Mesoglobules of thermoresponsive polymers in dilute aqueous solutions above the LCST

The colloidal stability and characteristics of particles formed by homopolymers of poly(N-vinyl caprolactam), poly(N-isopropyl acrylamide) and poly(vinyl methyl ether) in dilute aqueous solutions above the lower critical solution temperature, LCST, was followed by means of dynamic and static light scattering. Depending on the solution concentration, the homopolymers precipitate or form stable dispersions of monodisperse spherical particles. To obtain colloidally stable aggregates, also called mesoglobules, no stabilising agent was added. The stability of the mesoglobules upon time and dilution at temperatures above the LCST suggests that the particle surfaces possess a hydrophilic character. The size of the formed particles depends on the concentration and the heating rate of the solutions. However, internal structure and shape of mesoglobules are affected neither by the way, how the mesoglobules were prepared, nor by molar mass of individual macromolecules. Mesoglobules of PNIPAM obey the M∝R^2.7 scaling law. Origin of stability of the dispersions vs. expected precipitation is discussed.