Abstract: The present invention relates to a process for the functionalization, and preferably the maleation of a polyolefin, preferably polypropylene, by use of a selected class of peroxides which will not cause the molecular weight of the polyolefin to significantly degrade. The class of peroxide initiators which are capable of successful use in the present invention may be more broadly classified as peroxides which have radical fragments when the peroxide is dissociated, which are a combination of R.multidot. and R0.multidot., where R is an aliphatic hydrocarbon, and 0 is oxygen. The preferred peroxide initiators for use in carrying out the present invention so as to obtain the results indicated above are t-butyl peroxypivalate and isononanoyl peroxide. The composition resulting from the practice of the process of the invention is a maleated polypropylene in which the polypropylene has more than 0.3 weight percent grafted maleic anhydride and preferably greater than 0.4 weight percent, for example, from 0.