title: Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch". High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers.
abstract: 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 (Đ= 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 ε-caprolactone (εCL), 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 εCL [kpapp(AOMEC)/kpapp(εCL)] changes from 400 atT= -40 °C to 50 atT= 30 °C and 10 atT= 100 °C. Therefore, by decreasing the copolymerization temperature from 30 °C to -40 °C, the conversion of εCL can be switched "off", and by increasing the temperature to 30 °C, the conversion of εCL can be switched "on" again. The addition of AOMEC atT= -40 °C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of εCL 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.
authors: Department of Fibre and Polymer Technology, KTH Royal Institute of Technology , SE-100 44, Stockholm, Sweden.
authors: Peter
authors: P
authors: Olsén
authors: Department of Fibre and Polymer Technology, KTH Royal Institute of Technology , SE-100 44, Stockholm, Sweden.
authors: Karin
authors: K
authors: Odelius
authors: DWI - Leibniz Institute for Interactive Materials and Institute of Technical and Macromolecular Chemistry, RWTH Aachen University , Forckenbeckstraße 50, D-52056 Aachen, Germany.
authors: Helmut
authors: H
authors: Keul
authors: Department of Fibre and Polymer Technology, KTH Royal Institute of Technology , SE-100 44, Stockholm, Sweden.
authors: Ann-Christine
authors: AC
authors: Albertsson