Triethylene glycol

The experimental composites were composed of Bis-phenol A diglycidyl dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) at a 50:30:20 mass ratio. All monomers were purchased from Esstech (Essington, PA, USA). Photoinitiators were added to the monomers as follows: 0.2 wt.% of dl-camphoroquinone (Polysciences Inc., Warrington, PA, USA), 0.8 wt.% of a tertiary amine (EDMAB – ethyl 4-dimethylaminobenzoate; Avocado, Heysham, England), and 0.2 wt.% inhibitor (BHT – 2,6-di-tert-butyl-4-methylphenol; Sigma–Aldrich, St. Louis, MO, USA).
Six thiourethane oligomers were synthesized in solution in the presence of catalytic amounts of triethylamine. Two multi-functional thiols – pentaerythritol tetra-3-mercaptopropionate (PETMP) or trimethylol-tris-3-mercaptopropionate (TMP) – were combined with three di-functional isocyanates – 1,6-hexanediol-diissocyante (HDDI) or 1,3-bis(1-isocyanato-1-methylethyl) benzene (BDI) (aromatic) or 1-isocyanato-4-[(4-isocyanatocyclohexyl) methyl] cyclohexane (DHDI) in 60 ml of methylene chloride. In addition, 1 mol of 3-(triethoxysilyl)propyl isocyanate was also added to each of the six combinations described above – this is the source of trimethoxy silane to be used for the subsequent silanization step. The reaction was catalyzed by triethylamine. The isocyanate:thiol mol ratio was kept at 1:2.5 (with thiol in excess) to avoid macro-gelation of the oligomer during reaction, according to the Flory–Stockmayer theory²¹ , leaving pendant thiols and trimethoxy silanes. Oligomers were purified by precipitation in hexanes and rotoevaporation, and then characterized by mid-IR and NMR spectroscopy^{6 (link)}. The disappearance of the isocyanate mid-IR peak at 2270 cm⁻¹ and the appearance of NMR resonance signals at 3.70 ppm were used as evidence for completion of isocyanate reaction and thiourethane bond formation, respectively³⁶ .
For the silanization procedures, thiourethane oligomers were combined with 65 ml of an ethanol: distilled water solution (80:20 vol%), previously acidified by the addition of glacial acetic acid (pH = 4.5). Thiourethane was added at 2 wt%, in relation to the solution mass. Five grams of neat barium silicate glass filler (average size = 1.0 μm; Kavo Kerr Corporation, Orange, CA) was added to the solution, kept under magnetic stirring for 24 hours, filtered, and dried for 4 days in an oven at 37 °C.
The TU fillers were introduced at 50 wt% to the monomer matrix with a centrifugal mixer (DAC 150 Speed Mixer, Flacktek, Landrum, SC, USA) operated for 2 min at 1800 rpm. All procedures were carried out under yellow light.
Control groups were prepared with a commercially available unsilanized (UNS) and methacrylate-silanized (SIL-MA) barium glass filler particles (average size = 1.0 μm; Kerr Corporation, Orange, CA). All photocuring procedures were carried out using a mercury arc lamp (EXFO Acticure 4000 UV Cure; Mississauga, Ontario, Canada) filtered at 320–500 nm (light guide diameter = 5 mm). In order to verify the achieved functionalization and its efficiency, the different filler particles were analyzed by thermogravimetric analysis (TGA) over a temperature range of 50 °C to 850 °C at 10 °C/minute.

Ethylene glycol dimethacrylate (EGDMA), triethylene glycol dimethacrylate (TIEGDMA), tetraethylene glycol dimethacrylate (TTEGDMA), 1,4-butanediol dimethacrylate (BDDMA), tetraethylene glycol diacrylate (TTEGDA) and 1,4-butanediol diacrylate (BDDA) were purchased from Sartomer Co. (Exton, PA, USA)and used without any purification. 4,4′-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) (98%), 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) (98%) and 4,4′-(9-fluorenylidene)dianiline (AFL) (98%) were purchased from Sigma-Aldrich (St. Louis, MO, USA) or TCI Chemicals (Zwijndrecht, Belgium) and additionally purified by vacuum sublimation. The photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA) (99%) (Sigma-Aldrich) was used as received. m-Cresol (99%) was distilled under reduced pressure. N-methyl-2-pyrrolidone and methanol were used without any purification.

MEL (99%, purity), BUP (99%, purity) and dosage form inactive components as dimethyl sulfoxide, maleic acid, triethylene glycol and triacetin were kindly supplied from ADWIA Company for Pharmaceutical Industries, 10th of Ramadan, Cairo, and sodium deocyl sulfate (SDS) from sigma Aldrich company, Cairo, Egypt.