The present invention is related to high molecular weight polycarbonates based on aromatic dihydroxy compounds which contain 5 to 100 mol % preferably 20 to 100 mol % of structural units derived from .alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-hexakisaryl-1,3-and/or -1,4-dimethyl benzene dihydroxy compounds. In a preferred embodiment, the polycarbonate is a copolymer of the hexakisaryl dihydroxy compounds and bisphenols known to be useful in producing polycarbonates. The residues of the hexakisaryl compound may be 5 to 90 mol %, preferably 20 to 70 mol % of the structural units. An especially preferred copolymer is that between the hexakisaryl compounds and .alpha.,.alpha.'-(hydroxyphenyl)-diisopropyl benzenes. These polycarbonates show improved heat stability and higher second order transition temperature points than conventional polycarbonates and are useful in applications involving high service temperatures such as electrical insulating film.