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The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 degrees C for 24 h, the a-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface, This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.

We report on the self-assembly and molecular dynamics in a series of poly(gamma-methyl-L-glutamate-co-gamma-stearyl-L-glutamate) [poly(MLG-co-SLG)] using thermodynamic (differential scanning calorimetry), structural (wide-angle X-ray scattering and (13)C solid-state NMR), as well as dynamic (dielectric spectroscopy and site-specific solid-state NMR) techniques. Stearyl crystallization takes place in the copolymers with W(PSLG) >= 18% which reflects changes of the hydrocarbon side chains conformation. Extruded fibers of the copolymers are composed of both alpha-helical and beta-sheet secondary structures oriented along the fiber axis with a bottleneck structure with MLG/SLG sequences forming the neck and more distant SLG sequences forming the bottle. This supramolecular organization has direct consequences on the dynamics. Two dielectrically active processes with strong temperature dependences were found. Site-specific NMR allowed the identification of the geometry of motions. One is associated with small-amplitude motions of amorphous segments along the polypeptide backbone and at the chain ends that freeze at the liquid-to-glass transition. The slower process is associated with the relaxation of the alpha-helical peptide secondary structure. The analysis of the dielectric strength associated with the slower process revealed that helices are objects of low persistence. Macromolecules