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The growth of branched polymer structures up to the gel point has been examined in a polyester system at two different branch agent concentrations. Several independent measurements of the size and molecular weight of these polymers were made using elastic light scattering, quasi-elastic light scattering, intrinsic viscosity [SI, and size-exclusion chromatography with low-angle light scattering detection. In all cases, scaling relationships between these various properties were displayed for the whole range of molecular weights examined. The weight-average molecular weight scaled as @,p ) T , where p is the extent of reaction and pc is the extent of reaction at the gel point. The exponent y was found to be 1.8 f 0.3. Scaling exponents from the radius-M, and [+M, relationships were evaluated for unfractionated samples. Using these exponents, another critical exponent of gelation, T, and the exponent relating size to molecular weight for a branched polymer in a good solvent, $, could be evaluated. These were compared with values for the same exponents obtained through size-exclusion chromatography of the polymers. The critical exponent 7 was obtained from this fractionation experiment through the shape of the observed distribution function and from the scaling relation between the molecular weight M-, corresponding to the fraction making the largest contribution to light scattering in this separation, and M , for each sample. Good agreement was observed between these two separate measures of T and the one from the unfractionated samples, as well as from both fractionated and unfractionated samples. The measured values were T = 2.29 f 0.03 and $ = 0.48 f 0.02. The distribution functions for polymers were described by a single universal distribution function. The critical exponents for gelation were compared to percolation and Flory-Stockmayer predictions and were found to favor the percolation results, but the agreement with percolation for the exponent 7 was marginal.

The ability to form blends of polymers offers the opportunity of creating a new class of materials with enhanced properties. In addition to the polymer components, recent advances in nanoengineering have resulted in the development of nanosized inorganic particles that can be used to improve the properties of the blend, such as the flammability and the mechanical properties. While traditional methods using copolymer compatibilizers have been used to strengthen polymer blends, here, we show that the inorganic nanosized filler additive can also serve as a compatibilizer as it can localize to the interface between the polymers. We use experimental and theoretical studies to show the fundamental mechanisms by which inorganic fillers with large aspect ratio and at least one-dimension in the nanometer range, can act as non-specific compatibilizers for polymer blends. We examine a series of nanosized fillers, ranging from nanotubes to nanoclays (with varying aspect ratios) in a model polystyrene (PS)/poly(methylmethacyralate) (PMMA) blend. Using a number of experimental techniques such as transmission electron microscopy (TEM), scanning tunneling X-ray microscopy (STXM), and atomic force microscopy (AFM) we postulate that the mechanism of compatibilization occurs as a result of the fillers forming in situ grafts with the immiscible polymers. We also use theoretical studies to show that the aspect ratio and the bending energy of the fillers play a key role in the compatibilization process. Our results indicate that the compatibilization is a general phenomenon, which should occur with all large aspect ratio nanofiller additives to polymer blends.Studies have also demonstrated how colloidal particles are interfacially active agents. [9] Several groups have demonstrated that when nanoscale fillers are added to phase-segregating (wileyonlinelibrary.com)