Abstract: A process for the free-radical polymerization of vinyl aromatic monomers in at least two thermally distinct polymerization stages each between the temperatures of about 70.degree. C and 150.degree. C in the presence of at least two free-radical initiators, one of which initiators is particularly effective at the lowest temperature stage and has the formula ##STR1## wherein R is an alkylene, alkynylene or alkenylene diradical, R.sub.1 is alkyl, alkenyl, alkyn or alkoxy and Rhd 2 is lower alkyl and R.sub.3 is hydrogen or a lower alkyl and a second of which initiators has a 10 hour half-life temperature of at least about 80.degree. C which temperature is at least about 15.degree. C above the 10 hour half-life temperature of the compound of the above formula.

Abstract: Heat formable elastomer products are made by vulcanizing block polymers having a central block of thermoplastic and terminal blocks of vulcanizable elastomer, preferably after addition of separately prepared compatible vulcanizable elastomer. The products when heated, shaped, and cooled, will retain the new shape until reheated, but with altered physical properties. When reheated, they tend to return to their vulcanized condition of shape and physical properties.