Thermoreversible aggregation and gelation of poly(n-hexyl isocyanate)

The molecular and supramolecular structure of poly(n-hexyl isocyanate) in n-octane has been studied in the sol state and in the gel state by neutron and light scattering. In the sol state the chains appear stiff with dimensional characteristics consistent with the literature on this polymer. The gel consists of a network phase and free chains. The network phase appears to be an array of cross-section polydispersed fibers which can be described with a cross-section radius distribution function of the type w(r) ∼ r ^-1 with two cut-off radii r_max = 6.7 ± 0.4 nm and r_max = 1.3 ± 0.1 nm. These resulte are compared to the morphology revealed by electron microscopy. The sol state was also studied by dynamic light scattering as a function of concentration, time, and temperature. This revealed the presence of slow and fast modes which could be correlated respectively with the aggregates leading to gelation and to the individual polymer chains. The sol optical activity properties of the pregels revealed a reduction in the population of kinked helical reversals along the backbone consistent with the close parallel packing in the fibers as suggested both by electron micrscopy and neutron scattering.