Crystal Growth and Solid-State Structure of Poly(lactide) Stereocopolymers
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- 作者：Hideki Abe ; Mariko Harigaya ; Yoshihiro Kikkawa ; Takeharu Tsuge ; and Yoshiharu Doi
- 刊名：Biomacromolecules
- 出版年：2005
- 出版时间：January 2005
- 年：2005
- 卷：6
- 期：1
- 页码：457 - 467
- 全文大小：501K
- 年卷期：v.6,no.1(January 2005)
- ISSN：1526-4602
文摘
Solid-state structure and melting behavior for random stereocopolymers of L-lactide with meso-lactide(P(L-LA-co-meso-LA)) with different meso-LA compositions of 0, 2, 4, and 10 mol % were investigatedunder various isothermal crystallization conditions. The crystalline morphology of P(L-LA-co-meso-LA)samples changed from the spherulitic aggregates to hexagonal lamellae stacking with a rise in crystallizationtemperature. Under each crystallization condition, P(L-LA-co-meso-LA) samples formed 
-crystal modifications for homopolymer of L-LA. By using the atomic force microscopy and small-angle X-ray scattering,the stacking structure of lamellar crystals was examined for the isothermally crystallized P(L-LA-co-meso-LA) thin films. The lamellar thickness of P(L-LA-co-meso-LA) ranged from 6.2 to 15.5 nm, and the valuesincreased with crystallization temperature. Melting profiles of crystalline regions were examined by thedifferential scanning calorimetry (DSC) for the P(L-LA-co-meso-LA) samples. Distinct two melting peakswere detected in the DSC thermograms of several samples. Investigations on the time-dependent changesin lamellar structure and melting temperature of the P(L-LA-co-meso-LA) samples under isothermalcrystallization conditions provided the evidence that a small amount of D-lactyl units was trapped in thecrystalline regions during early stage of crystallization process under the certain crystallization condition.In addition, it was found that the D-lactyl units trapped in crystalline regions were excluded from crystallinelamellae to form the thermally stable crystals without changes in crystal thickness during further isothermalstorage at a crystallization temperature. The equilibrium melting temperature (
) of P(L-LA-co-meso-LA)samples was estimated by using modified Hoffman-Weeks methods, and the obtained 
values decreasedfrom 215 to 184 
C as the meso-LA composition was increased from 0 to 10 mol %. Furthermore, thecrystal growth kinetics of the P(L-LA-co-meso-LA) samples was analyzed by using the secondary nucleationtheory. Transitions of crystalline regime both from regime III to regime II and from regime II to regime Iwere detected for each sample. The transition temperature from regime II to regime I of each of theP(L-LA-co-meso-LA) samples was very close to the temperature region revealed the morphological changesin the crystalline aggregates from the spherulitic aggregates to hexagonal lamellae stacking.
-crystal modifications for homopolymer of L-LA. By using the atomic force microscopy and small-angle X-ray scattering,the stacking structure of lamellar crystals was examined for the isothermally crystallized P(L-LA-co-meso-LA) thin films. The lamellar thickness of P(L-LA-co-meso-LA) ranged from 6.2 to 15.5 nm, and the valuesincreased with crystallization temperature. Melting profiles of crystalline regions were examined by thedifferential scanning calorimetry (DSC) for the P(L-LA-co-meso-LA) samples. Distinct two melting peakswere detected in the DSC thermograms of several samples. Investigations on the time-dependent changesin lamellar structure and melting temperature of the P(L-LA-co-meso-LA) samples under isothermalcrystallization conditions provided the evidence that a small amount of D-lactyl units was trapped in thecrystalline regions during early stage of crystallization process under the certain crystallization condition.In addition, it was found that the D-lactyl units trapped in crystalline regions were excluded from crystallinelamellae to form the thermally stable crystals without changes in crystal thickness during further isothermalstorage at a crystallization temperature. The equilibrium melting temperature () of P(L-LA-co-meso-LA)samples was estimated by using modified Hoffman-Weeks methods, and the obtained values decreasedfrom 215 to 184 C as the meso-LA composition was increased from 0 to 10 mol %. Furthermore, thecrystal growth kinetics of the P(L-LA-co-meso-LA) samples was analyzed by using the secondary nucleationtheory. Transitions of crystalline regime both from regime III to regime II and from regime II to regime Iwere detected for each sample. The transition temperature from regime II to regime I of each of theP(L-LA-co-meso-LA) samples was very close to the temperature region revealed the morphological changesin the crystalline aggregates from the spherulitic aggregates to hexagonal lamellae stacking.