Chemistry Takes the Peel Out of Paint When a polymer is produced from monomer a decrease in volyne oceon because many of the spacings b e h e e n molecules are converted into covalent bonds, which are about 0.5 A shorter. If the polymerization takes place in a thin film on a substrate the shrinkage may produce lateral stresses large enough t o produce failure oi the film. Prepolymerisntion by heat bodying did not solve the problem because varnishes of useful consistoucy conld not be made from the large rnaeromdecdes withnot dilolion. Meanwhile, a theoretical analysis was made of the percentage of shrinkage that, a film eoold tolerate before failing, and t,his figure wnu lower than carbowto-carbon condensstions could att,ain. Heat bodying in the presence of air helped because i t introduced a small amount of flexible peroxy crasslinks; hut i t was not until recent yeam t h a t air blowing under 1 0 0 T produced prepolymer that had the right molecular weight and axygw content to dry without excessive shrinkage. In eftect,, this latest development has takeu the peel out of paint.
Volume 46, Number 3, March 1969
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