Determination of Hydroxyl Groups in Polyethylene Glycol Silation - Spectrophotometry

Method 3.1 Determination of Hydroxyl Groups in Polyethylene Glycol. Silation - Spectrophotometry [9] 

This silation spectrophotometric method is capable of determining down to 0.1% of hydroxy groups in a polyethylene glycol (PEG) with a molecular weight of 3000. 

Gas chromatograph equipped with flame ionisation detectors. The carrier gas was helium. 

1-Napthyl dimethyl (dimethylamino) silane (preparation). A10% solution of 1 equiv monochlorosilane (naphthyl dimethyl chlorosilane) in hexane (in benzene if necessary for solubility reasons) is stirred in a flask equipped with a reflux condenser cooled at -20 °C. From a communicating flask 2.2 equiv of dimethylamine vapour is slowly introduced over the solution and the mixture kept at room temperature overnight. After filtration and evaporation of the solvent, the residue is distilled. 

2 dimethoxyethane solution of the PEG is silylated with naphthyl dimethyl dimethylamino-silane. After some working up the extract is dissolved in ethanol and the chromophore concentration evaluated spectrophotometrically. The method is calibrated against PEG of known equivalent weight. 

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