Fourth and fifth generation poly(propylene imine) dendrimers and methyl and benzyl functionalized copolymers of these dendrimers are solution blended with poly(vinyl chloride) (PVC). The methyl-derivative copolymer is observed to be dispersed in PVC as judged by optical and dynamic scanning calorimetry measurements. This dispersion leads to a substantial reduction in the glass transition temperature and a commensurate plasticization effect, demonstrating that functionalized dendrimer copolymers can successfully plasticize semicrystalline polymers. This plasticization is thought to occur as a result of additional free volume from the highly branched structure of the dendrimer. (c) 2007 Wiley Periodicals, Inc.