Polymerization of N-carboxy anhydrides by organotin catalysts

✍ Scribed by S. Freireich; D. Gertner; A. Zilkha

• Publisher: Elsevier Science
• Year: 1974
• Tongue: English
• Weight: 362 KB
• Volume: 10
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(74)90209-2

✦ Synopsis

The polymerization was studied in detail using ),-benzyl N-carboxy-L-glutamate anhydride (BGA). Compounds such as tributyltin methoxide, bis(tributyltin)oxide, and N-tributyltin imidazole polymerized BGA while others like dibutyltin dichloride, which are Lewis acids, failed. Polymerization of BGA in dioxane at various monomer to dibutyltin dimethoxide ratios showed a first order reaction to monomer. The plot of In Mo/M , vs time showed two stage kinetics, the second one being faster. The pseudo first order rate constants were smaller than those for primary amine initiated polymerizations and much smaller than that for polymerization initiated by sodium methoxide. The molecular weights were independent of the monomer to initiator ratio both in dioxane and in DMF. In the reaction of an equimolar amount of tributyltin methoxide with NCA, the methyl ester of the amino acid was formed.

The mechanism suggested is that of addition of the organotin compound to the NCA forming an organotin carbamate which decarboxylates, leaving an active --N--Sn--group which adds to another NCA molecule. This process is repeated in every step of the propagation.