Polycarbonates made using highly selective catalysts
Poly(propylene carbonates) are prepared from propylene oxide and CO 2 with less than 10% cyclic propylene carbonate by product using cobalt based catalysts of structure preferably in combination with salt cocatalyst, very preferably cocatalyst where the cation is PPN + and the anion is Cl − or OBzF 5 − . Novel products include poly(propylene carbonates) having a stereoregularity greater than 90% and/or a regioregularity of greater than 90%.
1. A method for preparing a copolymer of C 2 -C 10 alkylene oxide and CO 2 , with less than 10% cyclic alkylene carbonate by-product, comprising the step of reacting a C 2 -C 10 alkylene oxide and CO 2 at a CO 2 pressure ranging from 1 to 1,000 psi and a reaction temperature of 0 to 150° C. and a time of 0.1 to 50 hours in the presence of a catalyst at an alkylene oxide to catalyst ratio on a cobalt basis ranging from 200:1 to 100,000:1, said catalyst having the structure
where R 1 is a hydrocarbon bridge which may be substituted with C 1 -C 20 alkyl, C 1 -C 20 alkoxy, halogen, nitro, cyano or amine; where R 2 , R 3 and R 4 can be the same or different and are selected from the group consisting of H, C 1 -C 20 alkyl, C 6 -C 20 aryl, and C 1 -C 20 fluorocarbon and where R 1 and R 2 or R 2 and R 3 or R 3 and R 4 can form a phenyl ring which can substituted with H, C 1 -C 20 alkyl, C 6 -C 20 aryl, C 1 -C 20 alkyl C 6 -C 20 aryl substituted with C 1 -C 20 alkyl, C 1 -C 20 alkoxy, phenoxy, C 1 -C 20 carboxylate, C 1 -C 20 acyl, amino, C 1 -C 20 fluoroalkyl, cyano, nitro and halogen (e.g., Cl, Br, I); and where X is any nucleophile which can ring open an epoxide; with the proviso that when X is Br and R 1 is ethyl and R 3 and R 4 form a phenyl ring, the substituent on the phenyl ring on the carbons which are not part of another ring are not all H; and when X is Br and R 1 is 1,2-cyclohexanediyl, and R 3 and R 4 form a phenyl ring, the substituent on carbon on the phenyl ring which is not part of another ring and is closest to —O— is not H; with the further proviso that X is not O 2 CCCl 3 or a nitrophenol when R 1 is 1,2-cyclohexanediyl.
2. The method of claim 1 where the CO 2 pressure ranges from 750 to 850 psi, the reaction temperature ranges from 20 to 25° C., the reaction time ranges from 0.5 to 4 hours, the catalyst has the structure (VIII)
where X is Br, Cl or OBzF 5 and the alkylene oxide to catalyst ratio, on a cobalt basis, ranges from 400:1 to 600:1.
3. The method of claim 2 where the alkylene oxide is rac-propylene oxide.
4. The method of claim 2 where the alkylene oxide is enantiomerically-enriched propylene oxide.
5. A method for preparing poly(C 2 -C 10 alkylene carbonate, with less than 10% cyclic alkylene carbonate by-product, comprising the step of reacting C 2 -C 10 alkylene oxide, e.g., propylene oxide, and CO 2 at a CO 2 pressure ranging from 10 psi to 300 psi, a reaction temperature of 20 to 25° C., a reaction time of 0.5 to 10 hours in the presence of the catalyst system for epoxide/CO 2 copolymerization comprising as a catalyst
R 1 is a hydrocarbon bridge which may be substituted with C 1 -C 20 alkyl, C 1 -C 20 alkoxy, halogen (e.g., Cl, Br, I), nitro, cyano or amine; where R 2 , R 3 and R 4 can be the same or different and are selected from the group consisting of H, C 1 -C 20 alkyl, C 6 -C 20 aryl, and C 1 -C 20 fluorocarbon and where R 1 and R 2 or R 2 and R 3 or R 3 and R 4 can form a phenyl ring which can substituted with H, C 1 -C 20 alkyl, C 6 -C 20 aryl, C 1 -C 20 alkyl C 6 -C 20 aryl substituted with C 1 -C 20 alkyl, C 1 -C 20 alkoxy, phenoxy, C 1 -C 20 carboxylate, C 1 -C 20 acyl, amino, C 1 -C 20 fluoroalkyl, cyano, nitro and halogen (e.g., Cl, Br, I); and where X is any nucleophile which can ring open an epoxide; with the proviso that when X is Br and R 1 is ethyl and R 3 and R 4 form a phenyl ring, the substituent on the phenyl ring on the carbons which are not part of another ring are not all H; and when X is Br and R 1 is 1,2-cyclohexanediyl, and R 3 and R 4 form a phenyl ring, the substituent on carbon on the phenyl ring which is not part of another ring and is closest to —O— is not H; with the further proviso that X is not O 2 CCCl 3 or a nitrophenol when R 1 is 1,2-cyclohexanediyl, and as a cocatalyst a salt which is bulky and non-coordinating where the cation is a phosphorus and/or nitrogen based cation of at least 50 g/mol, e.g., selected from the group consisting of [R 4 N] + , [R 4 P] + , [R 3 P═N═PR 3 ] + and [P(NR 3 ) 3 ] 3+ where R is C 1 -C 20 alkyl, C 6 -C 20 aryl, C 6 -C 20 alkoxy or a solid support and the anion is a nucleophile which can ring open an epoxide and the R groups can be the same or different.
where the ratio of alkylene oxide to cocatalyst to catalyst ranges from 500-100,000:0.5-1.5:0.5-1.5.
6. The method of claim 5 where the cocatalyst of the catalyst system is selected from the group consisting of [PPN]Cl and [PPN][OBzF 5 ].
7. The method of claim 6 where the catalyst has the structural formula (VIII)
where X is Cl and the cocatalyst is [PPN][OBzF 5 ].