Oxaspiro monomers

Chart 11.9 Oxaspiro monomers used in non-shrinking dental formulations [30]. 

While these approaches did provide for reductions in polymerization shrinkage and improvements in adhesion, the oxaspiro monomers were more sluggish in free... 

Another compound, DDFB, was also investigated to determine its potential as a dual radical/cationic polymerization initiator with the SOCM monomer. The dark DDFB solid had only limited solubility in the monomer (approximately 0.5 wt%). The activated SOCM sample was heated to 100 C for 10 min which produced a darkened polymer that was predominantly crosslinked. An unactivated SOCM control sample also received the same heat treatment and was recovered unchanged. The IR spectrum of the polymer showed extensive carbonate formation in the 1800 and 1750 cm regions and a nearly complete disappearance of the spiro absorption bands. This initiator appeared to have little affinity for the methacrylate double bond since a strong 1637 cm band was still present. The attempted polymerization of oxaspiro monomer 10 with DDFB at 100 C yielded no polymer and no reaction. The DDFB-containing SOCM monomer sample was then irradiated under the sunlamp with no polymer formation observed after 30 min. 

Among the systems with chemical different donor and acceptor molecules, the photocopolymerization between maleic anhydride (MSA), which functions as an acceptor, and electron-rich monomers has been widely investigated. As donor monomers such compounds as styrene (Sty) [19-29], cyclohexene [30], N-vinylcarbazole [31], 2-vinyl naphthalene [32], vinyl acetate [33], 2.4.8.10-tetra-oxaspiro[5.5]undecan [34] and phenyl glycidyl ether (2,3-epoxypropyl phenyl ether, PGE) [35] have been used. In all the above cases, using high concentrations of both monomers, the absorption of the CT has been obtained in various solvents. Thus, with spectroscopic methods the complex formation constant Kct can be calculated (e.g., MSA-cyclohexene Kcl = 0.0681 mol -1 [33], MSA-tetrahydrofuran Kct = 0.331 mol-1 [36]), and a selective excitation of the CT is possible in many cases. 

The hydroxy oxaspiro intermediate 7 (3.28 g, 20 mmol) was combined with triethylamine (2.23 g, 22 mmol) in 30 mL of toluene. The solution was cooled to 5 C under argon and freshly distilled methacryloyl chloride (2.09 g, 20 mmol) diluted with 7 mL of toluene was added dropwise. The mixture was stirred at room temperature for 18 h and then filtered to remove the amine hydrochloride precipitate. The majority of the solvent was removed under reduced pressure and the residue was eluted through a small silica gel pad with hexane-ethyl acetate (1 1). Evaporation of the solvent under reduced pressure provided the SOCM monomer 3 as a pale yellow liquid in 93% yield. 

The IR spectra in Figure 4 trace the synthetic pathway to the SOCM monomer 3. The entire series is dominated by the strong IR bands characteristic of the spiro orthocarbonate group. IR absorptions associated with the shortened CO4 centr ether bonds occur near 1200 cm while the external ether bands are found near 1050 cm. Intermediates 6 and 7 produce a strong OH band around 3400 cm and 7 also yields peaks due to the oxaspiro-based double bond at 1698 and 880 cm". Addition of the methacrylate group in monomer 3 eliminates the OH band and gives rise to the carbonyl and methacrylate vinyl absorptions at 1720 and 1637 cm", respectively. 

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