Jitka Horská

Aggregation behaviour of stereoregular poly(methyl methacrylates) in dilute solution: light scattering and proton n.m.r. study

Abstract The aggregation behaviour of syndiotactic and isotactic poly(methyl methacrylate) in methyl ethyl ketone, n-butyl acetate, and 2-ethoxyethanol was investigated by light scattering and 1 H n.m.r. spectroscopy. Syndiotactic poly(methyl methacrylate) remains in its molecular form in solution at temperatures above 60°–70°C; on cooling it undergoes aggregation followed by macroscopic separation (precipitation) of the polymer from solution. The rate of these processes depends on temperature, concentration of the polymer, and solvent. Molecular solutions of isotactic poly(methyl methacrylate) can be prepared only by long-term heating at temperatures above 100°–130°C. During cooling, isotactic macromolecules prior to separation form stable associates in the region limited by discrete temperatures, and below this region polymer precipitates. The individual stereo forms of poly(methyl methacrylate) are separated from solution at different temperatures which are above the θ-temperatures of the atactic polymer.

Hydrodynamic properties of linear poly(dimethyl siloxanes) in bromocyclohexane at the theta temperature

Hydrodynamic quantities (sedimentation coefficients s°0,θ, and intrinsic viscosities [η]θ in bromocyclohexane at 310K) and weight-average molecular weights (by light scattering) have been measured for poly(dimethyl siloxane) fractions (45 ⩽ Mw × 10−3 ⩽ 300). The ratio [η]θs°0,θ was found to be invariant with respect to M, and the value of (〈R2〉0M)∞ (where 〈R2〉0 is the mean-square end-to-end distance) computed from [η]θs°0,θ was in good agreement with that found by other methods. It is concluded that the translational friction behaviour is similar to that of other flexible chain polymers and that anomalies indicated by some authors are due to inaccuracies in experimental data.