Synthesis of star-shaped poly(ε-caprolactone) by samarium-based tetrafunctional initiator and its dilute-solution properties

An in situ-generated tetrafunctional samarium enolate from the reduction of 1,1,1,1-tetra(2-bromoisobutyryloxymethyl)methane with divalent samarium complexes [Sm(PPh2)(2) and SmI2] in tetrahydrofuran has proven to initiate the ring-opening polymerization of epsilon-caprolactone (CL) giving star-shaped aliphatic polyesters. The polymerization proceeded with quantitative conversions at room temperature in 2 h and exhibited good controllability of the molecular weight of polymer. The resulting four-armed poly(epsilon-caprolactone) (PCL) was fractionated, and the dilute-solution properties of the fractions were studied in tetrahydrofuran and toluene at 30 degrees C. The Mark-Houwink relations for these solvents were [eta] = 2.73 x 10(-2) M-w(0.74) and [eta] = 1.97 x 10(-2) M-w(0.75), respectively. In addition, the unperturbed dimensions of the star-shaped PCL systems were also evaluated, and a significant solvent effect was observed. (c) 2006 Wiley Periodicals, Inc.