▁Hor ne ▁studied ▁the ▁Z ieg ler ▁catal yst ▁variables ▁as ▁well ▁as ▁other ▁process ▁variables ▁and ▁their ▁effect ▁on ▁poly but ad iene ▁structures . ▁He ▁demonstrated ▁that ▁a ▁wide ▁variety ▁of ▁mixed ▁c is ▁and ▁trans ▁structures ▁could ▁be ▁obtained ▁by ▁the ▁proper ▁choice ▁of ▁r ati os ▁of ▁tit an ium ▁t et rach lor ide ▁to ▁org ano - al umin um . ▁By ▁replacing ▁the ▁tit an ium ▁t et rach lor ide ▁with ▁tit an ium ▁t etra iod ide , ▁he ▁obtained ▁poly but ad iene ▁with ▁ 9 0 - 9 5 % ▁c is - 1 , 4 - struct ures . ▁ ▁Catal yst s ▁based ▁on ▁c ob alt ▁sal ts ▁were ▁very ▁useful ▁for ▁prepar ation ▁of ▁c is - 1 , 4 - poly but ad ien es . ▁Although ▁many ▁c ob alt ▁sal ts ▁were ▁suitable , ▁Hor ne ▁used ▁c ob alt ▁oct o ate . ▁He ▁showed ▁that ▁c ob alt ▁can ▁function ▁under ▁heter ogeneous ▁or ▁hom ogeneous ▁conditions . ▁He ▁prepared ▁at ▁- 7 8   ° C ▁a ▁poly but ad iene ▁with ▁ 9 9 . 8 % ▁c is - 1 , 4 ▁structure , ▁which ▁was ▁the ▁highest ▁percentage ▁of ▁c is - 1 , 4 ▁structure ▁he ▁had ▁ever ▁seen . ▁He ▁defined ▁the ▁effect ▁of ▁temperature , ▁sol vent , ▁and ▁other ▁add it ives ▁to ▁the ▁catal yst ▁to ▁produce ▁the ▁highest ▁percentage ▁of ▁c is -