Block copolymers by combination of cationic and radical routes: 4. Cationic polymerization of tetrahydrofuran initiated by difunctional azo-oxocarbenium initiator

The kinetics of the bulk polymerization of tetrahydrofuran initiated by 4,4-azobis(4-cyanopentanoyl chloride) in conjunction with silver salts have been studied at -20, 0 and 10°C. Propagation rate constants increase with increasing temperature (k_p = 4.7 × 10^-4 at -20°C, 3.7 × 10^-3 at 0°C and 1.2 × 10^-2 l mol^-1 s^-1 at 10°C) and an Arrhenius plot gives an activation energy of 57.6 kJ mol^-1. The enthalpy and entropy changes were estimated to be ΔH_p = -24 kJ mol^-1 and ΔS°_p = -86.7 JK^-1 mol^-1 respectively. Spectroscopic and degradation studies showed that polymers obtained via this initiation method contained one azo linkage per macromolecule chain.