Kinetic study on reactions between polymer chain-ends. Coupling reactions of living polystyrene with chloro-ended polystyrene

The reaction of living polystyrene with chloro-ended polystrene was studied to examine “the kinetic excluded volume effect” on the intermolecular reaction between reactive chain-ends of two monodisperse polymers. The reaction of living polystyrene with 1-chloropentane was also studied as a model reaction (small molecule-polymer reaction). The second-order rate constants, k₂, for the polymer polymer reaction in benzene (with a small amount of tetrahydrofuran to break the association of living-ends) is independent of the degree of polymerization, DP, for the range of DP studied (up to 400). The ratios of the rate constants for the polymer-polymer and the polymer-small molecule reactions, k₂/k₂⁰, are the same in benzene and in cyclohexane (good and poor solvent for polystyrene respectively), showing that the effect of the coil expansion is not large enough to be detected. These results confirm the Flory basic concept that the reactivity of a functional group attached to an inert polymer is not affected by the presence of the polymer chain in activation-controlled reactions.