Radical polymerization of butadiene mediated by molecular iodine: a kinetic study of solution homopolymerization

Homopolymerization of butadiene (Bu) in 1,4-dioxane (Dox) was performed at 70 degrees C using molecular iodine (I-2) in the presence of 4,4'-azobis(4-cyanovaleric acid) (ACVA), resulting in alpha-carboxyl omega-iodine heterotelechelic polybutadiene. Effect of Dox concentration, molar ratio of ACVA to I-2 and initiator type on the Bu conversion was studied. Inhibition of the reaction by molecular I-2 was observed until complete consumption of the I-2 (induction period). Then, polymerization initiated by carboxyl-functionalized alkyl iodides in situ generated during induction period. ACVA decomposition rate constant (k(d)), induction time (t(ind)) and k(p)(2)/k(t) ratio were calculated using Bu conversion as a function of time data. A good agreement between the theoretical and experimental changes in the conversion versus time was observed, indicating accuracy of the kinetic parameters estimated in this work. Experimental t(ind) was always less that theoretical one. It was attributed to reaction between Bu and I-2, resulting in butadiene diiodide (I-Bu-I) compound. Formation of I-Bu-I species was further confirmed by H-1-NMR analysis of end functional groups (i.e. alkyl iodide and allyl iodide) of polybutadiene chains. Based on the (HNMR)-H-1 analysis, [I-Bu-I]/[I-2](0) ratio was obtained for reaction B4 to be 0.235. It was found that among 1,2 and 1,4 additions, 1,2 addition of I-2 to Bu is the dominant reaction. Exchange constant between the growing and dormant species (C-ex) was estimated using GPC and conversion data to be in the range of 3.20-3.94. Then, M-n and D evolution with conversion was investigated theoretically. Fraction of alpha-carboxyl, omega-iodide heterotelechelic PBu chains (f(HOOC-PBu-I)) relative to all chains was estimated from H-1-NMR data to be 87% for reaction B4.

Automated summary

Homopolymerization of butadiene in 1,4-dioxane was conducted using molecular iodine in the presence of ACVA, resulting in heterotelechelic polybutadiene. The effect of reaction conditions on butadiene conversion was studied, showing the interactions between molecular iodine and butadiene. The study provided insights into the factors affecting the conversion rate of butadiene in this system.