Thermal degradation in a trimodal poly(dimethylsiloxane) network studied by (1)H multiple quantum NMR.

Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation.

Spin system assignment of homo-o-phenylene ethynylene oligomers.

We previously reported the synthesis and solution characterization of short o-phenylene ethynylene (oPE) foldamers. Proton correlation techniques are not adequate for NMR assignment in these compounds as the ethynylene linkers interrupt proton connectivity. In order to facilitate structural characterization and more fully harness the power of NMR, it is necessary to know the sequence of spin systems along the molecular backbone.

Liquid crystalline order from ortho-phenylene ethynylene macrocycles.

Triangular ortho-phenylene ethynylene (o-PE) cyclic trimers represent a novel member of shape-persistent macrocycles. Shape-persistent cyclic structures remain of great interest as molecular components in the fields of supramolecular materials, host-guest chemistry, and materials science. Novel discotic liquid crystalline properties are reported from triangular-shaped o-PE macrocycles containing branched alkoxy- and/or triethylene glycol (TEG) side chains using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD).

Biomimetic facially amphiphilic antibacterial oligomers with conformationally stiff backbones.

A foldamer has been designed with a conformationally stiff backbone that is facially amphiphilic. The oligomer has excellent antimicrobial activity and was found to be 18 times more active toward bacterial cells than human red blood cells. The oligomer is built from arylamide bonds around a central 4,6-dicarboxy pyrimidine ring.

Solution 1H NMR confirmation of folding in short o-phenylene ethynylene oligomers.

Oligomers based on an o-phenylene ethynylene (oPE) backbone with polar substituents have been synthesized using Sonogashira methods. Folding of these extremely short oligomers was confirmed via 1D and 2D (NOESY) NMR methods. Utilizing electron-rich and electron-poor phenylene building blocks, variations of these oPE oligomers have been synthesized to determine the folded stability of pi-rich vs pi-poor vs pi-rich-pi-poor systems.

Synthesis of alkoxy-substituted ortho-phenylene ethynylene oligomers.

[structure: see text] This Letter describes the first published synthesis and characterization of alkoxy-substituted ortho-phenylene ethynylene (o-PE) oligomers. Sonogashira coupling was used to assemble discrete chain lengths, using a key monomer with orthogonal groups. Deprotection or activation allowed stepwise coupling to produce the dimer, trimer, and tetramer, while convergent coupling of appropriately substituted trimers produced the hexamer.