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Precipitation temperature-concentration measurements on fractions of different molecular weight were used to obtain the theta temperature of isotactic poly-(methyl methacrylate) in acetonitrile, 27.6°. Intrinsic viscosities of a number of fractions were measured at 20, 27.6, 35, and 50°. These measurements were used to calculate the intrinsic viscosity-molecular weight relationship at each temperature and various derived quantities for each molecular weight used.

Calibration of gel-permeation columns would be most directly performed by using narrow fractions of the polymer under study. However, obtaining fractions sufficiently narrow for this purpose is laborious and not always feasible. Further, for columns with a wide distribution of pore sizes, e.g., lo3-lo7 A, a simple, two-parameter, semilog relation will not always adequately represent the dependence of molecular weight on elution volume. This note describes a novel approach for calibrating gel-permeation columns by use of polymers whose molecular weight distributions may be approximated by a generalized, two-parameter, single-peak distribution function similar to that suggested by Schulzl and Zimm.z This distribution function should be valid for most linear polymers having a single-peaked molecular weight distribution.According to this function, the weight fraction dw of a species having a molecular weight between M and M + dM is: dw = p' + qr(z + 1)]-lMZe-~WM

The dilute solution properties (intrinsic viscosity, weight‐average molecular weight, and mean square radius of gyration) of fractions of high conversion, free‐radically initiated poly(methyl methacrylate) samples indicate a slight amount of branching in these samples, consistent with the chain transfer constant with polymer (exclusive of endgroups), Cp = 2.2 ± 0.7 × 10−5, found by Schulz and co‐workers. The dilute solution properties of these fractions are compared with those of fractions of low conversion poly(methyl methacrylate) of comparable molecular weight and with the dilute solution properties of fractions of deliberately branched sample, also of comparable molecular weight. Some evidence was obtained which indicated that impurities in the monomer used for polymerization can lead to additional branching sites in the polymer chains.