Photo-Crosslinking of Thioxanthone Group Containing Copolymers for Surface Modification and Bioanalytics

Abstract

We report on the synthesis of photoreactive copolymers with high reactivity toward UV irradiation at λ = 365 nm. To this, first thioxanthone moieties are incorporated into polymer chains via free radical polymerization. Then, upon brief UV irradiation, the thioxanthone moieties become activated and through a (formal) C,Hinsertion crosslinking (CHic), polymer networks are formed. When the photopolymer is coated onto a material containing CH groups, the network becomes simultaneously covalently attached to its surface. As the reactivity of thioxanthone photosensitizers is strongly enhanced by activator substances, tertiary amines in particular, copolymers with and without a built-in activator (2-dimethylaminoethyl) methacrylate, are generated. The efficiency and the kinetics of the formation of surfaceattached networks on various substrates are studied. To demonstrate the potential of the described systems for biomedical applications, they are used to manufacture functional beads that can be used for immunoassays.

Kinetics of Photocrosslinking and Surface Attachment of Thick Polymer Films

“…In a negative photoresist, a thin polymer film becomes insoluble in light-exposed areas, mostly through crosslinking. The most popular negative photoresists are epoxy-based polymers (e.g., SU-8) ,, and off-stoichiometry thiol-enes. , Typical negative photoresists can also contain photoreactive groups such as benzophenone, − thioxanthone, − anthraquinone, − benzoin ether, , and acylphosphine moieties. , Upon irradiation through a mask, a negative photoresist transits from compounds, such as oligomers or (low molecular weight) polymers, to crosslinked polymers which have an infinite molecular weight (i.e., spanning the whole irradiated area). Accordingly, the polymer becomes completely insoluble in all irradiated locations, whereas in the shaded areas under the mask, it remains uncrosslinked and is washed away in a following development step.…”

“…During network formation, the polymer chains simultaneously attach to any organic substrate. In this context, benzophenones, , thioxanthones, sulfonylazides, − diazo compounds, and anthraquinones were used as photoreactive groups to induce the network formation and surface attachment. If the substrates have no C–H bonds, the formation of a self-assembled layer, for example, through silanization, can be performed prior to the CHic reaction.…”

“…As C,H groups are usually abundantly present in the polymer layers, even small amounts of crosslinking groups are already sufficient enough to covalently crosslink polymer chains. The main advantage of CHic is that it can react with different kinds of materials containing C,H groups. ,,,,,, …”

“…The main advantage of CHic is that it can react with different kinds of materials containing C,H groups. 10,12,17,22,27,28,32 Korner et al 27 proposed a model for the kinetics of crosslinking in SAPNs through CHic reactions by using calculations on a Bethe lattice. In this model, the polymer chains are represented as the sites of the lattice.…”

Synthesis of Photoreactive Poly(ethylene oxide)s for Surface Modification

“…The grafting-to approach conjugates a presynthesized polymer onto the surface using a coupling reaction or an activated species generated by external energy [e.g., heat, ultraviolet (UV) light, and electron beam]. In particular, polymers possessing reactive functional groups that are activated by external signals are highly useful when immobilized onto a material because they can directly form covalent bonds between the polymer and a wide variety of substrates. − …”