A program was undertaken to identify an acceptable alternative to Dapon 35, an o-diallyl phthalate (DAP) prepolymer no longer available. Three o-DAP prepolymers from the Osaka Soda Company and four laboratory-scale prepolymers from Bendix-Kansas city were characterized and evaluated in DAP-fiberglass molding compounds. Gel permeation chromatography results for the Osaka prepolymers showed all three to be very close to one another in molecular weights (mw) and mw distributions, but slightly lower in both than Dapon 35. They are also slightly higher in monomer content. All three processed readily into DAP-fiberglass molding compounds and passed required physical property tests. One Osaka prepolymer was compounded into both asbestos and Orlon-DAP compounds on a production scale. Both compounds have passed all certification tests. The Bendix prepolymers were deliberately varied in mw and mw distribution and higher in monomer content than Dapon 35. Processing difficulties were encountered with both the lowest and highest molecular weight compounds, and the lowest molecular weight compound failed a number of physical property tests. The two intermediate molecular weight compounds processed readily and passed property tests. Guidelines were established for acceptable o-DAP prepolymers: (1) weight average mw (relative to polystyrene standards): 30,000 to 150,000; (2) mw distribution: 3.0 to …