Xin-De Feng

Synthesis of star-shaped poly(d,l-lactic acid-alt-glycolic acid) with multifunctional initiator and SnOct2 catalyst

Abstract d , l -3-methylglycolide (MG) was successfully polymerized with multifunctional initiator (trimethylolpropane (TMP) or pentaerythritol (PTOL)) and stannous octoate (SnOct 2 ) catalyst in bulk at 110°C. The effects of molar ratios of monomer to initiator, monomer to catalyst and monomer conversion on the molecular weight of polymer were studied. For the homopolymerization of MG with TMP initiator and SnOct 2 catalyst, the molecular weight of polymer increases from 6840 to 35 010 with the molar ratio of monomer to initiator (45–450), and the molecular weight distribution is from 1.15 to 1.35. The results indicate that in the homopolymerization of MG, the molecular weight of polymer is proportional to the molar ratio of monomer to initiator and the monomer conversion. The molar ratio of monomer to catalyst has no influence on the molecular weight of polymer at least within the range of 500–4000. 1 H NMR spectra of the resulting polymers obtained from the homopolymerization of MG show that the homopolymerization of MG with TMP or PTOL initiator and SnOct 2 catalyst produced two types of three-arm or four-arm star-shaped polymers. The bulk ring-opening homopolymerization of MG proceeds through a “coordination–insertion” mechanism and follows the selective acyl–oxygen bond cleavage reaction. 13 C NMR spectroscopy indicates that the obtained poly( d , l -lactic acid-co-glycolic acid) (50:50, in molar ratio; d , l -PLGA50) has an alternating structures of lactyl and glycolyl units.

Synthesis of poly(D,L‐lactic acid‐alt‐glycolic acid) from D,L‐3‐methylglycolide

D,L-3-Methylglycolide (MG) was synthesized via two step reactions with a good yield (42%). It was successfully polymerized in bulk with stannous octoate as a catalyst at 110 °C. The effects of the polymerization time and catalyst concentration on the molecular weight and monomer conversion were studied. Poly(D,L-lactic acid-co-glycolic acid) (D,L-PLGA50; 50/50 mol/mol) copolymers were successfully synthesized from the homopolymerization of MG with high polymerization rates and high monomer conversions under moderate polymerization conditions. 1 H NMR spectroscopy indicated that the bulk ring-opening polymerization of MG conformed to the coordination-insertion mechanism. 13 C NMR spectra of D,L-PLGA50 copolymers obtained under different experimental conditions revealed that the copolymers had alternating structures of lactyl and glycolyl.

Living polymerization of D,L-3-methylglycolide initiated with bimetallic (Al/Zn) μ-oxo alkoxide and copolymers thereof

D,L-3-Methylglycolide (MG) was successfully polymerized with bimetallic (Al/Zn) μ-oxo alkoxide as an initiator in toluene at 90 °C. The effect of the initiator concentration and monomer conversion on the molecular weight was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates the first order in the monomer, and no induction period was observed. 1H NMR spectroscopy showed that the ring-opening polymerization proceeds through a coordination–insertion mechanism with selective cleavage of the acyl–oxygen bond of the monomer. On the basis of 1H NMR and 13C NMR analyses, the selective cleavage of the acyl–oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P1 = 0.84, P2 = 0.16). Therefore, the main chain of poly(D,L-lactic acid-co-glycolic acid) (50/50 molar ratio) obtained from the homopolymerization of MG was primarily composed of alternating lactyl and glycolyl units. The diblock copolymers poly(ϵ-caprolactone)-b-poly(D,L-lactic acid-alt-glycolic acid) and poly(L-lactide)-b-poly(D,L-lactic acid-alt-glycolic acid) were successfully synthesized by the sequential living polymerization of related lactones (ϵ-caprolactone or L-lactide). 13C NMR spectra of diblock copolymers clearly show their pure diblock structures.