A series of homopolymer polypropylenes (PPs), within a weight-average molecular weight (M-w) range of 100-1600 kg/mol, were manufactured as dumbbell microspecimens. The effects of the molecular weight and shear-induced crystallization on the mechanical properties and morphology,were studied to gain a better understanding of the structure-property relationship. The results showed that the crystallinity decreased from 50 to 41% and the lamellar thickness increased as M-w increased. Tensile tests demonstrated that the stiffness and especially the tensile strength rose to extremely high values (Young's modulus =2400 N/mm(2), stress at 30% strain =120 N/mm(2)). Furthermore, the strain hardening effect was strongly affected by the lamellar thickness and highly oriented superstructures. Dynamic mechanical analysis demonstrated that the mobility of the molecular chains depended on M-w and on the lamellar thickness. In addition, the viscoelastic properties of unannealed and annealed samples indicated further the existence of shish-kebab structures caused by shear-induced crystallization during injection molding. (c) 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:519-533,2007