PURPOSE: To obtain the titled composition improved in heat resistance, etc. without impairing strength, etc., suitable for even speed jointing boots, etc., by incorporating a chloroprene rubber with a combination of a specific quinoxaline derivative, four kinds of metal compounds as acid acceptor and an imidazole-based deterioration inhibitor.

CONSTITUTION: The objective composition can be obtained by incorporating (A) 100pts.wt. of a chloroprene rubber with (B) 0.1W3(pref. 1W2)pts.wt. of a quinoxaline derivative of formula (R is H, alkyl, etc.), (C) 2W30(pref. 4W10)pts. wt. of four kinds of metal compounds as acid acceptor made up of C1: zinc oxide, C2: magnesium oxide, C3: calcium carbonate, and C4: calcium hydroxide and (D) 0.1W2(pref. 0.3W0.75)pts.wt. of an imidazole-based deterioration inhibitor [e.g. 1,3-bis(dimethylaminopropyl)-2-thiourea].