The Collaborative International Dictionary of English v.0.48:

Unimpassioned \Unimpassioned\
   See impassioned.

WordNet (r) 3.0 (2006):

unimpassioned
    adj 1: free from emotional appeal; marked by reasonableness;
           "answered with an unimpassioned defense"; "the
           unimpassioned intellect"

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "unimpassioned":
   affectless, anesthetized, arctic, autistic, blunt, catatonic,
   chill, chilly, cold, cold as charity, cold-blooded, coldhearted,
   common, commonplace, cool, dispassionate, drugged, dull,
   emotionally dead, emotionless, flat, frigid, frosted, frosty,
   frozen, heartless, humdrum, icy, immovable, impassible, impassive,
   inexcitable, insipid, insusceptible, matter-of-fact, mundane,
   nonemotional, objective, obtuse, ordinary, out of touch,
   passionless, pedestrian, plain, poetryless, prosaic, prose,
   prosing, prosy, self-absorbed, soulless, spiritless, tiresome,
   unaffectionate, unagitated, undisturbed, unembellished,
   unemotional, unexcited, unfeeling, unflustered, unidealistic,
   unimaginative, unimpressionable, unloving, unpassionate,
   unperturbed, unpoetic, unresponding, unresponsive, unromantic,
   unruffled, unstirred, unsusceptible, unsympathetic, untouchable,
   untroubled, vapid