We have been using the same MMA, BP and DP ratio. I'm stumped that we never had issues in the past and all of a sudden we are having this issue. Perhaps 1 or 2 blocks out of 25-30 or so but now it is the total opposite. We have 1 or 2 polymerizing out of 25-30.
Your protocol doesn't mention removal of inhibitor from MMA. Commercial MMA contains an inhibitor (usualy MEHQ). The easiest wayto remove the inhibitor is to pass the MMA through basic aluminium oxide.
I expect that the oxygen content within you MMA liquid is too high. You might try to illuminate the sample by UV after the procedure or using a larger amount of a thermal initiator (is the initiator okay?). I suggest infiltrating the sample with the thermal initiator just before adding to the "warm/hot" MMA liquid to surround the bone by polymer. If you want to cure the whole block all at once use a larger amount of thermal imitator within the MMA solution. Be careful using an initiator not resulting in bubbles (e.g. oxygen).
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