Synthesis Of Poly(Hydroxyalkanoates): Routes To Poly(3- Hydroxybutyrate) And Poly(3-Hydroxypropionate) From The Carbonylation And Ring-Opening Polymerization Of Epoxides

Abstract

New methods for the syntheses of poly(3-hydroxybutyrate) (P3HB) and poly(3-hydroxypropionate) (P3HP) from epoxides are reported. Epoxides are readily available, inexpensive starting materials that can be transformed into valuable biodegradable and biocompatible polyesters. We successfully developed a one-pot synthesis of P3HB from propylene oxide and carbon monoxide using a multicatalytic transformation. The intermediate !-butyrolactone was formed and subsequently polymerized in situ. The carbonylation of propylene oxide to !-butyrolactone was accomplished using a catalyst of the form [Lewis acid]+[Co(CO)4]-, and the lactone monomer was then polymerized by a (BDI)ZnOAc (BDI = !-diiminate) catalyst. The two catalysts were found to have orthogonal reactivity, and were compatible with each other as well as with the solvent, substrate, and any reaction side-products. The reaction proceeded with high activity and selectivity to synthesize P3HB with high molecular weights. Furthermore, this dual-catalyst approach eliminated exposure to the toxic !-butyrolactone monomer. We also report the synthesis of P3HP from ethylene oxide and carbon monoxide. The carbonylation of ethylene oxide proceeded in greater than 99% yield and high selectivity with the bimetallic catalyst [(ClTPP)Al(THF)2]+[Co(CO)4](ClTPP = meso-tetra(4-chlorophenyl)porphyrinato; THF = tetrahydrofuran). Ringopening polymerization of !-propiolactone by organic ionic compounds afforded poly(3-hydroxypropionate) (P3HP) in high yields. The catalyst [P(N=P(N(CH2)4)3)4]+ [tBuCO2]- displayed the highest activity for the ring-opening polymerization of propiolactone, and produced polyesters with molecular weights over 100,000 g/mol and narrow molecular weight distributions. P3HP can be pyrolyzed to produce acrylic acid. This method allows for the synthesis of acrylic acid from the inexpensive feedstocks of EO and CO.