A new organic guanidine compound

i.e. creatinine-guanidinium lactate (CGLA)

was synthesized for the first time by the direct reaction of creatinine with lactic acid under selected conditions (50℃

3 h

water solution).Evaporating off water in vacuo the solid was recrystallized in water for three times

and a snow-white product was obtained. 1H-NMR characterization indicated that the synthesized CGLA was of high purity (99%).Using CGLA as a mono-component organic initiator the ringopening polymerization (ROP) of L-lactide (LLA) was conducted for the first time.Bulk ROP of LLA was carried out at 100℃ under vacuum producing a poly(L-lactide) (PLLA) with narrower molecular weight distribution (［LLA］0/［CGLA］0=100， t=87 h， Mn＝1.20×104～1.3×10 4，PDI=1.29).Investigation on the kinetics of the polymerization in toluene showed that plots of ln［M］0/［M］t versus time and Mn versus conversion were linear which were the typical features of living polymerization.To know the nature of the propagation species

an experiment on additiveadding effect of the polymerization was carried out as follows.2

2

6

6-Tetramethyl-1-prperidinyloxy (TEMPO; a freeradical capturer)

H2O and CH3COOH (terminators for cation and anion) were added to the three started polymerization systems after the polymerization was conducted for 24 h (polymerization in toluene at 100℃

［M］0/［I］0=50

24 h

Conv.=30.2％，Mn=4.3×103).Maintaining the original polymerization conditions for another 24 h

then the contents in the three reactors were checked simultaneously.The experimental results revealed that the polymerizations were not stopped

but continued synchronously in the three reactors.The molecular structure characterization of the propagating polymer species by 1H-NMR indicated that the growing polymer bore a creatinineguanidinium-alkoxy bond as its active end.Based on the experimental investigations

the mechanism of the CGLA-initiated ROP of LLA was postulated as follow:initiation occurred through a monomer-activated mode.The association of the creatinineguanidinium (CG+) with the acyl-oxygen atom in the LLA molecule greatly increased the nucleophilic activity of the lactate anion (LA-) in the CGLA molecule.Initiatin occurred when a lactate anion attacked at the carbonyl carbon causing the cleavage of the RCO-O bond in LLA molecule.Owning to that the reaction of CG+ with the cleavaged LLA residue RO- formed a molecule with polar covalent bond CGOR

but not an ionic bond

the propagation was postulated to follow the coordination insertion mode through the repeatedly insertion of the monomer in the CG-O bond in the propagating polymer molecule.Homonuclear decoupled 1H-NMR characterization of the methine in the product indicated that the synthesized PLLA possessed higher isotacticity (76%).