New ultra high molecular weight acrylic processing aids for rigid PVC foaming

Foaming of rigid polyvinyl chloride (PVC) is studied as a function of high molecular weight acrylic processing aids. The industrial process to evaluate quality of foam is discussed in detail. The role of acrylic processing aids to improve melt strength and hence foaming of PVC is explained. It is demonstrated that increase in molecular weight of acrylic processing aids increases its effectiveness. It is found that ultra-high molecular weight processing aids is 25%–30% more efficient than relatively lower, but still high, molecular weight acrylic processing aids. The higher molecular weight processing aids provided comparable foaming performance at lower loading levels. Foaming reduced the density of PVC compounds to 0.32–0.34 g/cm³. More than 1000% expansion is achieved in the melt extrusion process using a chemical blowing agent. Fusion characteristics are also studied. Fusion times for initial fusion peaks are in the range of 42–44 s while the fusion times of the second fusion peaks are in the range of 74–94 s. The higher molecular weight processing aids maintained fusion characteristics of PVC compounds, warranting no significant changes in commercial process.     

The Discovery of Phenylbenzamide Derivatives as Grb7‐Based Antitumor Agents

Grb7 is a non‐catalytic protein, the overexpression of which has been associated with the proliferative and migratory potentials of cancer cells. Virtual screening strategies involving a shape‐based similarity search, molecular docking, and 2D‐similarity searches complemented by experimental binding studies (Thermofluor and isothermal titration calorimetry) resulted in the identification of nine novel phenylbenzamide‐based antagonists of the Grb7 SH2 domain. Moderate binding affinities were observed, ranging from K_d=32.3 μM for lead phenylbenzamide NSC 104999 ( 1 ) to K_d=1.1 μM for a structurally related compound, NSC 57148 ( 2 ). Deconvolution of the affinity data into its components revealed differences in lead binding, from being entropy based (lead 1 ) to enthalpically driven (NSC 100874 ( 3 ), NSC 55158 ( 4 ), and compound 2 ). Finally, the lead compound 1 was found to decrease the growth of MDA‐MB‐468 breast cancer cells, with an IC₅₀ value of 39.9 μM . It is expected that these structures will serve as novel leads in the development of Grb7‐based anticancer therapeutics.     

Macrocyclization of Organo‐Peptide Hybrids through a Dual Bio‐orthogonal Ligation: Insights from Structure–Reactivity Studies

Macrocycles constitute an attractive structural class of molecules for targeting biomolecular interfaces with high affinity and specificity. Here, we report systematic studies aimed at exploring the scope and mechanism of a novel chemo‐biosynthetic strategy for generating macrocyclic organo‐peptide hybrids (MOrPHs) through a dual oxime‐/intein‐mediated ligation reaction between a recombinant precursor protein and bifunctional, oxyamino/1,3‐amino‐thiol compounds. An efficient synthetic route was developed to access structurally different synthetic precursors incorporating a 2‐amino‐ mercaptomethyl‐aryl (AMA) moiety previously found to be important for macrocyclization. With these compounds, the impact of the synthetic precursor scaffold and of designed mutations within the genetically encoded precursor peptide sequence on macrocyclization efficiency was investigated. Importantly, the desired MOrPHs were obtained as the only product from all the different synthetic precursors probed in this study and across peptide sequences comprising four to 15 amino acids. Systematic mutagenesis of the “i?1” site at the junction between the target peptide sequence and the intein moiety revealed that the majority of the 20 amino acids are compatible with MOrPH formation; this enables the identification of the most and the least favorable residues for this critical position. Furthermore, interesting trends with respect to the positional effect of conformationally constrained (Pro) and flexible (Gly) residues on the reactivity of randomized hexamer peptide sequences were observed. Finally, mechanistic investigations enabled the relative contributions of the two distinct pathways (side‐chain→C‐end ligation versus C‐end→side‐chain ligation) to the macrocyclization process to be dissected. Altogether, these studies demonstrate the versatility and robustness of the methodology to enable the synthesis and diversification of a new class of organo‐peptide macrocycles and provide valuable structure–reactivity insights to inform the construction of macrocycle libraries through this chemo‐biosynthetic strategy.     

Effects of Solids Loading on Sintering and Properties of Freeze‐Cast Kaolinite–Silica Porous Composites

Kaolinite–silica nanocomposites with a green porosity ranging from 75% to 87% were prepared using a freeze‐casting technique. The initial solids loading values (kaolinite platelets plus silica nanospheres) greatly influence the sintering behavior as well as the phase and strength of the resulting porous composites. The composites with lower solids loading exhibit faster sintering (e.g., larger shrinkage, more extensive thickening of the pore walls) when sintered at 1250°C, which in turn, results in a rapid increase in flexural strength. All the composites maintain a high porosity (above 50%) after sintering at 1250°C for 72 h, whereas the flexural strength of the composites increases from roughly 0.2 MPa for the green samples to 13.3, 7.5, and 6.5 MPa for 12, 18, and 24 vol% solids samples, respectively, after sintering. It is believed that solids loading affects kaolinite–silica packing during the sol‐to‐gel transition as a minimum amount of silica nanoparticles is required to build the gel network. This particle packing difference influences the amount of kaolinite–silica interfacial contact, which in turn affects the strength. The strength increase through solids loading change is a combined effect of changes in the porous structure during sintering plus the development of a new phase at the silica–kaolinite interface.     

Characterizing Weave Geometry in Textile Ceramic Composites Using Digital Image Correlation

Techniques for characterizing tow architectures and defects in woven ceramic composites are required for generating high‐fidelity geometric models and subsequently probing effects of defects on composite performance. Although X‐ray computed tomography (CT) has been shown to provide the requisite information with potentially sub‐μm resolution, the technique is inherently limited to probing only small volumes: on the order of a few unit cells of typical weaves. Here, we present an assessment of the efficacy of a complementary 2D technique, based on surface topography mapping via 3‐D (three‐dimensional) digital image correlation (DIC), with potential for ascertaining long‐range features in weaves and defects that cannot be gleaned from CT imaging alone. Upon comparing surfaces reconstructed from CT and DIC data, we find that DIC is capable of resolving surface heights with a root mean square(RMS) error of ~10 μm (about twice the CT voxel size, 4.4 μm) and a spatial resolution of ~20 μm over areas of several cm². Achieving this level of resolution requires use of sufficiently small speckles (~50 μm) and small subset size (~300 μm) relative to the characteristic tow dimensions (~1 mm). The error is somewhat higher (about 20 μm) in areas where surface discontinuities or rapid changes in topography exist (e.g., at tow boundaries).     

SELF-ADHESION HYSTERESIS IN POLYDIMETHYLSILOXANE ELASTOMERS

The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a silver substrate pretreated with meta-aminothiophenol (m-ATP) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to determine the molecular structure of the interphase. It was found that m-ATP was adsorbed dissociatively onto silver substrates through the thiol groups. The tilt angle for m-ATP molecules adsorbed on silver substrates was determined using RAIR to be approximately 39°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the molecular axes. When PA was deposited onto m-ATP pretreated silver substrates, anhydride groups of PA reacted with amino groups of m-ATP to form amic acids. When PA/m-ATP/Ag samples were chemically cured in acetic anhydride and pyridine or triethylamine, isoimide was the predominant product regardless of the use of pyridine or triethylamine as catalyst. These results were different from those obtained from PA/APDS/Au systems in which imide was the major product in the presence of triethylamine. These differences in the relative composition of cured products between two model systems were explained by the effect of substituents attached to APDS and m-ATP benzene rings.     

Surface Mechanical Properties of the Spore Adhesive of the Green Alga Ulva

The mechanical properties of the adhesive produced by spores of the green, marine, fouling alga Ulva linza are reported. Atomic force microscopy studies were performed and nanoindentation data were analyzed using a model for an asymmetric indenter. Freshly secreted adhesive is characterized by multiple layers. We found that the modulus of the outer ～600-nm thick layer was about 0.2 ± 0.1 MPa, whereas the modulus of the inner layer was about 3 ± 1 MPa. Older adhesive showed the formation of a “crust” of harder material with a yield strength of ～20 MPa at a loading rate of 2.5 × 10^?6 N · s^?1. Mechanical properties under tension are also described, and extension profiles that showed either constant or nonlinear force changes with tip-sample separation were observed. Models for both kinds of behavior are described. The work of adhesion between poly-dimethylsiloxane (PDMS)-coated AFM tips and the adhesive was determined to be less than 1.5 mJ · m^?2.     

Percolated Network Structure Formation and Rheological Properties in Nylon 6/Clay Nanocomposites

To understand the effect of the percolated clay network structure formed by the exfoliated clay layers in nanocomposites, the clay network structure in nylon‐6‐based nanocomposites is characterized using TEM and FFT analyses. A MMT volume fraction between 0.013 and 0.014 is the percolation threshold for strong network formation. The volume spanning MMT network leads to a very high flow activation energy as compared with that of neat nylon 6, resulting in the pseudo‐solid like response under molten state in N6CNs. A canonical NVT‐MD simulation was conducted in the system made up by nylon 6 molecules/Si(OH)₄ molecules. The formation of the strong interfacial interaction between nylon 6 molecules and Si(OH)₄ molecules induced by OH groups is suggested.