The melt rheology of highly-purified ring polystyrenes in a wide range of molecular weights (10K ≤ M w ≤ 240K g/mol) was investigated. All the rings revealed no obvious rubbery plateau and faster terminal relaxation compared to the linear counterparts. The rheological data obtained were compared with some theoretical models such as the Rouse ring model and the lattice-animal model. Moreover, two rheological parameters, zero-shear viscosities η0 and the steady-state recoverable compliances J e, were estimated, and their M w dependence was discussed. From these data analysis, it was found that relaxation mechanisms of ring chains can be divided into three categories depending on their M w as follows: (i) Smaller rings (M w ≤ 20K) exhibit faster terminal relaxation than the predicted Rouse rings. This behavior is related to the difference of the local chain conformation from linear chains. (ii) Rings with the moderate molecular weight (40K ≤ M w ≤ 90K) exhibit dynamic moduli similar to the Rouse ring prediction. (iii) A larger ring (M w > 90K) also shows deviant behavior from the Rouse chain because its relaxation time is much longer than the Rouse ring prediction and also the lattice-animal model, where some intermolecular interactions are considered to occur.

The persistence length of isotactic poly(hydroxy butyrate) was measured using small-angle neutron scattering. The value obtained from these measurements reflects a high degree of local chain persistence. If this local persistence is accounted for, scattering from these chains can be globally fit with Gaussian scaling. A global scattering function, the unified equation, is used, which decomposes the chain structure into two levels, one corresponding to the Gaussian regime and one to the persistence regime. The persistence length obtained using this global scattering function is compared to that obtained using the graphical approach of Kratky and Porod with good agreement. Additionally, the global fitting approach of Sharp and Bloomfield is also considered. The Kratky and the Sharp and Bloomfield approaches appear to yield different values for the persistence length. Additionally, the Sharp and Bloomfield function does not allow inspection of the component parts of the fit. One advantage of both global functions is that the level of statistical confidence in the persistence length can be determined in a least-squares fit. Another advantage is the removal of ambiguity concerning an apparent regime of non-Gaussian scaling between the persistence scaling regime and the Gaussian regime.

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We prepared five pairs of hydrogenous and deuterated ring polystyrene samples over a wide range of molecular weights (10 kg/mol ≤ M w ≤ 400 kg/mol) and investigated their chain conformations in bulk by small-angle neutron scattering (SANS) measurements. From the SANS profiles obtained, we estimated the radii of gyration R g of the ring polymers by the Guinier approximation. R g can be related to the degree of polymerization N as R g ∼ N 0.47 . This scaling exponent ν = 0.47 ± 0.01 is evidently smaller than that for the Gaussian chains (ν = 0.50) but higher than previous experimental reports (ν = 0.42−0.43). Then our data were compared with various simulation and experimental data by introducing the entanglement degree of polymerization N e for linear polymers as a normalized parameter. R g of three smaller rings, i.e., R-10, R-30, and R-70, where the numbers denote molecular weights in kg/mol unit, are in good agreement with simulation results, while two larger rings, R-100 and R-400, exhibit higher R g values than the simulations. Considering that the latter two higher molecular weight samples include maximum 3% of linear contamination, their effects on chain dimension were calculated. As a result, it has been confirmed that 3% of linear contaminations can overestimate R g of rings as much as 6% for R-100 and 12% for R-400. Thus, R g for pure large rings should be considerably lower than the present experimental values. We conclude Flory's exponent v in R g ∼ N v for rings may not be constant but rather show molecular weight dependence due to their topological constraint.