Effect of high pressure on reactions in the styrene-stable iminoxyl radical system at 80°C

Conclusions

• 1. The length of the induction period for 2,2, 6, 6-tetramethylpiperidin- 1-oxyl-inhibited thermal poly-merization of styrene at 80°C can be considerably reduced by raising the pressure, reduction resulting from the effect of pressure on the initiation reaction and the addition of stable radicals at the styrene double bond.

• 2. The volume changes accompanying activation in thermal initiation and stable radical addition at the styrene double bond have been evaluated.

• 3. Once the induction period has been passed through, the rate of thermal polymerization and the molecular weight of the product polymer are the same as for the uninhibited reaction.

• 4. The rate of thermal polymerization of styrene increases by two orders as the pressure is increased from 1 to 6000 kgf/cm², the corresponding total volume change in activation being −32.5 cm³/mole. The molecular weight of the product polymer remains unchanged as the pressure is carried from 1 to 2000 kgf/ cm²; beyond this point the molecular weight falls off somewhat as the pressure rises, being less by a factor of 1.5 at 5000 kgf/cm² than at atmospheric pressure.

• 5. The existence of an induction period in stable iminoxyl-radical-inhibited polymerization is clearly the result of radical interaction with an active intermediate formed according to the Mayo reaction scheme.