Green Polymer Chemistry: Synthesis of Poly(isobutylene-b-ε-caprolactone) Using Enzyme Catalysis

The synthesis of a poly(isobutylene-b-e-caprolactone) block copolymer was accomplished by the combination of living cationic polymerization of isobutylene (IB) with the ring-opening polymerization (ROP) of e-caprolactone (e-CL). The synthesis involved the living cationic polymerization of IB using 1,2-propylene oxide/TiCl₄ as the inititating system. Termination with allyltrimethylsilane yielded an asymmetric thelechelic polyisobutylene (PIB): allyl-PIB-OH with M_n=4,306 g/mol and M_w/M_n=1.21. The structure was confirmed by ¹H NMR.  The allyl-PIB-OH was successfully used as a macroinitiator for the ROP of e-CL in the presence of Candida Antarctica Lipase B (CALB), producing a poly(IB-b-e-CL) copolymer. The block copolymer was characterized by ¹H and ¹³C NMR spectroscopy and SEC. The block copolymer had M_n= 6,625 g/mol and M_w/M_n=1.26. The amorphous PIB and the semicrystalline PCL block segments will phase separate, creating a nanostructured phase morphology.