The polymer PP, which consists of a poly(p-phenylene) backbone with sulfonate ester and dodecyl side groups, is synthesized by a Pd-catalyzed coupling of the 1,3-propanediol diester of 2-dodecyl-5-methyl-1,4-benzenediboronic acid with 2,2′-bis(3,5-di-tert-butylbenzenesulfonato)-4,4′-dibromobiphenyl. Polymers with various molar masses are obtained, which are soluble without aggregation in conventional organic solvents. The good solubility of this rodlike polymer allows the accurate determination of the molar mass by light scattering, osmometry, and SEC with universal calibration. The dependence of the intrinsic viscosity [η] on the molar mass is determined from both the Mark-Houwink-Sakurada equation and the wormlike chain model. The low value of the persistence length (13 nm) indicates that these polymers are relatively flexible. It is shown that an approximate value of the persistence length, together with the parameters of the Mark-Houwink-Sakurada equation and the wormlike chain model, can be determined using only a single polydisperse sample.

Calculations based on an extended Flory-Huggins-Staverman model demonstrate that miscibility gaps in virtually immiscible blends may encompass a complex pattern of metastable and unstable equilibria that differ little in Gibbs free energy. Examples are given that demonstrate the development of near immiscibility by sideways coalescence of upper-critical and lower-critical gaps upon an increase of the chain lengths of the constituents. The mechanisms of merging are discussed, as well as the effect of chain-length distribution and copolymer composition. The conceivable occurrence of nonstable equilibria may lead to a change in physical properties of immiscible blends with time, here called thermodynamic aging of the second kind.

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Cloud-point and spinodal pressures up to 900 bar were investigated for the system methylcyclohexane/polystyrene using a pressure-pulse-induced scattering technique based on the theory of Debye. The molar-mass range of the polymer samples is 9-50 kg/mol. The values determined isothermally in a large concentration range for a polymer sample with weight-average molar mass Hw = 17,5 kg/mol lead to isopleths which allow the construction of phase diagrams displaying cloud-point and spinodal curves (in terms of temperature or pressure against concentration). Critical isopleths have been determined for three further samples with M,,, = 9,0, M, = 28,5 and M, = 50,O kg/mol. A semi-phenomenological treatment of the data is presented which allows an accurate description of experimental phase diagrams and isopleths for one single sample (PS 17,5). A prediction of the critical P ( T ) curves for the other samples, of different average molar mass, then fails completely. Fitting the model parameters to the critical data of all four samples improves the description of the critical curves but produces phase diagrams showing considerable deviations from the data. One reason for the failure of the model may be sought in its inherent incapability to deal with dilute polymer solutions in which the individual coils are separated by regions of pure solvent. A first rough attempt to deal with this effect already brings a marked improvement in the agreement between experiment and model calculation for the critical curves, albeit at the cost of introduction of a number of adaptable parameters.