Polymer compsn. comprises (a) a polyboroxiloxane of structural formula (BO;Si) - (CH3)2SiO - and ave. mol. wt. 2000-5000 (where molar ratio B/Si is 1/4-1/5; (b) polysiloxane rubber, (c) polyolefin, copolymer of olefin and diene or halogenated polyolefin; (d) polyorganosiloxane of ave. mol. wt. 2000-5000; (e) SiO2; and (f) polyvalent metal oxide. Pref. the polyolefin is polyisobutylene, polyethylene or polypropylene. Compsn. is used for the prodn. of electrically insulating tape.
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