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Effects of a vanadium post-metallocene catalyst-induced polymer backbone inhomogeneity on UV oxidative degradation of the resulting polyethylene film

Atiqullah, M. and Winston, M. S. and Bercaw, J. E. and Hussain, I. and Fazal, A. and Al-Harthi, M. A. and Emwas, A.-H. M. and Khan, M. J. and Hossaen, A. (2012) Effects of a vanadium post-metallocene catalyst-induced polymer backbone inhomogeneity on UV oxidative degradation of the resulting polyethylene film. Polymer Degradation and Stability, 97 (7). pp. 1164-1177. ISSN 0141-3910. doi:10.1016/j.polymdegradstab.2012.03.042.

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A Group 5 post-metallocene precatalyst,(ONO)VCl(THF)_2 (ONO = a bis(phenolate)pyridine LX_2 pincer ligand), activated with modified methylaluminoxane(MMAO-3A) produced a linear ethylene homopolymer (nm-HomoPE) and an unusual inhomogeneous copolymer (nm-CopolyPE) with 1-hexene having very low backbone unsaturation. The nm-CopolyPE inhomogeneity was reflected in the distributions of short chain branches, 1-hexene composition, and methylene sequence length. The 1-hexene incorporation into the polyethylene backbone strongly depended on the molecular weight of the growing polymer chain. (ONO)VCl(THF)_2, because of site diversity and easier removal of a tertiary (vs. a secondary) hydrogen, produced a skewed short chain branching (SCB) profile, incorporating 1-hexene more efficiently in the low molecular weight region than in the high molecular weight region. The significant decrease in molecular weight by 1-hexene showed that the (ONO)VCl(THF)_2 catalytic sites were also highly responsive to chain-transfer directly to 1-hexene itself, producing vinyl and trans-vinylene termini. Subsequently, the effect of backbone inhomogeneity on the UV oxidative degradation of films made from both polyethylenes was investigated. The major functional group accumulated in the branched nm-CopolyPE film was carbonyl followed by carboxyl, then vinyl/ester, whereas that in the linear nm-HomoPE film was carboxyl. However, (carbonyl, carboxyl, vinyl, and ester)_(nm-CopolyPE film) >> (carboxyl)_(nm-HomoPE film). The distributions of the tertiary ≡ C-H sites and methylene sequence length in the branched nm-CopolyPE film enhanced abstraction of H, decomposition of hydroperoxide group ROOH, and generation of carbonyl compounds as compared with those in the linear nm-HomoPE film. This clearly establishes the role played by the backbone inhomogeneity. The effect of short chain branches and sequence length distributions on peak melting temperature T_(pm), and most probably lamellar thickness L_0, was modeled from a nanoscopic viewpoint. The accumulation of the above oxygenated functionalities and its effect on % crystallinity are explained considering polyethylene UV autooxidation mechanism, and Norrish I and Norrish II chain scissions.

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Additional Information:© 2012 Elsevier Ltd. Received 29 January 2012; Received in revised form 22 March 2012; Accepted 26 March 2012; Available online 16 April 2012. The authors thank the King Abdullah University of Science & Technology (KAUST) Center-in-Development for Transformative Research in Petrochemicals and Polymers, established at King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia for supporting this research. The technical assistances provided by the Department of Chemistry and Chemical Engineering at California Institute of Technology (Caltech), Pasadena, USA; the King Fahd University of Petroleum & Minerals (KFUPM) Center of Refining & Petrochemicals (CRP) at the Research Institute, the Center of Research Excellence in Petroleum Refining & Petrochemicals (CoRE-PRP), and the Department of Chemical Engineering; Polymer Char, Spain; and KAUST are also gratefully acknowledged. The authors also thank Jubail United Petrochemical Company for donating 1-hexene.
Funding AgencyGrant Number
King Abdullah University of Science and Technology (KAUST)UNSPECIFIED
Subject Keywords:Post-metallocene catalyst; UV oxidative degradation; Short chain branch; Polyethylene
Issue or Number:7
Record Number:CaltechAUTHORS:20120813-093717652
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Official Citation:M. Atiqullah, M.S. Winston, J.E. Bercaw, I. Hussain, A. Fazal, M.A. Al-Harthi, A.-H.M. Emwas, M.J. Khan, A. Hossaen, Effects of a vanadium post-metallocene catalyst-induced polymer backbone inhomogeneity on UV oxidative degradation of the resulting polyethylene film, Polymer Degradation and Stability, Volume 97, Issue 7, July 2012, Pages 1164-1177, ISSN 0141-3910, 10.1016/j.polymdegradstab.2012.03.042. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33117
Deposited By: Aucoeur Ngo
Deposited On:13 Aug 2012 17:22
Last Modified:09 Nov 2021 21:32

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