Covalently Linked Plasticizers: Triazole Analogues of Phthalate Plasticizers Prepared by Mild Copper‐Free “Click” Reactions with Azide‐Functionalized PVC

Abstract

Copper-free azide-alkyne click chemistry is utilized to covalently modify polyvinyl chloride(PVC). Phthalate plasticizer mimics di(2-ethylhexyl)-1H-triazole-4,5 dicarboxylate (DEHT), di(nbutyl)-1H-1,2,3-triazole-4,5-dicarboxylate (DBT), and dimethyl-1H-triazole-4,5-dicarboxylate(DMT) are covalently attached to PVC. DEHT, DBT, and DMT have similar chemical structures to traditional plasticizers di(2-ethylhexyl) phthalate (DEHP), di(n-butyl) phthalate (DBP), and dimethyl phthalate (DMP), but pose no danger of leaching from the polymer matrix and forming small endocrine disrupting chemicals. The synthesis of these covalent plasticizers is expected to be scalable, providing a viable alternative to the use of phthalates, thus mitigating dangers to human health and the environment.

Phthalate plasticizers covalently linked to PVC via copper-free or copper catalyzed azide-alkyne cycloadditions

“…Synthetic modification of commercial PVC results in polydisperse products, which are not amenable to easy characterization by 1 H NMR, 13 C NMR, or mass spectroscopy. Therefore, (1-azidoethyl) benzene [27] was investigated as a model compound to confirm the viability of azide/alkyne cycloaddition reactions with these newly synthesized phthalate derivatives. For the unactivated ether derivative 14, copper catalyzed cycloaddition was utilized at room temperature to form the triazole 21.…”

“…These two complimentary conditions were then applied to modify PVC. Azide functional groups were incorporated into PVC by nucleophilic substitution of some of the chlorines [27]. PVC with 5% or 15% substituted azide was used in the cycloaddition reactions with phthalates tethered to terminal alkynes.…”

“…PVC (5.003 g) was dissolved in 60 mL of tetrahydrofuran (THF) at room temperature, followed by precipitation with 180 mL of methanol. PVC-azide (5% and 15%) was prepared according to our previously published procedure [27]. For 21% PVC-azide, 2.019 g of PVC and 2.006 g of sodium azide were stirred in 20 mL of DMF at 60 °C for 4 h. 13 C NMR.…”

“…Cycloadditions of azides and alkynes in a (3+2) fashion to form triazoles [25,26] have become widely popular due to both the chemoselectivity and mild reaction conditions. Inspired by the structural similarity between phthalate esters and 4,5-diester 1,2,3-triazoles, we recently demonstrated the covalent attachment of the phthalate mimics using thermal Huisgen cycloaddition of PVC-azide with electronpoor di(2-ethylhexyl) acetylenedicarboxylate [27]. Experimental values for the glass transition temperatures (T g ) of pure PVC, 15% displacement of chlorine by azide (15% PVC-Azide), and 15% plasticized PVC bearing 2-ethylhexyl triazole diester (15% PVC-DEHT) 6 were 83 °C, 76 °C, and 65 °C, respectively, indicating plasticization by the phthalate mimic (Fig.…”

Opening New Gates for the Modification of PVC or Other PVC Derivatives: Synthetic Strategies for the Covalent Binding of Molecules to PVC

“…Many different strategies [8][9][10][11][12][13][14][15] have been proposed to solve this migration problem, one of them being the covalent binding of the plasticizer to the PVC chains [16][17][18][19][20]. This binding reaction can be carried out by simple nucleophilic substitution of the chlorine atoms.…”