Dynamic light-scattering measurements have been made on the ''soft'' polymer: poly(n-laurylmethacrylate) (PLMA) in solution in ethyl acetate over the concentration range 0.1 Γ΅ C Γ΅ 0.9 g/mL as well as melt PLMA. With the concentrated solutions, the hydrodynamic screening length (j h ) scales with an exponent of 00.7 below C Γ 0.3 g/mL. Importantly, j h decreases above 0.3 g/mL, and the concentration dependence increases strongly above this concentration. The latter contrasts with the behavior in a variety of well-studied poly(styrene) solutions, which are inevitably investigated close to the glass point, and for which there is a pronounced increase of j h over the same concentration range. In PLMA solutions, the decrease in j h parallels the behavior of the static screening length (j s ) which has been observed in other flexible polymer systems.
Dynamic ''clusters'' (also termed ''long-range density fluctuations'') contribute a large part of the scattered intensity above the concentration 0.6 g/mL and also in melt PLMA which contrasts with poly(styrene) systems in which they are absent. In common with the clusters recently observed in another polymeric melt, poly(methyl-p-tolylsiloxane) (ref. 9) this component is diffusive. While, however, in the latter system the clusters ''melt out'' at 90ΠC, we find in the well-matured PLMA systems that the cluster amplitude is temperature-independent (within the temperature-time range studied) in the solutions up to at least 80ΠC and up to at least 150ΠC in the melt, which were the highest temperatures examined. The clusters in the PLMA systems have a correlation length of the magnitude 65 nm in the melt, whereas in the solutions this dimension varies between 73 nm at 0.9 g/mL to 126 nm at 0.7 g/mL. In PLMA the clusters are presumed to arise from local segregation owing to the large paraffinic side groups on the chain.