Copolymerization studies. II. Effect of high pressures on monomer reactivity ratios

Studies of the effect of pressure on comonomer reactivity ratios in the styrene—acrylonitrile and methyl methacrylate—acrylonitrile systems show that the values of r1 and r2 increase in both cases and that the relative activation volumes (ΔV11‡ − ΔV12‡) are −9.8 and −9.5 cc./mole respectively, where acrylonitrile is monomer 2. The product r1r2 increases toward unity in both systems. A study of the effect of temperature on these reactivity ratios shows that (ΔH11‡ — ΔH12‡) is essentially zero for methyl methacrylate—acrylonitrile, but 500 cal./mole for styrene—acrylonitrile. Within the pressure range studied, it has been found that the e values for the two monomer pairs are dependent upon pressure, tending to become equal, the higher the pressure, while the Q values are relatively unaffected by pressures up to 1000 atm.