| abstract |
This invention relates to a method of making crystallizable stereoblock rubbery copolymers by block polymerization of 1olefins having from 2 to 12 carbon atoms. This involves forming successive and alternating polymeric blocks, one of which is formed by contacting simultaneously ethylene or propylene with a dissimilar 1-olefin having from 3 to 12 carbon atoms with a nonstereospecific catalyst in an inert liquid hydrocarbon solvent at 0*-100*C. The feed is so regulated that the thus formed block is an amorphous non-crystallizable atactic copolymer containing from 100 to 2,000 monomer units and in which the molar ratio of the ethylene or propylene component to the dissimilar 1-olefin is from 20:80 to 80:20. The other polymeric block referred to is formed by contacting a single 1-olefin having from 2 to 12 carbon atoms under the same polymerization conditions, the feed being controlled so that the block thus formed is a crystallizable homopolymer block containing from 20 to 200 monomer units in the case of ethylene and from 200 to 1,000 monomer units in the case of 1-olefins having from 3 to 12 carbon atoms. The nonstereospecific catalyst is an ionic-coordination complex of the Ziegler-type capable of polymerizing alpha-olefins in atactic isomery. This invention also relates to the resulting crystallizable stereoblock rubbery copolymers and vulcanizates thereof. The unvulcanized copolymers are amorphous in the undeformed state and are capable of crystallization upon stretching. They have at least three successive and alternating polymeric blocks as described above. |