The polyglutamate which grafts with flexible alkyl side-chain by ester exchange reaction is like rod-hairy molecule. The numbers of methylene group of side-chain and the graft-density affect the molecular packing of poly(gama-alkyl-L-glutamate)s. To be sure the correct chemical structure of poly(gama-alkyl-L-glutamate)s by Fourier transform infrared spectrometer (FTIR), and find out the graft-density of each sample by proton nuclear resonance spectrometer (1H-NMR). Phase behavior of poly(gama-alkyl-L-glutamate)s were studied via differential scanning calorimetry (DSC) and variable temperature x-ray diffraction (XRD).We combine the results from C. C. Hsu(24). When the side-chain length is long enough (m>10), side-chains will crystallize into a 3D hexagonal lattice. The results of DSC and XRD analyses show that the side-chain crystalline phase will melt at Tm1, where as a liquid crystalline (LC) phase transition exists at Tm2. Poly(gama-alkyl-L-glutamate)s with shorter side-chain (m<8) tend to form 2D hexagonal LC structure. On the other hand, longer side-chains (m>10) tend to give lamellar structure. The critical number of methylene group of side-chain between hexagonal and lamellar structure is between 8 and 10.

Thermal behavior and molecular packing of a series of £\-helical poly(L-glutamates), with n-alkyl side chain of various lengths (m(number of carbons in the alkyl group) = 1, 2, 6, 12,18), were studied by means of differential scanning calorimetry, polarizing light microscopy and X-ray diffraction. For polymers of m = 1 and 2, There is a pseudohexagonal structure below ca. 130 oC and above this temperature the stable phase is the hexagonal columnar phase. There exists a layered structure in the polymer of m = 6, as well as a solvent induced hexagonal columnar structure which formed during solution casting process. In the polymer of m = 12, a layered structure was formed in the temperature range between 20 to 255 oC. However, for longer side chain, m = 18, tendency of crystallization of alkyl long side chain forced the backbone to pack into layer structure. There are two distinct melting temperature at ca. 60 oC, and the enthalpy are ca. 53 and 19 J/g, which corresponding to the melting of hexagonal and monoclinic side chain crystallines. The polymers with longer side chain (m = 6, 12 and 18) tend to be lyotropic liquid crystalline phase within lamellar inter-rod distance of 1.25 nm in solution state, and the structure will remain after drying. However, the inter-rod distance will collapse at the temperature above ca. 200 ¢J and will not recover after cooling.

ABSTRACT Structural evolution and its effect on optical absorption/emission behavior of derivative of PPVs upon isothermal heat treatment at elevated temperatures were studied by means of a combination of polarized light microscopy, x-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, and photoluminescence spectroscopy. The main physical picture drawn from results of this study over a series of PPVs with flexible side-chains may be summarized as the following: (1) They are generally liquid-crystalline in nature, typically biaxially nematic in optical texture but morphologically characterized as of lamellar or hexagonal columnar structure. This is consistent with the nematogenic nature one would expect from the rigid backbone as well as the smectogenic nature one would expect from the aliphatic side-chains. (2) The aggregates formed in solutions and the supramolecular assemblies formed in the bulk state are structurally similar (in terms of the similar level of conjugation), and hence possibly of the same thermodynamic origin. This surfactant-like self-ordering behavior is consistent with the tendency towards segregation between the aromatic, rigid backbone and the aliphatic, flexible side-chains. (3) The collapse of these conjugated polymers with flexible side-chains into aggregates appears to be a general phenomenon upon slow to moderate solvent removal and not limited to the present case of poor solvency power. This is consistent with the strong tendency toward phase separation in rigid rod solutions delineated by Flory some 30 years ago. (4) All the above observations may be explained in terms of lyotropic or thermotropic self-assembly of hairy-rod chains into coiled helical conformation with ellipsoidal cross section for the conjugated backbone as shown schematically in Figure 4-42 and 4-43. The flexible side-chains generally tend to fill the space within the ellipsoidal cylindrical structure. As the side-chain length is increased, the increased Van der Waals attraction among side-chains results in more extended period of helical twist or more straighten backbone conformation, rendering preference of lamellar structure over hexagonal helical structure. (5) As a consequence, supramolecular aggregation is basically enhanced by increased side-chain length or backbone rigidity. This in turn results in more extended conjugation length or more fully developed