Polylactide high-molecular weight

Polylactide is the generaUy accepted term for highly polymeric poly(lactic acid)s. Such polymers are usuaUy produced by polymerization of dilactide the polymerization of lactic acid as such does not produce high molecular weight polymers. The polymers produced from the enantiomeric lactides are highly crystalline, whereas those from the meso lactide are generaUy amorphous. UsuaUy dilactide from L-lactic acid is preferred as a polymerization feedstock because of the avaUabUity of L-lactic acid by fermentation and for the desirable properties of the polymers for various appUcations (1,25). 

High molecular weight polylactides, 20 298 High molecular weight polymeric... 

Polylactones and polylactides of high molecular weight are exclusively produced by the ROP of the corresponding cyclic monomers. A polyester is formed when cyclic esters are reacted with a catalyst or initiator. Scheme 1 presents the reaction pathway for the ROP of a cyclic ester. 

R121 X. Chen, Y. Shen and R. A. Gross, High-Molecular-Weight [L]-Polylactides Containing Pendant Functional Groups , p. 129 vol. 765,2000... 

In another example, two polymerization techniques, ATRP and ROP, were coupled to synthesize polystyrene-b-polylactide (PS-b-PLA) heterografted block brushes of high molecular weight. A diblock backbone was first prepared by the RAPT block copolymerization of solketal methacrylate and 2-(bromoisobutyryl)ethyl... 

Hirata, M., Kobayashi, K., and Kimura, Y. (2010) J. Synthesis and properties of high-molecular-weight stereo diblock polylactides with nonequivalent D/L ratios. Polym. Chem., Part A, 48, 794-801. 

The PDLA, PLLA or high d- or L-lactide copolymers have regular structures. The polylactides are either amorphous or semicrystalline at room temperature, depending on the molecular weight and content of l, d or meso-lactide in the main chain. PLA can be totally amorphous or up to 40% crystalline. PLA resins containing more than 93% L-lactic acid can crystallize. However, high molecular weight can reduce the crystallization rate, and therefore the... 

Eitenmuller.J., Muhr, G., David,J. (1990) Treatment of ankle fractures with completely degradable plates, and screws of high molecular weight polylactide. Proced. 92nd Cong. Francais de. Chirgie, Paris, France. 

Many technical processes involve esterification reactions and these have traditionally been of main importance in the preparation of polyesters. Previous chapters have dealt with the preparation of mainly high molecular weight LA polymers involving polycondensation. This chapter focuses on processes where the polycondensation is a process step in the ROP polylactide manufacturing chain and the PLA prepared is generally of low molecular weight. 

The fourth step in the manufacturing process is the polymerization of lactic acid to polylactide, or PLA. PLA can be polymerized via direct polycondensation reaction through azeotropic dehydration. High molecular weight polymers are difficult to synthesize due to the equilibrium between the free acids, water, and the polymer. Dean-Stark trap can be used to remove excess water during the reaction. m-Xylene can be added to lactic acid that added together in a flask at 138 C for 30 hours. After water is removed, the Dean-Stark trap can be replaced with a molecular sieve to recycle the azeotropic mixture. The resultant mixture can be polymerized to PLA at 138°C (Kim and Woo 2002). 

Eitenmiiller, J., Muhr, G., Gerlach, K. L. and Schmickal, T. (1989) New semirigid and bioabsorbable osteosynthesis devices with a high molecular weight polylactide (an experimental investigation), J. Bioact. Compat. Polym., 4, 215-41. 

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