Preparation and characterization of polymers formed by gamma irradiation of (+)-limonene oxide, α-Pinene oxide and β-pinene oxide

Using cobalt-60 gamma rays, the radiation-induced cationic polymerization (in bulk) of α-pinene oxide, &beta-pinene oxide and (+)-limonene oxide has been studied at room temperature. Typical conversions of monomer to polymer of the order of 40.0%, 5.3% and 7.8% per Mrad were recorded for (+)-limonene oxide, α-pinene oxide and β-pinene oxide respectively for the polymers obtained at 25°C. The number average molecular weight (M_n) determined by vapor pressure osmometry (for monomers irradiated at 25°C) indicated the average degree of polymerization (DP_n) of (+)-limonene oxide, a-pinene oxide and α-pinene oxide to be 12.4, 5.8 and 4.0.

Structural analysis with nuclear magnetic resonance (proton and carbon-13) and infra-red (I.R.) spectroscopy showed that upon the opening of the epoxide ring, the bicyclic bridge structure (cyclobutane ring) in α-pinene and β-pinene oxides undergoes a rearrangement during the propagation sequence. There was little or no polymerization through the isopropenyl pendant group of (+)-limonene oxide. The polymerizations of (+)-limonene and β-pinene oxides were strongly retarded by tripropylamine (a known cationic scavenger). Evidence from end groups for proton transfer was found in all three polymerizations. In addition, kinetic evidence for the dependence of the molecular weights on chain transfer was also obtained. Thermal analysis using Differential Scanning Calorimetry (D.S.C.) showed that these polymers have a softening range between 65°C and 85°C.