Ethylene purification with molecular

The polymerization apparatus (see Fig. 3.2) consists of a 11 three-necked flask, fitted with stirrer, thermometer, gas inlet with tap, and gas outlet.On the inlet side the gas stream passes through three wash bottles one as a safety bottle (A), one for the purification of ethylene, filled with 30 ml of petroleum ether (bp 100-140 °C) and 5 ml of diethylaluminum chloride (B),and one filled with molecular sieves 5 A (C).The last of these dries the ethylene further and also serves to trap aluminum hydroxide carried over from B. On the outlet side there are two wash bottles the first is a safety bottle (D), and the second, (E), is filled with 50 ml of dry bis(2-hydroxyethyl) ether (diglycol), and isolates the apparatus from the external atmosphere. 

Molecular Weight. Measurement of intrinsic viscosity in water is the most commonly used method to determine the molecular weight of poly(ethylene oxide) resins. However, there are several problems associated with these measurements (86,87). The dissolved polymer is susceptible to oxidative and shear degradation, which is accelerated by filtration or dialysis. If the solution is purified by centrifiigation, precipitation of the highest molecular weight polymers can occur and the presence of residual catalyst by-products, which remain as dispersed, insoluble soHds, further compHcates purification. 

Most commercial products are mixtures because of the way they are manufactured. For instance many surfactant hydrophobes come from assorted products such as petroleiun alkylate cuts or triglyceride oils, with a molecular weight distribution that could be narrow or wide. Usually, a purification and separation of single isomeric species would be too costly and, in most cases, pointless. Moreover, the synthesis reactions involved in the surfactant manufacturing might be the intrinsic reason of the production of a mixture, such as in the case of polycondensation of ethylene oxide which results in an often wide spread ethylene oxide munber (EON) distribution. A residual content of some intermediates or by-products might also be a significant cause for mixture effects. 

The synthesis and purification of polystyrene methacryloyl macromonomers (PS-MA) in the molecular weight range Mn= 1000-2000 g mol 1 by living anionic polymerization of styrene (S), termination with ethylene oxide (EO), and subsequent reaction with methacrylic chloride has already been described in detail elsewhere [180] (see also Scheme 16). In this context it has to be emphasized that the hydroxyethyl-terminated PS-MA macromonomer precursor (PS-OH) as obtained after purification of the crude PS-OH by silica column chromatography (cyclohexane/dichloromethane 1/1 v/v) and as charged in the PS-MA synthesis still contains up to about 15 wt-% of non-functionalized polystyrene (PS-H). This PS-H impurity of the PS-MA macromonomer does not interfere with the PS-MA synthesis and the subsequent TBA/PS-MA copolymerization and is easily and conveniently removed from the resulting PTBA-g-PS graft copolymer (see below). 

Poly (ethylene glycol) (PEG), PEG I and PEG II are purchased from Fluka and used without further purification. The average molecular weights of the two PEG samples are determined by gel permeation chromatography (GPC) (compare Table 1). The commercially available pentanol (> 99%, Fluka), xylene (> 99%, Roth) and sodium do-decylsulfate (SDS, > 99%, Fluka) are used as obtained. CdCl2 and (NH4)2S are purchased by Merck-VWR, and water is purified with the Modulab PureOne water purification system (Continental). 

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