Normal and cross‐linked polystyrene. II. Viscosity behavior of polystyrene cross‐linked in emulsion polymerization

Abstract

By emulsion polymerization at 55°C., samples of styrene‐divinylbenzene copolymer were prepared, whose content of divinylbenzene varied from 0 to 0.150%. Measurements of intrinsic viscosity and of the slope constants β and k′ were made, at 25.0°C. in butanone and in benzene, of these samples and of fractions obtained from them by fractional precipitation. In both solvents the intrinsic viscosity of unfractionated polymer was at a maximum at a divinylbenzene content of about 0.005% and k′ was at a maximum at about 0.10%. Since the gel point was also in the neighborhood of 0.10%, it is concluded that a maximum in k′ is a better indication of the gel point than a maximum in [η]. As with linear polymers, [η] was smaller and k′ larger in the poorer solvent. For the higher fractions of a given lightly cross‐linked sample, k′ increased with increasing intrinsic viscosity, deviating progressively more from the value (0.40 in butanone) characteristic of the low fractions and of linear polystyrene. This progressive deviation appeared to begin at an intrisic viscosity which for different samples decreased with increasing proportion of divinylbenzene. These effects are accounted for qualitatively in termas of Baker's “microgel” concept and the effects of the two solvents on the dissolved molecules and dispersed microgel particles.

Fractionation of Pectins From Sunflowers, Sugar Beets, Apples, and Citrus Fruits

“…T h e values for this increase in slope, calculated as k l in the Huggins equation (20), were 0.042, 0.107, 0.500, 0.657, and 0.513 (100 ml/g) for the fractions from sunflo~~,er pectic acid in order of precipitation. I t has been claimed that k l increases \vith an increase in degree of branching in a polymer (21) and the present data may therefore indicate structural differences between the various fractions from a single pectic acid. Certainly, if the pectic acids were linear polymers, it would be expected that the larger molecules I\-ould be precipitated first and have the higher viscosities.…”

A Study of Graft Copolymers: I. Preparation and Viscosity Behavior

“…Even a very little (i.e., O.O1yo) divinylbenzene copolymerized with styrene was found to produce sufficient non-linearity in the polymer t o increase k ' appreciably (6,19). Indeed, a great deal of evidence has been accumulated for many different polymers showing that non-linearity in polymers leads to high values of kt.…”

“…If one uses polymerization nlethods iilvolving chain trailsfer (1, 3, 13), or copolymerizes lilIanz~so.ipt receioed J a n z~a r y 1 3 , 19. Scltolarslzip, 1955Scltolarslzip, -1954 a monomer with a cross-linking agent, such as a divinyl compound (6,28), or irradiates a partially halogenated polymer in the presence of its monomer (15,16), one obtains a complex mixture of linear and branched polymers that is often difficult to resolve into its components. AIoreover, these methods do not yield polymers with simple branches, but rather encourage the growth of branches on branches or the formation of gel.…”

AN EFFECT OF POLYMERIZATION TEMPERATURE ON THE HUGGINS CONSTANT k′ FOR A DIENE POLYMER

“…In earlier papers, evidence was presented that the Huggins slope constant k' (8) can be a useful measure of branching in high polymers (10,5,3,4). When polymers containing branched species were carefully fractionated, the values of k' obtained with the fractions decreased regularly with the intrinsic viscosity of the fractions, finally reaching, with the lower fractions, a constant value h' characteristic of linear species of the same polymer (5,3,4).…”

“…When polymers containing branched species were carefully fractionated, the values of k' obtained with the fractions decreased regularly with the intrinsic viscosity of the fractions, finally reaching, with the lower fractions, a constant value h' characteristic of linear species of the same polymer (5,3,4). When samples of poly(butadiene-co-styrene), prepared a t several different temperatures but alike in other respects, were studied in this way, the extent of branching was found to decrease with decreasing polymerization temperature.…”