Configurational structures of lactic acid stereocopolymers as determined by 13C{1H} n.m.r.

Chabot, F.; Vert, Michel; Chapelle, Stella; Granger, Pierre

doi:10.1016/0032-3861(83)90080-0

Cited by 242 publications

(175 citation statements)

References 10 publications

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“…10 The polymerization of D,Llactide was Ðrst conducted with dry powdered zinc metal under various conditions, including normal or argon atmospheres (Table 1). Rather low zinc/monomer molar ratios were selected in order to limit molecular weights and allow end-group characterization.…”

Section: Polymerization In the Presence Of Zinc Metalmentioning

confidence: 99%

Ring opening polymerization ofD,L-lactide in the presence of zinc metal and zinc lactate

et al. 1998

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Section: Polymerization In the Presence Of Zinc Metalmentioning

confidence: 99%

Ring opening polymerization ofD,L-lactide in the presence of zinc metal and zinc lactate

et al. 1998

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“…Assignments of signals due to the isotactic (i) and syndiotactic (s) sequences of the lactate units are shown in Figure 4 according to the literature. 24,[38][39][40][41] The degree of racemization of polymer was calculated from the integral ratio of these sequence signals (see Table II). PDLLA (50/50) spectrum shows predominantly isotactic polymer chains with racemization of 40.0%, which is much different from that of poly(D,L-lactide) prepared by ROP process.…”

Section: Racemization and Sequence Length Of Plgamentioning

confidence: 99%

Direct Synthesis with Melt Polycondensation and Microstructure Analysis of Poly(L-lactic acid-co-glycolic acid)

Gao

Lan

Shao

et al. 2002

Polym J

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ABSTRACT:High-molecular-weight poly(L-lactic acid-co-glycolic acid) (PLGA) was prepared through melt polymerization from glycolic acid (GA) and L-lactic acid (L-LA) and then characterized. High resolution 1 H and 13 C NMR were performed for microstructure analysis of polymer. The solubility in chloroform, compositions, and sequence lengths of PLGA suggest higher reactivity of GA compared with L-LA and shortening GA blocks with reaction time. The racemization of L-LA blocks and transesterification in PLGA are enhanced by increase of GA fractions. PLGA (90/10) samples show crystallization of relatively long L-LA sequences in copolymer chains and the absence of the crystallization of GA blocks. All these results demonstrate the influence of racemization and transesterification on the microstructure of PLGA.KEY WORDS Direct Synthesis / Microstructure / Poly(L-lactic acid-co-glycolic acid) / Poly(Llactic acid) / Poly(D, L-lactic acid) / Aliphatic polyesters derived from lactic acid (LA), glycolic acid (GA), and ε-caprolactone (CL) should have promising applications to biodegradable plastic as well as biomedical materials because of their excellent mechanical, processable, biocompatable, and degradable properties. 1-4 Present in carbohydrate metabolism in nature, LA consists of two optical isomers, L-LA and D-lactic acid (D-LA). The D,L-lactic acid (DL-LA) containing equimolar L-LA and D-LA is racemic. Poly(lactic acid) (PLA) with low molecular weight (M w ) was first prepared by Carothers through the polycondensation of lactic acids 5 in 1932. Poly(Llactic acid) (PLLA), Poly(D, L-lactic acid) (PDLLA), and Poly(L-lactic acid-co-glycolic acid) (PLGA) can be prepared via both direct synthesis and ring-opening polymerization (ROP). The direct synthesis refers to the polycondensation of LA and/or GA. The ROP refers to the polyaddition of lactides and glycolide, 3,4,[6][7][8][9][10][11][12][13][14] which are prepared by depolymerizing the oligomers of LA and GA. The synthesis and isolation of these lactones cause PLA polymers high-priced, which prevents commodity applications of PLA.ROP has been preferred to get polymers with high M w because of the inability of the direct synthesis to increase polymer M w . Thus the direct synthesis has been used to prepare low M w polymers of hydroxy-acids, which can be used in drug delivery systems. [15][16][17][18][19][20][21] In the direct synthesis of PLLA, poly(glycolic acid) (PGA), and PLGA, factors in the obtain of high M w polymers consist both in driving the dehydration equilibrium to the direction of esterification and in reducing the depolymerization of PLLA to lactide at high temperature and under vacuum. Since 1995, Ajioka group 22, 23 has developed solution polycondensation of hydroxy-acids, which brought a breakthrough for the direct synthesis. High-molecular-weight PLA and PLGA could be prepared from LA and GA after a relatively long reaction period at 160 • C under high vacuum in diphenyl ether solution. However, the use of solvents leads to the complexity of process con...

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“…This means has been exploited for various applications. However, it is now known that all the ester bonds forming stereocopolymer chains are not equivalent, a feature that was suspected many years ago [12]. Actually, the cleavage of ester bonds engaged in various diads, triads, tetrads, etc.…”

Section: Poly(l-lactic Acid-co-d-lactic Acid)smentioning

confidence: 99%

Degradation of polymeric systems aimed at temporary therapeutic applications: Structure-related complications

Vert

2005

E-Polymers

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The number of degradable or biodegradable polymers that are aimed or claimed as aimed at therapeutic purposes is rapidly increasing in literature. In most cases, contributions deal primarily with synthesis. However it is the matching of degradation characteristics to application requirements that is important. This contribution, based on personal experience, is aimed at discussing some of the structure-related complications that can be expected when a polymeric therapeutic device degrades in an aqueous medium or in an animal organism. It is shown that dramatic changes can be observed because of selective degradation of some parts leading to the formation of undesired degradation by-products or undesired changes of properties.

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Configurational structures of lactic acid stereocopolymers as determined by 13C{1H} n.m.r.

Cited by 242 publications

References 10 publications

Ring opening polymerization ofD,L-lactide in the presence of zinc metal and zinc lactate

Ring opening polymerization ofD,L-lactide in the presence of zinc metal and zinc lactate

Direct Synthesis with Melt Polycondensation and Microstructure Analysis of Poly(L-lactic acid-co-glycolic acid)

Degradation of polymeric systems aimed at temporary therapeutic applications: Structure-related complications

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