Synergist Immobilization Method for Photo‐Grafting: Factors Affecting Surface Selectivity

Abstract

The surface‐selectivity of photo‐grafting has been used as a crucial parameter to evaluate the ‘grafting‐from’ efficiency of the synergist immobilization method developed in our recent work. The factors that affect surface‐selectivity of photo‐grafting have been further investigated. It was shown that the competition of solvent with the membrane surface towards the generation of starter radicals led to a decrease in the degree of grafting and surface‐selectivity of photo‐grafting. High UV intensity made the functionalization mechanism more complicated, due to the generation of a new type of starter radical at the membrane surface with immobilized synergist in the absence of BP and because it could lead to cross‐linking in the grafted layer. An appropriately low photo‐initiator concentration was also required in order to achieve the ideal surface‐selectivity of photo‐grafting. In addition, this method has been successfully applied to the track‐etched PET membranes. Pore size distributions as well as ethanol and water permeability of the membranes were used to retrieve information about the effective thickness of the grafted polymer layers.magnified image

Visible light‐induced living surface grafting polymerization for the potential biological applications

“…Conventional surface photoinitiated free‐radical polymerization can be directly used on substrate surfaces, which has significant advantages: an easy operation, a low cost, mild reaction conditions, the potential reduction or even avoidance of negative effects on the bulk polymer, and a permanent chemical stability 9. In this process, the typical “Type II” photointiators, normally benzophenone (BP), have been frequently used to abstract hydrogen atoms from the surface polymer chains, thus forming surface radicals 10, 11…”

Protein adsorbers from surface-grafted copolymers with selective binding sites

“…For our new grafting approach, affinity adsorbers were prepared from track-etched poly(ethylene terephthalate) (PET) membranes with a pore diameter of about 700 nm with the same bisphosphonato co-monomer building blocks as mentioned above, via the so-called ''synergist immobilization'' method for photo-initiated ''grafting-from''. 9,10 The ''synergist'', which was chemically immobilized on the substrate surface, is a co-initiator for a dissolved ''type II'' photoinitiator. The regular cylindrical pore structure of these base membranes was advantageous when the surface functionalization of the membranes was evaluated because the accessible surface area is well-defined and the effective grafted layer thickness can well be estimated from permeability measurements.…”

Tailored “Grafting‐From” Functionalization of Microfiltration Membrane Surface Photo‐Initiated by Immobilized Iniferter

“…[1] However, as analyzed in the recent paper, [11] each grafting approach may have its own limits or disadvantages. This is also true for the ''synergist immobilization'' method developed in our previous work, [8,9] which exhibited a high photo-grafting efficiency and surface-selectivity in organic solutions. However, low grafting efficiency was still observed for certain acidic or anionic monomers, presumably due to complexation of the surface-immobilized synergist (a tertiary amine).…”

“…[5][6][7][8][9][10] Thus, the functionalized membranes have been explored for many applications according to base membrane structure and newly endowed functions. [1,11] For example, via tailored grafted functional polymeric layers on their entire surface, porous polymer base membranes are rendered waterwettable and low-fouling for filtration and fractionation processes, can been turned into highly efficient membrane adsorbers or are developed toward stimuli-responsive materials where the pores open or close upon changes of, e.g., pH value or temperature.…”