Process for the preparation of bitumen-polymer composition

A process for the preparation of bitumen-polymer compositions wherein, at a temperature comprised between 100.degree. C. and 230.degree. C., bitumen is mixed with a block copolymer of styrene and of a conjugated diene selected from the group consisting of butadiene, isoprene, chloroprene, carboxylated butadiene and carboxylated isoprene, said block copolymer being used in a quantity comprised between 0.7% and 10% by weight of bitumen, and with a coupling agent M containing a sulphur-donor compound, and the mixture is kept within said temperature range and under stirring for a duration of at least ten minutes, wherein said coupling agent M is comprised of, by weight, from 1% to 100% of a component. A consisting of at least one sulphur-donor vulcanization accelerator and from 99% to 0% of a component B consisting of elementary sulphur vulcanizing agent, wherein said coupling agent is used in a proportion to furnish a quantity of sulphur representing, by weight, from 0.5% to 10% of the block copolymer used to produce the bitumen-polymer composition and wherein said at least one sulphur-donor vulcanization accelerator is selected from the group consisting of morpholine disulphide, N,N'-disulphide of caprolactame and the thiuram polysulphides of the formula ##STR5## wherein the R's are identical or different and each is a C.sub.1 -C.sub.8 alkyl or two of said R radicals attached to the same nitrogen atom are interbonded to form a C.sub.2 -C.sub.8 bivalent hydrocarbon radical and x is a number from 2 to 6.