Synthesis And Application Research Of Cyclic Poly(Caprolactone)

Polycaprolactone(PCL),a biocompatible,biodegradable,semicrystalline,shape memory polyester,is widely used in many domains,especially in medical treatment,such as sutures,bandages and straighteners owing to its special monomer structure containing five nonpolar methylene and one polar ester group.As we know by now,the cyclic PCL has smaller hydrodynamic volume,higher melting point,higher glass transition temperature,higher crystallization rate and crystallinity compared with the linear precursor due to the influence of the cyclic topological structure.Therefore,cyclic PCL has more advantages in many potensial applications based on these features.In this thesis,the cyclic PCL with two hydroxyl groups had been successfully prepared via efficient Cu-catalyzed azide-alkyne cycloaddition(CuAAC)reaction and was rigorously characterized.Cross linked shape memory polyurethanes with self-healing properties were prepared base on cyclic PCL and crosslinkers containing furan/maleimide dynamic covalent bond.And the effects of cyclic topology on shape memory and self healing properties were then discussed.Specific research contents are as the follows:(1)Synthesis and characterization of cyclic PCLIn this work,l-PCL-20H was firstly prepared via ring-opening polymerization of caprolactone initiated by ethylene glycol.l-PCL-2alkynyl was obtained via modifying the end group to the alkyne group using the acid anhydride.Then,intermolecular cyclization reaction between l-PCL-2alkynyl with alkynyl as end groups and small molecule with two azido groups was performed to get the cyclic PCL(c-PCL-20H)with two definite hydroxyl groups via CuAAC reaction.The polymers were rigorously characterized by size exclusion chromatograph(SEC),fourier transform infrared spectroscopy(FT-IR),proton nuclear resonance(1H NMR),matrix assisted laser desorption/ionization time of flight(MALDI-TOF)mass spectra,traveling wave ion mobility(TWIM)mass spectra and so on.And the differential scanning calorimetry(DSC)showed that the crystallinity of cyclic PCL was higher than that of the linear precursor.(2)Shape memory and self-healing properties research of polyurethane materials based on cyclic PCLIn the second section,cross linked polyurethanes(PUs)were then prepared base on cyclic PCL,hexamethylene diisocyanate and tetrahydroxy functionalized crosslinkers with furan/maleimide dynamic covalent bond.The PUs made by cyclic PCL resulted in more compact networks than those made from linear polymer due to the topology effects,which significantly lowered the crystallinity of cyclic polymers in PUs.It was found that the shape memory of the cross linked PUs was not dominated by crystallinity but the degree of cross linking.The PUs from cyclic PCL conveyed higher shape fixity ratio(-95%)than those from linear PCL(-80%);however,the recovery ratio of cyclic PCL made PUs was slight lower.And the discrepancy of the shape memory performance was attributed to the different cross linked network arising from topology effect.Self-healing tests denoted that the cyclic PCL or linear PCL derived PUs showed good and approximate self-healing ability.