Recyclable Thermoplastic Elastomer from Furan Functionalized Hairy Nanoparticles with Polystyrene Core and Polydimethylsiloxane Hairs

Abstract

Polymers synthesized with end-of-life consideration allow for recovery and reprocessing. "Living-anionic polymerization (LAP)" and hydrosilylation reaction were utilized to synthesize hair-end furan functionalized hairy nanoparticles (HNPs) with a hard polystyrene (PS) core and soft polydimethylsiloxane (PDMS) hairs via a one-pot approach. The synthesis was carried out by first preparing the living core through crosslinking styrene with divinylbenzene using sec-butyl lithium, followed by the addition of the hexamethylcyclotrisiloxane (D3) monomer to the living core. The living polymer was terminated by dimethylchlorosilane to obtain the HNPs with Si-H functional end groups. The furan functionalization was carried out by the hydrosilylation reaction between the Si-H of the functionalized HNP and 2-vinyl furan. Additionally, furan functionalized polystyrene (PS) and polydimethylsiloxane (PDMS) were also synthesized by LAP. ¹H NMR and ATR-IR spectra confirmed the successful synthesis of the target polymers. Differential scanning calorimetry showed two glass transition temperatures indicative of a polydimethylsiloxane soft phase and a polystyrene hard phase, suggesting that the HNPs are microphase separated. The furan functionalized HNPs form thermo-reversible networks upon crosslinking with bismaleimide (BMI) via a Diels-Alder coupling reaction. The kinetics of the forward Diels-Alder reaction between the functionalized polymer and BMI were studied at three different temperatures: 50 °C, 60 °C, and 70 °C by UV-Vis spectroscopy. The activation energy for the furan functionalized HNPs reaction with the bismaleimide was lower compared to the furan functionalized polystyrene and polydimethylsiloxane linear polymers. The crosslinked polymer network formed from the Diels-Alder forward reaction dissociates at around 140-154 °C, and the HNPs are recovered. The recovered HNPs can be re-crosslinked at 50 °C. The results suggest that furan functionalized HNPs are promising building blocks for preparing thermo-reversible elastomeric networks.

Keywords: Diels–Alder reaction (DA); dynamic covalent bond; glass transition temperature (Tg); kinetics; living anionic polymerization (LAP); thermoplastic elastomer.

Figure 1

Schematic illustration of crosslinking and decrosslinking of furan functionalized HNPs with bismaleimide.

Scheme 1

Synthesis of furan functionalized HNP-F.

Figure 2

ATR-FTIR spectrum of (a) HNP-SiH (black), (b) HNP-F (red).

Figure 3

The 500 MHz ¹H NMR spectra of (a) Silylhydride functionalized HNP(HNP-SiH) and (b) Furan functionalized HNP(HNP-F).

Figure 4

DLS data of HNP before (a) and after (b) functionalization.

Figure 5

(a) TGA first-derivative curve and (b) DSC thermograms of HNP-F (red), PS-F (blue), PDMS-F (pink).

Scheme 2

The crosslinking of HNP-F with bismaleimide (BMI).

Figure 6

(a) 10% (w/w) HNP-F and BMI dissolved in DMF and THF (1:1) before crosslinking; (b) crosslinked gel after heating for 2 h at 50 °C; (c,d) decrosslinking after heating at 150 °C for 1 min and quench cooling; (e,f) crosslinking again at 50 °C for 2 h.

Figure 7

ATR-FTIR spectra of (a) crosslinked HNP-F with BMI (black) and (b) HNP-F (red).

Figure 8

(A) UV absorbance of BMI reaction with HNP-F with time; (B) first-order kinetics of HNP-F with BMI; (C) second-order reaction kinetics of HNP-F; and (D) activation energies of HNP-F, PS-F, and PDMS-F reactions with BMI.

Figure 9

(a) Heating curve of DSC analysis of crosslinked HNP-F with BMI; (b) heating curve of the DSC analysis of PS-F with BMI. The retro-DA peak, which indicates the cleavage of PS-BMI, is observed at 143 °C. (c) PDMS shows cleavage of PDMS-BMI at around 150 °C.

Figure 10

SEM image of (a) uncrosslinked HNP-F with BMI, (b) crosslinked HNP-F with BMI, and (c) decrosslinked HNP-F after heating at 150 °C. AFM images of crosslinked HNP-F with BMI at different magnifications (d,e).