Controlling polymer properties through the shape of the molecular-weight distribution

The manipulation of a polymer’s properties without altering its chemical composition is a major challenge in polymer chemistry, materials science and engineering. Although variables such as chemical structure, branching, molecular weight and dispersity are routinely used to control the architecture and physical properties of polymers, little attention is given to the often profound effect of the breadth and shape of the molecular-weight distribution (MWD) on the properties of polymers. Synthetic strategies now make it possible to explore the importance of parameters such as skew and the higher moments of the MWD function beyond the average and standard deviation. In this Review, we describe early accounts of the effect of MWD shape on polymer properties; discuss synthetic strategies for controlling MWD shape; describe current endeavours to understand the influence of MWD shape on rheological and mechanical properties and phase behaviour; and provide insight into the future of using MWDs in the design of polymeric materials. Controlling polymerization is required to fully understand and tune the function of a polymer. Alongside variables such as dispersity, molecular weight and chemical composition, the shape of the molecular-weight distribution has substantial influence on polymer properties. In this Review, we discuss methods to systematically control the shape of a polymer’s molecular-weight distribution, as well as explore the profound effects of shape on polymer properties.