Analysis of a vinyl pyrrolidone/poly(propylene fumarate) resorbable bone cement

A resorbable bone cement was formulated from N-vinyl-2-pyrrolidinone (VP), the unsaturated polyester poly(propylene fumarate) (PPF), and the inorganic filler tribasic calcium phosphate (hydroxy apatite). Cure, initiated by benzoyl peroxide and accelerated by N,N-dimethyl-p-toluidine, resulted in the formation of VP crosslinks between polyester chains. During cure the cement hardened from a viscous moldable putty to a rigid structure with a shore D hardness of 50-60. The purpose of this study was to determine the fractions of PPF and VP incorporated into the crosslinked structure. Dissolution of the cured cement in water followed by extraction of the residue in tetrahydrofuran indicated that over 90% of the PPF was crosslinked over the range of PPF/VP ratios explored, but that the fraction of VP used in formation of crosslinks depended linearly on the PPF/VP ratio. Kinetic analysis of these data suggests that k'pp/kpf (the reactivity ratio) was approximately 2.0 where k'pp is the rate constant for the addition of VP radical to VP monomer leading to formation of poly(vinyl pyrrolidone), and kpf is for the addition of VP radical to PPF unsaturation.