The self-assembly of poly(styrene-alt-dimethyl-N,N-propylamide) (SMI) polymers into nanotubes was studied using semiempirical PM3 calculations. Ordered polymer self-assembly results from pi-stacking of styrenes and van der Waals interactions between the maleimide chains. Every styrene, and half of the maleimide chains, in a racemo-di-isotactic SMI polymer form pi-stacks and chain-chain pairs with neighboring racemo-di-isotactic polymer. Racemo-di-isotactic polymers in bent associations form a minimum-energy nanotube structure. Nanorods were observed experimentally with diameters of similar to 5 nm.