Semicrystalline macromonomers based on poly(pentadecalactone), PPDL, have been synthesized by the lipase-catalyzed ring-opening of the otherwise chemically inert pentadecalactone monomer. The macromonomers were designed to have reactive thiols as end groups by the appropriate choice of initiator and chain terminator. The thiol functional macromonomers were then used together with ene monomers to give crosslinked thin films after irradiation in the molten state by UV light in the presence of a photoinitiator (Irgacure 651). Two different ene monomers were used, i.e., a tetrafunctional norbornene species and a trifunctional allyl ether maleate species, and resulted in semicrystalline cured films when cured with PPDL. An amorphous, commercially available, trifunctional thiol, trimethylolpropane tri(3-mercaptopropionate), TRIS, was also used for network formation in order to better understand the effect of crystallinity. All thiol-ene systems were found to be readily photopolymerised to high conversion. The PPDL-based networks were semicrystalline in the crosslinked state where the degree of crystallinity was found to depend on the nature of the cross-linker. Networks based on TRIS were found to be amorphous.

Summary: An enzymatic one‐pot procedure has been developed for the synthesis of difunctional polyesters containing terminal thiols and acrylates. Candida antarctica lipase B was used as a catalyst for the ring‐opening polymerization of ω‐pentadecalactone. The polymerization was initiated with 6‐mercaptohexanol, then terminated with γ‐thiobutyrolactone or vinyl acrylate to create two types of difunctional polyesters with a very high content of thiol‐thiol or thiol‐acrylate end‐groups.Difunctionalization of poly‐PDL.magnified imageDifunctionalization of poly‐PDL.

2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the enzymatic ring-opening polymerization (ROP) of omega-pentadecalactone (PDL) and epsilon-caprolactone (CL). The lipase B from Candida antarctica was found to catalyze the cleavage of the ester bond in the HEMA end group of the formed polyesters, resulting in two major transesterification processes, methacrylate transfer and polyester transfer. This resulted in a number of different polyester methacrylate structures, such as polymers without, with one, and with two methacrylate end groups. Furthermore, the 1,2-ethanediol moiety (from HEMA) was found in the polyester products as an integral part of HEMA, as an end group (with one hydroxyl group) and incorporated within the polyester (polyester chains acylated on both hydroxyl groups). After 72 h, as a result of the methacrylate transfer, 79% (48%) of the initial amount of the methacrylate moiety (from HEMA) was situated (acylated) on the end hydroxyl group of the PPDL (PCL) polyester. In order to prepare materials for polymer networks, fully dimethacrylated polymers were synthesized in a one-pot procedure by combining HEMA-initiated ROP with end-capping using vinyl methacrylate. The novel PPDL dimethacrylate (>95% incorporated methacrylate end groups) is currently in use for polymer network formation. Our results show that initiators with cleavable ester groups are of limited use to obtain well-defined monomethacrylated macromonomers due to the enzyme-based transesterification processes. On the other hand, when combined with end-capping, well-defined dimethacrylated polymers (PPDL, PCL) were prepared.