Study On The Synthesis Of Poly (Lactic Acid)

Polylactides(PLA)are derived from renewable resources,and can be degraded to carbon dioxide and water under compost condition after usage.PLLA is nontoxic, bioabsorbable and biocompatible.It also has good mechanical properties and can be processed by traditional processing methods.Therefore,it has found wide applications not only in biomedical fields as drug delivery carriers,surgical implants and tissue engineering scaffolds,but also in industrial and agricultural fields as general plastics.Because of its bright prospects,PLA has attracted much attention from both industrial and academic fields.This polymer has usually been prepared by ring-opening polymerization of laetide.Unfortunately,PLA obtained by this method usually has high price because the purification of lactide generally need repeated cristallization.The key of direct method to synthesize PLA is the exclusion of H₂O from reaction system.In order to optimize technology parameters,the effects on PLA molecular weight caused by catalyst,temperature,time et al.were studied.The monomer we used in the polymerization is an aqueous solution of lactic acid containing about 85-90%pure monomer.The new procedures are much simple,cheap,convenient and afford polymers with high yield and molecular weight and narrow polydispersity.The novel melt polymerization of D,L-LA was firstly conducted with the catalyst system we have used.Furthermore,aqueous lactic acid is cheap and comes from renewable resource.The characteristic features of polylactic acid obtained by this direct process were analyzed by NMR,IR,GPC,TG and DTA et al.1.Polylactic acid was synthesized from commercial available cheap aqueous lactic acid (85%-90%w/w)usingε-caprolactam and SnCl₂·2H₂O as catalyst in the absence of organic solvents.As a result,polylactic acid with a molecular weight of 50000g/mol and yield of 87-94% was prepared in 16 h.The suitable amount ofε-caprolactam is 1wt%,the SnCl₂·2H₂O is 1wt%and the phosphorous acid is 0.1 wt%.The new procedure is much simple and cheap.The start material is renewable aqueous lactic acid.2.Direct polycondensation of aqueous lactic acid co-catalyzed by succinic anhydride and ZnCl₂.As a result,the P(D,L)LA with Mw of 30200g/mol was prepared through melt polymerization co-catalyzed by succinic anhydride(0.05mol%)and ZnCl₂(0.5mol%)at 180℃for 24 hours under 0.015Mpa.The yield is 60-80%and the polydispersity is 1.2-1.4.This kind of polymer might be useful in biomedical applications.3.Melt polycondensation of aqueous lactic acid to poly(lactic acid)catalyzed by zinc acetate dihydrate.It is a good catalyst not only for obtaining a high molecular weight polymer with a narrow polydispersity in bulk at 180℃for 24 hours under 0.015Mpa,but also a high yield(60-80%).The suitable amount of zinc acetate dihydrate is 0.5mol%.The catalytic system is environmentally benign and notoxicity.4.In this research,we found that FeCl₃-6H₂O is a very efficient catalyst in bulk polycondensation of LA.To the best of our knowledge,ferric compounds have no toxicity or low toxicity.Polylactic acid was synthesized from commercial available cheap aqueous lactic acid(80%w/w)using FeCl₃·6H₂O as catalyst in the absence of organic solvents.As a result,polylactic acid with a molecular weight of 30626g/mol and yield of 80-91%was prepared in 21 h.The best proper reaction condition is 180℃for 21 h under 0.015 MPa,0.7mol%FeCl₃·6H₂O relative to the monomer.5.In this study,Polylactic acid was synthesized from commercial available cheap aqueous lactic acid(80%w/w)using SnCl₂·2H₂O as catalyst in 14h.Then using 2,4-toluylene diisoeyanate(TDI)as chain extender,the appropriate conditions for the chain extension synthesis were studied.The best chain extend condition is 180℃for 10 minutes under 0.015 MPa,4ml TDI relative to 25mL LA.As a result, viscosity-average molecular weight(My)of chain extension product could be 5.6 times higher than before(from 8900 to 50000).The yield is increased from 67.6%to 82.9%.