Thermal analysis of typical poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK) has been carried out from 130 to 650 K for samples variously crystallized between 593 and 463 K or quenched to the glassy state. The heat capacity, Cp, is crystallinity independent to 240 K. Between 240 K and the glass transition temperature Tg (419-430 K depending on crystallization conditions) the amorphous solid has a slightly higher Cp. Above Tg poorly crystallized samples show a rigid-amorphous fraction that does not contribute to the increase in Cp at Tg. Crystallinity reduces the heat capacity hysteresis at Tg. On crystallization three types of crystallinity must be distinguished: ivc(H), wc(L), and wc(C). Fusion peaks at high and low temperatures characterize uf(H) and wc(L), respectively; u>c(C) forms on cooling after crystallization and causes an increase in Cp starting at about 460 K. The metastability, sequence of crystallization, recrystallization, and reorganization on analysis by heating at a constant rate and on stepwise crystallization are analyzed.

Frank-Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with "soft" spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.self-assembly | Frank-Kasper phases | quasicrystal phases | giant surfactants | POSS I n addition to the close-packing schemes of identical atoms (such as hexagonal close-packing and face-centered cubic), atoms with different radii and electronic states in metal alloys are able to pack into more complex phases composed of spheres, such as the Frank-Kasper (F-K) phases (1, 2), which combine the Frank lattice (icosahedron with a coordination number of 12) and the Kasper lattice (with higher coordination numbers of 14, 15, and 16). A few F-K phases such as the A15-(space group of Pm 3n) and σ-(space group of P4 2 /mnm) phases are periodic approximants of different quasicrystals. Quasicrystals, first identified in supercooled metal alloys, are aperiodic, and possess 5-, 7-, 8-, 10-, or 12-fold rotational symmetry but no long-range translational periodicity (3-5). Stabilization of these phases in metals originates from both geometric factors and the tendency to enhance low orbital electron sharing due to fewer surface contacts among the atoms (6).F-K phases have also been identified in soft-matter systems, including small-molecule surfactants (7-9), block copolymers (10-12), dendrimers (13-15), liquid crystals (16, 17), colloidal particles (18), and, very recently, molecular giant tetrahedra (19). In contrast to metal alloys that use atoms as the motifs, organic/hybrid molecules first self-assemble into spheroidal motifs...

This paper reports a comprehensive study on the synthesis and self-assembly of two model series of molecular shape amphiphiles, namely, hydrophilic [60]fullerene (AC(60)) tethered with one or two polystyrene (PS) chain(s) at one junction point (PS(n)-AC(60) and 2PS(n)-AC(60)). The synthesis highlighted the regiospecific multiaddition reaction for C(60) surface functionalization and the Huisgen 1,3-dipolar cycloaddition between alkyne functionalized C(60) and azide functionalized polymer to give rise to shape amphiphiles with precisely defined surface chemistry and molecular topology. When 1,4-dioxane/DMF mixture was used as the common solvent and water as the selective solvent, these shape amphiphiles exhibited versatile self-assembled micellar morphologies which can be tuned by changing various parameters, such as molecular topology, polymer tail length, and initial molecular concentration, as revealed by transmission electron microscopy and light scattering experiments. In the low molecular concentration range of equal or less than 0.25 (wt) %, micellar morphology of the series of PS(n)-AC(60) studied was always spheres, while the series of 2PS(n)-AC(60) formed vesicles. Particularly, PS(44)-AC(60) and 2PS(23)-AC(60) are synthesized as a topological isomer pair of these shape amphiphiles. PS(44)-AC(60) formed spherical micelles while 2PS(23)-AC(60) generated bilayer vesicles under identical conditions. The difference in the self-assembly of PS(n)-AC(60) and 2PS(n)-AC(60) was understood by the molecular shape aspect ratio. The stretching ratio of PS tails decreased with increasing PS tail length in the spherical micelles of PS(n)-AC(60), indicating a micellar behavior that changes from small molecular surfactant-like to amphiphilic block copolymer-like. For the series of PS(n)-AC(60) in the high molecular concentration range [>0.25 (wt) %], their micellar morphological formation of spheres, cylinders, and vesicles was critically dependent upon both the initial molecular concentration and the PS tail length. On the other hand, the series of 2PS(n)-AC(60) remained in the state of bilayer vesicles in the same concentration range. Combining both of the experimental results obtained in the low and high molecular concentrations, a systematic morphological phase diagram was constructed for the series of PS(n)-AC(60) with different PS tail lengths. The versatile and concentration-sensitive phase behaviors of these molecular shape amphiphiles are unique and have not been systematically explored in the traditional surfactants and block copolymers systems.

Thermal analysis was performed on poly(buty1ene terephthalate), PBT, between 210 and 560 K. By combination of experimental heat capacities with computations with an approximale frequency spectrum of 65 group and 19 skeletal vibrations, preliminary recommended ATHAS (1988) heat capacities are proposed for the solid state from 0 to 600 K. The Tarasov parametei s used for the computation of the skeletal vibrations were 8, = 542 K and 8, = 80 K for crystalline PBT and O3 = 40 K for amorphous PBT. The glass transition temperature of amorphoL s PBT was found on efficiently quenched samples to be 248 K, much lower than for semicrystaline PBT where a 310-325 K glass transition temperature is typical. The increase in heat capacity calculated for 100% amorphous samples is 107 J/(K . mol) at 248 K and 77 J/(K . mol) at 320 K. The equilibrium melting temperature is estimated to be 518 K. The unique existence c f rigid-amorphous fractions of the semicrystalline polymers is discussed with quantitative data for samples crystallized from the glass and from the melt between 275 and 490 K. The rigidamorphous fraction varies between above 0,9 for cold-crystallized samples to 0,3 for sampk s crystallized at 490 K . The crystallinity varied from below 0,l to 0,5. The crystallinity could t e separated into four parts, melting at high, medium, and low temperatures, and a pal t crystallized on cooling after isothermal crystallization. The sequence of crystallization c f differently melting crystals was established.