Stereoregulated polymerization in the free propagating species. III. Effect of temperature on the polymerization of vinyl chloride

Abstract

Theoretical treatment had shown that syndiotactic propagation should be slightly favored energetically over isotactic propagation in free radical vinyl chloride polymerization. This prediction has been confirmed experimentally by x‐ray and infrared investigations of vinyl chloride polymers prepared at various temperatures. The initiator was a peroxide, azodiisobutyronitrile, or tri‐n‐butylboron, and had no detectable influence on the x‐ray and infrared results. As the polymerization temperature is lowered, the number of lines or arcs in the x‐ray diffraction pattern and their sharpness gradually increase as a result of the increased crystallinity arising from improved regularity. The regular sequences are indicated to have the syndiotactic configuration from the chain repeat distance. The change in the infrared absorbance ratio of two carbon‐chlorine stretching bands with polymerization temperature can be interpreted in agreement with increasing syndiotacticity at decreasing temperature. With the use of simplifying assumptions, the activation energy difference between isotactic and syndiotactic propagation is estimated to be of the order of one‐half kcal/mole. The stereoregulated free radical polymerization of vinyl chloride is thus qualitatively similar to that disclosed for other monomers.

New initiator for the low‐temperature polymerization of vinyl chloride

“…We can therefore consider a reaction order with respect to methanol; in the composition range where its effect is great, the order is -0. 4 (Fig. 12) if the order with respect to monomer is actually unity arid no sigriificance is attached to the high value derived from Fippre 3.…”

“…Un ordr6 de r6action de -0. 4 par rapport au m6thanol a 6t6 trouv6. Les courbes de vitesve dkcroissaient rapidement avec le temps, ce qui sugghre une diminution de vitesse de production de radicaux en cows de polym6rkation.…”

“…CeXs' + CH30H CeXa(CH30H)-+ X - (4) (where X may be any ion or molecule different from CH30H) have different reactivities towards tetraethyllead (for the sake of simplicity, higher complexes have been neglected). Increasing the monomer concentration must cause the methanol concentration to decrease so that equilibrium (4) is shifted to the left.…”

“…Poly(viny1 chloride) obtained at low temperature is, therefore, mainly syndiotactic. 4 The increase in syndiotacticity and the decrease in structural irregularities, e.g. branching, caused by lowering the temperature lead to more crystalline polymer.…”

The Problem of Order in Polymers.

“…Polymers prepared by stereoregular polymerization mechanisms usually contain stereo-sequence of limited extent. The increasing interest in the properties of isotactic polymers has given rise to a number of papers on the characterization of stereoregular polymers (167,148), determination of tacticities and the extent of the helical conformation (22,169,8,20,231,80), and examination of the properties of polymers with random stereo sequences, by statistical analysis (38,62,63,64,82,153,151,152).…”