The interaction of elastomers with fine particles has been a subject of great interest and much controversy for many years. This is easy to understand when it is remembered that reinforcement is one of the three great developments that underlie the extensive use of elastomers in our modern world. The other two are, of course the discovery of the principle of vulcanization, and the development of synthetic elastomers, including many having special properties superior to those of natural rubber. A large part of the controversy currently includes specifically the question of the special position—or lack of it—of carbon black as a particulate filler for elastomers. The resolution of this question is beyond the scope of our present knowledge, although strong opinions are held on both sides of the question. However, for two reasons, the present review will be restricted almost entirely to a consideration of the nature of the interaction of carbon black with hydrocarbon elastomers. The first reason for this is the undeniable technological importance of these systems. The second is the relatively small amount of work that has been reported on other types of fillers. In addition, the inclusion of other fillers would certainly add to the complexity of any attempt to analyze polymer-filler interactions at this time. However, it must be admitted that the possibility exists of explaining all polymer-filler interactions ultimately in similar and relatively nonspecific terms. In the past few years, an enormous amount of work has been reported that has a bearing on this problem. From the results of these investigations, a coherent explanation appears to be emerging. This paper attempts to review some of the more important work in this field in order to present an over-all picture of our present knowledge. The problem can be summarized in three questions:

A series of linear polyaryloxysilanes having various combinations of methyl, phenyl, vinyl, and allyl substituents was synthesized by melt-condensing , '-biphenol and dianilinosilanes. These soluble thermo-

SynopsisA series of polyaryloxysilanes was prepared from aromatic diols and dianilino-and diphenoxysilanes. High molecular weight polymers were obtained at temperatures of 200°C. or higher by using melt-polymerization procedures. The polymers, which combine the structures of silicones and polyaromatics, possessed high thermal stabilities and were obtained as materials which ( 1 ) failed to melt or soften at 35OoC., (2) were gumlike at elevated temperatures, or (3) were soluble, film-and fiber-forming polymers capable of being processed as conventional thermoplastics and having potentially useful mechanical properties. The preparation of monomers, general polymerization procedures, and certain structure-property relationships for the thermoplastic polyaryloxysilanes are considered.

GPC appearance volumes have been determined for a series of linear polyethylene, polystyrene, and polybutadiene fractions (Mw/Mn < 1.1) in trichlorobenzene at 130°C. and for the latter two series in tetrahydrofuran at 23°C. A polymer‐type independent relationship between appearance volumes and the equivalent hydrodynamic radii of the polymer molecules has been demonstrated. The equivalent hydrodynamic radius is calculated from intrinsic viscosity data. It is proposed that this relationship can be used to construct a universal GPC calibration curve for polymers that assume a spherical conformation in solution. Methods for applying the universal curve to the determination of molecular weight averages and molecular weight distribution are described. In addition, a method is outlined by which the universal calibration curve can be empolyed for determining number‐average Mark‐Houwink constants from polydisperse samples.