Abstract

Polyolefins are of paramount importance in the world of polymers due to their technological and economic potential.1 However, their nonpolar character significantly restricts the compatibility and adhesion properties, which consequently limits their versatility. Moreover, an intensified demand for materials from renewable resources can also become a problematic venture for the current polyolefin industry.2 Although Braskem and DOW presented an innovative and economically viable approach towards biomass-based ethylene produced via dehydration of bio-ethanol prepared from sugar cane, the relatively low scale of the process by far does not cover the worldwide demand for this monomer.3 Therefore, one class of interesting additions to petrochemical polyolefins is polymers with polyolefin-like properties based on renewable monomers. Two types of renewable polymers have been reported to have polyolefin-like properties viz. polyhydroxybutyrate (PHB) resembling those of isotactic polypropylene and linear fatty acid-based polyesters, which have been reported to resemble high density polyethylene.4 It is well-known that these polyesters can be produced via enzymatic5 or catalytic6 ring-opening polymerization (ROP) of cyclic esters. This concept can be successfully extended to a large variety of functionalized or branched lactones. For example, it is anticipated that copolymerization of macrolactones with branched lactones produces linear low-density polyethylene (LLDPE)-like materials. Although enzymes are highly active and selective, the enzymatic ROP leads to products with limited control over the copolymers' microstructure.7 Alternatively, various organic or metal-based ROP catalysts are known to provide excellent control over the polymer molecular weight, stereo-regularity, copolymer-microstructure and properties of ring-strained lactones.8 Hitherto, there are only a few catalytic systems known that are capable of polymerizing macrolactones to high molecular weight products in a controlled way.6a,9 In search for highly efficient living or immortal catalysts, a Zn complex containing a tridentate phenoxy-imine ligand was selected (Fig. 1). This type of catalyst showed excellent performance, demonstrating quasi-living behavior, in ROP of e.g. cyclic carbonates and lactide,10 and was therefore expected to be a suitable candidate for forming high molecular weight homo- and co-polymers of all types of cyclic monomers including macrolactones.

Authors (8)