Copolymerization of isoprene with polar vinyl monomers: Reactivity ratios, characterization and thermal properties

Reactivity ratios for the copolymers isoprene (IP)-co-maleic anhydride (MAH) and isoprene (IP)-co-glycidyl methacrylate (GMA) are reported. Copolymers were prepared by free radical polymerization using benzoyl peroxide (BPO) as initiator at 70 °C. These copolymers were characterized by FTIR and 1H NMR. The monomer compositions in the copolymer were determined by 1H NMR and the reactivity ratios (ri) were calculated applying diverse linear methods, namely Finemann–Ross (FR), Inverted Finemann–Ross (IFR), Kelen–Tüdös (KT), Extended Kelen–Tüdös (EKT) and the nonlinear method of Tidwell–Mortimer (TM). By using the latter procedure, the values of the reactivity ratios were estimated as 0.119 and 0.248 for the system IP (1) and GMA (2) respectively; whereas for the IP and MAH system were 0.057 and 0.078 respectively. These values suggest the formation of nearly-alternating copolymers in both systems. Molecular weights were determined by gel permeation chromatography (GPC). Glass transition temperatures (Tg) of the copolymers were obtained by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Good agreement is obtained between experimental Tg values and the model of Couchman. Tg increases when the concentration of polar monomer in the copolymer increases.