Light and small-angle X-ray scattering measurements were taken on cyclohexane and toluene solutions of a polystyrene (PS) polymacromonomer (PM) having side chains consisting of 19 styrene residues and an n-butyl group (butyl-PS PM) at each end. The second virial coefficient, A(2), of the butyl-PS PM in cyclohexane was positive in the temperature range of 15.0-34.5 degrees C, differing from previous results for PS PMs with benzyl ends (benzyl-PS PM) whose A(2) vanished at 34.5 degrees C. The mean-square radius of gyration, < S-2 >, for the butyl-PS PM in cyclohexane at 34.5 degrees C was much larger than that for the benzyl-PS PM with the same side-chain length, indicating large effects of the side-chain ends on intramolecular interactions, whereas the difference in < S-2 > between these polymers in toluene at 15.0 degrees C was quite small. From these data, the stiffness parameter and the excluded-volume strength were determined with the aid of theories for the wormlike chain model. The effects of the side-chain ends on these parameters are discussed according to recently developed theories. Polymer Journal (2012) 44, 252-256; doi:10.1038/pj.2011.132; published online 14 December 2011