Molecular weight of SPS

Table V shows yields and structural parameters of SP-300 fractions. These fractions were black solid materials like the feed coal, as compared to dark-brown viscous liquids of the HVL-P fractions. The overall average molecular weight of SP-300 was more than three times that of HVL-P. SP-300 fractions have much larger R, RN and //cl than HVL-P fractions. The //cl values disclosed that there were, on the average, 2.8 aromatic clusters per molecule in SP-300, as compared to 1.1 aromatic clusters per molecule in HVL-P. Thus SP-300 fractions are high molecular weight materials,in which the degree of depolymerization is relatively low. This in turn suggests that SP-300 has retained more of the original structures of the parent coal than has HVL-P.

As in the previous section, hydrogen increases the concentration of the active sites. Moreover, we think that the polymerization is preceded by the formation of a titanium hydride complex. If this is correct, hydrogen also increases the overall catalytic activity. The effects of hydrogen pressure on catalytic activity and molecular weight of SPS are summarized in Table 17.7. 

Duff et al. [27] reported a study made by means of DSC and WAXD on SPS/ PPE blends of various compositions, precipitated from ethylbenzene solutions, compression molded at 330 °C for 2 min and then slowly cooled to room temperature. In particular, the WAXD patterns show that in sPS-rich blends (>50 50 wt%) sPS is in a 0 or (3 form, while small amounts of a are present in the 50 50 wt% blend. The kinetics of crystallization and the mechanism of nucleation of sPS were investigated under isothermal and nonisothermal conditions as a function of blend composition and molecular weights of the components. The experimental curves show that the half-time to crystallization, t j2, increases with increasing content and molecular weight of PPE, but is not influenced by the molecular weight of sPS. The crystallization kinetics were... 

If the data for PS shown In Figure 1 are now used to calculate the proportionality constant K" and the measured radii of gyration and molecular weights of SPS at the two lowest concentrations are Inserted In Equation 3 then a reduction of up to 40% In iired predicted for the SPS solutions. Clearly, this naive calculation cannot be expected to predict solution viscosity precisely, but Its Implication Is nonetheless of great Importance the presence of aggregation at low SPS concentrations In THF Is not Inconsistent with decreased solution viscosity. 

Besides the cocatalyst, there are some other additives that are capable of influencing the performance of catalyst systems during styrene polymerization. The addition of a proper amount of triisobutylalu-minum (TIBA) to various titanium complex/MAO systems increases the catalyst activity, whereas the addition of TMA or triethylaluminum (TEA) inhibits polymerization. A relatively high molar ratio of TIBA/MAO will cause a reduction in activity and a sharp decrease in the molecular weights of sPS. When a haloalkylaluminum such as AlEt2Cl is used with the CpTiCb/MAO system, only atactic polystyrene is produced by a noncoordination polymerization process, that is, a cationic... 

In addition to chain transfer processes arising from the P-H elimination reaction, the growing polymer chain can also be terminated by transfer reactions to alkylaluminum, MAO and monomer, all of which lead to a decrease of the molecular weights of sPS. In the presence of TIB A, the chain transfer reaction to aluminum is the dominant chain transfer reaction instead of P-H elimination. No unsaturated end group could be detected in the obtained polystyrene after deactivation with acidic... 

Figure 19.9 Plot of the average molecular weight of SPS-t-B versus l/[9-BBN],...

Five-membered unsubstituted lactone, y-butyrolactone (y-BL), is not polymerized by conventional chemical catalysts. However, oligomer formation from y-BL was observed by using PPL or Pseudomonas sp. lipase as catalyst. Enzymatic polymerization of six-membered lactones, 8-VL and l,4-dioxan-2-one, was reported. 8-VL was polymerized by various lipases of different origins. The molecular weight of the enzymatically obtained polymer was relatively low (less than 2000). 

Miller and Macmillan [4] carried out purification of pectinesterase from Fusarium oxysporum f. sp. vasinfectum culture fluid (fivefold degree of purification). According to the obtained data the purified enzyme possessed very low polygalacturonatlyase one. Disk electrophoresis at pH 4.3 revealed two protein components. The authors did not study distribution of pectinesterase activity in these components. Molecular weight of fungal pectinesterase determined using gel — filtration on Sefadex G — 75 was found to be 35,000. 

W-SP concentrations are 2500 ppm the viscosity reflects the relative molecular weight of the W-SP. 

Miller and Macmillan49 purified pectinesterase produced by Fusarium oxysporum f. sp. vasinfectum by chromatography on DEAE-Sephadex A-25, Sephadex G-75, CM-Sephadex C-50, and CM-cellulose. The homogeneity of the pectinesterase obtained was confirmed by disc electrophoresis an apparent molecular weight of 35,000 was estimated by its behavior on a column of Sephadex G-75 (Superfine). 

This scaffold comprises two hydrogen bond acceptors and no hydrogen bond donor. The molecular weight of the scaffold is low (MW = 156). Two of the residues exit the scaffold in plane, whereas the aldehyde emerging substituent is attached to a sp carbon (Fig. 6). 

As shown in Table 3 an almost homogeneous preparation of protocatechuate 4,5-dioxygenase purified from a Pseudomonas sp. grown with protocatechuic acid as the major carbon source has a specific activity of 160 /imoles/min/mg of protein with a molecular weight of approximately 150,000. One g-atom of ferrous iron is present per mole of enzyme94. The enzyme has also been purified from extracts of p-hydroxybenzoate-induced Pseudomonas testeronil2S The enzyme has a molecular weight of about 140,000 with a specific activity of about 12. 

To obtain the amount by volume, the value found is divided by the density of acetone (o-8). The results may be referred to methyl ethyl ketone by replacing in the formula the molecular weight of acetone (58) by that of methyl ethyl ketone (72), and dividing by 0 84 (mean sp. gr. of acetone oil) to obtain the quantity by volume. 

Different a,co-dihydroxy-terminated oligo(propylene succinate)s (SP) were prepared by the thermal polycondensation of excess 1,3-propanediol and succinic acid, as illustrated in the first part of Scheme 9 [4]. The molar ratio of 1,3-propanediol to succinic acid was maintained in the range of 1.05-1.25. The molecular weight of the products depended on the excess 1,3-propanediol used, but it usually ranged between 900 and 2400. The molecular characterization and appearance of some typical samples are given in Table 2. 

Three forms of glucoamylase occur in the culture supernatants of Rhizopus sp. They have molecular weights of 74000, 58000 and 61000, and have been designated GA-I, GA-II and GA-III.150 GA-I bound and hydrolyzed native starch granules, but GA-II and GA-III neither bound nor hydrolyzed native starch granules.151 The three glucoamy-lases had the same C-terminal end, but differed in their N-terminal ends.152 Two... 

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