We have analyzed fractionated samples of poly(methacrylic acid) produced in a propagating front for the amount of anhydride that formed and determined that a large percentage of acid groups exist as anhydrides (> 20%). By analyzing the samples after cleavage, we found that the molecular weight dropped significantly (from M(n) = 1.4 X 10(5) to M(n) = 1.0 X 10(4)). We conclude that the high molecular weights observed previously were the result of intermolecular anhydride formation. Poly(butyl acrylate), which cannot form anhydride bonds, produced in fronts had broad (M(w)/M(n) = 1.7-2.0) but unimodal molecular weight distributions with M(w) < 10(5). The average molecular weight decreased with increasing initiator concentrations.