Free‐radical copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate studied by ¹H NMR kinetic experiments

Abstract

The free-radical copolymerization of m-isopropenyl-␣,␣Ј-dimethylbenzyl isocyanate (TMI) and styrene was studied with 1 H NMR kinetic experiments at 70°C. Monomer conversion vs time data were used to determine the ratio k p ϫ k t Ϫ0.5 for various comonomer mixture compositions (where k p is the propagation rate coefficient and k t is the termination rate coefficient). The ratio k p ϫ k t Ϫ0.5 varied from 25.9 ϫ 10 Ϫ3 L 0.5 mol Ϫ0.5 s Ϫ0.5 for pure styrene to 2.03 ϫ 10 Ϫ3 L 0.5 mol Ϫ0.5 s Ϫ0.5 for 73 mol % TMI, indicating a significant decrease in the rate of polymerization with increasing TMI content in the reaction mixture. Traces of the individual monomer conversion versus time were used to map out the comonomer mixture composition drift up to overall monomer conversions of 35%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed was observed. This depletion became more pronounced at higher levels of TMI in the initial comonomer mixture.

Judicious selection of bifunctional molecules to chemically modify graphene for improving nanomechanical and thermal properties of polymer composites

“…Several benets are associated with our work: (i) m-TMI does not homopolymerise through radical initiators or heating due to the steric hindrance of its a-methyl group; 13,14 (ii) the isocyanate (NCO) group of m-TMI is less sensitive to water because of the adjacent isopropyl group; 13 (iii) GO covers many hydroxyl and carboxyl groups that are available for reacting with NCO of m-TMI; 15,16 and (iv) the vinyl-benzyl groups of m-TMI easily copolymerise with vinyl monomers such as acrylates and styrene. Several benets are associated with our work: (i) m-TMI does not homopolymerise through radical initiators or heating due to the steric hindrance of its a-methyl group; 13,14 (ii) the isocyanate (NCO) group of m-TMI is less sensitive to water because of the adjacent isopropyl group; 13 (iii) GO covers many hydroxyl and carboxyl groups that are available for reacting with NCO of m-TMI; 15,16 and (iv) the vinyl-benzyl groups of m-TMI easily copolymerise with vinyl monomers such as acrylates and styrene.…”

Free‐radical homo‐ and copolymerization of vinyl acetate and n‐butyl acrylate: Kinetic studies by online 1H NMR kinetic experiments

“…Free-radical copolymerization of the BA and VAc was performed in benzene-d 6 by using BPO as the initiator at 70 C. Kinetics of this copolymerization system were investigated completely by online 1 H NMR kinetic experiments. Comonomer reactivity ratios were obtained by the TUM at low and medium/high conversions as well as by the simplified PUM with r 2 ¼ 0.…”

“…Although approximately 10 min has passed from insertion of sample into the cavity relative to the first scan, negligible conversion has occurred due to the low overall rate of reaction. It should be noted that all kinetic samples contained high amounts of benzene-d 6 . This high amount of benzene-d 6 had to be used because of better thermal conductivity of benzene relative to the comonomer mixture, maintaining the system isothermal due to the decreased concentration of comonomers and thereby decreased polymerization rate and to avoid an excessive viscosity increase at higher conversions.…”

“…[5][6][7][8][9]19,20 Kinetic parameters of the comonomer reactivity ratios and overall polymerization rate coefficients can be derived by this online technique. Davis et al 5,6 applied this technique for copolymerization of styrene with other comonomers and estimated the overall polymerization rate coefficient. Our group determined copolymer composition and then the comonomer reactivity ratios for conventional free-radical copolymerization of various comonomer pairs by online 1 H NMR kinetic experiments.…”

“…[1][2][3][4] Following the reaction conversion by online 1 H NMR spectroscopy so called online 1 H NMR kinetic experiment has been successfully used to study kinetics of the free-radical homo-and copolymerization reactions. [5][6][7][8][9] Online 1 H NMR kinetic experiments allow us to simultaneously calculate individual and overall comonomer conversions as well as the comonomer mixture and copolymer compositions as a function of reaction progress. This is one of the advantages of this online technique in comparison with the offline techniques and some of the online techniques.…”