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Functionalized polyolefins

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Functionalized polyolefins are olefin polymers with polar and nonpolar functionalities attached onto the polymer backbone.[according to whom?] There has been an increased interest in functionalizing polyolefins due to their increased usage in everyday life. Polyolefins are virtually ubiquitous in everyday life, from consumer food packaging to biomedical applications; therefore, efforts must be made to study catalytic pathways towards the attachment of various functional groups onto polyolefins in order to affect the material's physical properties.

Based on the polyolefin structure, functionalized polyolefin can be categorized into four main groups: randomly functionalized polyolefins, end-functionalized polyolefins, block polyolefins, and graft polyolefins.[1]

Randomly functionalized polyolefin

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Randomly functionalized polyolefins have differing types, location, and amount of functionality on the polyolefin backbone. Randomly functionalized polyolefins can be synthesized through many familiar combination of polymerization techniques including: post-functionalization, ROMP/hydrogenation, ADMET/hydrogenation, radical polymerization, and catalytic copolymerization.[1]

Post-functionalization

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Carbene insertion[2]

Post-functionalization of polyolefin occurs as the name suggests: functionalization occurs after a non-functionalized polyolefin is synthesized. One of the most common way to attach functionality onto a preexisting polymer backbone is through free radical reaction. Free radicals can be formed through plasma, peroxide initiation, etc.[3] When there is a free radical on the polyolefin chain, maleic anhydride[4] can be attached to promote further functionalization. Another approach is through direct insertion of carbenes onto the polyolefin backbone.[5] Though post-functionalization techniques are viable for the insertion of functional groups, harsh conditions must be used since regular non-functionalized polyolefins are highly unreactive.

Ring-opening metathesis polymerization (ROMP)

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Tungsten complex catalyzed ring-opening metathesis polymerization[6]

Ring-opening metathesis polymerization (ROMP) must occur first followed by hydrogenation of the opened product. For example, functionalized cyclooctenes can result in functionalized polyolefins via ruthenium complex catalyzed ROMP. Copolymers of ethyl and vinyl acetate can be synthesized via this process.[6] First, a cycloctene functionalized with an ester functionality at the position 5 carbon reacts with a ruthenium complex. Next, the resulting open-ringed product is treated with hydrazine to hydrogenate the double bond resulting in ethane and vinyl acetate copolymer.

Acyclic diene metathesis (ADMET)

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ADMET copolymerization with Ru catalyst[7]

Acyclic diene metathesis (ADMET) is similar to ROMP in that subsequent hydrogenation is required. ADMET requires a certain type of diene in order for the polymerization to occur. Ruthenium complexes can once again be used for ADMET polymerization.[8] In this case, an α,ω-diene monomer with functionality is required.

Radical polymerization

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Copolymer via radical polymerization[9]

Radical polymerization occurs with an olefin and a vinyl monomer. Since olefins are not very reactive, harsh conditions must be met in order for the polymerization to occur. Ethylene and ethyl acrylate can react together to perform free radical polymerization.[10] In this process, boron trifluoride can be used as the protected group for the ethyl acrylate.

Catalytic polymerization

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TMS functionalized polyolefin via Ti complex catalysis[11]

Catalytic polymerization appears to have the most control compared to other polymerization methods for randomly functionalized polyolefins.[12] Catalytic routes predominantly undergo a coordination/migratory insertion pathway. The functionality of the olefin highly affects the reactivity of the olefin, and hence its relative rate of coordination. Examples of early transition metal catalysts includes titanium and zirconium complexes. Early transition metals can easily form oxides; therefore, protection groups, like the use of methylaluminoxane (MAO) due to its Lewis acidity, can be used to prevent side reactions from happening.[13] As a cocatalyst, MAO is well known for their use in metallocene chemistry as they activate metallocene complexes for olefin polymerization.[14] To remove the MAO protecting group, the reaction can be treated with acid. Instead of MAO, trimethylsilyl (TMS) have also been used to protection functional groups such as amine, since the amine functionality can easily react with other olefins to form branched polymer chains.[15]

Another useful reaction is the use of zirconium metallocene complexes to copolymerize olefin with borane monomer. After reaction with a borane monomer, such as 9-borabicyclonoane (9-BBN), subsequent functionalization can result in hydroxyl functionalities.[16]

Turning from early transition metals to late transition metals, palladium and nickel catalysts have been used to copolymerize ethylene and methylacrylate.[13][17]

End functionalized polyolefin

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End functionalized BBN oxidation[16]

End functionalized polyolefins are polyolefin with functionality either at one end or at both ends of the chain. One example of end functionalization is through living polymerization. Using a vanadium terminated polypropene chain, subsequent reaction with carbon monoxide and acid can result in an aldehyde terminated polypropene chain.[18] This reaction moves forward under low temperature conditions (~-78 °C). Through metallocene supported polymerization, chain transfer can occur with the use of a borane chain transfer agent, which results in an end functionalized polymer chain.[19] One advantage of this chain transfer process is the limited use of metals, which decreases cost.

Block and graft polyolefin

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Graft vs block chain

Block and graft polyolefin can provide high amount of functional groups onto the polymer chain. Synthesis of both block and graft functionalized polyolefin proceed through a combination of polymerization reactions, most notably via coordination/insertion mechanism and radical polymerization.[20] Some disadvantages of this method include the lack of controlled polymerization and the requirement of multi-step mechanisms.

References

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  1. ^ a b Franssen, Nicole M. G.; Reek, Joost N. H.; Bruin, Bas de (2013-06-10). "Synthesis of functional 'polyolefins': state of the art and remaining challenges" (PDF). Chemical Society Reviews. 42 (13): 5809–5832. doi:10.1039/c3cs60032g. PMID 23598658.
  2. ^ Boaen, Nicole K.; Hillmyer, Marc A. (2005-02-22). "Post-polymerization functionalization of polyolefins". Chemical Society Reviews. 34 (3): 267–275. doi:10.1039/b311405h. PMID 15726162.
  3. ^ Kuzuya, M.; Kamiya, K.; Yanagihara, Y.; Matsuno, Y. (1993-01-01). "Nature of plasma-induced free-radical formation of several fibrous polypeptides". Plasma Sources Science and Technology. 2 (1): 51. Bibcode:1993PSST....2...51K. doi:10.1088/0963-0252/2/1/012. ISSN 0963-0252. S2CID 250753324.
  4. ^ De Roover, B.; Sclavons, M.; Carlier, V.; Devaux, J.; Legras, R.; Momtaz, A. (1995-04-15). "Molecular characterization of maleic anhydride-functionalized polypropylene". Journal of Polymer Science Part A: Polymer Chemistry. 33 (5): 829–842. Bibcode:1995JPoSA..33..829D. doi:10.1002/pola.1995.080330509. ISSN 1099-0518.
  5. ^ Aglietto, M.; Alterio, R.; Bertani, R.; Galleschi, F.; Ruggeri, G. (1989-06-01). "Speciality Polymers '88Polyolefin functionalization by carbene insertion for polymer blends". Polymer. 30 (6): 1133–1136. doi:10.1016/0032-3861(89)90093-1.
  6. ^ a b Hillmyer, Marc A.; Laredo, Walter R.; Grubbs, Robert H. (2002-05-01). "Ring-Opening Metathesis Polymerization of Functionalized Cyclooctenes by a Ruthenium-Based Metathesis Catalyst". Macromolecules. 28 (18): 6311–6316. Bibcode:1995MaMol..28.6311H. doi:10.1021/ma00122a043.
  7. ^ Lehman, Stephen E.; Wagener, Kenneth B.; Baugh, Lisa Saunders; Rucker, Steven P.; Schulz, Donald N.; Varma-Nair, Manika; Berluche, Enock (2007-03-24). "Linear Copolymers of Ethylene and Polar Vinyl Monomers via Olefin Metathesis−Hydrogenation: Synthesis, Characterization, and Comparison to Branched Analogues". Macromolecules. 40 (8): 2643–2656. Bibcode:2007MaMol..40.2643L. doi:10.1021/ma070085p.
  8. ^ Brzezinska, Krystyna; Wolfe, Patrick S.; Watson, Mark D.; Wagener, Kenneth B. (1996-06-01). "Acyclic diene metathesis (ADMET) polymerization using a well-defined ruthenium based metathesis catalyst". Macromolecular Chemistry and Physics. 197 (6): 2065–2074. doi:10.1002/macp.1996.021970622. ISSN 1521-3935.
  9. ^ Guironnet, Damien; Roesle, Philipp; Rünzi, Thomas; Göttker-Schnetmann, Inigo; Mecking, Stefan (2008-12-30). "Insertion Polymerization of Acrylate". Journal of the American Chemical Society. 131 (2): 422–423. doi:10.1021/ja808017n. PMID 19115853.
  10. ^ Logothetis, A. L.; McKenna, J. M. (1977-06-01). "Alternating ethylene–alkyl acrylate copolymers. I. polymer preparation". Journal of Polymer Science: Polymer Chemistry Edition. 15 (6): 1431–1439. Bibcode:1977JPoSA..15.1431L. doi:10.1002/pol.1977.170150614. ISSN 1542-9369.
  11. ^ Amin, Smruti B.; Marks, Tobin J. (2008-02-28). "Versatile Pathways for In Situ Polyolefin Functionalization with Heteroatoms: Catalytic Chain Transfer". Angewandte Chemie International Edition. 47 (11): 2006–2025. doi:10.1002/anie.200703310. ISSN 1521-3773. PMID 18203235.
  12. ^ Berkefeld, Andreas; Mecking, Stefan (2008-03-25). "Coordination Copolymerization of Polar Vinyl Monomers H2C=CHX". Angewandte Chemie International Edition. 47 (14): 2538–2542. doi:10.1002/anie.200704642. ISSN 1521-3773. PMID 18297672.
  13. ^ a b Boffa, Lisa S.; Novak, Bruce M. (2000-03-24). "Copolymerization of Polar Monomers with Olefins Using Transition-Metal Complexes". Chemical Reviews. 100 (4): 1479–1494. doi:10.1021/cr990251u. PMID 11749273.
  14. ^ Hanawa, Hideo; Abe, Noriko; Maruoka, Keiji (1999-07-16). "Double coordination and activation ability of methylalumoxane (MAO) for hetero functionality: Pivotal role as polymerization cocatalyst". Tetrahedron Letters. 40 (29): 5365–5368. doi:10.1016/S0040-4039(99)01024-2.
  15. ^ Schneider, Martin Julius; Schäfer, Rüdiger; Mülhaupt, Rolf (1997-05-01). "Aminofunctional linear low density polyethylene via metallocene-catalysed ethene copolymerization with N,N-bis(trimethylsilyl)-1-amino-10-undecene". Polymer. 38 (10): 2455–2459. doi:10.1016/S0032-3861(96)00785-9.
  16. ^ a b Ramakrishnan, S.; Berluche, E.; Chung, T. C. (2002-05-01). "Functional group-containing copolymers prepared by Ziegler-Natta process". Macromolecules. 23 (2): 378–382. Bibcode:1990MaMol..23..378R. doi:10.1021/ma00204a004.
  17. ^ Carlini, Carlo; De Luise, Valentina; Martinelli, Marco; Galletti, Anna Maria Raspolli; Sbrana, Glauco (2006-01-01). "Homo- and copolymerization of methyl methacrylate with ethylene by novel Ziegler-Natta-Type nickel catalysts based on N,O-nitro-substituted chelate ligands". Journal of Polymer Science Part A: Polymer Chemistry. 44 (1): 620–633. Bibcode:2006JPoSA..44..620C. doi:10.1002/pola.21161. ISSN 1099-0518.
  18. ^ Doi, Yoshiharu; Murata, Masahide; Soga, Kazuo (1984-12-01). "Reaction of carbon monoxide with living polypropylene prepared with a vanadium-based catalyst". Die Makromolekulare Chemie, Rapid Communications. 5 (12): 811–814. doi:10.1002/marc.1984.030051206. ISSN 0173-2803.
  19. ^ Chung, T. C.; Xu, G.; Lu, Yingying; Hu, Youliang (2001-10-05). "Metallocene-Mediated Olefin Polymerization with B−H Chain Transfer Agents: Synthesis of Chain-End Functionalized Polyolefins and Diblock Copolymers". Macromolecules. 34 (23): 8040–8050. Bibcode:2001MaMol..34.8040C. doi:10.1021/ma011074d.
  20. ^ Chung, T. C. Mike (2002-02-04). Functionalization of Polyolefins. Academic Press. ISBN 9780080477930.
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