What Are Mercaptan Chain Transfer Agents?

Mercaptans, also known as thiols, are sulfur-containing organic compounds used across chemical manufacturing as intermediates, sulfur sources, and polymer modifiers. In polymer and resin manufacturing, selected mercaptans are widely used as chain transfer agents in free radical polymerization processes, where they help control polymer chain growth and final molecular weight. Chevron Phillips Chemical offers mercaptan chemistries used in polymer applications, including tertiary and normal mercaptans such as Sulfole^® 120 Mercaptan, Sulfole^® 100 Mercaptan, and related heavy mercaptans

How Mercaptans Work as Chain Transfer Agents

Mercaptans contain a sulfur-hydrogen group that can react with a growing polymer radical. During free radical polymerization, the mercaptan can donate hydrogen to the active radical chain, stopping the growth of that specific chain and generating a new sulfur-based radical. This new radical can then continue the polymerization process.
The result is controlled polymer chain length rather than uncontrolled chain growth. By adjusting mercaptan type and dosage, polymer manufacturers can influence molecular weight, viscosity, polymer distribution, and final application performance.

Chevron Phillips Mercaptan Grades for Polymerization

The table below provides a concise grade overview using commonly referenced product data. Final specifications should always be confirmed against the latest supplier TDS, SDS, COA, and regional documentation before formulation or plant use.

Applications in Polymer and Resin Manufacturing

Styrenic Resins and Polystyrene

Mercaptan chain transfer agents are used in styrenic polymerization systems where molecular weight control is required. In polystyrene and related styrenic resins, molecular weight affects melt flow, processing behaviour, toughness, rigidity, and end-use consistency.

Styrene–Butadiene Rubber

Styrene–butadiene rubber, or SBR, requires careful molecular weight control because viscosity, elasticity, mechanical performance, and processability are strongly linked to polymer chain length.

ABS Terpolymers

ABS terpolymers are based on acrylonitrile, butadiene, and styrene. These systems require controlled polymerization to achieve the right balance of toughness, impact resistance, rigidity, gloss, and processability.

Acrylic and Methacrylic Resins

Polyacrylates and methacrylates are used across coatings, adhesives, sealants, plastics, textiles, and specialty resin systems. In these applications, molecular weight influences viscosity, film formation, tack, adhesion, hardness, flexibility, and durability.

Polymer Modifiers, Coatings, and Adhesives

Sulfole^® 120 is positioned for applications where molecular weight control is critical, including polymer modifiers used in paint and coatings for emulsion polymerization, adhesives, and surfactants or emulsifiers.

Benefits for Polymer and Resin Manufacturers

Molecular Weight Control

The primary value of mercaptan chain transfer agents is molecular weight control. By limiting excessive chain growth, mercaptans help manufacturers target the right molecular weight range for their polymer or resin system.

Improved Processability

High molecular weight can increase viscosity and make a polymer system more difficult to pump, mix, filter, coat, or convert. Chain transfer agents can help keep polymerization systems within a more manageable processing window.

Batch-to-Batch Consistency

Polymer and resin customers often require narrow product specifications. Mercaptans help manufacturers reduce variation in chain length and molecular weight, supporting more consistent batch performance.

Performance Tuning

Different end uses require different polymer profiles. A pressure-sensitive adhesive may need a balance of tack, peel, and shear. A coating resin may need the right balance of hardness, flexibility, and film formation. A synthetic rubber may require specific viscosity and elasticity characteristics.