Exchange equilibria on anion resins, 2. Effect of chemical structure of functional groups in macroporous polystyrene resins

Anion exchange equilibria were studied by the batch technique on macroporous polystyrene resins with the following functional groups: \documentclass{article}\pagestyle{empty}\begin{document}$ - \mathop {\rm N}\limits^ + {\rm H}_{\rm 2} {\rm CH}_{\rm 3} ({\rm M),} - \mathop {\rm N}\limits^ + {\rm H(CH}_{\rm 3} )_2 ({\rm DE),} - \mathop {\rm N}\limits^ + {\rm (CH}_{\rm 3} )_3 ({\rm TM),} - \mathop {\rm N}\limits^ + {\rm H}_{\rm 2} {\rm CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH (E),} - \mathop {\rm N}\limits^ + {\rm H}_{\rm 2} {\rm (CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH)}_{\rm 2} ({\rm DE),} - \mathop {\rm N}\limits^ + {\rm (CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH)}_{\rm 3} ({\rm TE),} - \mathop {\rm N}\limits^ + {\rm CH}_{\rm 3} {\rm (CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH)}_{\rm 2} ({\rm MDE), and} - \mathop {\rm N}\limits^ + {\rm (CH}_{\rm 3} {\rm )}_{\rm 2} {\rm CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH (DME)}$\end{document}. The selectivity order for these groups in slightly acidic, dilute solutions for the following anion systems: Br^?/Cl^?, I^?/Cl^?, and ClO₄^?/Cl^? was found to be TM > DME > MDE > TE > DM > M > DE > E, but it was entirely reversed in the case of F^?/Cl^? system. These results are discussed in view of some known theories of ion exchange selectivity. It seems that the experimental data can be best explained in terms of the Chu-Diamond-Whitney theory which takes into consideration mainly changes of the water structure caused by counter-ions, co-ions, and functional groups of the ion exchanger.     

Formation of the intermediate cyclic six-membered oxonium ion in the cationic polymerization of β-propiolactone initiated with CH3CO⊕SbF

Analysis of the ¹H NMR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document} /β-propiolactone and of the model systems \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/(CH₃)₂O and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/CH₃COOCH₃ in liquid SO₂ in the temperature region ?70 to ?20°C revealed that the reaction of the acetylium cation with β-propiolactone leads to the cyclic six-membered oxonium ion 4 , participating as an intermediate in the initial stage of polymerization.     

Lösungsmittel-effekt bei der bildung von \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} doppelbindungssequenzen in polystyrol bei bestrahlung mit langwelligem uv-licht

Upon irradiation with long-wave range UV light of degassed chlorine-containing solutions of polystyrene conjugated double bonds \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} are formed along the polystyrene chain. The kinetics of their formation and their sequence lengths depend on the solvent. Aside from isolated CC double bonds sequences of \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} with n = 2 to n = 5 are formed.     

Investigation of the polymerization of octanelactam initiated with hydrochloric acid

The polymerization of octanelactame ( 1 ) initiated by HCl takes place according to the characteristic kinetic curves. Both characteristics, i.e., the fast initial and the extremely slow further stages, and the kinetic anomaly (in certain cases under otherwise identical conditions less polymer is formed at higher than at lower temperatures) can be interpreted easily on the basis of a mechanism already suggested by the authors. The two relevant chain growth reactions, i.e., lactam addition on \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\mathop {\rm N}\limits^ \oplus {\rm H}_{\rm 3} $\end{document}-groups and the reaction between \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\mathop {\rm N}\limits^ \oplus {\rm H}_{\rm 3} $\end{document} and N-acylamide groups, proceed through a tetrahedral intermediate in two directions, one of them being the known chain growth, the other one an amidine (or acylamidine) formation, in which the active groups, ensuring chain growth, desactivate. Both kinetic characteristics could be interpreted on the basis of the suggested mechanism, by measuring the amounts of amino and amidine groups with the progress of polymerization.     

Formation of Macrozwitterions in the polymerization of β-propiolactone initiated by betaine. 4th Communication on Macrozwitterions

The anionic polymerization of β-propiolactone at 25°C in ethanol initiated by the betain \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_3 )_3 \mathop {\rm N}\limits^ \oplus - {\rm CH}_{\rm 2} {\rm COO}^ \ominus $\end{document} was investigated. Macrozwitterions of the structure were produced, n being intentionally as low as ca. 11. The structure of the product was proven by the nitrogen content of the reprecipiated polymer, by IR and NMR spectroscopy and by titration of the carboxylate endgroups. Some carboxylic acid endgroups were formed by chain transfer with the solvent ethanol. The positive charge at the polymer chain was proven by electrophoresis of polymer after esterification of the carboxylate chain end. Furthermore the dielectric constant of dilute solutions of the polymer in CHCl₃ was determined and is discussed. The kinetics of the polymerization process were investigated by IR-spectroscopy. The initiation reaction between monomer and betain is about 5 times slower than the consecutive propagation by addition of monomer to the anionic chain end.     

Differences in exercise limb blood flow and muscle deoxygenation with age: contributions to O2 uptake kinetics

The adjustments of pulmonary oxygen uptake $ \left( {\mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} } \right), $ limb blood flow (LBF) and muscle deoxygenation (ΔHHb) were examined during transitions to moderate-intensity, knee-extension exercise in seven older (OA; 71 ± 7 year) and seven young (YA; 26 ± 3 year) men. YA and OA performed repeated step transitions from an active baseline (3 W; 100 g) to a similar relative intensity of ~80% estimated lactate threshold (θ_L), and YA also performed the same absolute work rate as the OA (24 W, 800 g). Breath-by-breath $ \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} , $ femoral artery LBF (Doppler ultrasound) and muscle HHb (near-infrared spectroscopy) were measured. Phase 2 $ \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} , $ LBF, and ΔHHb data were fit with a mono-exponential model. $ \tau \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} $ was greater in OA (58 ± 21 s) than YA_80% (31 ± 9 s) and YA_24W (29 ± 11 s). The increase in LBF per increase in $ \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} $ was not different between groups (5.3–5.8 L min^?1/L min^?1); however, the τLBF was greater in OA (44 ± 19 s) than YA_24W (18 ± 7 s). The overall adjustment in ΔHHb (τ′ΔHHb) was not different between OA and YA, but was faster than $ \tau \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} $ in OA. This faster τ′ΔHHb than $ \tau \mathop {{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} $ resulted in an “overshoot” of the normalized $ \Updelta {\text{HHb}}/\Updelta\mathop{{V}}\limits^{ \cdot } {\text{O}}_{{2\,{\text{p}}}} $ response relative to the steady state level that was significantly greater in OA compared with YA suggesting that the adjustment of microvascular blood flow is slowed in OA thereby requiring a greater reliance on O₂ extraction during the transition to exercise.     

Determination of the number-, weight-, and z-average dimensions of macromolecules by viscosity and GPC measurements

The molecular weight averages are calculated which have to be inserted into the Fox-Flory relationship \documentclass{article}\pagestyle{empty}\begin{document}$ {{\left[ \eta \right] = \Phi (\overline {r_{{\rm av}}^{\rm 2} } )^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern‐\nulldelimiterspace} 2}} } \mathord{\left/ {\vphantom {{\left[ \eta \right] = \Phi (\overline {r_{{\rm av}}^{\rm 2} } )^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern‐\nulldelimiterspace} 2}} } {M_{{\rm av}} }}} \right. \kern‐\nulldelimiterspace} {M_{{\rm av}} }} $\end{document} if the number-, weight-, or z-average dimensions are to be determined for polymolecular polymer samples. The resulting complex molecular weight averages \documentclass{article}\pagestyle{empty}\begin{document}$ M_{r_{\rm n} } \eta _{\rm w},{\rm }M_{r_{\rm w} } \eta _{\rm w} $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ M_{r_{\rm z} } \eta _{\rm w} $\en{document} are compared with simple molecular weight averages and for Schulz-Zimm and logarithmic normal distributions of the molecular weight their numerical relations to the viscosity-(M_η), number- (M_n), and weight-average molecular weight (M_w) calculated. A simple straight-forward method is outlined for the determination of the number-, weight-, and z-average dimensions of polymolecular polymers from viscosity and gel permeation chromatography measurements.     

Evaluation of the ratio of mean square inertia radii of branched and linear macromolecules from intrinsic viscosity measurements

A method for the evaluation of the ratio of the mean square inertia radii \documentclass{article}\pagestyle{empty}\begin{document}$ (\overline {R^2 } )^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern‐\nulldelimiterspace} 2}} $\end{document} of branched (b) and linear (1) molecules \documentclass{article}\pagestyle{empty}\begin{document}$ g[\eta ] = {{(\overline {R_{\rm b}^2 } )_{[\eta ]} } \mathord{\left/ {\vphantom {{(\overline {R_{\rm b}^2 } )_{[\eta ]} } {(\overline {R_{\rm l}^{\rm 2} } }}} \right. \kern‐\nulldelimiterspace} {(\overline {R_{\rm l}^{\rm 2} } }})_{[\eta ]} $\end{document} from intrinsic viscosity measurements is proposed. The evaluation is based on the solution of the equation: where erf \documentclass{article}\pagestyle{empty}\begin{document}$ x = \frac{2}{{\sqrt \pi }}\int\limits_0^{\rm x} {{\rm e}^{ ‐ t^2 } } {\rm d}t $\end{document}; a is the exponent in the Mark-Kuhn-Houwink relation [η₁] = KM^a, ε = (2a?1)/3 and ?(a) is the shielding function, tabulated by Debye and Bueche. The method is used for the evaluation of g[η] in Θ- and in good solvents from experimental data published in the literature. The results show that it is possible to find the dimensions of branched molecules from intrinsic viscosity measurements in good solvents using the above formula. These results are obtained by the analysis of changes of the macromolecular dimensions in different solvents and in part by the results of second virial coefficient measurements of different polymers.     

Coenzyme models, 21. Oxidative trapping of carbanion intermediates by a flavin immobilized in cationic polymers

Aromatic aldehydes 5 and α-keto acids 8 in the presence of cyanide ion, which usually give the benzoin condensation products, were converted oxidatively to the corresponding benzoic acids 10 by the catalytic action of the title flavin. The change in the reaction route cannot be achieved completely by flavin 1 . Product analyses and kinetic measurements established that the carbanion intermediate, \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}\hbox{---} \mathop {\rm C}\limits^ \ominus \left( {{\rm OH}} \right)\left( {{\rm CH}} \right)$\end{document}, which is formed through rate-limiting deprotonation or decarboxylation of the cyanide-adducts, is oxidized immediately by the title flavin. The influence of polymer structure on the efficiency of flavin trapping is discussed.     

The cationic polymerization of ketene acetals and the preparation and characterization of poly(1,3-diketones)

Various ketene acetals ( 1a – d ) were prepared and their cationic polymerization under homogeneous and heterogeneous conditions, in bulk and in solution between ca. 100 and ?100°C were investigated. Most of the reaction products formed in solution were viscous pale yellow fluids or sticky red solids, whereas those formed in bulk with solid, sparsely soluble initiators were white waxes or powders. For all systems for which solubility of product permitted DP determinations, the highest DPs (ca. 20) were found from bulk polymerization with solid CdCl₂. With a wide range of soluble initiators in different solvents over a wide range of concentrations, DPs greater than about 8 were exceptional. It is suggested that there are at least five chain-breaking reactions involving the growing dialkoxycarbenium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\hbox{---} {\rm CH}_2 \hbox{---} \mathop {\rm C}\limits^ \oplus \left( {{\rm OR}} \right)_2 $\end{document} and evidence is presented which accounts for the high rate of chain-breaking compared with that for other olefinic monomers. Acid hydrolysis of the polymers yielded the corresponding poly(1-oxoethylenes) (poly-(1,3-diketone)) ( 4a, b ), and various derivatives of both the keto and enol forms of these were prepared.     

Simultaneous anodic and cathodic polymerizations of acrylamide

The electrolysis of acrylamide in sodium nitrate/N,N-dimethylformamide solutions leads to polymer formations simultaneously in the anode and cathode compartments. The influences of monomer concentrations, current levels, nature of some electrode metals and supporting electrolytes on polymerization were examined. Anodic polymers of high molecular weights were obtained (ca. 10⁵). The current-voltage curves and other experimental findings strongly suggest that the direct reduction of acrylamide at the cathode leads to the cathodic polymerization which is like the polymerization by anionic initiators in which the monomer gives a polymer of amide structure via a hydrogen transfer process. On the other hand, the anodic polymerization is possibly initiated by the species produced by the anodic reaction of the supporting electrolyte and is analogous to the free-radical polymerization of acrylamide. Infrared spectra of the polymers show that the cathodic polymer is a polyamide \documentclass{article}\pagestyle{empty}\begin{document}$ \left( { \ldots \hbox{---} {\rm CH}_{\rm 2} \hbox{---} {\rm CH}_{\rm 2} \hbox{---} {\rm CO}\hbox{---} {\rm NH}\hbox{---} \ldots } \right) $\end{document} whereas the anodic has a C? C chain structure \documentclass{article}\pagestyle{empty}\begin{document}$ \left( { \ldots \hbox{---} {\rm CH}_{\rm 2} \hbox{---} {\rm CH}\left( {{\rm CONH}_{\rm 2} } \right)\hbox{---} \ldots } \right) $\end{document}.     

Synthetische lineare polymere XV.: Die abhängigkeit einiger spezifischer eigenschaften polymerhomologer oligomerverbindungen von der molekülgröße

Between the molecular weight of the members of polymerhomologous series and such specific properties which are derived from additive quantities the following relation exists: \documentclass{article}\pagestyle{empty}\begin{document}$\Phi _{{\rm sp}} = \frac{a} {m} + b$\end{document} where Φ_sp is any specific property, i.e. \documentclass{article}\pagestyle{empty}\begin{document}${\rm z}.{\rm B}.\frac{{\gamma ^{1/4} }}{d}$\end{document} = specific parachor, \documentclass{article}\pagestyle{empty}\begin{document}$- \frac{{\gamma ^{1/4} }} {d}\ {\rm log (}n\ { - 1)}$\end{document} = specific refrachor, \documentclass{article}\pagestyle{empty}\begin{document}$\frac{x} {d}$\end{document} = specific magnetic susceptibility, \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{2,9\ {\rm log}\ {\rm log }\ \eta { }}} {{\rm d}}$\end{document} = specific viscosity number, \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{v^{1/3} }} {d}$\end{document} = specific sound velocity, n = refractive index, \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{n^2 + 1}} {{n^2 + 2}} \cdot \frac{1} {d}$\end{document} = specific refraction, and M the molecular weight is a and b are constants the values of which can be used for the evaluation of the increments of the atoms of the base mole. Some of these specific properties are suitable for determination of molecular weights in the range of 10³?10⁵, i.e. in polymer plasticizer and synthetic fibers as polymides and polyesters.     

Odd-even effects in polymeric liquid crystals

Semiflexible mesophasic polymers of the general formula \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm OOC(CH}_{\rm 2} {\rm )}_{n - 2} - {\rm COO} - {\rm R}^1 \rlap{--} ]_{\rm X} ,n = 9,11,13,\rlap{--} [{\rm OOC(CH}_{\rm 2} )_{n - 2} - {\rm COO} - {\rm R}^2 \rlap{--} ]_{\rm X} ,n = 9,11,13,14, $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm OOCO} - {\rm (CH}_{\rm 2} {\rm )}_{n - 4} - {\rm OCOO} - {\rm R}^2 \rlap{--} ]_{\rm X} ,n = 9,11,13, $\end{document} where \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} = - {\rm C}_{\rm 6} {\rm H}_{\rm 5} - {\rm C}({\rm CH}_3 ) = {\rm CH} - {\rm C}_6 {\rm H}_5 - $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 2} = {\rm C}_{\rm 6} {\rm H}_{\rm 5} - {\rm C}({\rm CH}_3 ) = {\rm N} - {\rm N} = ({\rm CH}_3 ){\rm C} - {\rm C}_6 {\rm H}_5 - $\end{document} are prepared and their solid and liquid crystalline behaviour examined and compared to that of the corresponding homologues with n even. Evidence is given of relevant odd-even effects in the thermodynamic parameters of the clearing transition. The conclusion is drawn in favour of an anisotropic structuration also of the flexible parts of the polymer chain in the liquid crystal phase.     

Linear oligopeptides, 77. The effect of the insertion of a proline residue on the solid-state conformation of host peptides

The conformational properties of two series of monodispersed, chemically and optically pure, PEG

1 The following abbreviations have been used in the text: PEG, poly(ethylene glycol); -NHPEG, “amino-PEG”; -NHPEG-M, “amino-PEG” monomethyl ether; NPS, o-nitrophenylsulfenyl; t-Boc, tert-butoxycarbonyl; Z, benzyloxycarbonyl; Met, methionine; Pro, proline; OBzl, benzyloxy; OMe, methoxy; OEt, ethoxy; NHEt, ethylamino; Glu, glutamic acid; IR, infrared; MeOH, methanol; TFE, 2,2,2-trifluoroethanol.

-bound linear host oligopeptides of the general formula \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} (L - Met\rlap{--} )}_n {\rm NHPEG} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} [L - Glu(OBl)\rlap{--} ]}_n {\rm NHPEG - M} $\end{document} containing a single guest L -Pro residue at different positions in the main chain have been investigated in the solid state using IR absorption. The corresponding N-deblocked peptides have also been examined. The incorporation of a L -Pro residue in a central position of a β-conformation appears to induce the onset of a structural irregularity characterized by IR absorption bands in the vicinity of 3 325 cm^?1 and 1 575 cm^?1.     

Radical efficiency and ionic reactions of some unsymmetrical azo compounds

Compounds with the structure R¹? N?N? R² decompose either thermally or photochemically to yield nitrogen and the radicals \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}^{1 \atop {^\bullet}}\hbox{and}\ {\rm R}^{2\atop ^\bullet}$\end{document}. These radicals, under appropriate conditions, can either act as polymerization initiators or can be trapped by radical scavengers such as iodine. In the presence of suitable reagents the title compounds behave like diazonium salts and thus, since they are relatively stable, may provide a safe and readily available diazonium ion source.     

Hydrolysis kinetics of terephthalic and 5-sulfonatoisophthalic acid esters

The saponification reaction of bis(2-hydroxyethyl) terephthalate ( 3 ) and sodium 3,5-bis(2-hydroxyethoxycarbonyl)benzenesulfonate ( 6 ) was followed under pH-stat conditions in the alkaline pH range (pH 8 to 10 at 50 to 80°C) to determine the consecutive reaction rate constants for the hydrolysis of the diesters and the intermediate monoesters. The observed overall reaction rate constants were split into the individual rate constants for the hydrolysis catalyzed by the solvent, the OH^? ions, the SO groups and the COO^? groups (k₀, k_OH?, k_SO, kCOO?, respectively). No intermolecular catalysis by either the sulfonato or the carboxylato groups and no “autocatalysis” by the solvent was found. The activation parameters for the hydrolysis of the corresponding esters of both acids are equal; for the diesters 3 and 6 : ΔH^? = 73,7 (72,0) kJ mol^?1 [17,6 (17,2) kcal mol^?1], ΔG^? = 103,8 (104,7) kJ mol^?1 [24,8 (25,0) kcal mol^?1], ΔS^? = ?89,6 (?97,6) J mol^?1 K^?1 [?21,4 (?23,3) cal mol^?1 K^?1]; for the monoesters [terephthalic acid mono(2-hydroxyethyl) ester and 5-sodiumsulfonatoisophthalic acid mono(2-hydroxyethyl) ester]: ΔH^? = 80,4 (78,7) kJ mol^?1 [19,2 (18,8) kcal mol^?1], ΔG^? = 109,3 (109,7) kJ mol^?1 [26,1 (26,2) kcal mol^?1], ΔS^? = ?86,3 (?93,0) J mol^?1 K^?1 [?20,6 (?22,2) cal mol^?1 K^?1]. It is concluded that disorders in the fine structure of polyester fibers modified with sulfonato group containing comonomers may primarily be responsable for their lower hydrolytic stability and not any catalytic effects of these groups.     

Phase transitions in polyphosphazene films: Poly[bis(trifluoroethoxy)phosphazene]

The morphology of cast and annealed films from poly[bis(trifluoroethoxy)phosphazene] \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \{ PBFP,\rlap{--} [(CF}_{\rm 3} {\rm CH}_{\rm 2} {\rm O)}_{\rm 2} {\rm P = N\rlap{--} ]}_{\rm n} {\rm \} } $\end{document} has been studied by electron, scanning electron and optical microscopy. Several polymorphic forms and one mesophase (hexatic) have been established. From THF solution, PBFP has a chain folded morphology (α-orthorhombic) which transforms into a chain extended 2D hexagonal mesophase at T(1). It remains in this state until final melting occurs at T_m = 245°C approximately. Upon cooling the melt, it quickly reverts to the hexagonal mesophase again, but then passes into a chain extended (3D) γ-orthorhombic modification. This material is much more stable thermodynamically than the α-form, which is friable or brittle. PBFP cannot be quenched to a glassy form from the molten state, but it can be disordered as assessed by its reduced T(1) enthalpy and less well defined morphology assessed by electron microscopy. Another crystal modification (β-monoclinic) has been found in solution cast low molecular weight PBFP films.     

Linear oligopeptides, 60. Synthesis by the liquid-phase method and characterization by amino acid analyses of two complete monodispersed homologous series derived from L-alanine (to the octapeptide) and L-valine (to the hexapeptide)

The synthesis by the liquid-phase method of the two complete, monodispersed homo-oligopeptide series having the general formula t-Boc\documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--}(\ {\rm L} - {\rm X}\rlap{---} )$\end{document}_nGly-OPEG (I:X=Ala, n=1-8; II: X = Val, n = 1–6) is described. The chemical purity of the various products was assessed by thin layer chromatography and amino acid analyses. The influence of chain length and steric effects on the formation of peptide bonds and their stability to acid hydrolysis is also illustrated.     

Kinetics and mechanism of the polymerization of cyclic acetals, 5. Spectroscopic studies of the polymer end-groups in poly(1,3-dioxolane)

Polymerization of 1,3-dioxolane ( 1 ) was initiated in CH₃NO₂ and CH₂Cl₂ solvents with benzoylium hexafluoroantimonate (C₆H₅CO⁺SbF), terminated with sodium ethanolate (C₂H₅ONa), and the endgroups were determined by using UV spectrophotometry and ¹H NMR methods. Polymers with high polymerization degrees DP _n were obtained (M?_n up to 3·10⁵); DP _n calculated for living polymerization conditions (DP _n=([ 1 ]₀?[ 1 ]_e)/[C₆H₅CO⁺SbF]₀; i.e. one molecule of initiator gives one macromolecule) agree well with DP _n measured by osmometry and DP _n found from ¹H NMR and UV methods assuming one respective end- group per macromolecule. ¹H NMR studies were performed on polymers from perdeuterated 1 (1,3-dioxolane-d₆). These polymers, after purification, were shown to bear benzoyloxy and ethoxy end-groups: \documentclass{article}\pagestyle{empty}\begin{document}${\rm C}_6 {\rm H}_5 \hbox{---} {\rm CO\rlap{--} (O} \hbox{---} {\rm CD}_2 {\rm CD}_2 {\rm OCD}_2 {\rm \rlap{--} )}_n {\rm OCH}_2 {\rm CH}_3$\end{document} Similar results were obtained for polymers initiated with triethyloxonium hexafluoroantimonate ((C₂H₅)₃O⁺SbF), and terminated with triphenylphosphine ((C₆H₅)₃P). These results indicate that initiation with stable oxocarbenium or oxonium ions leads to predominantly linear macromolecules, while initiation with perchloric acid (according to the data reported by Plesch) leads to polymers of low molecular weight and claimed to be mostly cyclic after killing with C₂H₅ONa.     

The effect of acute simulated moderate altitude on power,performance and pacing strategies in well-trained cyclists

Athletes regularly compete at 2,000–3,000 m altitude where peak oxygen consumption declines ∼10–20%. Factors other than including gross efficiency (GE), power output, and pacing are all important for cycling performance. It is therefore imperative to understand how all these factors and not just are affected by acute hypobaric hypoxia to select athletes who can compete successfully at these altitudes. Ten well-trained, non-altitude-acclimatised male cyclists and triathletes completed cycling tests at four simulated altitudes (200, 1,200, 2,200, 3,200 m) in a randomised, counter-balanced order. The exercise protocol comprised 5 × 5-min submaximal efforts (50, 100, 150, 200 and 250 W) to determine submaximal and GE and, after 10-min rest, a 5-min maximal time-trial (5-minTT) to determine and mean power output (5-minTT_power). declined 8.2 ± 2.0, 13.9 ± 2.9 and 22.5 ± 3.8% at 1,200, 2,200 and 3,200 m compared with 200 m, respectively, P < 0.05. The corresponding decreases in 5-minTT_power were 5.8 ± 2.9, 10.3 ± 4.3 and 19.8 ± 3.5% (P < 0.05). GE during the 5-minTT was not different across the four altitudes. There was no change in submaximal at any of the simulated altitudes, however, submaximal efficiency decreased at 3,200 m compared with both 200 and 1,200 m. Despite substantially reduced power at simulated altitude, there was no difference in pacing at the four altitudes for athletes whose first trial was at 200 or 1,200 m; whereas athletes whose first trial was at 2,200 or 3,200 m tended to mis-pace that effort. In conclusion, during the 5-minTT there was a dose–response effect of hypoxia on both and 5-minTT_power but no effect on GE.