Light Scattering from Solubilized Polyacetylene

A solubilized form of polyacetylene (PA) has recently been created by grafting polyacetylene chains onto a polyisoprene carrier chain. The product of this grafting reaction is stable in toluene solution indefinitely. In the present paper static and dynamic light scattering is used to characterize the particles that exist in solution. Polyisoprene is nearly isorefractive in toluene so that nearly all the scattered intensity is due to the PA part. Also, the scattering from the polyacetylene is strongly resonance enhanced. This allowed PA concentrations near 10^-7g/mL to be studied. The excess depolarized (HV) Rayleigh scattering from the solutions is intense. This means that there is a high degree of orientation correlation between PA subunits in the particles. From the angular dependence of the scattered intensity a characteristic length for the polyacetylene part of the particles is calculated (350 Å). This is a lower bound for the radius of gyration for the PA subunits. Dynamic light scattering studies of the depolarized intensity allowed both the translational and rotational diffusion coefficient to be determined (D₀= 3.45 X 10^-8cm²/s) (θ = 153 s^-1). The overall shape was determined by solving the Perrin equations and gave a prolate ellipsoid with major axis a = 1800 Å and axial ratio ρ = 0.4. The present results suggest that the graft copolymer molecules form a micellar aggregate in solution. The polyacetylene subunits are highly ordered in the aggregate, but the degree of order has not yet been quantitatively determined.