A Bipedal Silica-Immobilized Azo-Initiator for Surface-Confined Radical Polymerizations

Abstract

The present study introduces the silica-anchored azo-initiator 4,4′-azobis(4-cyano-N-(3″-triethoxysilylpropyl)-valeric amide) (ACTA) for the surface-initiated polymerization of methyl acrylate (MA) with and without additional grafted reversible addition–fragmentation chain transfer (RAFT) agents 1,4-bis(3′-trimethoxysilylpropyltrithiocarbonylmethyl)benzene and 1,6-bis(o,p-2′-trimethoxysilylethylbenzyltrithiocarbonyl)hexane. While the sole use of silica-linked ACTA produced grafted poly(methyl acrylate) (pMA) of high molecular weight, due to a 2D Trommsdorff effect, the polymerization in combination with the fixed RAFT agents exhibited living behaviour with increasing molecular weights during polymerization. Silica-pMA hybrids were further analyzed via thermogravimetric analysis and scanning electron microscopy, which revealed significant differences between the three approaches.

Surface‐Initiated PLP‐SEC of Butyl Acrylate and Styrene from Silica Nanoparticles

“…The PLP‐SEC experiments of BA initiated by Si‐ACTA, depicted in Figure 2, were carried out at temperatures of 25 and 5 °C, respectively. In both cases, substantial amounts of poly(BA) in solution (dotted line) were present in spite of the low monomer conversion, which however, coincides with earlier findings and is probably in all cases caused by transfer reactions of surface‐tethered radicals to monomer molecules 31, 33. In addition to that, the SEC signals of the poly(BA) in solution exhibit a low molecular weight shoulder which seems to be more apparent at lower temperatures but whose origin is unclear.…”

“…2,2′‐Azobisisobutyronitrile (AIBN, AKZO) was recrystallized from diethylether. 4,4′‐azobis(4‐cyano‐ N ‐(3″‐triethoxysilylpropyl)‐valeric amide) (ACTA) was synthesized and immobilized on silica nanoparticles with 7 nm of nominal particle size according to literature 31. To remove the inhibitor, styrene and BA (Fluka) were passed through a basic alumina (Fluka, Brockmann I) column before use.…”

Smart Nanohybrids of RAFT Polymers and Inorganic Particles

“…Scheme 1.6c: Polymer loops can be created by anchoring both ends of a RAFT agent to the surface. [349][350][351] This can be done for the Z-(left) or the Rapproach (right). Both halves of the RAFT agent remain connected to the 37 1.2 Theoretical background surface throughout the course of the polymerization.…”

Shielding Effects in Polymer‐Polymer Reactions, 6

“…In order to produce surface‐anchored polymers at least three approaches are possible: i) the initiator is immobilized at the particle and the RAFT compound is in solution, ii) the stabilizing Z group of the RAFT agent is fixed on the surface (“Z‐group approach”), and iii) the RAFT agent is attached to the particle via its reinitiating R‐group (accordingly termed “R‐group approach”). Most recently, methods have been developed (based on both, Z‐ and R‐group technique) which allow not only the preparation of surface‐anchored chains (“tails,” “trails”) but also surface‐confined loops opening a new class of hybrid material …”

“…Most recently, methods have been developed (based on both, Z-and R-group technique) which allow not only the preparation of surface-anchored chains (''tails,'' ''trails'') but also surface-confined loops opening a new class of hybrid material. [11,12] For the Z-group approach, the RAFT agent is directly linked to the solid substrate resulting in sterical hindrance, which clearly is more pronounced than in case of the Rgroup approach, as in the latter case the RAFT moiety departs from the surface. Nevertheless, the controlling reaction of the growing radical with the thiocarbonyl bond is still shielded by the surrounding polymer segments.…”