Enhanced nonisothermal crystallization of a series of poly(butylene succinate-co-terephthalate) (PBST) by poly(vinyl butyral) (PVB) as a macromolecular nucleating agent has been examined systematically with various techniques and theoretical modeling. The role of PVB depends strongly on the butylene terephthalate content, PVB content, and cooling rate. The (0.3-0.7 wt %) PVB reduces the spherulitic size, but considerably increases the peak temperature of crystallization, for example, by 28 degrees C for the PBST with 50 mol % terephthalic acid. The effects of PVB are believed to stem from its unique molecular structure. Both the hydroxyl and butyral groups of PVB may synergistically participate in nucleating PBSTs for crystallization because of favorable secondary interaction and affinity of butyral groups with butylene succinate units of PBSTs. Only the Tobin model suffices to describe the nonisothermal crystallization kinetics, while the modified Avrami model is suitable for limited crystallinity. (C) 2017 Wiley Periodicals, Inc.