In the demanding field of photopolymerization, understanding the precise chemical properties of photoinitiators is crucial for successful formulation and application. 4-Benzoyl-4'-methyldiphenyl sulfide (BMS), identified by CAS No. 83846-85-9, is a highly sought-after Type II photoinitiator, and a detailed look at its properties reveals why it is so valued by manufacturers.

Chemical Identity and Structure

BMS, also known by synonyms such as SpeedCure BMS or Omnirad BMS, has the chemical formula C20H16OS and a molecular weight of approximately 304.41 g/mol. Its structure features a central sulfide linkage connecting two phenyl rings, one of which is substituted with a methyl group (p-tolylthio group), and the other is attached to a benzoyl group. This molecular architecture dictates its photochemical behavior and physical characteristics.

Physical Properties Relevant to Formulators

For chemists and product developers, the physical characteristics of a photoinitiator are as important as its chemical function:

  • Appearance: BMS typically presents as a white to off-white solid, often in crystalline powder form. This physical state is generally easy to handle and incorporate into various liquid or semi-solid formulations.
  • Melting Point: Its melting point is typically in the range of 75-85°C. This indicates it is a stable solid at room temperature and will melt and dissolve when heated or incorporated into liquid resin systems.
  • Solubility: BMS shows slight solubility in common organic solvents such as chloroform, ethyl acetate, and methanol. This solubility profile is important for formulating UV-curable coatings, inks, and adhesives, ensuring homogeneous distribution within the resin matrix. Its solubility in water is very low (e.g., 7.38 μg/L at 20°C), which is typical for many organic photoinitiators and often desirable to prevent interference in aqueous systems.
  • Purity: High purity, typically ≥98% or ≥99.0% (as determined by GC), is critical for consistent performance and predictable cure behavior. Manufacturers often specify purity levels to ensure product quality.
  • Volatiles and Ash Content: Low volatiles (≤0.5%) and ash content (≤0.1%) are indicators of high-quality, purified product, ensuring minimal interference with the curing process or the final properties of the cured material.

Thermal and Photochemical Characteristics

BMS's utility stems from its photochemical properties:

  • UV Absorption: It has absorption maxima at approximately 246 nm and 315 nm, making it effective with standard mercury vapor lamps and certain LED light sources.
  • Thermal Stability: While specific data on decomposition temperature may vary, it is generally stable under normal storage conditions.

Safety and Handling

As with all industrial chemicals, appropriate safety precautions must be observed when handling BMS. It is classified with hazard statements such as H315 (Causes skin irritation) and H319 (Causes serious eye irritation). Standard precautions like wearing gloves, eye protection, and ensuring adequate ventilation are recommended. Manufacturers can buy BMS with confidence knowing that with proper handling, it can be used safely in industrial settings.

Where to Buy High-Purity BMS

For manufacturers and formulators looking to source BMS, understanding these properties is key to selecting the right product. When you seek to buy BMS, prioritize suppliers who provide detailed technical specifications, high purity levels, and consistent quality. Manufacturers in China are often competitive sources for high-purity BMS (CAS 83846-85-9), offering a balance of quality and cost-effectiveness.