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Crystal growth and solid-state structure of poly(lactide) Stereocopolymers
Hideki Abe1, Mariko Harigaya, Yoshihiro Kikkawa
1Polymer Chemistry Laboratory, RIKEN Institute, Hirosawa, Wako-shi, Saitama 351-0198, Japan. habe@riken.jp
Biomacromolecules
|January 11, 2005
Summary
Investigating random stereocopolymers of L-lactide with meso-lactide (P(L-LA-co-meso-LA)) revealed that increasing meso-LA content lowers equilibrium melting temperature. D-lactyl units were found to be trapped and then excluded from crystalline regions during isothermal crystallization.
Area of Science:
- Polymer Science
- Materials Science
- Crystallography
Background:
- Stereocopolymers of L-lactide with meso-lactide (P(L-LA-co-meso-LA)) are biodegradable polymers with tunable properties.
- Understanding their crystallization behavior is crucial for controlling material properties.
Purpose of the Study:
- To investigate the solid-state structure and melting behavior of P(L-LA-co-meso-LA) with varying meso-LA content (0-10 mol%).
- To analyze the impact of isothermal crystallization conditions on morphology, crystal structure, and growth kinetics.
Main Methods:
- Isothermal crystallization at various temperatures.
- Atomic Force Microscopy (AFM) and Small-Angle X-ray Scattering (SAXS) for structural analysis.
- Differential Scanning Calorimetry (DSC) for melting behavior.
- Modified Hoffman-Weeks method for equilibrium melting temperature estimation.
- Secondary Nucleation Theory for crystal growth kinetics analysis.
Main Results:
- Crystalline morphology transitioned from spherulitic aggregates to hexagonal lamellae stacking with increasing crystallization temperature.
- Alpha-crystal modifications were observed, similar to L-lactide homopolymer.
- Lamellar thickness ranged from 6.2 to 15.5 nm, increasing with crystallization temperature.
- Two melting peaks were detected in DSC thermograms, indicating trapped D-lactyl units.
- Equilibrium melting temperature (T(m)0) decreased from 215 to 184 °C as meso-LA content increased from 0 to 10 mol%.
- Transitions between crystallization regimes (III-II and II-I) were observed.
Conclusions:
- A small amount of D-lactyl units can be trapped in crystalline regions during early crystallization stages, later excluded to form more stable crystals.
- The equilibrium melting temperature of P(L-LA-co-meso-LA) is significantly reduced by the incorporation of meso-LA.
- Crystallization regime transition temperatures correlate with morphological changes observed in the copolymers.