The aims of this study were to investigate the photoinitiation behaviors of acylphosphine oxide (APO) and bisacylphosphine oxide (BAPO) derivatives in comparison to D,L-camphorquinone (CQ)/tertiary amine (EDAB) system. Fifty six kinds of experimental unfilled, light-cured resins were prepared using APO, BAPO, CQ, EDAB, resin monomers, and adhesive monomers. The measurements of ultraviolet-visible (UV-VIS) spectroscopy, photopolymerization with differential scanning calorimeter (photo-DSC) and degree of conversion (DC) determination were performed. Results showed that the UV-VIS spectra of all APO and BAPO derivatives possessed λmax ranging between 365 and 416 nm. Their photoinitiation behaviors were not influenced by acidic adhesive monomers formulated in unfilled Bis-GMA-based resins (p<0.05). Although BAPO exhibited higher reactivity than CQ/EDAB in unfilled 6-methacryloyloxyhexcyl phosphonoacetate (6-MHPA)/ 2-hydroxyethyl methacrylate (HEMA) and 6-MHPA/glycerol monomethacrylate (GM)-based resins, it was found that there were no statistically significant differences in DC (％) between BAPO [44.2(6.5)-51.2(4.3)] and CQ/EDAB [42.4(4.4)-47.5(3.7)] (p<0.05). It was concluded that APO and BAPO photoinitiators exhibited reactivity comparable to that of CQ/tertiary amine system.

Camphorquinone (CQ) derivatives having acylphosphine oxide (APO) group are unknown. This study synthesized such a novel 7,7-dimethyl-2,3-dioxobicyclo[2.2.1]heptane-1-carbonyldiphenyl phosphine oxide (DOHC-DPPO = CQ-APO). Ultraviolet and visible (UV-VIS) spectra of CQ-APO, CQ, and APO were measured. Photopolymerization performances of experimental light-cured resins comprising these photoinitiators were investigated. Newly synthesized CQ-APO showed as a pale yellow crystal (mp 365K). UV-VIS spectrum of CQ-APO showed two maximum absorption wavelengths (λmax) [372 nm (from APO group) and 475 nm (from CQ moiety)] within 350-500 nm. Unfilled resin containing CQ-APO exhibited good photopolymerization time (9.6 sec) and relaxed operation time (50 sec), as well as a pronouncedly lower b value (4.0) in the CIELab color specification system than that containing CQ (84.0). Resin composites containing CQ-APO, exhibited high flexural strength . It was concluded that CQ-APO possessed two λmax peaks within 350-500 nm, and that CQ-APO-containing resins exhibited excellent color tone, good photopolymerization reactivity, relaxed operation time, and high mechanical strength.

The effect of the pH value of single-bottle, self-etching 2-hydroxyethyl methacrylate (HEMA)-free adhesives on their shelf lives with bonding ability was investigated. Two experimental adhesives [SA-1 (pH=3.0); SA-2 (pH=2.1)] comprising 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), 4-acryloyloxyethyltrimellitic acid (4-AET), Bis-GMA, water, and acetone, in which the pH values were controlled with 1N NaOH, were stored for 6 weeks at 50°C in air. Shear bond strengths of aged adhesives to ground and unetched enamel and dentin were measured at a crosshead speed of 1.0 mm/min, and the data were analyzed by ANOVA. The resin-tooth bonding interfaces were further observed with SEM. With SA-1, the bond strengths to the tooth substrates were maintained throughout the 6 weeks. However, with SA-2, bond strength significantly degraded from weeks 4 to 6 (p<0.05). Based on SEM observation, non-aged and 6-week-aged adhesive SA-1 appeared to be strongly adhered to both enamel and dentin. It was found that the stability of the self-etching adhesive was influenced by its pH value.

Thebehaviorofwater-solublephotoinitiatorswithcrownethersindentaladhesivesisunknown.Thisstudyinvestigatedthe effectofsodiumacylphosphineoxide(APO-Na)withcrownetherinahydrophobicadhesiveonadhesiontoteeth.Sodium 2,4,6-trimethylbenzoyl-phenylphosphine oxide (TMPO-Na = APO-Na) was synthesized in 67.1% yield and identified by 1 H NMR. APO-Na was dissolved in hydrophobic resins in the presence of a crown ether (ionophore effect). Thirty kinds of experimentalsingle-stepadhesivescomprisingAPO-Na,CE,Bis-GMA,6-methacryloyloxyhexylphosphonoacetate(6-MHPA), and4-methacryloyloxyethyltrimelliticacid(4-MET)weretherebyprepared.Shearbondstrengthtounetchedgroundteeth wasmeasuredatacrossheadspeedof1.0mm/min,andthedatawereanalyzedbyANOVA.Theshearbondstrengthresults of bonding resins containing APO-Na with 18-crown-6-ether (CE-6) were significantly higher than that without CE-6 (control) (p<0.05).Higherbondstrengthvalues[forenamel:BR24at19.3(3.2)MPa;fordentin:BR29at20.2(4.7)MPa]wereachieved with the adhesives containing APO-Na, CE-6, 6-MHPA, and 4-MET. Therefore, it was found that APO-Na with CE-6 contributed to the efficient bonding performance of single-step adhesive to teeth. However, in view of the biosafety hazard posedbycrownethers,thesearchisstillonforreagentsthatarebiologicallysaferthancrownethers-butwithionophor effects-tobeusedindentaladhesives.

The behavior of microencapsulated polymerization initiators in dental adhesives is unknown. This study investigated the effects of new microencapsulated initiators in novel, multi-purpose, PMMA-type adhesive resin on the bonding performance and polymerization reactivity. Microencapsulated BPO and 1,3,5-trimethylbarbituric acid (TMBA) with PEMA as a shell polymer were quantitatively synthesized at 97-98％ yield with 30-54 μm diameter. Adhesive-MC (comprising the synthesized microcapsules) and Adhesive-BR (comprising bare BPO and bare TMBA) were prepared and stored at 5℃, 23℃, and 40℃ for two months. MMA monomer was used as a solvent for the microcapsules. At the starting period, there were no significant differences between Adhesive-MC and Adhesive-BR in shear bond strength to enamel or dentin treated with or without surface treatment agent (p<0.05); moreover, their curing times (tc＝304 seconds) were almost the same. After two months'storage at 40℃, Adhesive-BR degraded in bond strength and showed markedly delayed polymerization reactivity as storage period progressed. In direct contrast, it was found that Adhesive-MC still retained its capabilities for adhesion to gold alloy and initiation of radical polymerization (p<0.05).

Simultaneous measurement of rheological behavior and conduction current was performed for an electrorheological (ER) suspension with a dilute concentration of cation exchange resin particles of 5 wt%. The stress under the electric field for the ER suspension showed a remarkable dip behavior at higher shear rates: The stress decreased with an increase in the shear rate, and it gradually increased again and approached the stress under no electric field. The apparent conductivity, which was sensitively probed by the conduction current passing through the ER suspension, showed a dip behavior. Further, the apparent conductivity showed a local maximum, which was not found for the ER suspensions with particle concentrations of 10 and 30 wt%.

The steady stress under static electric fields and the conduction current passing through the electro-rheological (ER) suspensions with cation exchange resin particles were investigated simultaneously as a function of the shear rate. The shear thinning behavior was found for a suspension with a higher viscosity of the continuous phase. Further, a remarkable dip behavior was found for a dilute ER suspension. The apparent conductivity, which was calculated from the conduction current, probed sensitively the corresponding behavior to the stress responses.

In expectation of the formation of a thermally stable, dielectric supramolecular assembly of a polypeptide with an amino acid sequence similar to that of type‐2 collagen, a sequential polypeptide consisting of the repetition of the Pro‐Pro‐Gly tripeptide was synthesized by solid‐phase synthesis. Column chromatography of an ethanol solution of (Pro‐Pro‐Gly)10NH2 showed the presence of a double helix or triple helix of the polypeptide. The pattern of a circular dichroism (CD) spectrum of an ethanol solution of (Pro‐Pro‐Gly)10NH2 was very similar to that of an aqueous solution of (Pro‐Pro‐Gly)10OH, strongly suggesting the presence of a triple helix of the polypeptide in ethanol. An oriented monolayer assembly of (Pro‐Pro‐Gly)10NH2 was formed on a thin gold film. The distribution of surface unevenness and the surface potential were investigated with Kelvin force microscopy. The rising spots carried an electric potential from room temperature to 150 °C. The correspondence showed the usefulness of the oriented monolayer of the sequential polypeptide materials for thermally stable, dielectric nanodevices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3632–3639, 2003