Abstract
Functional surface active monomers (surfmers) are molecules that combine the functionalities of surface activity, polymerizability, and reactive groups. This study presents an improved pathway for the synthesis of the active ester containing surfmer p-(11-acrylamido)undecanoyloxyphenyl dimethylsulfonium methyl sulfate (AUPDS). Further, the preparation of poly(methyl methacrylate) and polystyrene nanoparticles (NPs) by mini-emulsion polymerization using AUPDS is investigated, leading to NPs with active ester groups on their surface. By systematically varying reaction parameters and reagent concentrations, it was found that AUPDS feed concentrations between 2–4 mol% yielded narrowly distributed and stable spherical particles with average sizes between 83 and 134 nm for non-cross-linked NPs, and up to 163 nm for cross-linked NPs. By basic hydrolysis of the active ester groups in aqueous dispersion, the positive ζ-potential (ZP) was converted into a negative ZP and charge quantities determined by polyelectrolyte titrations before and after hydrolysis were in the same range, indicating that the active ester groups were indeed accessible in aqueous suspension. Increasing cross-linker amounts over 10 mol% also led to a decrease of ZP of NPs, probably due to internalization of the AUPDS during polymerization. In conclusion, by using optimized reaction conditions, it is possible to prepare active ester functionalized NPs in one stage using AUPDS as a surfmer in mini-emulsion polymerization.
Highlights
Polymeric nanoparticles (NPs) may exhibit unique physical properties that differ from the properties of their counterparts in the macroscale
Residual AAUA could not be reduced further due to the limited stability of AUPDS towards hydrolysis, excluding further extraction steps or column chromatography
We investigated this for PMMA-co-AUPDS, PS-co-AUPDS, PMMA-co-EGDMA-co-AUPDS, and PS-co-DVB-co-AUPDS particles using 2 mol% of AUPDS in the formulations, either non- or cross-linked with 10 mol% of cross-linker
Summary
Polymeric nanoparticles (NPs) may exhibit unique physical properties that differ from the properties of their counterparts in the macroscale. In miniEP the surfactant is generally used below its CMC, in order to prevent micellar nucleation, and the nano-sized droplets are formed by high shear forces, favoring an equal dissemination of surfactants among the monomer droplets. This mini-emulsification process leads to critically stabilized droplets, and their size is connected with the type and concentration of the surfactant used, because it affects the interfacial area between the water and the monomer phase and, the number and size of the monomer droplets. Concerning the choice for surfactant, sodium dodecyl sulfate (SDS) has been used as the standard anionic surfactant in miniEP systems and the use of cationic surfactants, such as cetyltrimethylammonium bromide (CTAB) is fairly recent, but their efficiency is comparable to that of SDS [8]
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