A series of polymacromonomer samples (F15) consisting only of polystyrene and having a fixed side chain length of 15 styrene residues have been prepared and studied by static light scattering in cyclohexane at different temperatures and in toluene at 15 °C. The measurement has also been made on polymacromonomer samples (F33) of the same kind but with 33 side chain residues in toluene. The second virial coefficient for the F15 polymer in cyclohexane vanishes at 34.5 °C, the ϑ temperature for linear polystyrene, as was previously found to be the case for the F33 polymer. Analysis of the measured mean-square radii of gyration based on the wormlike chain with or without excluded volume shows that, while the contour length per main-chain residue is insensitive to the side chain length, the Kuhn segment length λ -1 (or more generally the stiffness parameter in the helical wormlike chain) under the ϑ condition remarkably increases with increasing side chain length and that the λ -1 values (16 and 36 nm) for the polymacromonomers F15 and F33 in toluene, a good solvent, are about 1.6 times as large as those in the ϑ solvent. Thus, it is concluded that, in addition to the high segment density around the main chain, repulsions between the main chain and side chain and between neighboring side chains play an important role in the high stiffness of polymacromonomers.

ABSTRACT:Nine samples of a polymacromonomer consisting of polystyrene with a fixed side-chain length of 33 styrene residues and ranging in total weight-average molecular weight Mw from 1.9 x 10 5 to 1.1 x 10 7 have been prepared and studied by light scattering in cyclohexane at temperatures between 25 and 45°C. The second virial coefficient is found to vanish at 34.5 ( ± 2)"C, the e temperature for linear polystyrene in cyclohexane. The Mw dependence of z-average mean-square radius of gyration (S 2 )= at this temperature is analyzed on the basis of the wormlike chain to obtain 22 nm for Kuhn's statistical segment length A.-1 and 13000 nm-1 for the molar mass per unit contour length. The chain stiffness as indicated by this A.-1 value is one order of magnitude higher than that of linear polystyrene. Analysis of (S 2 )= at temperatures other than the e point is also made with the aid of the quasi-two-parameter theory for excluded-volume effects. It is found that }. Tsukahara et al. 1 -3 were the first to synthesize polymacromonomers consisting of the poly(methyl methacrylate) (PMMA) backbone and polystyrene (PS) side chains. These regular comb polymers have since called considerable attention of polymer physical chemists who are interested in molecular characterization of polymers in dilute solution. Analyses of dimensional and hydrodynamic data 4 -6 in toluene, a good solvent, based on the unperturbed wormlike chain 7 show that the polymacromonomers studied are much stiffer than linear PMMA and that the Kuhn segment length A -1 becomes larger as the molecular weight of the PS side chain increases. This pronounced effect of branching on chain stiffness raises a new matter of interest to be explained in terms of interactions between the main chain and side chains and those between neighboring side chains in a polymer molecule. For fundamental studies of such intramolecular interactions use of polymacromonomers composed of single polymer species is desirable to avoid complexity arising from interactions between the PMMA and PS sub-chains.In this work, we prepared nine samples of a polymacromonomer consisting only of PS and commenced their dilute-solution characterization by light scattering as a first step toward understanding the effects of molecular architecture and intramolecular interactions on chain stiffness. Figure 1 shows the chemical structure of the polymacromonomer, whose side chains have a fixed degree of polymerization (n) of 33. We note that Tsukahara et al. 3 • 8 already synthesized similar polymacromonomers but reported no solution data.At an early stage of the present study, we found that our polymacromonomer attains the e condition in cyclohexane around 34.5°C, the e temperature for linear PS. This first example of the e state found for polymacromonomers prompted us to see by measurements of the z-average mean-square radius of gyration (S 2 )z how much the PS backbone is stiffened by the presence of long branches. In the work reported below, the (S 2 )z data in cyclohexane obtained as a function o...

Viscosity measurements have been made on two series of polymacromonomer samples consisting only of polystyrene (PS) and having fixed side chain lengths of 15 and 33 styrene residues (designated F15 and F33) in cyclohexane at 34.5 °C (the ϑ temperature) and in toluene at 15 °C (a good solvent). The intrinsic viscosities [η] obtained as functions of (total) weight-average molecular weight M w (in the ranges from 5.1 × 103 to 6.5 × 106 for the F15 polymer and from 5.4 × 104 to 1.1 × 107 for the F33 polymer) are analyzed on the basis of the wormlike chain with or without excluded volume. They are described quantitatively by the current theories over the almost entire range of M w studied, when the contribution of side chains near the main-chain ends to the polymacromonomer contour is incorporated into the analysis. The estimated parameters are consistent with those derived previously from gyration radius data, confirming that while the contour length per main-chain residue in the ϑ or good solvent is close to the value expected for the all-trans conformation, the chain stiffness is much higher in the good solvent than in the ϑ solvent due to enhanced monomer−monomer repulsions. The hydrodynamic diameter for each polymacromonomer in cyclohexane, slightly smaller than that in toluene, is about twice as large as the unperturbed end-to-end distance expected for the linear PS molecule having the same degree of polymerization as the side chain.

ABSTRACT:Light scattering and viscosity measurements were made on cyclohexane and toluene solutions of a series ofpolymacromonomer samples consisting of polystyrene with 65 monomer units in each side chain to determine the z-average mean-square radius of gyration< s 2 >,and the intrinsic viscosity [I]] as functions of the weight average molecular weight in a range from 2.9 X 10 5 to 8.6 X 10 6 • The theta temperature for the polymacromonomer in cyclohexane was determined to be 34.5°C. The ,data in this solvent at 34.5°C and toluene at 15°C (a good solvent) were quantitatively described by the wormlike chain with II. 1 (the Kuhn segment length)=36 nm and ML (the molecular weight per unit contour length)=25000nm-1 in the former and with ll.-1 =75nm and ML=25000nm-1 in the latter. The molecular weight dependence of [I]] in each solvent was also explained by this model chain when the end effect arising from side chains near the main-chain ends was taken into account. The above II. -l values in the two solvents and the previous estimates for polystyrene polymacromonomers with shorter side chains were used to examine the dependence of the backbone stiffness on side chain length. It was found that II. -l increases almost linearly with the side-chain molecular weight for both solvents but with a larger slope in toluene than in cyclohexane.KEY WORDS Light Scattering I Intrinsic Viscosity I Polystyrene Polymacromonomer I Wormlike Chain I Chain Stiffness IIn previous studies of this series, 1 -4 we found from light scattering and viscosity measurements that two polymacromonomers consisting of polystyrene with 15 and 33 styrene units in each side chain (polymacromonomers F15 and F33) behave like wormlike chains in cyclohexane at the theta temperature and in toluene, a good solvent, at 15'C. The backbone stiffness expressed in terms of the Kuhn segment length A -1 was higher for the F33 polymer, being consistent with the earlier finding5-7 that for polymacromonomers consisting of the poly(methyl methacrylate) backbone and polystyrene side chains in toluene (a good solvent), A -1 increases with side chain length. We also found that A -1 is larger in the good solvent than in the theta solvent for both F15 and F33. These findings ought to be theoretically explained in terms of side chain-side chain and side chainmain chain interactions, but at present, we deem it necessary to extend the experimental work to a polystyrene polymacromonomer with a larger side chain length in order to establish the experimental relations between the backbone stiffness and the side chain length in both theta and good solvents.Thus we prepared polystyrene polymacromonomer samples with 65 side chain units and different mainchain lengths, and determined z-average mean-square radii of gyration < s 2 >z and intrinsic viscosities [7]] for them by static light scattering and viscometry in cyclohexane at the theta temperature and in toluene at 15°C. In the work reported below, we analyze the results on the basis of the wormlike chain and compare the e...

No abstract