Alternating Copolymers of Limonene with Methyl Methacrylate: Kinetics and Mechanism

The radical copolymerization of limonene (optically active) with methyl methacrylate in xylene at 80±0.1°C for 1 hr, initiated by benzoyl peroxide (BPO) yield alternating copolymer(s), under the inert atmosphere of nitrogen, as evidenced by reactivity ratios r1 (MMA)=0.07 and r2 (limonene)=0.012 using the Kelen–Tüdos method. The kinetic expression is Rα[I]0.5[MMA]1.0[Lim.]−1.0. The decrease in the rate of polymerization with increase in concentration of limonene is due to penultimate unit effect. The overall energy of activation is calculated as 49 kJ/mole. FTIR of the copolymer(s) shows the characteristic frequencies at 1732.40 and 2951.40 cm−1 due to –OCH3 of MMA and aromatic C–H stretching of limonene, respectively. 1H NMR spectra shows peak at 3.8–4.1 δ and 5.3–5.6 δ due to –OCH3 of MMA and trisubstituted olefinic protons [–CH=CH–CH2–] of limonene, respectively.