polymerization are the most important An example of cationic polymerization is... 

Few aHyl monomers have been polymerized to useful, weH-characterized products of high molecular weight by ionic methods, eg, by Lewis acid or base catalysts. Polymerization of the 1-alkenes by Ziegler catalysts is an exception. However, addition of acidic substances, at room temperature or upon heating, often gives viscous liquid low mol wt polymers, frequently along with by-products of uncertain stmcture. 

Several reports in which NHC-Pd complexes have been employed to catalyse the copolymerisation of alkenes with CO have appeared over the years. Herrmann and co-workers reported that the chelating dicarbene complex 38 (Fig. 4.14) is active for CO/ethylene [43], The highest TON [(mol ethylene + mol CO) mol Pd ] was 3 075 after a 4 h run. The modest TONs coupled with a very high molecular weight copolymer led the authors to conclude that only a small fraction of the pre-catalyst goes on to form an active species. Low molecular weight (M = 3 790) CO/norbomene copolymer resulted when complex 39 (Fig. 4.14) was tested by Chen and Lin [44]. The catalyst displayed only a very low activity, yielding 330 turnovers after 3 days. 

Hydroarylation of alkenes is applied to achieve step-growth co-polymerization of aromatic ketones and ct,c< -dienes such as 3,3,6,6-tetramethyl-3,6-disila-l,7-octadiene and 1,3-divinyltetramethyldisiloxane. Co-polymerization of acetophenone and 3,3,6,6-tetramethyl-3,6-disila-l,7-octadiene is catalyzed by Ru species which has been previously activated by treatment with styrene, and a significantly high molecular weight co-polymer, co-poly(3,3,6,6-tetra-methyl-3,6-disila-l,8-octanylene/2-acetyl-l,3-phenylene), is obtained (Scheme 21 ).166... 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

Despite this setback, this catalyst system could also be used for the hydroformylation of ethylene and indeed the long-term stability of the catalyst was found to be better than that of the catalyst derived from triphenylphosphine. Hence, this catalyst system allowed the hydroformylation of both high and low molecular weight alkenes under homogeneous conditions combined with facile product separation by simple decantation. 

The insertion of CO is in many instances thermodynamically unfavourable the thermodynamically most favourable product in hydroformylation and carbonylation reactions of the present type is always the formation of low or high-molecular weight alkanes or alkenes, if chain termination occurs via (3-hydride elimination). The decomposition of 3-pentanone into butane and carbon monoxide shows the thermodynamic data for this reaction under standard conditions. Higher pressures of CO will push the equilibrium somewhat to the left. 

The newly formed R may also add to another alkene molecule to give a trimer. The process whereby simple molecules, or monomers, are merged can continue, eventually giving high-molecular-weight molecules called polymers. This reaction of alkenes is called chain-growth (addition) polymerization. The repeating unit in the polymer is called the mer. If a mixture of at least two different monomers polymerizes, there is obtained a copolymer. 

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