Dual-Functional ROMP-Based Betaines: Effect of Hydrophilicity and Backbone Structure on Nonfouling Properties

Abstract

Foundational materials for nonfouling coatings were designed and synthesized from a series of novel dual-functional zwitterionic polymers, Poly[NRZI], which were easily obtained via ring-opening metathesis polymerization (ROMP) followed by a single step transformation of the cationic precursor, Poly[NR(+)], to the zwitterion, Poly[NRZI]. The resulting unique dual-functional structure contained the anion and the cation within the same repeat unit but on separate side chains, enabling the hydrophilicity of the system to be tuned at the repeat unit level. These dual-functional zwitterionic polymers were specifically designed to investigate the impact of structural changes, including the backbone, hydrophilicity, and charge, on the overall nonfouling properties. To evaluate the importance of backbone structure, and as a direct comparison to previously studied methacrylate-based betaines, norbornene-based carbo- and sulfobetaines (Poly[NCarboZI] and Poly[NSulfoZI]) as well as a methacrylate-based sulfobetaine (Poly[MASulfoZI]) were synthesized. These structures contain the anion-cation pairs on the same side chain. Nonfouling coatings were prepared from copolymers, composed of the zwitterionic/cationic precursor monomer and an ethoxysilane-containing monomer. The coatings were evaluated by using protein adsorption studies, which clearly indicated that the overall hydrophilicity has a major influence on the nonfouling character of the materials. The most hydrophilic coating, from the oligoethylene glycol (OEG)-containing dual-functional betaine, Poly[NOEGZI-co-NSi], showed the best resistance to nonspecific protein adsorption (Γ(FIB) = 0.039 ng/mm(2)). Both norbornene-based polymers systems, Poly[NSulfoZI] and Poly[NCarboZI], were more hydrophilic and thus more resistant to protein adsorption than the methacrylate-based Poly[MASulfoZI]. Comparing the protein resistance of the dual-functional zwitterionic coatings, Poly[NRZI-co-NSi], to that of their cationic counterparts, Poly[NR(+)-co-NSi], revealed the importance of screening electrostatic interactions. The adsorption of negatively charged proteins on zwitterionic coatings was significantly less, despite the fact that both coatings had similar wetting properties. These results demonstrate that the unique, tunable dual-functional zwitterionic polymers reported here can be used to make coatings that are highly efficient at resisting protein adsorption.

Structures and Synthesis of Zwitterionic Polymers

“…Figure 6. Zwitterionic monomers employed in ring opening metathesis polymerization (ROMP), including phosphobetaine 34 [352], sulfobetaines 35 and 36 [349,350,354,357], and carboxybetaines 37 and 38 [350,357]. Still, different from the phosphobetaine and sulfobetaine monomers, the carboxylate group is nucleophilic enough in the less acidic carboxybetaines (x > 1 in VII, Figure 1) to compete with other ligands for complexing the metal center of the ROMP catalysts.…”

“…As the cleavage of such an ester function often has the character of the deprotection step in protecting group chemistry, especially if tert-butyl esters are employed [93,94,349,357,[398][399][400][401][402], it generally provides excellent yields. Thus, chances are very high to obtain rather clean polyzwitterions if not the amine, but the quaternized ammonium derivative is already engaged as monomer in the polymerization.…”

Switchable Materials Containing Polyzwitterion Moieties

“…Structurally unusual polyzwitterionic polymers that contain anion and cation in the same repeated unit but on a separate side-chain, poly (21), poly (23), poly (25), poly (27) and poly (29) [65,66], were reported and the structures are shown in Table 4. The application of such polymers made it possible to tune the hydrophilicity of the system at a repeating unit level.…”

“…4 buffer, 20 min (attached to surface) [65] HCl, dioxane 4 h, RT (attached to surface) [65] The hydrolysis was investigated on a silicone substrate coated with copolymers with 5-bicycloheptenyl triethoxysilane that provided a stable linkage through Si-O-Si bonds. The zwitterionic forms poly (21), poly (23), poly (25) and poly (27) were prepared by treatment of the modified surface with 0.1 NaOH for 20 min, while the hydrolysis of polycarboxybetaine esters poly (28) to zwitterionic polymer poly (29) was carried out in an acidic medium and proceeded within 4 h at ambient temperature.…”

“…The zwitterionic forms poly (21), poly (23), poly (25) and poly (27) were prepared by treatment of the modified surface with 0.1 NaOH for 20 min, while the hydrolysis of polycarboxybetaine esters poly (28) to zwitterionic polymer poly (29) was carried out in an acidic medium and proceeded within 4 h at ambient temperature. Norbornene-based zwitterionic polymers of various architecture were investigated and compared in order to follow the effect of a backbone structure on the protein adsorption properties [65]. In comparison with the methacrylate based sulfobetaine, the analogue norbornene sulfobetaine and carboxybetaine poly(29) exhibited lower protein fibrinogen adsorption, being 3.39, 1.03 and 0.84 ng/mm 2 , respectively.…”