Copolymerization Kinetics of Dopamine Methacrylamide during PNIPAM Microgel Synthesis for Increased Adhesive Properties

Combining stimuli-responsive properties of gels with adhesive properties of mussels is highly interesting for a largefield ofapplications as, e.g., in life science. Therefore, the present paper focuseson the copolymerization of poly(N-isopropylacrylamide) (PNIPAM)microgels with dopamine methacrylamide (DMA). A detailed under-standing of reaction kinetics is crucial tofigure out an optimizedsynthesis strategy for tailoring microgels with adhesive properties. Thepresent study addresses the influence of relevant synthesis parameters asthe injection time of DMA during the microgel synthesis and the overallreaction time of the microgel. Reaction kinetics were studied by massspectrometry of time samples taken during the microgel synthesis. Thisallowed us to determine the monomer consumption of NIPAM, thecross-linkerN,N '-methylenebisacrylamide (BIS), and DMA. A second-order reaction kinetics was found for DMA incorporation.The amount of DMA incorporated in the resulting microgel was successfully determined by a combination of UV-vis and NMRspectroscopy to level offlimitations of both methods. The dependence of the hydrodynamic radius on temperature was determinedby DLS measurements for the microgels. While an early injection of DMA stops the PNIPAM polymerization due to scavenging, itgreatly enhances the reaction speed of DMA. The faster reaction of DMA and the incomplete NIPAM and BIS conversion alsocompensate for shorter reaction times with respect to the incorporated amount of DMA. On the contrary, a later injection of DMAleads to a full NIPAM monomer and BIS cross-linker consumption. An overall reaction time of 60 min ensures the DMAincorporation. Longer reaction times lead to clumping. First adhesion tests show an increased adhesion of P(NIPAM-co-DMA)microgels compared to pure PNIPAM microgels, when mechanical stress is applied

Automated summary

The combination of stimuli-responsive properties of gels with adhesive properties of mussels has great potential in various fields, including life science. This study focuses on the copolymerization of PNIPAM microgels with DMA to tailor microgels with adhesive properties. The reaction kinetics and synthesis parameters are investigated to optimize the synthesis strategy. The amount of DMA incorporated and the dependence of the hydrodynamic radius on temperature are successfully determined. Preliminary adhesion tests show that P(NIPAM-co-DMA) microgels exhibit increased adhesion compared to pure PNIPAM microgels when mechanical stress is applied.