A compacted particulate polymer additive composition in a dry granular form formed from a substantially uniform mixture of the following components: (a) at least one particulate sterically-hindered phenolic compound; and (b) one or more particulate polymer additives other than a sterically-hindered phenolic compound; wherein the particles of said composition are held together in compacted dry granular form exclusively or substantially exclusively by contact with dried surfaces of in situ desolvated particles from particles of one or more at least partially solvated components of (a), and optionally by contact with dried surfaces of in situ desolvated particles from particles of one or more at least partially solvated components of (b). Compositions of this type except that there is no component (b) are also described.