Effect of polymerization catalysts on the microstructure of P(<scp>L</scp>LA‐<i>co</i>‐εCL)

Choi, Eui-Jun; Park, Jung-Ki; Chang, Ho-Nam

doi:10.1002/polb.1994.090321505

Cited by 51 publications

(25 citation statements)

References 13 publications

(1 reference statement)

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“…The ratio of the integrated intensity at 5.2 ppm (the methyne group of LLA unit) to that at 4.1 ppm (the ␥-methylene group of CL neighbouring oxygen of ester bond) 16,26 was used to determine the chemical composition of the copolymer. w L was calculated from eq.…”

Section: Measurements and Observationmentioning

confidence: 99%

“…18 Recently, Choi et al also showed that P(LLA-CL) synthesized using stannous octoate were semicrystalline and of block-type in the entire range of monomer mixing. 26 Seppä lä et al synthesized P(LLA-CL) of different LLA contents using stannous octoate and investigated the change of physical properties during aging in phosphate buffered solution, 11,12,29 and Grijpma and Pennings studied crystallization at room temperature for P(LLA-CL) (50/50) synthesized using tin catalyst. 7,19 These studies demonstrated that the P(LLA-CL) copolymers changed their physical properties during storage at room temperature.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Enhanced crystallization of poly(L-lactide-co-ɛ-caprolactone) during storage at room temperature

Tsuji

Mizuno

Ikada

2000

J. Appl. Polym. Sci.

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ABSTRACT:Copolymer of L-lactide and -caprolactone [P(LLA-CL)] (50/50) was synthesized using stannous octoate and was stored at room temperature. The change in physical properties occurring during this storage at room temperature was investigated by differential scanning calorimetry (DSC), X-ray diffractometry, polarizing optical microscopy, tensile and bending tests, and light absorbance measurements. It was concluded that the increase in mechanical properties and light absorbance during storage can be ascribed to gradual selective crystallization of the L-lactide sequence in P(LLA-CL) at room temperature.

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Section: Measurements and Observationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Enhanced crystallization of poly(L-lactide-co-ɛ-caprolactone) during storage at room temperature

Tsuji

Mizuno

Ikada

2000

J. Appl. Polym. Sci.

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“…Figure 2 gives typical methine regions in the 1 H NMR spectra of PLLA, PDLLA, and PLGA samples. The molar fraction of GA moiety in PLGA can be calculated from the integrated area of peaks at 5.15 ppm due to methine protons in LA units 17,29,30 and that of peaks at 4.60-4.90 ppm owing to methylene protons in GA blocks in PLGA. 7,9,15 Assigning I L to integrated peak area at 5.15 ppm, I G integrated Table II.…”

Section: Synthesis and Molecular Weights Of Copolymersmentioning

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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“…6,7 Therefore, the copolymerization of PLLA with PCL is known to be an effective route to improve properties in comparison with each individual component. 8,9 In a copolymer, when one block can crystallize, the physical properties and degradability of other blocks will be affected since the morphology can also be dramatically altered at the microscale level. [10][11][12] It has been conrmed that the PLLA-PCL copolymer is weakly segregated in the melt depend on composition, 13,14 and the melting and crystalline temperature of the PLLA block are higher than those of the PCL block.…”

Section: Introductionmentioning

confidence: 99%

Crystallization and morphological transition of poly(l-lactide)–poly(ε-caprolactone) diblock copolymers with different block length ratios

et al. 2017

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The crystallization behavior, banded spherulite and morphological transition of poly(L-lactide) (PLLA) phases within the block copolymers were investigated. All experimental results showed that the structure and thermal properties of PLLA-PCL copolymers could be adjusted by varying the ratios of the chain length of the two blocks. Morphological results indicated that the banded spherulites of PLLA formed when PLLArich copolymers crystallized. PCL segments introduced unbalanced stresses around PLLA lamellar crystals, which resulted in a bending moment responsible for twisting of PLLA lamellar crystals. As the block length ratio of PCL to PLLA increased, an over accumulation of PCL segments influenced the twisting of PLLA lamellae. In addition, it was interesting to find that the banded spherulite morphology changed with increasing the crystallization temperature. The crystallization temperature has an effect on the relationship between the sense of lamellar twisting and the morphological transition of PLLA, which is reflected in the fact that the band spacing of banded spherulites showed strong temperature dependence when the crystallization temperature exceeds 115 C, while it exhibited weak temperature dependence below 115 C. In particular, above 125 C the band spacing disappeared and nonbanded spherulites formed.

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Effect of polymerization catalysts on the microstructure of P(LLA‐co‐εCL)

Cited by 51 publications

References 13 publications

Enhanced crystallization of poly(L-lactide-co-ɛ-caprolactone) during storage at room temperature

Enhanced crystallization of poly(L-lactide-co-ɛ-caprolactone) during storage at room temperature

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

Crystallization and morphological transition of poly(l-lactide)–poly(ε-caprolactone) diblock copolymers with different block length ratios

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