PURPOSE: To obtain the title composition of high adhesion to polyolefinic materials by using polydimethylsiloxane, a silane compound, a halogenation agent, and an alcoholate.

CONSTITUTION: The objective composition comprises (A) 100 pts.wt. of polydimethylsiloxane (preferably of 5,000 to 10,000,000 average molecular weight), (B) 30 to 300 pts.wt. of a silane to which 0.5 to 5.0 of 4 functional SiO2 structural units per (CH3)3Si structural unit are bonded, (C) 0.001 to 20 pts.wt. of, a halogenation agent such as N-bromosuccinimide), (D) 0.0001 to 5 pts.wt. of an alcoholate (based on 100 pts.wt. of solid silicone), and, when needed, an organic solvent.