Manfred J. R. Cantow

Sonic Degradation of Polyisobutylene in Solution

Narrow, well‐defined molecular weight fractions of polyisobutylene were irradiated in n‐hexadecane as 3% concentrations by a 10‐kc/sec sonic oscillator. The irradiated polymers were recovered by precipitation and evaporation; the molecular weight distributions were determined by column chromatographic fractionation. Narrow fractions for study had viscosity molecular weights of 15 100, 40 000, 74 400, and 137 000. The changes in distribution are compared with those from a broad distribution polymer with a molecular weight of 40 000. The limiting degree of polymerization below which degradation will not take place is at least as low as 200, and probably 100, for polyisobutylene in solution, considerably lower than the 1000–2000 reported for several polymers.

Polymer degradation VI—Distribution changes on polyisobutene degradation in laminar flow

Abstract Precisely established polymer molecular weight distribution changes with variations in shear degradation history are extensively interpreted. The systems consist of solutions of polyisobutenes degraded in homogeneous, laminar-flow, shear fields. The polymer solutions studied were 9·6 volume per cent in n-hexadecane and 9·7 volume per cent in 1,2,4-trichlorobenzene. The procedure for preparing equilibrium shear degraded systems is described. A new computer programme is used to derive integral and differential distributions as well as molecular weight averages from number to Z +1. The programme also computed distribution inhomogeneities and standard deviations from the different molecular weight averages. It is found that the standard deviation, derived from number and weight average, changes linearly with weight average molecular weight. A predominantly random mechanism of degradation in laminar flow shear is postulated to explain the results. The efficiency of bond rupture due to storage of shear energy in polymer bonds is shown to be low. Equivalent results were obtained in the two solvents.

Gel Permeation Chromatography with Organic Solvents

Abstract Fractionation of polymers either as a means of determining molecular-weight distributions for the characterization of polymers or the preparation of fractions with defined molecular-weight distributions, for subsequent physical and chemical testing, is a valuable and widely used technique. There are many ways of performing fractionations and of measuring molecular-weight distributions; see, for example, the forthcoming book Polymer Fractionation [1]. Gel permeation chromatography is the newest of the fractionation methods and has already found widespread applications; see, for example, the forthcoming review by Altgelt and Moore [2]. Because of its speed and high resolving power and the possibility of a high degree of automation gel permeation chromatography is the most promising current technique for the fractionation of polymers on an analytical scale and, probably, on a preparative scale.