Radiation-induced polymerization of β(+)-pinene and synthesis of optically active β(+)/β(−)pinene polymers and copolymers

Poly-β(+)-pinene (pB(+)p) was synthesized with γ irradiation of the monomer β(+)-pinene in bulk under vacuum at 1181 kGy. Also scalemic mixtures of β(+)-pinene and β(−)-pinene were irradiated at 1181 kGy to obtain synthetic copolymers of pB(+)/B(−)p. For comparison also β(−)-pinene was converted into poly-β(−)-pinene (pB(−)p) under the identical conditions adopted for its enantiomer. Furthermore pB(+)p and pB(−)p were also synthesized by thermal processing under the action of a chemical free radical initiator. The optical rotatory dispersion (ORD) of all pBp resins synthesized were accurately studied in the spectral range comprised between 375 and 625 nm and a curious asymmetry in the ORD of pB(+)p versus the ORD of pB(−)p is reported. Furthermore, it is shown that (+)-p-menth-1-ene and (−)-p-menth-1-ene are useful as a model compounds for the pBp resins and for the explanation of the amplification of the optical activity of the β(+)-pinene and β(−)-pinene after their ring-opening polymerization to pB(+)p and pB(−)p. The pBp resins were studied also by FT-IR spectroscopy and by thermal analysis (TGA and DTG).