Poly(1,2-butadiene) promotes crosslinking of branched polyethylene, which indeed indicates partial miscibility of the two polymers. Dynamic mechanical spectroscopy and transmission electron microscopy of blends of branched polyethylene and poly(1,2-butadiene) indicated that the polymers are partially immiscible even in the blend with only 3% of poly(1,2-butadiene). The thermal oxidative stability at temperatures above the melting point of samples stabilized with antioxidants was essentially unaffected by the percentage concentration of poly(1,2-butadiene), whereas the stability towards external partial discharges was lower in crosslinked polyethylene blends containing poly(1,2-butadiene) than in pure crosslinked polyethylene.