Higher aliphatic polyaldehydes. IV. Transitions in poly(n-valeraldehyde), poly(n-hexaldehyde), poly(n-heptaldehyde), and poly(n-octaldehyde)

Crystalline polymers of n-valeraldehyde, n-hexaldehyde, n-heptaldehyde, and n-octaldehyde were prepared by anionic polymerization with lithium tertiary butoxide as the initiator at low temperatures. The polymers were end-capped with acetic anhydride, and their thermal stability was studied primarily by DTG. It was found that all polymers degrade rapidly above 150°C. All polymers show a dual melting-point behavior. The first melting region, which is associated with the melting of the side chain, is 80–85°C for poly(n-valeraldehyde); 87–90°C for poly(n-hexaldehyde); 78–101°C for poly(n-heptaldehyde); and 41–69°C for poly(n-octaldehyde). Annealing and quenching of the samples showed that this melting-point region consisted of several endotherm peaks whose intensity changed according to the thermal history of the sample. Although the samples are apparently highly crystalline, the side-chain crystallinity is apparently only in the 20% range.