Excellent adhesion to low surface energy substrates such as polypropylene, polyethylene, poly(vinyl difluoride), and poly(tetrafluoroethylene) is obtained with acrylic polymerization initiated by trialkylboranes at room temperature and without need for surface pretreatment. The mechanism of adhesion is a consequence of a series of radical processes resulting from the initial oxidation of the trialkylborane followed by the production of alkoxy and alkyl radicals. This paper will elucidate the mechanism of adhesion using both experiment and theory.