Anomalous copolymerization behavior of styrene and ethyl methacrylate at high conversion

Abstract

SUMMARYStyrene and ethylmethacrylate were copolymerized in bulk at 62~and several monomer feed ratios. At moderately high conversion, anomalous copolymerization behaviour occurred. Although the onset of the departures from expected copolymerization behaviour seems to be related to the onset of the gel-effect, this relation did not hold when mimicking higher conversion by adding an amount of homopolymer.Obviously the propagation reactions are not only affected by changes in diffusion characteristics but also by changes in other medium characteristics e.g. interactions between monomeric and copolymeric species. INTRODUCTIONIn many cases the course of a copolymerization process can be described by models considering both monomer reactivity and ultimate unit dependent chain-end reactivity. Among these models, the well-known classical Alfrey-Mayo (AM) model is outstanding. From many studies on copolymers, however, the r-values appear to be dependent on the nature of the solvent (I-5) pressure (3) and temperature (6) but assumingly independent of conversion provided the degree of conversion is moderate and the system is diluted.However, from recent reviews it becomes clear that in some cases even the integrated Alfrey-Mayo model is inadequate to describe the copolymerization behaviour up to high conversions. For example, Johnson (7) and Dionisio (8) reported anomalous behaviour in the copolymerization of the system styrene methyl methacrylate, Kelen (9) in the copolymerization of vinylidene cyanide-maleic anhydride and Zil'Berman (10) in the copolymerization of methacrylamide-methacrylic acid. Recently, we have studied the system styrene-ethyl methacrylate in bulk. We found experimental curves of monomer feed ratio versus conversion that deviate significantly from the relationships to be expected on the grounds of the integrated AM model. Both monomer feed ratio (q) and conversion were calculated from data obtained by quantitatively monitoring monomer concentrations by means of GLC during the entire course of the reaction. This method, introduced by German and Heikens (11,12), is particularly useful in studies on high

Ultrabright Fluorescent Polymeric Nanoparticles Made from a New Family of BODIPY Monomers

“…The continuous lines in Figure represent the average molar fractions calculated by the Skeist equation knowing the initial molar fraction of the BODPY monomer and using the reactivity ratios tabulated for the corresponding model monomers, i.e., styrene (S) for πS 5 , phenyl methacrylate (PhMA) for πPhMA 1 etc. ). ,− In all cases the plots matched well the experimental data points. It can thus be concluded that the tabulated reactivity ratios for model monomers are valid to estimate the microstructure in the fluorescent copolymer.…”

“…styrene (S) for πS 5, phenyl methacrylate (PhMA) for πPhMA 1 etc.). 18,31,32,33 In all cases the plots matched well the experimental data points. It can thus be concluded that the tabulated reactivity ratios for model monomers are valid to estimate the microstructure in the fluorescent copolymer.…”

“…Evolution of the average molar fraction of BODIPY monomer in the copolymer with the overall molar monomer conversion (symbols, experimental values; lines, calculated with the reactivity ratios; initial molar fraction of BODIPY monomer = 2.6 mol %). Monomers πPhMA 1 (green ■ and line, r S = 0.25, r PhMA = 0.50), πPhA 2 (gray ◆ and line, r S = 0.38 determined by the Kelen-Tüdös method, r PhA estimated at 0.50), πEtMA 3 (yellow ∗ and line, r S = 0.46, r EtMA = 0.38), πEtA 4 (pink ▲ and line, r S = 0.8, r EtA = 0.2), πS 5 (blue ● and line, r S = 1, r S = 1).…”