A series of poly(butylene succinate-co-butylene 2-methyl succinate)s were prepared through variations in the molar fraction of succinic acid to 2-methyl succinic acid, and the effects of methyl substitution on the shear-induced crystallization, nonisothermal crystallization behavior, dynamic rheological properties, crystal morphology, and mechanical properties were investigated. Introducing 2-methyl succinic units reduced the melting temperature and crystallization temperature; this indicated that the substituted units retarded crystallization of the polymer. The Avrami exponents, estimated by modified Avrami plots, ranged from 2.1 to 3.5 and were a little diminished by the substitution. The substitution also reduced the rate of crystallization under shear. However, the effect was diminished with an increasing shear rate because most polymer chains were more regularly arranged at higher shear rates. Dynamic experiments in the solid state revealed that the peak on a plot of the loss tangent against the temperature became sharper at higher contents of the substituted unit, and the peak temperature, the glass-transition temperature, was reduced as the content of 2-methyl succinic acid increased. Wide-angle X-ray diffraction patterns showed that there was little effect of the 2-methyl succinic acid unit on the crystal morphology. The toughness of the polymer was abruptly increased up to 350% at the expense of the tensile modulus. (C) 2004 Wiley Periodicals, Inc.