The Mark–Houwink–Sakurada Equation for the Viscosity of Linear Polyethylene

Abstract:The photostabilization of polyvinyl chloride (PVC) films by Schiff bases was investigated. Polyvinyl chloride films containing 0.5 wt % Schiff bases were produced using the same casting method as that used for additive-free PVC films from tetrahydrofuran (THF) solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl, polyene and hydroxyl indices with irradiation time. The changes in viscosity average molecular weight of PVC with irradiation time were also monitored using THF as a solvent. The quantum yield of chain scission (Φ cs ) for the studied complexes in PVC was estimated to range between 4.72 and 8.99ˆ10´8. According to the experimental results, several mechanisms were suggested, depending on the structure of the additive. Ultra violet (UV) absorption, peroxide decomposition and radical scavenging were suggested as the photostabilizing mechanisms.

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“…The viscosity property was used to determine the average molecular weight of the polymer, using the Mark-Houwink Equation (4) [37].…”

Section: Determination Of the Average Molecular Weight (M V ) Using Tmentioning

confidence: 99%

Photostabilizing Efficiency of PVC in the Presence of Schiff Bases as Photostabilizers

et al. 2015

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“…23 Gel permeation chromatographic analysis were performed with Senshu Scientific High Temperature GPC (SSC-7100) equipped with two Shodex HT 806M columns and RI detector using 1,2-dichlorobenzene as an eluent at 140 C. Universal calibration was applied using Mark-Houwink constants for polystyrene (k ¼ 1:38 Â 10 À4 and a ¼ 0:7) and polyethylene (k ¼ 5:6 Â 10 À4 and a ¼ 0:7). 24,25 Differential scanning calorimetry (DSC) was performed on a TA DSC Q100 connected with TA DSC Refrigerated Cooling System. The polymer was heated to 170 C and cooled to À70 C. After 3 min at À70 C, second heating scan at a rate of 10 C/min was used for the melting temperature (T m ) measurement of the polymer.…”

Section: Characterizationmentioning

confidence: 99%

“…Results of the ethylene polymerizations are summarized in Table I. Catalyst 3e showed the highest polymerization activity at 0 C, while catalysts 3b, 3c, and 3d showed the highest polymerization activities at 25 C. Further comparison of the polymerization activity of the catalyst was stumbled, because of ethylene diffusion limit at the pressure employed in this study. 14 The polymerization activities at 50 C were lower than those at 25 C for all the catalysts, which attributed to the catalyst deactivation at increased polymerization temperature.…”

mentioning

confidence: 99%

“…6 The ethylene polymerizations were carried out with the (-diimine)nickel(II) catalysts activated by MAO in toluene at 0, 25, and 50 C. All polymerizations were carried out with a low catalyst load (0.5 mmol) and a short polymerization time to prevent stop of stirring. Ethylene polymerization with catalyst 3d at 25 C was conducted with a shoter polymerization time (7.5 min). Results of the ethylene polymerizations are summarized in Table I.…”

mentioning

confidence: 99%

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Ethylene Polymerizations with Unsymmetrical (α-Diimine)nickel(II) Catalysts

Jeon

Kim

2008

Polym J

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Four unsymmetrical (-diimine)nickel(II) catalysts were synthesized by sequential stepwise condensation of acenaphthenequinone with the corresponding aniline compounds and subjected to ethylene polymerizations with MAO. Interestingly, when the catalysts have the same composition of the ortho substituents, the catalyst with two ortho isopropyl substitients on one side and two ortho methyl substituents on the other side produced polyethylenes with higher branching densities and lower molecular weights than the catalyst with one ortho isopropyl and one ortho methyl substituent on each side. However, branch distribution was not changed by the position of the ortho substituents. The catalysts have unique characteristic, production of branched polyethylene only from ethylene monomers. A chain walking (-hydride elimination and readdition to the other carbon) followed by ethylene coordination and insertion produces a methyl branch. Repeated chain walkings followed by ethylene coordination and insertion make a longer branch.Control of ortho substituents on aromatic rings of (-diimine)nickel(II) catalysts is important to achieve a proper catalytic activity. 13 The ortho substituents have been reported to locate at axial site of the catalysts, and they retard chain transfer reactions, promote the chain walking, and accelerate the rate of migratory insertion. Therefore, as steric bulkiness of the ortho substituents increases, molecular weights of polyethylenes, branching densities of polyethylenes, and polymerization activities increased.14 Some researchers further modified the ortho substituents of the (-diimine)nickel(II) catalysts to get novel polymerization results. Brookhart et al. reported that electron withdrawing ortho substituents of the (-diimine)-nickel(II) catalyst increased turnover frequency of ethylene polymerization presumably because electron withdrawing ortho substituents made nickel more electrophilic.14 Rieger et al. reported chiral C 2 symmetric (-diimine)nickel(II) catalysts bearing ortho phenyl substituents produced high molecular weight polyethylenes with high activities.15 Guan et al. reported cyclophane-based (-diimine)nickel(II) catalyst which was highly active for ethylene polymerizations even at high temperature ($90 C). 16 Zhu et al. reported that molecular weights of the polyethylenes produced by rac-(-diimine)-nickel(II) catalyst were significantly higher than those produced by meso-(-diimine)nickel(II) catalyst. 17Another way to modify the ortho substituents of the (-diimine)nickel(II) catalysts is making the (-diimine)nickel(II) catalysts as unsymmetric. But there have been few reports on ethylene polymerizations with unsymmetrical (-diimine)-nickel(II) catalysts due to the lack of proper synthetic method for unsymmetrically substituted -diimine ligands. [18][19][20][21][22] In this study, new unsymmetrical (-diimine)nickel(II) catalysts were synthesized by stepwise acid catalyzed condensation reaction followed by condensation with TiCl 4 /DABCO. The catalysts were subjected to ethylene poly...

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“…(1) repeatability of the SEC chromatogram (2) calibration of the SEC 11 (3) baseline corrections (4) column and other broadening…”

mentioning

confidence: 99%