1 research outputs found
Multiarm Polycarbonate Star Polymers with a Hyperbranched Polyether Core from CO<sub>2</sub> and Common Epoxides
Multiarm star copolymers, consisting
of hyperbranched poly(ethylene
oxide) (<i>hb</i>PEO) or poly(butylene oxide) (<i>hb</i>PBO) polyether copolymers with glycerol branching points as a core,
and linear aliphatic polycarbonate arms generated from carbon dioxide
(CO<sub>2</sub>) and epoxide monomers, were synthesized via a “core-first”
approach in two steps. First, hyperbranched polyether polyols were
prepared by anionic copolymerization of ethylene oxide or 1,2-butylene
oxide with 8–35% glycidol with molecular weights between 800
and 389,000 g·mol<sup>–1</sup>. Second, multiple arms
were grown via immortal copolymerization of CO<sub>2</sub> with propylene
oxide or 1,2-butylene oxide using the polyether polyols as macroinitiators
and (<i>R</i>,<i>R</i>)-(salcy)-CoCl as a catalyst
in a solvent-free procedure. Molecular weights up to 812,000 g·mol<sup>–1</sup> were obtained for the resulting multiarm polycarbonates,
determined by online viscometry with universal calibration and <sup>1</sup>H NMR. Comparing the synthesis of different multiarm star
polycarbonates, a combination of a highly reactive macroinitiator
with a less reactive epoxide monomer was found to be most suitable
to obtain well-defined structures containing up to 88 mol% polycarbonate.
The multiarm star copolymers were investigated with respect to their
thermal properties, intrinsic viscosity, and potential application
as polyols for polyurethane synthesis. Glass transition temperatures
in the range from −41 to +25 °C were observed. The intrinsic
viscosity could be adjusted between 5.4 and 17.3 cm<sup>3</sup>·g<sup>–1</sup> by varying the ratio of polyether units and polycarbonate
units