Surface-Initiated Ring-Opening Metathesis Polymerization: A Method for Synthesizing Polymer-Functionalized Nanoparticles Exhibiting Semicrystalline Properties and Diverse Macromolecular Architectures

Abstract

Polymer-grafted nanoparticles are effective for designing hybrid materials with optimal component dispersion and enhanced material properties. The olefin chemistry accessible through ring-opening metathesis polymerization (ROMP) presents a route to polymer-grafted nanoparticles that possess unique chain architectures and chemical functionality difficult to achieve with common surface-initiated polymerization methods. Here, we show that surface-initiated ROMP (SI-ROMP) from silica nanoparticles ranging from 25 to 140 nm in diameter result in grafted polymer chains consisting of poly­(norbornene) (PNBE), poly­(cyclooctadiene) (PCOD), poly­(ethylene) (PE), and bottlebrush polymers with poly­(ethylene oxide) as the side chains. Furthermore, the brush heights of PNBE and PCOD polymer-grafted nanoparticles are experimentally measured and directly compared to expected scaling laws to present fundamental understanding into the polymer brush growth during SI-ROMP. It is found that polymer brush topology deviates from expectations near the particle surface. By the use of molecular weight and graft density characterization, it is reported that secondary chain transfer favors polymer network formation close to the surface, while linear chain topologies are favored at distances much further from the particle surface. The work presented here details the necessary SI-ROMP reaction conditions for successfully achieving polyolefin grafts with unique topology, chemical functionality, and thermal properties, which will open new avenues for polymer-grafted nanoparticles to be implemented into hybrid materials.

Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP): History, General Features, and Applications in Surface Engineering with Polymer Brushes

“…Before the functionalization, silica surfaces are usually cleaned by the Piranha solution [18,29,33], which generates exposed hydroxyl groups on the surface. Trichlorosilanes (RSiCl 3 ) [29,30] and trialkoxysilanes (RSi(OR) 3 ) [75,76] with olefin groups are often used to react with these hydroxyl groups and so functionalize the surface. It was reported that the trichlorosilanes and trialkoxysilanes were first hydrolyzed to give trihydroxylsilanes (R-Si(OH) 3 ) [75,[77][78][79], which then underwent condensation reactions with the hydroxyl moieties on the surface as depicted in Scheme 4.…”

“…Trichlorosilanes (RSiCl 3 ) [29,30] and trialkoxysilanes (RSi(OR) 3 ) [75,76] with olefin groups are often used to react with these hydroxyl groups and so functionalize the surface. It was reported that the trichlorosilanes and trialkoxysilanes were first hydrolyzed to give trihydroxylsilanes (R-Si(OH) 3 ) [75,[77][78][79], which then underwent condensation reactions with the hydroxyl moieties on the surface as depicted in Scheme 4. The remaining free hydroxyl groups on the silane molecule can participate in further condensations with the hydroxyl groups on either the silica surface or an adjacent silane, holding the attached olefin molecules onto the surface even more tightly.…”

“…The remaining free hydroxyl groups on the silane molecule can participate in further condensations with the hydroxyl groups on either the silica surface or an adjacent silane, holding the attached olefin molecules onto the surface even more tightly. Furthermore, it is worth mentioning that the same strategies were used to perform SI-ROMP on silica nanoparticles [47,75], which was used to improve the dispersion of these nanoparticles in polymer matrices (for instance, polyethylene and polynorbornene).…”

Hydrophobic and antifouling modification of graphene oxide with functionalized polynorbornene by surface-initiated ring-opening metathesis polymerization

“…The method of SI-ROMP has been increasingly applied in various substrates for the preparation of functional metal materials [32][33][34][35][36][37] and non-metal materials. [38][39][40][41][42][43][44] This polymerization technique can also be applied to the surface modification of GO with the advantage of living, controlled polymerization and easily functionalized monomers to enhance the mechanical stability and antipollution of the composite membrane materials. 45 Qiuping Zhang et al 46 employed SI-ROMP to prepare polymer-grafted GO by fixing Grubbs 1st generation catalysts on the surface of GO to carry out ROMP of norbornene (NBE).…”

Investigating Nanoparticle Organization in Polymer Matrices during Reaction-Induced Phase Transitions and Material Processing

“…Strategic blending of polymers and inorganic nanoparticles includes “softening” the penalties of mixing. Specifically, treatment of the particle surfaces with ligands, small molecules, or polymers will reduce the enthalpic penalties of mixing within the polymer phase. − Furthermore, high functional group density (σ) and the ratio between the degrees of polymerization of the grafted polymer chain ( N ) and the matrix ( P ) (e.g., N / P = α ≥ 0.2) prevent nanoparticle/polymer dewetting. , The compatibilization of polymer-functionalized nanoparticles within homopolymer, binary, and ternary blends, both within bulk phases and at film interfaces, is an active area of research. − While these strategies have been effective, surface modification methods tend to be extensive, and the solution blending and annealing processes make the materials challenging to scale. Oftentimes, surface-initiated polymerization on a functional particle surface is required to achieve sufficiently high group density at large enough molecular weights to have entropically favorable surface/matrix interactions. ,− …”