they may be linear or branched typical branched structures contain an elastomeric portion with at least three branches which can radiate out from a central hub or can be otherwise coupled together the non elastomeric blocks which make up 14 to 50 by weight of the block copolymer may comprise homopolymers or copolymers of vinyl monomers such as vinyl arenes vinyl pyridines vinyl halides and vinyl carboxylates as well as acrylic monomers such as acrylonitrile methacrylonitrile esters of acrylic acids etc monovinyl aromatic hydrocarbons include particularly those of the benzene series such as styrene vinyl toluene vinyl xylene ethyl vinyl benzene as well as dicyclic monovinyl compounds such as vinyl naphthalene and the like other non elastomeric polymer blocks may be derived from alpha olefins alkylene oxides acetals urethanes etc styrene is preferred the elastomeric block component making up the remainder of the copolymer is isoprene or butadiene which may or may not be hydrogenated as taught for example in u s pat no 3 700 633 this hydrogenation may be either partial or substantially complete selected conditions may be employed for example to hydrogenate the elastomeric block while not so modifying the vinyl arene polymer blocks other conditions may be chosen to hydrogenate substantially uniformly along the polymer chain both the elastomeric and non elastomeric blocks thereof being hydrogenated to practically the same extent which may be either partial or substantially complete typical of the rubbery block copolymers useful herein are the polystyrene polybutadiene polystyrene polystyrene polyisoprene polystyrene and e g polystyrene poly ethylenebutylene polystyrene and polystyrene poly ethylenepropylene polystyrene these.