Synthesis and kinetic analysis of poly(N-acryloylmorpholine) brushes via surface initiated RAFT polymerization

Abstract

Polymer brushes are promising many applications as smart materials and biocompatible surfaces. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most effective techniques for synthesis of well-defined polymer brushes. Herein, a biocompatible, uniform and stable poly(N-acryloylmorpholine)-silicon hybrid system was achieved using surface-initiated RAFT polymerization. Evidence of a well-controlled surface-initiated RAFT polymerization was confirmed by a linear increase of number average molecular weight (M_n) with overall monomer conversions. Water contact angle, ellipsometry, X-ray photoelectron spectroscopy and atomic force microscopy verified the presence of poly(N-acryloylmorpholine) (poly(NAM)) on silicon wafers. The grafting density (σ) and the average distance between grafting points (D) were estimated to be 0.58 chains/nm² and 1.5 nm, respectively. The ratio of D value to radius of gyration (Rg) value is smaller than 1 (D/2Rg < 1), which corresponds to the brush regime of all grafted poly(NAM) films.

Keywords: Polymer brushes; poly(N-acryloyl morpholine); surface-initiated RAFT polymerization.

Figure 1

Diagram for synthesis of Si-g-poly(NAM) brushes.

Figure 2

2D-3D AFM images (5 × 5 μm) and water contact angle photograph for Si-H surfaces.

Figure 3

(a) GA-FTIR, (b) O1s, C1, Si2s and Si2p core-level XPS spectra (c) survey scan XPS spectra, (d) 2D-3D AFM images (5 × 5 μm) and water contact angle photograph of Si-ED surfaces.

Figure 4

(a) GA-FTIR, (b) survey scan XPS spectra, (c) O1s, C1, S2p, Si2s and Si2p core-level XPS spectra, (d) 2D-3D AFM images (5 × 5 μm) and water contact angle photograph of Si-BPAT surfaces.

Figure 5

Relationships for (a) film thickness-polymerization time, (b) % conversion-polymerization time, (c) molecular weight – % conversion, (d) ln ([M]₀/[M]_t) - polymerization time, (e) film thickness-molecular weights.

Figure 6

(a) GA-FTIR spectra and (c) core-level XPS spectra of Si-g-poly(NAM) surfaces for all polymerization times, (b) O1s, C1, S2p, Si2s and Si2p of Si-g-poly(NAM) surface.

Figure 7

2D-3D AFM images (5 × 5 μm) and water contact angle photograph for polymer brushes synthesized for different reaction time a) 2 h, b) 4 h, c) 6 h, d) 8 h.