The employment of a monomer-specific on/off switch was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (D = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and epsilon-caprolactone (epsilon CL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and epsilon CL [k(p)(app)(AOMEC)/k(p)(app)(epsilon CL)] changes from 400 at T = -40 degrees C to 50 at T = 30 degrees C and 10 at T = 100 degrees C. Therefore, by decreasing the copolymerization temperature from 30 degrees C to -40 degrees C, the conversion of epsilon CL can be switched off, and by increasing the temperature to 30 degrees C, the conversion of epsilon CL can be switched on again. The addition of AOMEC at T = -40 degrees C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of epsilon CL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.