Halogeno-modified polystyrene: monomer reactivity ratios, thermal behaviour and flammability

Chemical modification based on incorporation of flame retardants into polymer backbones was used in order to reduce flammability of polystyrene (PSt). The halogeno-substituted styrenes: 4-chlorostyrene (ClSt), 4-bromostyrene (BrSt) and 2,3,4,5,6-pentafluorostyrene (5FSt) were applied as reactive flame retardants. Homo- and copolymers of these halogeno-substituted styrenes and styrene (St) were synthesized with various feed ratios using free radical bulk polymerization with azobisisobutyronitrile as a initiator. This yielded series of (co)polymers with various amounts of included ClSt, BrSt and 5FSt (5-50 mol% of modified St). Copolymer compositions were determined using H-1 NMR spectroscopy. The relative reactivity ratios of the used comonomers were determined by applying conventional linearization methods. The Jaacks (J) method was used for systems including BrSt and ClSt monomers whereas the Fineman-Ross method was additionally used to confirm the values of reactivity ratios of St-5FSt. The reactivity ratios of comonomer pairs obtained from J plots were 0.75 and 0.38 (St-ClSt), 1.65 and 0.46 (St-BrSt), 0.44 and 0.42 (St-5FSt). Glass transition temperature and thermal stability of obtained (co)polymers were determined using differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The thermal degradation kinetic of PSt, PClSt, PBrSt and P5FSt was studied applying TGA. Kinetic parameters such as thermal decomposition activation energy (E) and frequency factor (A) were estimated using Ozawa and Kissinger models. The resulting activation energies estimated using these two methods were quite close. The values of activation energy (kJ mol(-1)) increased in the following order: PClSt (E(O) = 216.1) < PSt (E(O) = 219.9) < PBrSt (E(O) = 224.7) < P5FSt (E(O) = 330.9). A pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. (c) 2014 Society of Chemical Industry