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Synthesis of high molecular weight poly (l - lactic acid) via melt / solid state polycondensation. II. / Bo Peng in Industrial & engineering chemistry research, Vol. 51 N° 14 (Avril 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 14 (Avril 2012) . - pp. 5190–5196 Titre : Synthesis of high molecular weight poly (l - lactic acid) via melt / solid state polycondensation. II. : Effect of precrystallization on solid state polycondensation Type de document : texte imprimé Auteurs : Bo Peng, Auteur ; Hongbing Hou, Auteur ; Fangchao Song, Auteur Année de publication : 2012 Article en page(s) : pp. 5190–5196 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Polycondensation  Precrystallization Résumé : To enhance the reaction rate of solid state polycondensation (SSP) of poly(l-lactic acid) (PLLA) and thus to prepare high molecular weight PLLA by SSP in a short time, the effects of precrystallization as well as SSP temperature (Ts) on the SSP of PLLA were investigated. It was found that precrystallization at low Tc (70 °C) and then SSP at step-raised Ts could greatly favor the growth of the molecular weight of PLLA. After precrystallization at 70 °C for 60 min and then SSP at 150–160 °C for 20 h, the product’s weight average molecular weight (Mw) exceeds 200 000 g·mol–1 while its optical purity remained as high as 90%. The prepolymer precrystallized at 70 °C for 60 min had smaller crystal size and looser packing of lamellae structure than that at Tcmax (110 °C) and moderate crystallinity of 45%. Such crystal properties may result in enhanced concentration and mobility of chain-end groups and improved diffusion of byproduct water in an amorphous area, so the SSP reaction is accelerated. PLLA continues to crystallize during SSP. The crystallinity and melting temperature increase rapidly at the early stage and slowly at the late stage, implying that the effect of precrystallization on the SSP rate is significant at the early stage, and weakens gradually at the late stage. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202192q [article] Synthesis of high molecular weight poly (l - lactic acid) via melt / solid state polycondensation. II. : Effect of precrystallization on solid state polycondensation [texte imprimé] / Bo Peng, Auteur ; Hongbing Hou, Auteur ; Fangchao Song, Auteur . - 2012 . - pp. 5190–5196. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 14 (Avril 2012) . - pp. 5190–5196 Mots-clés : Polycondensation  Precrystallization Résumé : To enhance the reaction rate of solid state polycondensation (SSP) of poly(l-lactic acid) (PLLA) and thus to prepare high molecular weight PLLA by SSP in a short time, the effects of precrystallization as well as SSP temperature (Ts) on the SSP of PLLA were investigated. It was found that precrystallization at low Tc (70 °C) and then SSP at step-raised Ts could greatly favor the growth of the molecular weight of PLLA. After precrystallization at 70 °C for 60 min and then SSP at 150–160 °C for 20 h, the product’s weight average molecular weight (Mw) exceeds 200 000 g·mol–1 while its optical purity remained as high as 90%. The prepolymer precrystallized at 70 °C for 60 min had smaller crystal size and looser packing of lamellae structure than that at Tcmax (110 °C) and moderate crystallinity of 45%. Such crystal properties may result in enhanced concentration and mobility of chain-end groups and improved diffusion of byproduct water in an amorphous area, so the SSP reaction is accelerated. PLLA continues to crystallize during SSP. The crystallinity and melting temperature increase rapidly at the early stage and slowly at the late stage, implying that the effect of precrystallization on the SSP rate is significant at the early stage, and weakens gradually at the late stage. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202192q