How to make opposites compatible Polyethylene (PE) and isotactic polypropylene ( i PP) are the two most widely used commodity plastics and thus make up a large fraction of the waste stream. However, the two plastics will not mix together, which limits options for dealing with mixed waste and decreases the value of recycled products. Eagan et al. report the synthesis of multiblock copolymers of i PP and PE by using a selective polymer initiator (see the Perspective by Creton). The high-molecular-weig ht blocks could be used to reinforce the interface between i PP and PE and allow blending of the two polymers. Science , this issue p. 814 ; see also p. 797