Negative thermal expansion of a polydiacetylene single crystal

Macroscopic thermal expansion in the chain direction has been measured for the first time on organic polymeric single crystals. Negative linear thermal expansion coefficients αM are reported and related to chain torsional motion and equilibrium point-defect formation for a solid-state polymerized phase of 2,4-hexadiyne-1,6-diol bisphenylurethane (HDU) which contains crystallographically located interstitial dioxane and for a dioxanefree phase obtained by thermal annealing. Data for as-polymerized single crystals (which are probably of extended chain morphology) between ?50 and 100°C give αM = ?(1.686 ± 0.039) × 10^?5 ? (1.35 ± 0.18) × 10^?7 t with t in °C. During volatilization of 11.7 ± 1.0 wt-% interstitial dioxane and a resulting crystal structure change, the as-polymerized fibers fibrillate and shrink irreversibly by 0.16 ± 0.04%. Although dichroism and diffraction measurements indicate both a high degree of crystallinity and chain alignment for the dioxane-free phase, the average thermal expansion coefficient, (?3.0 ± 1.0) × 10^?6 °C^?1 between ?50 and 150°C, is about an order of magnitude less than for the as-polymerized single crystals.     

Electrically conducting polyaromatic sulfides

Poly(p-phenylene sulfide), PPS, a melt and solution processible polymer, can be made highly conducting by doping with strong electron acceptors such as ASF5. Virgin PPS is an insulator with a relatively high ionization potential compared to polyacetylene. This, coupled with its high melting and solubilization points, restricts possible dopants to those which are particularly aggressive and capable of reacting with PPS in the solid state. These aggressive dopants induce a variety of chemical changes in the polymer backbone upon doping. While fluorination and crosslinking occur to some extent, infrared spectra and independent chemical synthesis suggest that the predominant chemical change is via intrachain bridging (cyclization) of adjacent phenyl rings. In an attempt to find processible systems with lower ionization potentials and which are less prone to chemical modification, a variety of polyaromatic sulfides were prepared. The influence of polymer structure, morphology, and dopant-induced chemical modifications upon conductivity is discussed.     

A host-guest optical sensor for aliphatic amines based on lipophilic cyclodextrin

A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10^–6 to 8.0 × 10^–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery.     

Raman spectral changes during the solid-state polymerization of diacetylenes

Raman spectral changes resulting from the solid-state 1,4-addition polymerization of conjugated diacetylenes are reported. The monomers show an intense C?C stretching frequency near 2260 cm^?1, where as the polymers showed two strong bands, a C?C vibration near 2100 cm^?1 and a C?C vibration near 1500 cm^?1. The presence of both double and triple bonds in the polymers suggests the backbone structure (?C? C?C? C?)_n. The alternate mesomeric structure (? C?C?C?C? )_n can be eliminated as a possibility by the presence of the strong C?C vibration in the polymer. Sequential Raman spectra obtained during radiation-induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate-state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.