Synthesis And Properties Of PLA/DOPA Polymer

As an environment-friendly material, polylactide (PLA) is considered as the mostpromising and competitive biodegradable polymer in the21st century. However, aliphaticPLA has some disadvantages in the thermal properties and degradation time. Its applicationsin terms of engineering and tissue scaffolds are limited. Introducing aromatic monomer, suchas3,4-dihydroxyphenylalanine (DOPA) into PLA chains are expected to improve the thermaland biodegradability properties of the material.Herein, two kinds of biodegradable PDOPA-PLA copolymers were prepared by suitablestructure design and different synthesis routes based on bio-based lactide (LA) and3,4-dihydroxyphenylalanine (DOPA).Firstly, phenolic dihydroxyl groups of DOPA were protected by slicane compound(TBDMS). Then, PDOPA(TBDMS)2was polymerized by amidation reaction. PDOPA wassubsequently obtained by deprotecting of TBDMS. Finally, PDOPA-g-PLA was prepared byring-opening polymerization of lactide in the presence of PDOPA. The structure of thePDOPA-g-PLA copolymer was confirmed by FT-IR and1H-NMR spectra. The molecularweight and its distribution were measured by GPC, and the results showed that the molecularweight of PDOPA-g-PLA increased with increasing the composition of LA and the copolymershowed narrow molecular weight distribution. When n(PDOPA): n(LA)was greater than1:20, thethe molecular weight did not increase significantly. In order to studing the wettability of thecopolymer, the copolymer films were prepared by film pressure method and measured byoptical contact angle (OCA). The results showed that the contact angle (CA) increased withthe increment of LA. The CA of PDOPA-g-PLA increased to107.4owhen n(PDOPA): n(LA)was1:100, indicating the formation of hydrophobic surface. The solubility, thermal, mechanicaland degradation properties of the copolymer were also investigated. The results showed thatthe PDOPA-g-PLA copolymer had great solubility in most of common organic solvents.PDOPA-g-PLA also showed high thermal decomposition temperature (360℃) and goodbiodegradability.Firstly, PLA-NH2was synthesized by ring-opening polymerization of lactide in thepresence of aminopropanol. H2N-PLA-COOH was prepared by ending modified withcarboxyl group. Then, the block copolymer PLA-b-PDOPA was prepared by amidationreaction of PDOPA(TBDMS)2and H2N-PLA-COOH. The structure of the copolymer wasconfirmed by FTIR and1H-NMR spectra. The molecular weight and its distribution weremeasured by GPC, and the results showed that the weight of copolymer increased withincreasing the molar ratios of PLA and PDOPA and the copolymer had the narrow molecularweight distribution. The wettability of the copolymer film was measured by OCA. The resultsshowed that the CA increased with the increment of LA and reached to100.7owhen n(PDOPA):n(LA)was1:10, indicating the formation of hydrophobic surface. The solubility, thermal,mechanical and degradation properties of the copolymer were also investigated. The resultsshowed that the PLA-b-PDOPA copolymer had great solubility in most of common organicsolvents. PLA-b-PDOPA also showed high thermal decomposition temperature (290℃) and good biodegradability.