Determination of density changes with expansion polymerization

Materials that polymerize without substantial volume contraction have numerous valuable applications in dentistry and other fields. Two new symmetrical aliphatic spiro‐orthocar‐bonates, formulated from cis‐ and trans‐2‐hydroxymethyl‐cyclohexanol to give 2,3,8,9‐di(tetramethylene)‐1,5,7,11‐tetraoxaspiro [5,5] undecanes, showed, by density determinations in dilute solution, that expansion occurs with polymerization. The cis / cis‐spiroorthocarbonate racemic mixture showed a 3.9% expansion upon polymerization, and the trans/trans racemic mixture showed a 3.5% expansion. The densities were determined by pycnometry, with a precision reliable to at least four figures. This method is thus recommended for cases of soluble monomer/polymer pairs for which the density difference will be small and where the partial specific volumes are independent of concentration, thereby avoiding the complexities of variable physical states of monomer and/or polymer. © 1993 John Wiley & Sons, Inc.