Chainbreaking

Chainbreaking refers to processes that terminate or cleave the growth of polymer chains, or the breaking of polymer chains after they have formed. In polymer chemistry, it often describes chain termination in radical polymerization, where active growing chains are ended by combination or disproportionation, effectively “breaking” the chain growth. It can also describe chain scission, the chemical or mechanical cleavage of the polymer backbone that reduces chain length after polymer formation.

In practice, chainbreaking occurs through various mechanisms. Thermal, mechanical, UV, or oxidative stress can induce chain scission, leading to random cleavage along the backbone (random scission) or specific bond breaks (beta-scission). Radiation or hydrochemical processes can similarly shorten chains. In radical polymerization, termination reactions remove active radical centers, stopping further propagation and producing shorter or end-capped chains.

The consequences of chainbreaking are typically a loss of molecular weight and a broadening of the molecular-weight distribution. This often results in lowered melt viscosity and altered mechanical properties, dimensional stability, and processability. Chainbreaking events also affect the aging and lifetime of polymer materials, influencing performance in applications ranging from plastics to coatings and composites.

Measurement and characterization commonly rely on gel permeation chromatography (GPC/SEC) to determine molecular-weight distributions, along with rheological tests and viscosity measurements. Stabilizers, antioxidants, UV absorbers, and controlled processing conditions are used to mitigate chainbreaking by inhibiting radical formation and oxidative degradation. Understanding chainbreaking is important for polymer design, durability, recycling, and lifetime prediction.