1 , 2 - dichlorodisilanes are reacted with organometallic derivatives of 1 , 2 - diethynyldisilane to yield the copolymer : -- c . tbd . c -- sir . sub . 2 sir . sub . 2 -- c . tbd . c -- sir &# 39 ;. sub . 2 sir &# 39 ;. sub . 2 --. sub . n where r and r &# 39 ; are alkyl or aryl groups having carbon atoms numbering less than ten .