Surface-Initiated Initiators for Continuous Activator Regeneration (SI ICAR) ATRP of MMA from 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO) Oxidized Cellulose Nanofibers for the Preparations of PMMA Nanocomposites

Abstract

An effective method of oxidation from paper pulps via 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO) compound to obtain TEMPO-oxidized cellulose nanofibers (TOCNs) was demonstrated. Following by acylation, TOCN having an atom transfer radical polymerization (ATRP) initiating site of bromoisobutyryl moiety (i.e., TOCN-Br) was successfully obtained. Through a facile and practical technique of surface-initiated initiators for continuous activator regeneration atom transfer radical polymerization (SI ICAR ATRP) of methyl methacrylate (MMA) from TOCN-Br, controllable grafting polymer chain lengths (M_n = ca. 10k-30k g/mol) with low polydispersity (PDI < 1.2) can be achieved to afford TOCN-g-Poly(methyl methacrylate) (PMMA) nanomaterials. These modifications were monitored by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA), and water contact angle analysis. Eventually, TOCN-g-PMMA/PMMA composites were prepared using the solvent blending method. Compared to the pristine PMMA (T_g = 100 °C; tensile strength (σ_T) = 17.1 MPa), the composites possessed high transparency with enhanced thermal properties and high tensile strength (T_g = 110 °C and σ_T = 37.2 MPa in 1 wt% TOCN containing case) that were investigated by ultraviolet-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile tests. We demonstrated that minor amounts of TOCN-g-PMMA nanofillers can provide high efficacy in improving the mechanical and thermal properties of PMMA matrix.

Keywords: PMMA nanocomposites; SI ICAR ATRP; TOCN.

Scheme 1

Modifications of cellulose and surface polymerization: (a) oxidation, (b) acylation, and (c) surface-initiated initiations for continuous activator regeneration (SI ICAR) atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA).

Figure 1

Fourier transform infrared (FT–IR) spectra (4000–400 cm⁻¹) and scanning electron microscopy (SEM) images (inserted) of (a) pristine cellulose, (b) TEMPO-oxidized cellulose nanofibers (TOCN), and (c) TOCN–Br.

Figure 2

Electron spectroscopy for chemical analysis (ESCA) adsorption spectra (a) pristine cellulose, (b) TEMPO-oxidized cellulose nanofibers (TOCN), and (c) TOCN–Br.

Figure 3

ESCA spectra (C1s) of (a) pristine cellulose, (b) TOCN, and (c) TOCN–Br.

Figure 4

(A) Kinetic plots of surface-initiated initiators for continuous activator regeneration atom transfer radical polymerization (SI ICAR ATRP) of methyl methacrylate (MMA) (MMA/EBiB/CuBr₂/PMDETA/AIBN = x/1/0.05/0.1/0.5 at 70 °C; [MMA]₀ = 2.0 M in anisole) where x= (B) 100, (C) 200, and (D) 300.

Figure 5

¹³C NMR spectra (100 MHz, DMSO–d₆) of (a) TOCN–Br and (b) TEMPO-oxidized cellulose nanofibers (TOCN)–g–PMMA.

Figure 6

Contact angle measurements of (1) TEMPO-oxidized cellulose nanofibers (TOCN), (2–4) TOCN–g–PMMAs with different grafting molecular weight (MW) (listed in Table 2), and (5) pure PMMA.

Figure 7

Fourier transform infrared (FT–IR) spectra (1080–730 cm⁻¹) of (a1–a5) TEMPO-oxidized cellulose nanofibers (TOCN)/PMMA blends and (b) TOCN–g–PMMA2 sample.

Figure 8

Thermogravimetric analysis (TGA) traces of (a) pure PMMA, (b) TEMPO-oxidized cellulose nanofibers (TOCN), (c) TOCN–g–PMMA2, and (d–f) TOCN–g–PMMA2/PMMA composites with different TOCN weight percentage.

Figure 9

(a1–d1) Apparent images and (a2–d2) ultraviolet visible (UV–Vis) spectra of pristine PMMA and composite films.

Figure 10

Dynamic mechanical analysis (DMA) traces of (squares) PMMA and (circles, up-, and down-triangles) composites (E’: solid symbols; tan δ: hollow symbols).

Figure 11

Stress–strain curves of (a) PMMA and (b–d) composite species.