The solid-state polymerization,physical properties,and crystal structures of diacetylene mixed crystals

Suitable substituted diacetylenes, 2,4-hexadiynylene di-p-toluenesulfonate (1a) and 2,4-hexadiynylene di-p-fluorobenzenesulfonate (1b) , were cocrystallized to form substitutional solid solutions. By solid state polymerization of mixed crystals of 1a and 1b single crystals of the corresponding copolymers were obtained. The polymerization rate can be varied over a wide range by admixture of the comonomer 1b in the lattice of 1a . The crystal structures of monomer 1b and of the corresponding polymer, 2b , were determined. It was found that the packing of the reactive triple bond systems is identical in both monomers. Comonomer 1b acts as a defect site with a high probability of chain termination.     

Photooxidation of poly(diacetylene) single crystals

Single crystals of poly(diacetylene) 1a with p-tosyloxymethyl side groups undergo photooxidation when irradiated with visible light of wavelength 520 nm or less. The presence of molecular oxygen adsorbed on the surface of the crystals and its subsequent photochemical reaction with the polymer were monitored using resonance Raman spectroscopy and the formation of holographic gratings. Reaction products which were identified include hydroperoxy groups, p-toluenesulfonic acid and poly(diacetylene) oligomers. The photooxidation reaction appears to proceed by the “ene” mechanism; the polymer reacts with singlet oxygen produced by energy transfer with the photoexcited poly(diacetylene) backbone.     

Solid state polymerization of a nitrophenoxy disubstituted diacetylene

The solid state polymerization of the disubstituted diacetylene 1,6-bis(2,4-dinitrophenoxy)-2,4-hexadiyne by thermal annealing at 130°C to yield high quality polymer single crystals is reported. This compound is unique in that it polymerizes by thermal annealing but not under ordinary x-ray conditions, thus allowing determination of the crystal structures of both the monomer and polymer by x-ray diffraction. The conditions for solid state polymerization and the structural changes during polymerization were investigated. In addition, the kinetics of polymerization were studied by differential scanning calorimetry. An induction period with activation energy E_A(slow) = 139,7 ± 3 kJ/mol (33,4 ± 0,7 kcal/mol) is followed by a rapid polymerization regime with activation energy E_A(fast) = 132,2 ± 6 kJ/mol (31,6 ± 1,5 kcal/mol) during which first order kinetics are obeyed. The total heat of polymerization is ? ΔH_p = 134,7 ± 6 kJ/mol (32,2 ± 1,5 kcal/mol). After polymerization, a disordering phase change takes place with continued isothermal annealing which becomes clearly evident at isothermal annealing temperatures higher than 130°C.     

Synthesis of polydiphenylgermylene single crystals from diphenyldichlorogermane

Polymer single crystals with a germanium backbone have been synthesized. The synthesis involves a thermally induced generation of divalent radicals, transport of these radicals and subsequent addition polymerization on a cold surface. The polymerization was carried out under vaccum. Crystallization during polymerization was found to occur resulting in extended chain macromolecular crystals. These crystals were prismatic with a number-average molecular weight of 11300. The melting range of the \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm GePh}_2 \rlap{--})_{\rm n} $\end{document} crystals is 285 to 295°C. The glass transition temperature of the same polymer in its amorphous state was found to be 96°C (20°C/min heating rate using differential thermal analysis). The crystal structure of the intermediate octaphenylcyclotetragermane is compared to that of octaphenylcyclotetrasilane and polydiphenylgermylene.     

Kinetics of virus production from single cells

The production of virus by infected cells is an essential process for the spread and persistence of viral diseases, the effectiveness of live-viral vaccines, and the manufacture of viruses for diverse applications. Yet despite its importance, methods to precisely measure virus production from cells are lacking. Most methods test infected-cell populations, masking how individual cells behave. Here we measured the kinetics of virus production from single cells. We combined simple steps of liquid-phase infection, serial dilution, centrifugation, and harvesting, without specialized equipment, to track the production of virus particles from BHK cells infected with vesicular stomatitis virus. Remarkably, cell-to-cell differences in latent times to virus release were within a factor of two, while production rates and virus yields spanned over 300-fold, highlighting an extreme diversity in virus production for cells from the same population. These findings have fundamental and technological implications for health and disease.     

Syntheses of diacetylene monomers from N-(nitrophenyl)amine substituted diacetylene alcohols

Several new classes of asymmetric diacetylene monomers of the type O₂N? Ar? NH? CH₂? C?C? C?C? CH₂? R have been synthesized from nitroaniline diacetylene alcohols. The solid state polymerization behavior of several members of these classes has been examined.     

Syntheses and solid-state polymerization of diacetylene derivatives bearing dodecylthio groups directly bound to sp-carbons

Diacetylenes were synthesized bearing dodecylthio groups directly bound to the sp-carbons. These compounds afford polydiacetylenes having sulfur atoms directly attached to the π-conjugated main chains. The exciton absorption peaks appear at ca. 750 nm, which is a longer wave length than of conventional polydiacetylenes.     

Investigation of the topochemical solid-state polymerization of a diacetylene by X-ray methods and brillouin-spectroscopy

The topochemical polymerization of the substituted diacetylene, 2,4-hexadiynylene bis(p-toluenesulfonate) ( 1 ), has been followed by X-ray crystallography and by determination of the elastic constants of polymerizing crystals. For the first time the crystal structure of a polymerizable diacetylene monomer has been solved and the coordinates of all atoms prior and after the reaction have been determined. The length of the growing polymer chains and their distribution in the monomer matrix can be determined by the evaluation of the Brillouin spectra in terms of a model which considers the polymerizing crystal as a composite material of high-modulus rod-like macromolecules dispersed in the low-modulus matrix of the residual monomer.     

Mechanical properties of hydroxyapatite single crystals from nanoindentation data

In this paper we compute elastoplastic properties of hydroxyapatite single crystals from nanoindentation data using a two-step algorithm. In the first step the yield stress is obtained using hardness and Young's modulus data, followed by the computation of the flow parameters. The computational approach is first validated with data from the existing literature. It is observed that hydroxyapatite single crystals exhibit anisotropic mechanical response with a lower yield stress along the [1010] crystallographic direction compared to the [0001] direction. Both work hardening rate and work hardening exponent are found to be higher for indentation along the [0001] crystallographic direction. The stress-strain curves extracted here could be used for developing constitutive models for hydroxyapatite single crystals.     

Kinetics of oxidative polymerization of 1,8-nonadiyne

A study was made of the influence of the concentrations of catalyst, monomer, water, ligand, and oxygen on the rate of oxidative polymerization of 1,8-nonadiyne ( 1 ) at 26°C in the presence of homogeneous catalysts derived from cuprous chloride (copper(I) chloride) and tertiary amines. In the initial stages the reaction is nearly first order in [Cu₂Cl₂] up to the solubility limit of the active catalyst, and second to first order in [ 1 ] for low to medium monomer concentrations. The reaction rate decreases with increasing water content and is enhanced by increasing ligand concentration and increasing basicity of the ligand: triethylamine (TEA) > N,N,N',N'-tetramethylethylenediamine (TMED) > pyridine. On the basis of these kinetic results and a study of the catalyst structure a reaction scheme is proposed. In this scheme the formation of water occurs in reversible reaction steps from acetylenic endgroups and a dimeric copper(II) complex [TMED. Cu(OH)] · 2Cl^?, followed by intramolecular oxidative coupling of two complexed acetylide ions.     

Kinetics of radical polymerization of tolyl methacrylates

The kinetics of radical polymerization of tolyl methacrylates, initiated with 2,2′-azodiisobutyronitrile and dibenzoyl peroxide were studied using dilatometric and gravimetric techniques. The initial rates of polymerization depend on the position of the methyl subsitution in the aromatic ring. With both initiators the initial rates of polymerization in the range within 50 and 70°C increase in the order: ortho < meta < para substitution. The overall rate constants and activation energies were determined. The different rates observed are discussed in terms of steric effects, monomer constitution, and other factors which might affect the reactivity of the radical propagation.     

Chlorination of polyethylene single crystals

Chlorination under mild conditions of suspensions of polyethylene single crystals demonstrated that a selective attack on the fold surface takes place. Two polyethylene molecular weight fractions (M_n = 47000 and M_n = 150 000) were used and single crystals were grown isothermally from p-xylene at 88°C. The chlorine content was changed from 4 wt.-% to 30 wt.-% and to this level no evidence for crystal attack and loss of crystallinity was found. The melting temperatures of chlorinated single crystals decrease with increasing chlorination up to about 15 wt.-% chlorine content and then stay constant for higher chlorine contents. Moreover, the heat of melting of the chlorinated single crystals is constant and is independent of the chlorine content up to 25 wt.-%. These results are compared with those of samples of chlorinated polyethylene recrystallized from solution and from the melt.     

The electro-initiated cationic polymerization of indene, 2. Kinetics of polymerization

The electrolytically initiated anodic polymerization of indene in the solutions of tetraethylammonium hexachloroantimonate and tetrabutylammonium perchlorate in nitrobenzene under constant electric current and constant potential electrolysis conditions was studied. The polymerization was followed either under continuous electrolysis or by addition of the monomer to the pre-electrolysed solution of the salt. The monomer consumption follows the first-order rate-law, log[M]₀/[M]_t=kt, and the rate constant of the polymerization increases with increasing current level. The polymer formation was greatly affected by the change of the dielectric constant of the medium, the anode material, and the nature of the supporting electrolyte. The mode of initiation process depends upon the type of the salt. Mechanisms for the initiation reaction were elucidated.     

Evaluation of strengthening mechanisms in calcite single crystals from mollusk shells

Biogenic single-crystal calcite is often reported to be harder and tougher than geologic calcite in the form of Iceland spar. However, the mechanistic origins of the superior mechanical properties of the biogenic materials are still debated. We investigate the hardness and modulus of biogenic calcite from the prismatic layer of the mollusk Atrina rigida compared with a pure geologic calcite, Iceland spar. On the {0 0 1} face, biogenic calcite is found to be 50–70% harder than geologic calcite. This range is due to the fact that changes in azimuthal angle of the indenter tip lead to a hardness variation of ～20% in A. rigida but only ～7% in Iceland spar. The higher hardness and increased anisotropy of biogenic calcite could be accounted for by hardening mechanisms based on hindered dislocation motion rather than crack deflection.     

Determination of uncertainty in parameters extracted from single spectroscopic measurements

The ability to quantify uncertainty in information extracted from spectroscopic measurements is important in numerous fields. The traditional approach of repetitive measurements may be impractical or impossible in some measurements scenarios, while chi-squared analysis does not provide insight into the sources of uncertainty. As such, a need exists for analytical expressions for estimating uncertainty and, by extension, minimum detectable concentrations or diagnostic parameters, that can be applied to a single noisy measurement. This work builds on established concepts from estimation theory, such as the Cramer-Rao lower bound on estimator covariance, to present an analytical formula for estimating uncertainty expressed as a simple function of measurement noise, signal strength, and spectral overlap. This formalism can be used to evaluate and improve instrument performance, particularly important for rapid-acquisition biomedical spectroscopy systems. We demonstrate the experimental utility of this expression in assessing concentration uncertainties from spectral measurements of aqueous solutions and diagnostic parameter uncertainties extracted from spectral measurements of human artery tissue. The measured uncertainty, calculated from many independent measurements, is found to be in good agreement with the analytical formula applied to a single spectrum. These results are intended to encourage the widespread use of uncertainty analysis in the biomedical optics community.