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 1C, differing from previous results for PS PMs with benzyl ends (benzyl-PS PM) whose A 2 vanished at 34.5 1C. The mean-square radius of gyration, /S 2 S, for the butyl-PS PM in cyclohexane at 34.5 1C 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 S between these polymers in toluene at 15.0 1C 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 2011Keywords: branched polymer; light scattering; polymacromonomer; polystyrene; small-angle X-ray scattering; solution properties INTRODUCTIONThe second virial coefficient, A 2 , of linear polystyrene (PS) with a butyl end in cyclohexane at the Y temperature (34.5 1C) was known to increase with decreasing molecular weight, M, when M is lower than 10 4 , which had been considered to be the effects of the threesegment interactions. 1 Yamakawa 2 interpreted this increase as an effect of chain ends in 1992. Since then, studies were undertaken to address the chain-end effect on A 2 for several kinds of polymers. 3-9 Among them, PS solutions were the most precisely examined. Because the chain-end effect on A 2 of linear PS with a benzyl end, in contrast to a butyl end, was negligibly small, 7 the increase in A 2 of PS at low M was ascribed to the effects of the butyl end. Recently, a similar study was carried out on the A 2 of a four-arm star PS with a butyl group at each arm end and showed that the increase in A 2 at Y with decreasing M begins at a higher value of M than that for linear PS with the same end group. 8 This study indicates that the chain-end effect becomes more significant with an increasing number of branches. Therefore, one may expect the chain-end effect to be much larger for comb polymers that have many more branches.Polymacromonomer (PM), a type of comb-branched polymer with dense side chains, is known to behave as a stiff chain in solution because of the interactions between its side chains. [10][11][12] We have studied PM consisting of a PS main chain and PS side chains with a benzyl group at each end (benzyl-PS PM) and showed that its A 2 in cyclohexane vanishes at 34.5 1C, which is identical to the Y temperature of linear PS in cyclohexane. [13][14][15][16] In contrast, the values of A 2 for PM consisting of a polymethacrylate main chain and PS sid...

The temperature coefficient d lnhR 2 i 0 =dT of the unperturbed mean-square end-to-end distance hR 2 i 0 with T the absolute temperature was determined from light scattering measurements for atactic polystyrene (a-PS) with the fraction of racemic diads f r ¼ 0:59 and atactic poly(-methylstyrene) (a-PMS) with f r ¼ 0:72, both in toluene (good solvent) and in the range of temperature 15.0-55.0 C, on the assumption that the binary-cluster integral and hence the gyration-radius expansion factor do not depend on T. It is then found that d lnhR 2 i 0 =dT is definitely negative for a-PS with a weak helical nature but almost vanishes for a-PMS with a strong helical nature. The results are consistent with the helical wormlike chain theory prediction. [