ABSTRACT:The effect of the monomethyl ether of hydroquinone (MEHQ) on the polymerization of acrylic acid was studied. The rate of polymerization was quantified at various levels of MEHQ by use of an in situ NMR technique. While oxygen functions as an inhibitor in acrylic acid polymerizations, MEHQ was shown to function as a retarder. The decrease in the rate of polymerization allowed the calculation of an inhibition constant for this system. MEHQ was found to remain in the polymerizing mixture throughout the course of the reaction, significantly reducing the rate of polymerization, but not reducing the molecular weight of the polymer. The data are consistent with direct reaction of MEHQ with initiator fragments, but not termination of growing chains. Superabsorbent polyacrylic acid gels were prepared and the properties measured.

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MATERIALS & METHODSTotal sulfite at concentrations s 50 ppm was determined in commercially available thixotropic materials based on methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) by extraction into an alkaline solution of 5% (whr) Na2S04 and subsequent separation by anion exclusion chromatography and electrochemical detection. Results were compared to those obtained by Monier-Williams distillation which was shown to suffer from low recovery, poor reproducibility and false positive response. Mean sulfite recode,, added at conceitrations of 10-50 oum SO, was 91 2 11% based on 12 determinations. Analysis time fo; ihe chrkmatographic method was < 25 min/determination. Aldehydes did not interfere at concentrations < lOO-fold excess.