Thermoplastic silicon block copolymers containing (A) a hard segment polymer constituent prepared from styrene, methylmethacrylate, butylacrylate, acrylonitrile, vinyl monomers, or mixtures therefore, and (B) a soft segment polymer constituent of general formula (I) G-[(SiR2O)mSiR2—X—]n(SiR2O)mSiR2-G wherein R is an optionally halogenated monovalent C1-18 hydrocarbon radical and X is a specific aryl group-containing, silicon bonded radical, and each G may be a radical (A)-Z-(Si) or Z′-(Si) wherein -Z- represents an aryl group-containing bivalent radical and Z′- represents a monovalent aryl group-containing radical, provided that there is, at most, one radical G and one radical Z′- in formula (I). In formula (I), m represents a whole number between 1 and 1000 and n represents 0 or a whole number between 1 and 20, provided that when n does not equal 0, 4≦n·m≦1000.