Studies of Dilute Solution Properties of Oligomers and Polymers

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On the basis of the helical wormlike (HW) chain model, an experimental study was made of dilute solution properties of flexible polymers over a wide range of molecular weight M, including the oligomer region. Static properties such as the mean-squar13EA\ : e radius of gyratio, mean-square optical anisotropy, mean-square electric dipole moment, and scattering function were determined from light and small angle X-ray scattering and dielectric measurements, and steady-state transport coefficients, i.e., the translational diffusion coefficient and intrinsic viscosity from dynamic light scattering and viscosity measurements for atactic polystirene (a-PS), atactic poly(methyl methacrylate) (a-PMMA), polyisobutylene, and poly(dimethylsiloxane) (PDMS)13EA\ : . From comparisons of the dependences of the above properties on M with the respective HW theoretical predictions, the validity of the model was examined and effects of the stiffness and local conformation of polymer chains on those proper … More ties were clarified. A special care was taken of the stereochemical composition in the case of the asymmetric chains, i.e., a-PS and a-PMMA, and the values of the fraction of racemic diads of the samples for each polymer were confirmed to be the same indepe13EA\ : ndent of M.The main results obtained in this study are as follows.1. All the present experimental results may be well explained by the corresponding HW theories, indicating the validity of the model.2. The four basic HW model parameters have been determined unambiguously for each of the above four polymers.3. On the basis of the model parameters thus determined, the following conclusions may be deduced. (1)The a-PMMA and PDMS chain contours retain large helical portions. (2)In contrast to the usual notion, the a-PMMA chain is stiffer than the a-PS cha13EA\ : in. (3)The PDMS chain is stiffer than usually considered. (4)The PDMS chain is very thin in the hydrodynamic sense.4. The draining effect exists in the steady-state transport coefficients of PDMS, which may be regarded as arising from the facts 3-(3) and -(4) above.5. The ratio of the hydrodynamic linear dimension of polymer chains determined from the steady-state transport coefficients to the static one determined from the mean-square radius of gyration is not a universal constant independent of polymer and s13EA\ : olvent. Less