C1 to C3 alkyl, branched C1 to C3 alkyl, phenyl, or benzyl groups, and, optionally: (aii) an antioxidant additive selected from the group consisting of tetra(thioether)pentaerythritols, or (ai) a thiopropionate anti-oxidant additive of formula: wherein R5 is an alkyl group having from 1 to 15 carbon atoms inclusive and x is an integer of between 1 and 4 inclusive, or phosphites (c). 11.