EFFECT OF RESIDUAL MONOMER CONTENT ON SOME PROPERTIES OF A POLY(METHYL METHACRYLATE)-BASED BONE-CEMENT

Through this article, the degree of polymerization attainable in a com mercial acrylic bone cement based on poly(methyl methacrylate) (PMMA) was investigated by differential scanning calorimetry (DSC) and gas ch romatography( GC). The results obtained revealed a marked dependence b etween the maximum monomer conversion and the cure temperature. Specim ens for the mechanical evaluation of the cement were subjected to two different cure conditions: one set of samples was allowed to cure at r oom temperature and an additional set was also postcured at 140 degree s C for 2 h. The latter thermal treatment permitted one to discard the presence of the unreacted monomer in the hardened material. The effec t of the unreacted monomer on the mechanical behavior was evaluated by measuring the flexural modulus (E), the compressive yield stress (a,) , and the fracture toughness (K-IC). Samples prepared at room temperat ure for mechanical evaluation contained residual monomer which acts as a plasticizer of the matrix, increasing K-IC and decreasing E and a,. The cure temperature and mold dimensions influence the amount of the residual monomer in the hardened material. Thus, differences in the va lues of the mechanical properties measured for the same commercial for mulation may be attributed to a different mold dimension used in the t est. (C) 1998 John Wiley & Sons, Inc.