Star-Branched Polymers. 5. The ι Temperature Depression for 8- and 12-arm Polyisoprenes in Dioxane

The θ temperature depression for a series of low molecular weight 8- and 12-arm polyisoprene stars has been measured in dioxane. Previously, Hadjichristidis and Roovers demonstrated that the low molecular weight 4- and 6-arm starshaped polyisoprenes did not show, in dioxane, depressed 6 temperatures. This was ascribed to the 1/3 - X2 term having a nearzero value in this solvent. However, our results show that the 1/3 - X2 term values are greater than zero for the 8- and 12-arm star cases and that these values increase as the degree of branching increases. Values for the term V3 - X2 have been calculated for two separate cases of g values, to wit, g theoretical and g (limiting) as Mw→À. The calculation of the V3 - X2 values was accomplished using a modification of the three-parameter theory of Candau, Rempp, and Benoit. The modification was necessary since the Candau, Rempp, and Benoit treatment was found to poorly approximate the experimentally observed decrease in 8 temperature of the 8- and 12-arm polyisoprenes.