Poly(ethylene-co-butyl acrylate). Phase behavior in ethylene compared to the poly(ethylene-co-methyl acrylate)-ethylene system and aspects of copolymerization kinetics at high pressures

Cloud point data for poly(ethylene-co-butyl acrylate) (EBA)-ethylene and poly(ethylene-co-methyl acrylate) (EMA)-ethylene mixtures are presented to 250 degrees C and 2600 bar as a function of butyl acrylate (BA) content from 5.2, 17.0, 25.2, 40.3, and 100 mol % BA and of molecular weight, and as a function of methyl acrylate (MA) content from 10, 18, 31, 41, and 100 mol % MA. Cloud point pressures initially decrease with increasing BA content at rate of similar to 17 bar/mol % BA up to similar to 40 mol % BA and then they remain relatively constant with further increases in BA content. The cloud point pressures increase with increasing weight-average molecular weight (M(w)), at a rate of similar to 4 bar/10000 M(w). However, cloud point pressures for the EMA-ethylene mixtures initially decrease as the MA content increases to similar to 20 mol % but then increase rapidly as the MA content is further increased. in fact, it is not possible to dissolve poly(methyl acrylate) in ethylene to 240 degrees C and 2600 bar, although poly(butyl acrylate) readily dissolves in ethylene at pressures as low as 800 bar at 50 degrees C. The experimental data are modeled using the SAFT equation of state with two mixture interaction parameters. The EBA copolymers used in this study were synthesized in two different types of continuous-flow reactors at variable-feed compositions, temperatures to 225 degrees C, and pressures to 2000 bar. The number-average degree of polymerization decreases with increasing temperature, and it is significantly affected by transfer reactions to monomer. The chain transfer to butyl acrylate monomer plays a dominant rule among transfer reactions at 150 degrees C, as indicated by the decrease in EBA molecular weight with increase in BA content in the copolymer. The molecular weight polydispersity decreases slightly from 3.0 to 2.5 as the BA content in the copolymer increases to 25 mol %.