Quantification of Grafting Densities Achieved via Modular “Grafting‐to” Approaches onto Divinylbenzene Microspheres

Abstract

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 “grafting‐to” 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 = 4200 g 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 functionalization 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 Mn = 26 000 g mol−1, or 2.82 × 1019 and 1.38 × 1019 chains 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.

Modular design of glyco-microspheres via mild pericyclic reactions and their quantitative analysis

“…The phosphorous-containing group (2) has already been employed in the grafting of polymers to microspheres. 16 However, a disadvantage lies in the fact that phosphorus cannot be detected by most elemental analyzers, which in the current case provides the only means of a quantitative analysis of the grafting density. Therefore utilizing a phosphorous-carrying RAFT agent would imply grafting densities based on an elemental analysis that are always disputable as the mass balance would never be closed.…”

“…Cp-moieties have been put on the surface of a polymeric microsphere made of pDVB before, 16 but three steps were necessary. The pGMA microspheres Fig.…”

Porous polymer particles—A comprehensive guide to synthesis, characterization, functionalization and applications

“…Moreover, the thiol bead was treated with 9 different click reagents in parallel and the ranking is found as follows based on fastest conjugation kinetics: isocyanate > norbornene > acrylate ≈ isothiocyanate > maleimide ≈ isolated ene > α-bromo ester > epoxide ≈ aziridine. Finally, another novel highly efficient functionalization reaction involving the catalysis and heat free grafting of PS chains onto precipitation polymerized porous DVB particles via hetero-Diels-Alder chemistry was developed by Barner-Kowollik et al [367]. The microspheres were functionalized with cyclopentadiene and PS chains were furnished with thiocarbonyl moiety as dienophile.…”

Combining RAFT Radical Polymerization and Click/Highly Efficient Coupling Chemistries: A Powerful Strategy for the Preparation of Novel Materials

“…The same groups have also applied this methodology to the preparation of star polymers, [68,69] star block copolymers, [70,71] surface modified microspheres, [72,73] and other AB diblock copolymers using a combination of RAFT, ATRP, and heteroatom Diels-Alder chemistry. [74] For example, the synthesis of star polymers involved the reaction of RAFT prepared PSty, with CTAs shown in Scheme 18, which was subsequently coupled to 2, 3, and 4-arm diene reagents, Scheme 19.…”