Polymer Brushes via Surface-Initiated Polymerization catalysts in the final polymer brushes might have undesirable consequences for applications, such as in the biomedical or electronic industry. However, some methods, in particular A(R)GET ATRP, have been developed that allow to reduce the amount of copper to the level of a few ppm. 72 Surface-Initiated Reversible-Addition Fragmentation Chain Transfer (SI-RAFT) PolymerizationIn contrast to ATRP, where the equilibrium between the dormant and active, propagating chains is based on reversible termination, reversible-addition fragmentation chain transfer (RAFT) polymerization is based on reversible chain transfer. [114][115][116] A distinct advantage of RAFT polymerization is its relative simplicity and versatility, since conventional free radical polymerizations can be readily converted into a RAFT process by adding an appropriate RAFT agent, such as a dithioester, dithiocarbamate, or trithiocarbonate compound, while other reaction parameters, such as monomer, initiator, solvent, and temperature, can be kept constant. RAFT polymerization has also been successfully used to prepare polymer brushes via surface-initiated polymerization. SI-RAFT can be performed using two different strategies, which use either surface-immobilized conventional free radical initiators or surface-immobilized RAFT agents (Scheme 2). These two different strategies will be discussed in more detail in the following paragraphs.

As synthetic analogs of the natural pigment melanin, polydopamine nanoparticles (NPs) are under active investigation as non-toxic anticancer photothermal agents and as free radical scavenging therapeutics. By analogy to the widely adopted polydopamine coatings, polydopamine NPs offer the potential for facile aqueous synthesis and incorporation of (bio)functional groups under mild temperature and pH conditions. However, clear procedures for the convenient and reproducible control of critical NP properties such as particle diameter, surface charge, and loading with functional molecules have yet to be established. In this work, we have synthesized polydopamine-based melanin-mimetic nanoparticles (MMNPs) with finely controlled diameters spanning ≈25 to 120 nm and report on the pH-dependence of zeta potential, methodologies for PEGylation, and the incorporation of fluorescent organic molecules. A comprehensive suite of complementary techniques, including dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), X-ray photoelectron spectroscopy (XPS), zeta-potential, ultraviolet–visible (UV–Vis) absorption and fluorescence spectroscopy, and confocal microscopy, was used to characterize the MMNPs and their properties. Our PEGylated MMNPs are highly stable in both phosphate-buffered saline (PBS) and in cell culture media and exhibit no cytotoxicity up to at least 100 μg mL−1 concentrations. We also show that a post-functionalization methodology for fluorophore loading is especially suitable for producing MMNPs with stable fluorescence and significantly narrower emission profiles than previous reports, suggesting they will be useful for multimodal cell imaging. Our results pave the way towards biomedical imaging and possibly drug delivery applications, as well as fundamental studies of MMNP size and surface chemistry dependent cellular interactions.

Thin, phenylboronic acid-containing polymer coatings are potentially attractive sensory layers for a range of glucose monitoring systems. This contribution presents the synthesis and properties of glucose-sensitive polymer brushes obtained via surface RAFT polymerization of 3-methacrylamido phenylboronic acid (MAPBA). This synthetic strategy is attractive since it allows the controlled growth of PMAPBA brushes with film thicknesses of up to 20 nm via direct polymerization of MAPBA without the need for additional post-polymerization modification or deprotection steps. QCM-D sensor chips modified with a PMAPBA layer respond with a linear change in the shift of the fundamental resonance frequency over a range of physiologically relevant glucose concentrations and are insensitive toward the presence of fructose, thus validating the potential of these polymer brush films as glucose sensory thin coatings.

In this Article, we studied the surface immobilization of five organic-acid-modified atom-transfer radical polymerization (ATRP) initiators based on salicylic acid, catechol, phthalic acid, and m- and p-benzoic acid on alumina, and we also investigated the growth of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(poly(ethylene glycol)methycrylate) (PPEGMA6) brushes from the resulting initiator-modified substrates. Whereas the surface immobilization of phthalic acid- and benzoic acid-based initiators results in only very thin brushes or no brush growth at all, SI-ATRP of HEMA and PEGMA6 from alumina surfaces modified with salicylate or catechol generates brushes with thicknesses comparable to those obtained using organosilane-based initiators. Most interestingly, the surface immobilization of the catechol- and salicylate based-initiators was found to be pH-dependent, which allowed facile variation of the ATRP initiator surface concentration and, concomitantly, the polymer brush grafting density by adjusting the pH of the aqueous solution that was used to immobilize the initiator. This is in contrast to organosilane-based initiators, where the variation of the grafting density is usually accomplished using mixtures of the ATRP initiator and an ATRP inactive "dummy". Another difference between the organosilane-based initiators and the organic acid analogues is the stability of hydrophilic brushes grown from alumina. After a certain threshold thickness was exceeded, organosilane-tethered PPEGMA6 brushes were observed to detach from the substrate, in contrast to brushes grown from catechol or salicylate initiators, which did not show signs of degradation. Finally, as a first proof-of-concept, the salicylate-based initiator was used to develop an all-aqueous protocol for the modification of alumina membranes with hydrophilic PHEMA and succinic anhydride post-modified polymer brushes. The water permeation properties of these hybrid membranes can be controlled by adjusting the brush thickness in the case of the neutral PHEMA brush coating or can be pH-gated after post-polymerization modification to introduce carboxylic acid groups.