TPO is a mono-acylphosphine oxide Type I photoinitiator exhibiting very broad UV/Vis absorption (effective peak 350–400 nm, tailing to ≈ 420 nm). Upon irradiation it undergoes α-cleavage to produce both benzoyl and phosphonyl radicals, giving rapid, low-odour, low-yellowing cure of acrylate, methacrylate, vinyl-ether and styrenic systems. The crystalline product is practically insoluble in water (< 1 mg L⁻¹ at 25 °C), freely soluble in chloroform, acetone, toluene and most UV-curable resins, and can be recrystallised from ethanol. Commercial material is supplied at ≥ 99 % purity and remains stable for ≥ 2 years when stored sealed at < 25 °C under dry nitrogen .
Key Physicochemical Data:
Melting point: 91–94 °C
Density: 1.12 g cm⁻³ (25 °C)
Flash point: 268 °C (closed cup, predicted)
Log P (octanol/water): 5.2 (predicted)
Thermal onset: > 230 °C
Typical Uses:
Universal Type I photoinitiator for UV-LED or mercury-lamp curing of white/pigmented coatings, screen/flexo/offset inks, wood finishes, adhesives, optical-fibre coatings and dental composites at 0.3–5 % w/w .
Photosensitiser for thick-section (> 4 mm) and highly coloured (TiO₂, carbon-black) formulations with low shrinkage and excellent through-cure; exhibits photobleaching and low volatility .
Building block for photocurable urethane-acrylates, stereolithography resins and UV-patternable dielectrics .
Quality Specification (Commercial Grade):
Purity (HPLC): ≥ 99 %
Water content (KF): ≤ 0.3 %
Loss on drying: ≤ 0.2 %
Ash: ≤ 0.1 %
Acid value: ≤ 0.5 mg KOH g⁻¹
Heavy metals: ≤ 20 ppm
Hazard Statement:
Harmful if swallowed (H302), causes skin irritation (H315), serious eye irritation (H319), may cause respiratory irritation (H335); harmful to aquatic life with long-lasting effects (H411) . Avoid breathing dust; use gloves, goggles and local exhaust. Store in a cool, dry place under nitrogen, away from light and oxidants. SDS available on request.
