The cluster function given by eq 12 is shown in Figure 6f for an athermal solution arid in Figure 6g for a system with x = 0.45. The cluster function determined from eq 6 is given byThe cluster function derived from eq 7 differs from eq 16 only in the additional term of eq 16, muz/(l + mc). Calculated curves based on these equations are shown in Figure 6i.The Flory-Leonard equation with x = 0.45 gives computer curves in good agreement with the experimental data, whereas x = 0.6 gave a better fit to the al -v1 data ( Figure 5). The Wee equations, derived to determine the effect of flexible side chains on phase equilibria, do not fit as well. This is not surprising, as the rodlike character of the main chain still plays a significant role in the activity expression at low concentration, in contrast to the Flory-Leonard expression.It is clear from the comparison of the experimental data with various theories that the free energy associated with the initial solution process is controlled by polymer side chainsolvent mixing. This is in marked contrast to more dilute polymer solutilons, where the rodlike behavior of the molecules is of major importance to the thermodynamics of this system.3s12ABSTRACT : The Diels-Alder step-growth polymerization of biscyclopentadienones with bisacetylenes, which can produce either para or rneta catenation in the benzene ring formed from the reaction, was shown by a model reaction to yield both types of catenation. The model reaction of 3-(4-biphenylyl)-2,4,5-triphenylcyclopentadienone with 4-ethynylbiphenyl gave products in which the ratios (para to meta) varied with the reaction temperature from 0.55 at 100" to 1.0 at 255". The application of the Arrhenius law to thle data yields a difference in theenthalpy of activation of (AH,* -AH, *) of -1.6 kcal/mol and a difference in the entropy of activation (ASrn * -AS, *) of 3.0 eu. The polymerization reaction of 3,3'-(oxydi-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) followed a second-order rate law, and the rate constants at the temperatures of 225, 200, and 175" were found to be 1 14 X 10-3, 4.6 X I./(mol sec), respectively. The Arrhenius activation parameters as calculated from the rate constants were A H * = 12.4 kcal/mol and AS* = -48 eu, consistent with a Diels-Alder reaction which requires a low AH and a large negative AS. and 2.6 x he Diels-Alder reaction, or diene synthesis, has long