Polymerization of 2,5‐dimethyl‐3,4‐dihydro‐2H‐pyran‐2‐carboxyaldehyde (methacrolein dimer). Part II

Abstract

Abstract2,5‐Dimethyl‐3,4‐dihydro‐2H‐pyran‐2‐carboxyaldehyde (methacrolein dimer) gave a polymer consisting of only recurring bicyclic structure of 1,4‐dimethyl‐6,8‐dioxa‐bicyclo‐[3,2,1] octane with the use of Lewis acid and protonic acid as catalyst at room temperature. On the other hand, the polymer obtained by using BF3·(C2H5)2O under −78°C. was found to have the structures produced by the aldehyde group polymerization as well as the bicyclic ones. The polymer obtained at −40°C. had a low decomposition temperature (164°C.) owing to the presence of polyacetal group, whereas the fully saturated bicyclic polymer had a considerably high one (346°C.). The main factors affecting the polymerization were polymerization temperature and catalyst. Lowering temperature increased the polymerization of the aldehyde group. Anionic catalysts and weak cationic catalyst such as Al(C2H5)3H2O, which were active catalysts for acrolein dimer, did not initiate the polymerization of methacrolein dimer. The fact that the relative viscosity of the polymer increased with polymerization time shows the polymerization of this monomer is a successive reaction.