High molecular weight, linear chains

Elemental phosphorus itself exists in several polymeric forms. If the white allotropic form, which consists of P4 tetrahedral molecules, is put under high pressure, preferably at elevated temperatures, it can be catalytically converted to other modifications.41 It first becomes red, then violet, then black as the degree of polymerization increases. These materials are very difficult to characterize because of branching and the formation of cyclics. In the extreme limit, the structure approaches that of graphite, and shows good electrical conductivity.42 No evidence exists at all for the formation of high-molecular-weight, linear chains of elemental phosphorus. 

It is sometimes desirable to be able to use viscosity data to estimate Z, or conversely to estimate jy for a given polymer when very few data exist. Certain approximations appear reasonably valid for a variety of pol3nners examined here, and we will now proceed to employ these to reduce this general result to an approximate correlation useful in many cases. Thus, except for some branched chains and perhaps very high molecular weight linear chains, for which the above correlation is not adequate, we shall here assume that... 

In addressing this question, we will consider a single molecular architecture—high molecular weight, linear chains. We shall arbitrarily classify such chains into five broad structural classes ... 

Allene has been polymerised to high molecular weight linear polymers by various Ziegler-Natta catalysts based on compounds of such transition metals as Ti, V, Cr, Mn, Fe, Co and Ni as precursors and alkylaluminium compounds as activators [439-441], Crystalline and amorphous polymers have been produced, in various proportions, with each of the catalysts used. The crystalline polymers consist predominantly of 1,2-linked (head-to-tail) monomeric units formed by insertion polymerisation as in scheme (68), but some regioirregular-ities resulting from the 2,1-insertion, leading to head-to-head and tail-to-tail arrangements, may be present in the polymer chain ... 

A derivative of the Ziegler ethylene polymerization process (Alfene process producing 2-linear olefins), this technique is used to produce high molecular weight linear alcohols with an even number of carbon atoms (C4 to C2 -). It was developed by Continental Oil Company, and employs the growth reaction of polyethylene from triethytahinrimim. The rupture of the chain is caused by oxidation of the product ... 

Pure polyethylene should not absorb ultraviolet radiation of wavelength above 200 nm since pure paraffins are transparent in that region of the spectrum. However, it is well established [ 20] that even carefully purified polyethylene differs from a simple high molecular weight straight chain paraffin in being to some extent unsaturated. The total unsaturation has been estimated to be about 0.25% C=C by weight [21]. Olefinic unsaturation of different types has been detected by infrared spectroscopy [21, 22] it seems to be mainly of the vinyl type in linear polyethylene, while most unsaturation is of the vinylidene type in branched polyethylene [22]. Attention has also been drawn to the fact that a structure seems to be present in low density polyethylene which leads to a triene on ultraviolet irradiation [23]. 

The dipropargyl ether of bisphenol A undergoes oxidative polymerization in which the two terminal acetylenic hydrogen atoms react to form a high molecular weight linear polymer with two conjugated triple bonds in their main chain. 

Recently in the Sijbesma group, high-molecular-weight linear coordination polymers of diphenylphosphine telechelic polytetrahydrofuran with palladium (II) dichloride were developed [3]. Molecular weights of these polymers could be altered reversibly by ultrasotmd and it has been shown that polytetrahydrofuran chains remain intact during sonication [78]. This implies that only the reversible palladium-phosphorus bonds are broken and coordinatively unsaturated palladium complexes were produced by the application of mechanical forces on these coordination polymers [79]. Furthermore, polymers which include both Pd and Pt were sonicated and it was shown that force selectively breaks the weaker Pd-phosphine bonds which were randomly distributed along the polymer backbone [80]. 

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