Ondřej Procházka

Association of a three-block copolymer B-A-B in selective solvents for blocks B: spherical micelles

Abstract A theoretical model is proposed for micellization of a three-block copolymer B-A-B in solvents selective for outer blocks B. The association number, the micellar dimensions and the Gibbs energy change accompanying micelle formation are expressed in terms of the structural and thermodynamic parameters of a given block copolymer-selective solvent system.

Light scattering characterization of thermodynamic interaction of polymers in dilute solution. Effect of experimental error and temperature

Abstract Interaction between non-identical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by the interaction parameter A 24 , which is the second virial coefficient for interaction of unlike species. The value of A 24 may be experimentally obtained by light scattering. The determination of A 24 is very sensitive to experimental error in the input data, particularly for mixtures in which one polymer is greatly in excess, and for mixtures of polymers having molecular weights differing by orders of magnitude. A slight rise in A 24 with temperature has been observed for solutions of mixtures of polystyrene and poly(methyl methacrylate) in diethyl malonate in the range 25–100 C. This change in A 24 reflects the increased mutual miscibility of the polymers in solution at elevated temperatures.

Light scattering behaviour of low-molecular-weight polymers in mixed solvents with very high selective sorption

Abstract Some low-molecular-weight polymers (poly(butyl methacrylate), nylon 6, nylon 12) in the solvent system m -cresol/ n -heptane, with effective refractive index increments ( ∂n / ∂c ) μ in the range 0.34−0.81 ml/g, have been studied by light scattering. These extremely large values, measured by differential refractometry of solutions in the state of dialysis equilibrium, are mainly due to very great selective sorption of one solvent component ( m -cresol) on the polymers studied. The effect inherent to these systems, viz. that of the free solvent composition change, has been discussed and exemplified by the light scattering behaviour of solutions of oligomers of butyl methacrylate. The light scattering anomalies observed with solutions of some nylons in m -cresol/ n -heptane have been interpreted as due to interaction of polymer end-groups. It has been demonstrated that the determination of M w of the order of 10 3 by light scattering in systems with large ( ∂n / ∂c ) μ values, i.e. with large scattering power, is possible with good accuracy.

Spherical particles obtained by dispersion polymerization: model calculations

Abstract A model of particles formed in dispersion polymerization is suggested and the Gibbs energy of a single particle at infinite dilution is calculated. By minimizing the energy at fixed particle mass and composition, the particle dimensions are calculated and the degree of swelling of the particles is predicted. The estimated geometric radii are somewhat smaller than the experimental values of the hydrodynamic radii.

Analysis of the effect of experimental errors on the determination of molecular parameters of polymers in dilute solutions

Abstract The effect of experimental error on the determination of molecular parameters of polymers was analysed; the error in their estimation using linear extrapolation to zero concentration was found to be directly related to the slope of the concentration dependence of the measured quantity. The evaluation of light scattering data is discussed in more detail to illustrate the application of the derived relations.