Catalysts polymer molecular weight

M0CI5 and WCl6 alone can induce the polymerization of various monosubstituted acetylenes. The use of a suitable organometallic cocatalyst enhances the catalytic activity. With these catalysts, polymer molecular weight is low or medium (<10 ) for 1-hexyne and phenylacetylene but reaches one million for sterically crowded monomers like t-butylacetylene and or /2o-substituted phenylacetylenes. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

In the suspension process, which was the first method to be commercially developed, propylene is charged into the polymerisation vessel under pressure whilst the catalyst solution and the reaction diluent (usually naphtha) are metered in separately. In batch processes reaction is carried out at temperatures of about 60°C for approximately 1-4 hours. In a typical process an 80-85% conversion to polymer is obtained. Since the reaction is carried out well below the polymer melting point the process involves a form of suspension rather than solution polymerisation. The polymer molecular weight can be controlled in a variety of... 

In 1968 the Monsanto Company announced the availability of novel soluble low molecular weight polyphenylene resins. These may be used to impregnate asbestos or carbon fibre and then cross-linked to produce heat-resistant laminates. The basic patent (BP 1037111) indicates that these resins are prepared by heating aromatic sulphonyl halides (e.g. benzene-1,3-disulphonyl dichloride) with aromatic compounds having replaceable nuclear hydrogen (e.g. bisphenoxy-benzenes, sexiphenyl and diphenyl ether). Copper halides are effective catalysts. The molecular weight is limited initially by a deficiency in one component. This is added later with further catalyst to cure the polymer. 

Since the publication by the discoverers (3) of chromium oxide catalysts a considerable number of papers devoted to this subject have appeared. Most of them (20-72) deal either with the study of the chromium species on the catalyst surface or with the problem of which of this species is responsible for polymerization. Fewer results have been published on the study of processes determining the polymer molecular weight (78-77) and kinetics of polymerization (78-99). A few papers describe nascent morphology of the polymer formed (100-103). 

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

Conjugation between the imino and acyl [121], or nitrile (in complex 1.47) [122] moieties permitted the remote activation of nickel. Another catalyst (1.48) exhibiting coordination via an alkenyl moiety is noteworthy because of its sterically small size, which should prohibit the production of high molecular weight polymers [123], This is believed to be possible because of the catalyst s unique electronic properties. As bulkier imino-aryl substituents are introduced, polymerization activity and polymer molecular weight increases, as expected [124],... 

It is not possible to determine from A atr ) alone whether the polymerization will be controlled fast activation and more importantly fast deactivation are required to achieve good control over polymer molecular weights and molecular weight distributions. Therefore, precise measurements of the activation (kj and deactivation (kj rate constants should be used for correlation with catalyst, alkyl halide, and monomer structures. 

Although examples of the methodology will utilize entirely reaction rates or reactant concentrations, the procedures are equally valid for other model responses. They have been used, for example, with responses associated with catalyst deactivation and diffusional limitations as well as with copolymer reactivity ratios and average polymer molecular weights. 

A Iky nes have been polymerized using ionic and radical initiators, but the polymer molecular weights are low. High molecular weights are obtained by using Ziegler-Natta coordination catalysts (Sec. 8-4d-2) [Chien et al., 1980]. The polymers are of considerable interest in terms of their potential as (semi)conducting materials. 

A series of copolymers has been made from THF and 7-oxabicyclo-[2 2 l]-heptane using FeCl3-SOCl2 as catalyst. Low molecular weight polymers with melting points ranging from 150 to 320° C were reported (109). 

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