Study On The Polymerization Of L-alanine And Its Characteristics

Poly(amino acid) is a kind of biodegradable macromolecule materials with lowtoxicity, excellent biocompatibility, biodegradability and bioabsorbability in vivo.They are used very widely, especially are used in pharmaceutical and biomedicalareas such as drug delivery systems and tissue engineering. But the application ofpoly (amino acid) is closely associated with the polymer's molecule weight, there aremany methods of synthesis poly (amino acid), however the majority of amino acidjust polymerizes through the method of amino N-Carboxyl-α-amino acidAnhydride(NCAs) that can get high molecule weight poly(amino acid). At present thechiefly reports are poly(glutamic acid), poly(aspartic acid) and poly(leucine acid) etc.,and that as the most important part of silk albumen the research of poly(alanine) isvery lack. The paper relates to the preparation of L-Ala-NCAs from L-Alanine andresearches the influence of initiator, reaction temperature, solvent and catalyst on themolecular weight of poly(alanine) in L-ala-NCAs ring-opening polymerization, setthe stage for synthesis functional macromolecule materials with accessible moleculeweight.The excess of gaseous phosgene passed into the suspension of L-Alanine andpurified anhydrous tetrahydrofuran(THF)at 0 ℃ and then heated to 30 ℃, theCarboxyl-L-Alanine acid anhydride (L-ala-NCAs) was synthesized. The solvents inthe experiment just are purified to remove the water by 4? molecular sieve, simplifiedthe procedure of the experiment, it different from conventional gaseous phosgenemethod that the solvents must be rigorously purified to remove all traces of water. Theproduct was confirmed by IR. The L-Ala-NCAs was refined from ligroine and ethylacetate and its yield was 61.8 %.This paper relates to investigate the characteristic of L-ala-NCAs's ring-openingpolymerization and the influence of various factor on the molecule weight ofpoly (alanine). Nitrobenzene as solvent, triethylamine as initiator, monomerconcentration is 0.05 g/mL, reaction temperature is 40 ℃, n(monomer)/n(initiator) III40 and reaction time is 5 h , the intrinsic viscosity [η] of poly(alanine) thus obtainedexhibits 0.83 dL/g at concentrations 5mg/mL solution. The influence of dichloroaceticon the intrinsic viscosity [η] was also examined. The result showed that thedichloroacetic had no influence on the intrinsic viscosity [η] of poly(alanine) and theresult of polyalanine's intrinsic viscosity is reliable. The result of experiment alsoshowed that the ring-opening polymerization of L-Ala-NCAs in nitrobenzene solventhad stepwise polymerization characteristic. The monomer disappeared soon in theearly stage and converted to oligomer, the conversion was also very high at the firststage.The decomposing point of poly(alanine) was measured by Differential ScanningCalorimetry(DSC), the result of the decomposing point of poly(alanine) was 396.8 ℃.The poly(alanine) was characterized by Fourier transform infrared spectrometry ( FT-IR), 13C nuclear magnetic resonance spectroscopy(NMR), all results can besummarized to confirm that the sample was poly(alanine) and possessed the followingchemical structure: OC CH NH n CH3The chain of poly(alanine) have the similarity as polyamide, but the poly(alanine)didn't dissolve in the polyamide's solvent, it could dissolve in dichloroacetic ortrifluoroacetic acid.The result also showed the UV and microorganism had degradable effect on thepoly(alanine). For peptide bond existing in the poly(alanine) main chain, thepoly(alanine) can be degraded to non-toxic short peptide and amino acid monomerunder the microorganism and enzymes action, so the poly(alanine) are biocompatibleand biodegradable polymers.