Quantification of grafting densities achieved via modular "grafting-to" approaches onto divinylbenzene microspheres

The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels-Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "graftingto" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn = 4200g mol-1; polydispersity index, PDI = 1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2 × 1020 chains per gram of microspheres. In the second approach, the f unctionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn = 6000 g mol-1, PDI = 1.25; Mn = 26 000 g mol-1, PDI = 1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T= 60°C) yet in the absence of a catalyst In this case the surface grafting density is close to 7 chains nm-2 for Mn = 6000 g mol-1 and 4 chains nm-2 for M n = 26000 g mol-1, or 2.82 × 1019 and 1.38 × 1019chains g-1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry