Stabilised transparent styrene]/butadiene] block copolymer food packaging compositions

摘要

A transparent moulding composition containing (i) an anionically-polymerised star block copolymer of structure (A)m-X where A = a segment of total molecular weight 5000-300000 containing polystyrene (molecular weight 3000-230000) and polybutadiene (molecular weight 2000-30000) blocks with sharp or indistinct block transitions; m = 3-15; and X = residue of an m-functional coupler; and/or (ii) a linear block copolymer with at least 2 polystyrene and at least 1 polybutadiene block of molecular weight values as given above is stabilised against light-, atmospheric oxygen- and/or light-induced degradation by the presence (based on the block copolymer weight) of (a) 0.01-1% alpha-tocopherol; (b) 0.1-2% organic phosphite RO3P where R = alkyl, aryl or cycloalkyl; and preferably also (c) 0.01-0.1% food-grade light stabiliser. Preferably, the compositions contain block copolymers of structure (A)n-X-(B)p. A has total molecular weight 5000-250000; B is a segment of total molecular weight 5000-75000 with at least 1 polystyrene block (molecular weight 2000-60000) and at least 1 polybutadiene block (molecular weight 2000-30000), the block transition being sharp or indistinct; n + p = 3-15; and X = residue of an n + p-functional coupler, with the provisos that n is at most p and at least 1 polystyrene block in A has at least 1.5 times the molecular weight of at least 1 polystyrene block in segment B.