Real-time imaging of crystallization in polylactide enantiomeric monolayers at the air-water interface.
A newly developed planar array infrared reflection-absorption spectrograph (PA-IRRAS) offers significant advantages over conventional approaches including fast acquisition speed, excellent compensation for water vapor, and an excellent capacity for large infrared accessories, e.g., a water trough. In this study, the origin of stereocomplexation in a polylactide enantiomeric monolayer at the air-water interface was investigated using PA-IRRAS. PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of polymer chains during the compression of the monolayers. It was found that a mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the two-dimensional monolayer developed at the air-water interface before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. PA-IRRAS spectra of the stereocomplex exhibited distinct band shifts in crystalline sensitive components, e.g., the vas(C-O-C, h) mode, as well as amorphous-dependent components, e.g., the vs(C-O-C) mode, when compared with the spectra of PLLA alone. On the other hand, time-resolved PA-IRRAS spectra, which were obtained as the films were being compressed, revealed that both monolayers of PLLA and mixed PLLA/PDLA stereocomplex were crystallized into a 10(3)-helix and a 3(1)-helix, respectively, with a distinct band shift in crystalline sensitive components only. Fourier self-deconvolution of the spectra demonstrated that the band shift in crystalline sensitive components is correlated with the intermolecular interaction of polymer chains.
Kim
Young Shin
YS
Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, USA.
Snively
Christopher M
CM
Liu
Yujuan
Y
Rabolt
John F
JF
Chase
D Bruce
DB
D003460:Crystallization; D005740:Gases / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry*; D011312:Pressure; D012997:Solvents; D013057:Spectrum Analysis; D013237:Stereoisomerism; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D005740:Gases; D011091:Polyesters; D012997:Solvents; D014867:Water; C033616:poly(lactide)