Relative Degree Of Polymerization Research Articles

Oxygen isotope partitioning between immiscible silicate melts with H2O, P and S

Differences between the δ18O values of immiscible Si- and Fe-rich melts in the systems Fe2SiO4–Fe3O4–KAlSi2O6–SiO2, Fe3O4–KAlSi2O6–SiO2, and Fe3O4–Fe2O3–KAlSi2O6–SiO2, with H2O, H2O+P or H2O+S have been determined in isothermal, isobaric experiments at 1100 and 1200°C and 200MPa. The Δ18O values for conjugate Fe2SiO4–Fe3O4–KAlSi2O6–SiO2+H2O and, Fe3O4–KAlSi2O6–SiO2·KAlSi2O6–SiO2+H2O melts are only 0.4–0.6‰ and do not differ significantly from those for anhydrous melts of similar composition. The Δ18O values for melts with added H2O+P or S are more variable, ranging from 0.0 to 0.8‰. Partitioning of 18O between the immiscible melts is 0.6–1‰ less than the partitioning reported for melt–mineral and mineral–mineral pairs. The partitioning of 18O in the network modifier-bearing immiscible melts is not controlled by the relative degree of polymerization in the melts or fO2. The upper limit of the range of Δ18O values (<1‰), and the variation in the δ18O values of conjugate melts that occurs with the inclusion of network modifying constituents, suggest that in some cases, oxygen isotope ratios might be useful to distinguish lithologies evolved from coexisting immiscible silicate melts, from lithologies that have evolved by crystal fractionation only.

Relation of Highly Polymerized Procyanidin to the Potential Browning Susceptibility in Pear Fruits

The European pears, 'Bartlett' (Ba), 'Aurora' (Au), 'Conference' (Co), and 'La France' (LF) were less susceptible to browning than were 'General Leclerc' (GL), 'Grand Champion' (GC), 'Beurre Hardy' (BH), and 'Josephine de Malines' (JM). The acetone extracts (AE) of Ba, Au, Co and LF had less phenolics than did GL, BH, GC and JM. The ratio of the phenolics in AE to total phenolics was also bigger in the latter 4 cultivars. The amount of monomeric and/or oligomeric flavan-3-ols (procyanidin) in methanol extracts (ME) was larger than that in the AE of Ba, Au, Co and LF, whereas the amount of procyanidin in the AE was similar to or higher than that in the ME of GL, BH, GC and JM. The relative degree of polymerization (RDP) of procyanidin assessed by the butanol-HCI method and the vanillin-sulfuric acid method showed that RDP of procyanidin in Ba and Au was low, RDP in LF, GL, BH, GC and JM was high in both ME and AE. Polyphenoloxidase (PPO) activity of 8 cultivars varied, the highest activity occurred in LF and the lowest in GC. Highly polymerized procyanidin in AE did not react with PPO directly in a test solution, whereas browning of the mixture occurred in the presence of PPO and chlorogenic acid. The resulting brown color was darker than it was in the mixture of chlorogenic acid and PPO only, indicating that highly polymerized procyanidin plays an important role in tissue browning and its level is strongly related to the potential browning in pear fruits.

Relationship between protein-precipitating capacity of fodder tree leaves and their tannin content

Protein-precipitating capacity (PPC), milligrams of protein precipitated in a solution by 100 mg tanniferous forages, of fodder tree leaves of Bauhinia racemosa, Dichrostachys nutans, Ficus bengalensis, Ficus religiosa, Gymnosporia spinosa, Prosopis cineraria and Zizyphus nummularia was determined using a 0.3% solution of bovine serum albumin (BSA) or groundnut cake albumin (GNCA) in 0.2 M acetate buffer, pH 5.0, containing 0.17 M NaCl. The PPC of tree leaves was 2.10–13.88 in the case of BSA and 1.82–8.39 in the case of GNCA. The PPC of tree leaves using BSA was significantly positively correlated with PPC using GNCA and with the contents of total polyphenols, tannins, condensed tannins and with their relative degree of polymerization.

Composition, tannin levels and in-sacco dry matter digestibility of fresh and fallen oak (Quercus incana) leaves

The crude protein, neutral detergent fibre, acid detergent fibre, hemicellulose, cellulose and lignin in fresh and fallen oak leaves were determined. The per cent in-sacco dry matter digestibility of fresh and fallen leaves was 30·47 and 13·47 respectively. The contents of total phenols, ellagitannins, gallotannins, condensed tannins and proanthocyanidins in fallen leaves were less than those of fresh leaves. The protein precipitation capacity of tannins in fallen leaves was also about 70% lower. The relative degree of polymerization was higher for fallen leaves. Fallen leaves might replace straws in ruminant feeds.

Kinetics of thermal depolymerization of trimethylsiloxy end-blocked polydimethylsiloxane and polydimethylsiloxane- N-phenylsilazane copolymer

The thermal degradation of Me 3SiO end-blocked polydimethylsiloxane (eb-PDMS) and polydimethylsiloxane- N-phenylsilazane (eb-PDMS-NPhSz) copolymer was studied. For both polymers, relative degree of polymerization( DP / DP 0 ) as a function of conversion ( C = 1 − W/ W 0) data were obtained. For eb-PDMS with three different molecular weights, the results were consistent with a mechanism involving a rate-determining random siloxane bond cleavage initiation step followed by a rapid and complete depropagation of the active fragments evolving volatile cyclic oligomers. Rate constants for initiation were obtained at four temperatures from plots of DP −1 vs. time for eb-PDMS of M n = 6.83 × 10 4 . An Arrhenius activation energy of ∼ and is consistent with a SiOSi scission transition state. The degradation of eb-PDMS-NPhSz appears to follow the same depolymerization process evolving cyclic oligomers. Although DP / DP 0 vs. C data suggest a random cleavage-complete depolymerization mechanism, an Arrhenius plot suggests a more complex degradation mechanism. The role of impurities as degradation catalysts is discussed.

Mechanism of thermal depolymerization of trimethylsiloxy‐terminated polydimethylsiloxane

Abstract“Catalyst‐free” trimethylsilyl end‐blocked polydimethylsiloxanes of Mn = 68,300 and 111,000 were isothermally depolymerized above 400°C. The volatilized products were a mixture of cyclic oligomers and trace quantities of Me3Si(OSiMe2)nOSiMe3 (n = 0,1). The relative degree of polymerization was followed as a function of fractional conversion. The data were consistent with the oretical curves for a mechanism involving initiation by random siloxane bond cleavage followed by a rapid and complete unzipping of the kinetically active fragments. It is suggested that catalysis may be responsible for the initiation process, thus accounting for the low activation energy (43 Kcal/mol) relative to the siloxane bond energy (108 kcal/mol).

Polydisperse polymers with random trifunctional branching. II. Weight‐averaging of chosen molecular size‐dependent functions and a restatement of the approximate distribution function

AbstractThe product gzbZa is weight‐averaged over the distribution of molecular species in a polydisperse polymer possessing randomly distributed trifunctional branch points. This permits comparison between branched and nonbranched polydisperse polymers of certain physical properties that depend upon the relative degree of polymerization, z, and upon the ratio of branched to nonbranched molecule mean‐square radii, g = Rbr2/Rl2. Values of a, b, and γ (a branching index) are chosen for specific physical reasons and the computed ratios, \documentclass{article}\pagestyle{empty}\begin{document}$ (1 - \gamma )^a \int_0^\infty {g_z ^b z^a } W_z dz/\int_0^\infty {z^{a + 1} e^{ - z} dz} $\end{document} are tabulated. The distribution function for the polydisperse polymer possessing randomly distributed trifunctional branch points is restated in terms of a modified Bessel function of the first kind. This form is of use since properties of the Bessel function are known and the tabulated values of this function are generally available.