Theoretical, chemical properties of acidic monomers with varied core structure

Hypothesis: monomers with increasingly flexible central core structures will result in polymers with higher toughness, which may be more suitable for restorative resins.  The calculation of the rotational energy about the central core of a series of similar monomers should structural criteria for monomer design.  Objective:  Synthesize a series of monomers that are structurally related to pyromelletic-dimethacrylate (PMDM) with 1 to 4 phenyl rings and 0 to 2 ether linkages between the rings and develop chemical models of this series. Methods: dianhydride (one mole) was reacted with HEMA (2.05 mole) using polyvinyl pyridine (catalyst) in anhydrous acetone at 50°C.   The synthesized monomers were PMDM, biphenyl-dimethacrylate (BPDM), oxydiphthalic-dimethacrylate (ODPDM), hydroquinone-diether-dimethacrylate (HQDEDM), and (isopropylidene-diphenoxy)bis(phthalic)-dimethacrylate (IPDM).  The monomers were filtered and the acetone was evaporated.  Fourier transform infrared (FTIR) spectra were taken (mid-IR range:  4000 cm^-1 to 600 cm^-1) before and after synthesis.  Energy of rotation was calculated through chemical modeling of the monomers using CAChe® (Fujitsu Ltd, Portland, OR).  The lowest energy through the dihedral angle at the central core was calculated for each 5 degree increment as the dihedral was rotated 360 degrees. Results:  Anhydride carbonyl peaks (~1850 cm^-1 and 1785 cm^-1) shifted to 1725 cm^-1, signifying synthesis of ester linkages (carbonyls) for methacrylates.  Modeling of the monomers showed energy maxima, and minima consistent with the degree of rigidity of the monomer.  BPDM showed a planar arrangement of the molecular structure due to the rigid connection between the aromatic rings. In contrast, the structure of ODPDM with the more flexible ether linkage showed the rings arranged perpendicular to one another. Conclusions:  Monomers of varying rigidity were synthesized and were used to compare and predict structure/function properties.  The flexible linkage at the core of the monomer is expected to result in tougher polymers. Supported by NIDCR R21-DE016298, ADAF and NIST.