Organocatalyzed Group Transfer Polymerization of Alkyl Sorbate: Polymer Synthesis, Postpolymerization Modification, and Thermal Properties

Abstract

The current work presents the organocatalyzed group transfer polymerization (GTP) of alkyl sorbate, the postpolymerization modification at the double bond of the poly­(alkyl sorbate) (PAS) backbone, and its thermal properties. The selected alkyl sorbate includes ethyl, n-hexyl, and n-octadecyl sorbate with the carbon number of the n-alkyl side chain being three times between every two neighboring monomers. The polymerization kinetics and mechanisms are briefly discussed for both the t-Bu-P4- and Me3SiNTf2-catalyzed GTPs of ethyl sorbate. Both of the two GTPs only undergo 1,4-addition to produce trans-rich PASs in which the former affords 81.9–85.4% trans content and the latter a much higher value as trans > 96%. The hydrogenation and epoxidation of the internal double bond turn out to be quantitative to provide the hydrogenated and epoxidized polymers, PAS-H2 and PAS-epoxy. The hydrogenation process makes the diastereochemistry and stereoregular structures of the two chiral carbons in the monomeric unit distinguishable by 13C NMR spectra, from which we know that the t-Bu-P4-catalyzed GTP produces erythro-rich PASs (erythro content = ca. 64%), while the Me3SiNTf2-catalyzed GTP gives relatively threo-rich PASs (threo content = 56–58%). However, the diisotactic/disyndiotactic ratios determined by 13C NMR spectra do not show an obvious difference between each other. Thermogravimetric analyses suggest that PAS-H2 shows the highest thermal stability and PAS-epoxy the lowest, due to the different polarity of the newly formed C–C bond in the main chain before and after the chemical modification of the internal double bond. For the amorphous poly­(ethyl sorbate) (PES) and poly­(n-hexyl sorbate) (PHS), change of the ethyl side group to n-hexyl greatly decreases the glass transition temperature (T g). As for the same PES/PHS series polymers, either the hydrogenation or the epoxidation of the internal double bond drastically changes the T g value of the final polymer product. In addition, the ca. 10% difference in the trans-cis composition for unmodified PES or PHS almost has no effect on T g values, while the erythro/threo content shows a prominent influence for the chemically modified polymers as the T g value can be changed from several to tens of Celsius degree when the same polymer changes from erythro-rich to threo-rich. On the contrary, crystallizable poly­(n-octadecyl sorbate) (PODS) and its modified polymers possess melting points (T m) in a pretty narrow temperature range of 34.7–41.4 °C, which is almost the same as the T m of n-octadecyl sorbate. It is likely that the T m values of PODS and its derivative polymers are only determined by the crystallization of the long n-octadecyl side chain, almost irrespective of the chain length, the trans-cis isomerization, the diastereochemistry, and the stereochemistry of the main chain.

A biorenewable cyclobutane-containing building block synthesized from sorbic acid using photoenergy

“…As a liquid, this ester can be more easily utilized in solvent-free polymerization. ( Ball-Jones et al., 2016 ; Hosoi et al., 2017 ; Liu et al., 2021 ) Additionally, CBDE-3 was found to be more soluble than CBDA-3 in most of the common and/or green solvents such as acetone, ethanol, and MeTHF, as was expected. As most organic reactions are performed in organic solvents, this is a highly useful property.…”

“…These C=C bonds are reactive functional groups that could be exploited to fine-tune the properties of the polymers made from CBDA-3 by reacting them with various reagents to create derivatives (e.g., epoxides). ( Liu et al., 2021 ; Ma et al., 2016 ) These C=C bonds may also be useful in making cross-linked polymers with CBDA-3 through radical polymerization or additional [2 + 2] cycloaddition reactions. Last but not least, a one-dimensional (1D) linear network of hydrogen bonds (O C=O ···O OH = 2.62 − 2.67 Å, Figure 5 C and ESI) in the crystal of CBDA-3 shows its potential in preparing supramolecular materials like hydrogen-bonded organic frameworks (HOFs) ( Hou et al., 2014b ; Wang et al., 2014 ) and green metal-organic materials (GMOMs).…”

Thermoresponsive Properties of Poly[oligo(ethylene glycol) sorbate]s Prepared by Organocatalyzed Group Transfer Polymerization

“…t-Bu-P 4 -Catalyzed GTPs of MeEG 2 S, MeEG 3 S, EtEG 3 S, and MeEG 4 S. t-Bu-P 4 -catalyzed GTPs of MeEG 2 S, MeEG 3 S, EtEG 3 S, and MeEG 4 S using MTS Me as an initiator were carried out in THF using the same procedure from our previous report. 39 Herein, the polymerization under [MeEG 2 S] 0 /[MTS Me ] 0 /[t-Bu-P 4 ] 0 = 25/1/0.1 is typically described as follows: A stock solution of MeEG 2 S (1.0 mL, 1.0 mol L −1 in THF) was added to a mixed solution of MTS Me (100 μL, 0.4 mol L −1 in THF) and t-Bu-P 4 (stock solution, 80 μL, 0.05 mol L −1 in THF) at room temperature. After stirring for 5 min, the polymerization was quenched by adding a small amount of benzoic acid.…”

“…The hydrogenation and epoxidation experiments were followed accordingly by our previously reported method. 39 ■ RESULTS AND DISCUSSION t-Bu-P 4 -Catalyzed GTP of Oligo(ethylene glycol) Sorbate (REG m S). The four REG m S monomers, namely, MeEG 2 S, MeEG 3 S, EtEG 3 S, and MeEG 4 S, are prepared by reacting sorbic acid with diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and tetraethyleneglycol monomethyl ether, respectively, using dicyclohexylcarbodiimide as a dehydrating agent to give target products with moderate yields, and their detailed syntheses are described in the Supporting Information and 1 H and 13 C NMR spectra are given in Figures S1−S4.…”

“…39−41 Therefore, this study describes (1) the synthesis and characterization of PREG m Ss by the t-Bu-P 4catalyzed GTP, which has been successfully applied to the synthesis of poly(alkyl sorbate)s in our previous report. 39 It is metal-free nature would exclude the influence of metal catalysts because any residual containment of hydrophilic metal ions in thermoresponsive polymers will significantly affect the phasetransition behavior; 42 (2) the chemical postpolymerization modification of PREG m Ss to alter the main-chain structures; and (3) a comprehensive survey on the thermoresponsive properties of PREG m Ss and their modified polymers in terms of the polymer mass concentration, molecular weight, length and end group of the OEG side chain, and main-chain structure, by turbidity, temperature-dependent 1 H NMR and DLS methods. The monomer and polymer structures together with the synthetic routes are shown in Scheme 1.…”