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A comparative study of cold crystallization behavior in poly(l-lactide) (PLLA) annealed below and just above the glass transition temperature (Tg) has been conducted. Annealing benefits the generation of local order and the subsequent cold crystallization process, which becomes significant in PLLA annealed just above Tg. Surprisingly, morphological observation reveals high density nuclei in PLLA annealed below Tg, contrary to its relatively slow crystallization kinetics. This unusual crystallization behavior in physically aged PLLA arises from the retarded crystal growth rate because of incomplete recovery of reduced segmental mobility above Tg. In contrast, annealing just above Tghas little influence on the crystal growth rate, and the increased nucleation density alone accounts for the accelerated crystallization rate. [ABSTRACT FROM AUTHOR]

We identified a set of thiosemicarbazone (TSC) metal ion chelators that reactivate specific zinc-deficient p53 mutants using a mechanism called zinc metallochaperones (ZMCs) that restore zinc binding by shuttling zinc into cells. We defined biophysical and cellular assays necessary for structure-activity relationship studies using this mechanism. We investigated an alternative class of zinc scaffolds that differ from TSCs by substitution of the thiocarbamoyl moiety with benzothiazolyl, benzoxazolyl, and benzimidazolyl hydrazones. Members of this series bound zinc with similar affinity and functioned to reactivate mutant p53 comparable to the TSCs. Acute toxicity and efficacy assays in rodents demonstrated C1 to be significantly less toxic than the TSCs while demonstrating equivalent growth inhibition. We identified C85 as a ZMC with diminished copper binding that functions as a chemotherapy and radiation sensitizer. We conclude that the benzothiazolyl, benzoxazolyl, and benzimidazolyl hydrazones can function as ZMCs to reactivate mutant p53 in vitro and in vivo .

In asymmetric poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends, the pre-existing stereocomplex crystals can impose confinement effects on homocrystallization of uncomplexed PLLA among them. However, confinement effects are very weak in the blend films because of relatively large PLLA domains distributed in the skeleton of stereocomplex crystals. As a comparison, in the electrospun blend fibers, fine distribution of uncomplexed PLLA results in strong confinement effects. This is manifested by the significant decrease in the crystallization temperature and melting point. Even so, confinement effects have little influence on the crystal form, and PLLA α-crystals prevail in the electrospun blend fibers after melt crystallization. Finally, confinement effects in the electrospun blend fibers depend on annealing temperatures and almost disappear when the samples are annealed above the melting point of stereocomplex crystals.

Crystallization and the polymorphic transition of poly(vinylidene fluoride) (PVDF) in its miscible blends with poly(butylene succinate) (PBS) from the melt has been investigated. The presence of a miscible PBS component lowers the crystallization temperature and the melting point of the PVDF component in the blends. It becomes more significant above a critical PBS content between 40 and 50 wt % where PVDF chains are dispersed in the matrix composed by PBS chains. On the other hand, the β form of the PVDF component can be induced at low temperatures, which also has a transition at the critical PBS content.

The conformational and polymorphic transformations in the melt-spun monofilament of syndiotactic polypropylene upon annealing and subsequent stretching have been first explored by micro-FTIR studies. The results indicate that annealing of as-spun monofilament gives rise to an unusual increase in the molecular orientation of helical conformations in both amorphous phase and ordered crystals as a result of structural transitions of transplanar conformations to helical ones as well as mesophase to ordered crystals. The increased molecular orientation in the annealed monofilament is mainly responsible for the enhanced strength during stretching. Furthermore, high stress exerted by the molecular chains of annealed monofilament is confirmed by the significant structural transitions opposite to that induced by annealing.

A study on the mechanism for the degraded toughness in nylon 6/clay nanocomposite is explored in this article. Such a nanocomposite exhibits lower specific essential work of fracture we and specific nonessential work of fracture betawp than its pure nylon 6 counterpart, as revealed by essential work of fracture (EWF) measurements. Furthermore, the molecular orientation in a small region (20x20 microm2) ahead of crack tip, obtained from micro-FTIR measurements for the first time, is found to be lower in the nanocomposite during crack initiation and propagation. The decreased molecular orientation, mostly resulted from severe microvoiding at crack tips, is responsible for the reduced specific essential work of fracture we. Meanwhile, the molecular orientation around crack tip also indicates that lower plastic deformation occurs in the plastic zone, which is well correlated with decreased specific nonessential work of fracture betawp in the nanocomposite.

In this article, molecular orientation of crystalline and amorphous phases of both linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) and epitaxy in the LLDPE/iPP blends prepared via dynamic packing injection molding have been investigated with the aid of polarized Fourier transform infrared (FTIR) spectroscopy and two-dimensional X-ray scattering (2D-WAXS). In LLDPE-rich blends, LLDPE was oriented along the shear flow direction, and iPP kept very low orientation. No epitaxial growth between LLDPE and iPP was observed. However, for the blends with LLDPE content less than 50 wt %, where iPP was the matrix and LLDPE formed the droplets, iPP was highly oriented along shear flow direction and LLDPE epitaxially grew onto iPP. The contact planes were (100)LLDPE and (010)iPP, and LLDPE molecules were about 50 degrees apart from the shear direction. The epitaxy fraction in LLDPE/iPP blends could be tentatively calculated from the values of orientation function of the LLDPE crystalline a-axis (fa) and that of crystalline b-axis (fb). Both tensile strength and tensile modulus decreased with the increase of LLDPE composition, indicating they were composition dependent, though shear-induced orientation and epitaxial crystallization might play some role. The impact strength of the blend samples reached a plateau in the LLDPE composition range of 20-50%, due to the contribution of orientation and epitaxy.

Irradiation of ultrahigh molecular weight polyethylene (UHMWPE) with a dose of 150 kGy by an electron beam can effectively increase the entanglement density in the amorphous phase and has little influence on the properties of the crystalline phase, which provides examples to comparatively investigate the role of lamellar coupling and entanglement density in determining the strain-hardening effect in semicrystalline polymers. The strain-hardening modulus, deduced from the Haward plots of true stress-strain curves, is inversely temperature-dependent and has a sharp transition around 65 degrees C that corresponds to the mechanical alphaI-process of the crystalline phase for both nonirradiated and irradiated samples, irrespective of the entanglement density in the amorphous phase. Lamellar coupling takes more effect in determining the strain-hardening behavior before the mechanical alphaI-process is activated. With further increasing temperature, lamellar coupling becomes weaker and the role of the entangled amorphous phase is gradually presented. However, the same temperature dependence of the strain-hardening modulus in both nonirradiated and irradiated samples indicates that the strain-hardening behavior in semicrystalline polymer is mostly determined by lamellar coupling rather than by entanglement density.