Polycarbonate polyol compositions and methods

A method for the synthesis of aliphatic polycarbonate polyols having a high percentage of —OH end groups, the method comprising the steps of:

• a) contacting a reaction mixture comprising one or more epoxides in the presence of carbon dioxide with a polymerization system comprising:
• a metallosalenate metal complex;
• and
• a chain transfer agent having a plurality of sites capable of initiating copolymerization of epoxides and CO2;
• wherein the chain transfer agent has a structure Y-A-(Y)n,
• where:
• each —Y group is independently a functional group capable of initiating chain growth of epoxide CO2 copolymers and each Y group may be the same or different;
• -A- is a covalent bond or a multivalent moiety;
• and
• n is an integer between 1 and 10, inclusive;
• wherein the molar ratio of metal complex to epoxide ranges from 1:100 to 1:1,000,000
• b) allowing the polymerization reaction to proceed until a desired molecular weight aliphatic polycarbonate polyol has formed, wherein in the aliphatic polycarbonate polyol composition
• at least 97% of the end groups are hydroxyl groups, and
• more than 95% of the linkages formed by the metal complex are carbonate linkages;
• and
• c) terminating the polymerization.