Mesoporous Thin Films, Zwitterionic Monomers, and Iniferter-Initiated Polymerization: Polymerization in a Confined Space

Abstract

Polymer modification of mesoporous materials is a relevant topic for applications from sensing and separation to drug delivery. Especially the combination of structure and responsive, charged polymer functionalization opens new possibilities, such as gating of drug release. Thereby, zwitterionic polymers are interesting, because of their antifouling characteristics and their influence on ionic permselectivity. The control on polymerization in confinement of a mesopore including spatial polymer location is crucial for the resulting mesopore function such as ionic permselectivity. The amount of generated polymer and polymerization kinetics should be influenced by the confinement of mesopores: Diffusion is limited by the pore size, pore connectivity, and wall charge. These parameters influence termination, which depends on radical concentration and proximity. Concerning the total surface area, the size of the internal surface area of mesoporous materials largely dominates over the size of the outer surface area. This might tempt one to relate observed functionalization effects to the internal surface. Here, we investigate iniferter-initiated polymerization in thin mesoporous silica films concerning the type of iniferter, the generated amount of polymer, the polymerization inside the mesopores versus the external surface, and the used monomer. Our results clearly indicate potential bottlenecks of iniferter-initiated polymerizations in mesopores. The charge of the monomer can be crucial for the generated amount of polymer inside the mesopores and the exterior surface can dominate the polymerization. These results emphasize that polymer distribution in mesoporous materials must be analyzed carefully before data interpretation and that polymerization inside nanometer-sized pores can be controlled by confinement effects. We expect these results to have great impact, e.g., on the design of miniaturized separation and sensing devices, and to open new confinement-controlled functionalization strategies.

Photochromic spiropyran- and spirooxazine-homopolymers in mesoporous thin films by surface initiated ROMP

“…7e). This might be due to the lower molecular weight inside the pores as observed for RAFT polymerization 49 or due to interaction with the silica pore walls. The determined rate constants (k UV ) for grafted PSP and PSPO at plasma treated mesoporous surfaces and nonplasma treated mesoporous surfaces are summarized in Table 2.…”

Insights into the Role of Counterions on Polyelectrolyte-Modified Nanopore Accessibility

“…It should be noted however, that modifying the grafting density, and hence the overall charge of the system, has a profound impact on the final behavior of the system. For a thorough discussion on this effect we refer the interested reader to reference 27 .…”

Optimisation of Surface-Initiated Photoiniferter-Mediated Polymerisation under Confinement, and the Formation of Block Copolymers in Mesoporous Films

“…Polymerisation in spatially confined mesoporous materials is a key technology that has been widely investigated over the last decade with advances in both soft chemistry and controlled/“living” radical polymerisation (CLRP) techniques [ 7 , 8 , 17 , 18 ]. A number of CLRP techniques have been successfully applied to the functionalisation of mesoporous silica including atom transfer radical polymerisation (ATRP) [ 19 , 20 , 21 ], reversible addition‒fragmentation chain transfer (RAFT) polymerisation [ 22 ], nitroxide-mediated radical polymerisation (NMP) [ 23 ], and photoiniferter-mediated polymerisation (PIMP) [ 23 , 24 ] through a grafting from or surface-initiated approach. While the successful grafting of pre-formed polymer to the interior and exterior surface has been reported in large-pore (15 nm) membranes [ 25 ], this approach is preferred for gated membranes with sterics limiting the molecular weight, grafting density, and pore filling achievable [ 8 , 17 , 22 , 26 ].…”