Advances in Internal Plasticization of PVC: Copper-Mediated Atom-Transfer Radical Polymerization from PVC Defect Sites To Form Acrylate Graft Copolymers

Dedicated to Barry Trost: celebrating a lifetime of exploring the beauty of transition-metal catalysis in organic synthesis.

Abstract

Internally plasticized PVC copolymers were prepared by grafting PVC with butyl acrylate and 2-(2-ethoxyethoxy)ethyl acrylate by atom-transfer radical polymerization, resulting in well-behaved polymers with a wide range of glass transition temperatures (–54 °C to 54 °C). When the grafted side chains made up more than 50% of the polymer by weight, the glass transition temperatures were below 0 °C. The covalent attachment of the plasticizing grafts requires one simple procedure starting from commercial PVC, making this strategy an industrially relevant and environmentally friendly alternative to the use of conventional small-molecule plasticizers.

Key words

polyvinyl chloride - copper catalysis - atom-transfer radical polymerization - graft copolymerization - butyl acrylate - ethoxyethoxyethyl acrylate

Publication History

Received: 07 December 2020

Accepted: 15 January 2021

Article published online:
12 February 2021

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• 36 PVC-g-50%PBA-co-50%P2EEA (Table [1], Entry 5); Typical Procedure A 10 mL Schlenk flask was charged with PVC (500.7 mg, 8.011 mmol) and DMF (3 mL), and the mixture was stirred and slightly warmed to fully dissolve the polymer. BA (1.43 mL, 9.97 mmol) and 2EEA (1.85 mL, 9.99 mmol) were then added to the solution. A 2 mL vial was charged with CuBr (34.22 mg, 0.2386 mmol) and 0.75 mL of DMF to form a suspension, which was transferred to the PVC solution by pipette. Residual CuBr was washed into the PVC solution with DMF (0.25 mL), and PMDETA (50 μL, 0.24 mmol) was added. The mixture was degassed by four freeze–pump–thaw cycles, then heated to 100 °C and stirred under N₂ for 2 h. An aliquot of the crude reaction mixture was taken and analyzed by ¹H NMR with CDCl₃ as solvent (conversion = 60 wt%). The polymer was precipitated by adding the mixture to MeOH (200 mL), followed by stirring for 30 min. The MeOH was decanted and the residual polymer was left overnight in additional MeOH (100 mL) without stirring. The solution phase was decanted and the polymer was dried under mild vacuum. The polymer, containing residual solvent, was washed with additional MeOH (5 mL), and the solvent was decanted. The product was thoroughly dried under vacuum to give a pale-green pliable polymer; yield: 1.5567 g (percentage wt. of plasticizer by gravimetry: 68%). FTIR (neat): 2974 (m, alkane C–H), 2931 (m, alkane C–H), 2873 (m, alkane C–H), 1736 (s, ester C=O), 1169 (s, ester C–O), 1119 (m, ether C–O). ¹H NMR (500 MHz, CDCl₃): δ = 4.65–4.54 (br m), 4.54–4.38 (br m), 4.38–4.25 (br m), 4.25–4.12 (br m), 4.12–3.93 (br m), 3.72–3.65 (br m), 3.65–3.60 (br m), 3.60–3.55 (br m), 3.52 (q, J = 7.0 Hz), 2.49–2.23 (br m), 2.23–1.97 (br m), 1.97–1.81 (br m), 1.74–1.57 (br m), 1.51–1.43 (br m), 1.43–1.29 (br m), 1.21 (t, J = 7.0 Hz), 0.94 (t, J = 7.3 Hz). From ¹H NMR integration: (PBA + P2EEA)/PVC = 0.9:1.0; PBA/P2EEA = 1.0:1.0; plasticizer = 60 wt%.
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