Chain scission

Chain scission is a term used in polymer chemistry describing the degradation of a polymer main chain.^[2] It is often caused by thermal stress (heat) or ionizing radiation (e.g. light, UV radiation or gamma radiation), often involving oxygen. During chain cleavage, the polymer chain is broken at a random point in the backbone to form two - mostly still highly molecular - fragments.^[3]

IUPAC definition

chain scission: A chemical reaction resulting in the breaking of skeletal bond.^[1]

Depolymerization, on the other hand, is the elimination of low molecular weight substances (monomers, dimers and suchlike) from a polymer.^[4]