Hydroxyl-modified polypropylcncs (PPOH) with side chains containing OH groups were synthesized by the copolymerization of propylene with undecenyl- oxytrimethylsilane monomer. Copolymers with OH concentration ranging from 1.3 to 3.9 mol% were produced and their properties compared with unmodified polypropylene. The presence of intermolecular H-bonding between the OH groups affected the base polypropylene structure as well as its thermal and rheological properties. As predicted by Flory's theory of melting point depression in copolymers, the melting point reduced with increasing [OH]. While the crystal structure remained unaffected, the crystal size reduced by approx. 15%. Crystallinity for PPOH polymers was also reduced by as much as 40% because of the hindrance to the ordered packing of backbone chains into the lamellar structure. On the other hand, the rheological properties such as the melt strength and the elasticity increased for the PPOH polymers. PPOH with only 3.9 mol% OH groups displayed a gel-like rheological behavior suggesting the formation of a weak clastic network in the melt.