Controlled Preparation And Properties Of Lactic Acid-based Poly(Ester-urethane)

Lactic acid (LA), polyethylene glycol (PEG) and polyvinyl alcohol (PVA) wereused as raw materials to prepare LA-based macromolecular diol and polyolrespectively. Then the diol or polyol was reacted with isocyanate to prepare LA-basedpolyurethane. By adjusting the composition, molecular weight, and the proportion ofreactans, the LA-based polyurethanes were tailor-made. The structure, morphology,and properties of intermediate and the poly(ester-urethane) were analyzed. In addition,polyurethane/hydroxyapatite composites were prepared by using physical andchemical methods. The structure, morphology and properties of composites were wellcharacterized. The results were summarized as following:A diol was prepared via the esterification between LA and PEG of variousmolecular weights. Subsequently, the poly(ester-urethane) was synthesized throughthe addition polymerization of the LA-based diol and toluene2,4-diisocyanate (TDI)with1,4-butanediol as chain extender. The structure, morphology, and properties ofthe intermediate and the poly(ester-urethane) were analyzed with IR,1H NMR, GPC,XRD, DSC, POM and TGA. The results indicated that the intermediate was a diol ofconjugating quite short lactate sequences with PEG oligomer, and the structure of thepoly(ester-urethane) was as expected. The thermal transition, thermal decompositiontemperature, and crystallinity of the polymer samples depended on the molecular sizeof PEG. In vitro degradation property of the poly(ester-urethane) also relied on themolecular weight of PEG. The weight loss percentages of LPEU is19.1%while theblank contrast sample PEU1K degradation rate is only4.1%after12-days immersingin phosphate-buffer saline at37℃.The addition reaction among a lactic acid-based diol intermediate (LPEG),hydroxyapatite and TDI was employed to form covalent hybrid of hydroxyapatite andlactic acid-based polyurethane. The structure, thermal and degradation properties ofthe hybrid were analyzed and compared with the corresponding blends. The resultsconfirmed that the covalent hybrid of lactic acid-based polyurethane and hydroxyapatite was successfully obtained. The stability of hybrid system wassignificantly higher than that of the blend.The RAFT radical polymerization and alcoholysis were used to prepare PVA ofdifferent molecular weights with narrow distribution. Then, LPVA diol was obtainedthrough esterification reaction of LA and PVA. LPVA and IPDI were utilized tosynthesize another kind of LA-based polyurethane (LPVU) with differentcrosslinking degree by controlling the reaction conditions. IR, TGA, DMA andscanning electron microscopy (SEM) were applied to characterize the structure andmorphology of LPVA and LPVU. The swelling ratios and degradation performancesof LPVU samples in PBS were analyzed. The results showed that the crosslinkingdegree, Tg, mechanical properties and degradation properties of LPVU could beregulated by changing the amount of IPDI.The LPVU/HA composite was prepared by alternate immersion method. XRDand EDX testing verified the structure of LPVU/HA composite. The mechanicalproperties of the composite and the HA content could be controlled by the number ofalternating immersion. After immersed6cycles, the storage modulus of LPVU211raised from40.01MPa to71.62MPa, and its Tg varied from39.55℃to45.21℃. Thecontent of hard segment of polyurethane also had impact on the content of HA in thecomposites.In summary, labile lactate groups were introduced onto two kinds ofwater-soluble polymers via esterification reaction. By regulating the composition andamount of diol or polyol and isocyanate, the structure and properties of the LA-basedpolyurethane were controlled. To further improve the mechanical properties ofLA-based polyurethane and provide more possibilities for its future application, thecomposite of HA LA-based polyurethane was also inverstigated.