The facile and efficient functionalization of porous poly(glycidyl methacrylate) (pGMA) microspheres via hetero Diels-Alder (HDA) chemistry with poly(3-O-acryloyl-1,2:5,6-di-O-isopropylidene-a-Dglucofuranoside) (pAIpGlc) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization employing electron deficient thiocarbonylthio compounds (benzyl pyridin-2yldithioformate (BPDF)) is described in detail. The efficiency of the employed 'grafting to' approach is qualitatively and quantitatively analyzed. Initially the microspheres are functionalized with a highly reactive diene -cyclopentadiene (Cp) -in one step with sodium cyclopentadienide, and subsequently reacted with a protected glycopolymer (number-average molecular weight, M n ¼ 4200 g mol À1 ; polydispersity index, PDI ¼ 1.2) that carries a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved under mild conditions (T ¼ 50 C) with trifluoroacetic acid (TFA) as a readily removable catalyst. Deprotection of the grafted pAIpGlc to poly(3-O-acryloyla,b-D-glucopyranoside) (pAGlc) can be performed after functionalization in one pot with formic acid at ambient temperature. The obtained loading capacity is 2.63 Â 10 19 chains per g and the grafting density is close to 0.16 chains per nm 2 . Quantitative analysis of the grafting densities is achieved via elemental analysis; the pore size distribution before functionalization was analyzed by inverse size exclusion chromatography (iSEC). Further employed characterization techniques include scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and high resolution attenuated total reflectance (ATR) FT-IR microscopy supporting the successful modification of the microspheres.
The current contribution describes the combination of an efficient reversible deactivation radical polymerization process (reversible addition−fragmentation chain transfer (RAFT) polymerization) with a mild light-induced modular ligation technique. A novel RAFT-agent was synthesized which carries a photoactive group based on ortho-quinodimethane (photo-enol) chemistry. The novel photoreactive RAFT-agent controls the polymerization of a wide range of monomers such as styrene, N,Ndimethylacrylamide and a protected glycomonomer (2-(2′,3′,4′,6′-tetra-O-acetyl-β-D-mannosyloxy)ethyl acrylate) with dispersities between 1.07 and 1.17 (3500 g•mol −1 ≤ M n ≤ 10100 g•mol −1 ) and quantitative end-group functionalization. The photoenol group reacts with dieneophiles under mild irradiation (λ max = 320 nm) at ambient conditions − so that the RAFT-group remains intact − and without any catalyst to form block copolymers in a matter of minutes. Furthermore, the RAFT-polymers can be photografted onto porous polymeric (poly(glycidyl methacrylate)) microspheres, after a one-step prefunctionalization with maleimide moieties. The successful photografting is evidenced by scanning electron microscopy (SEM), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS) and high resolution attenuated total reflectance (ATR) FT-IR microscopy, which leads to qualitative as well as quantitative grafting data. The grafting densities obtained for polystyrene are close to 0.11 chains per nm 2 (M n = 3900 g•mol −1 ) and for poly(N,N-dimethylacrylamide) close to 0.12 chains per nm 2 (M n = 3500 g•mol −1 ). To highlight the additional benefit of employing a light-induced grafting reaction, Janus microspheres were prepared with poly(N,Ndimethylacrylamide) employing a Pickering emulsion approach and illustrated via ATR-FT-IR microscopy.
A general approach of size exclusion chromatography (SEC)-NMR is introduced for the determination of the classical molar mass parameters M(W), M(N), and M(P). It can be used for the determination of molar mass distributions of homopolymers and copolymers. The main advantage of SEC-NMR of copolymers is the possibility of detecting each monomer unit simultaneously with NMR as a quantitative concentration detector. Therefore, it is possible to provide the chemical compositions of copolymers at any elution volume without calibrations. In this respect, a new method will be presented for getting correct signal quantities of onflow data with sufficient NMR sensitivities. As the consequence, the chemical composition of copolymers can be correctly quantified under typical chromatographic conditions with respect to sample concentration and flow rate. Finally, the molar mass calibrations of the copolymers can be easily adjusted according to their chemical compositions. The methods were applied to polystyrene-b-poly(methyl methacrylate) block copolymers of different molar masses. The results of the molar mass distributions and the chemical composition distributions obtained by SEC-NMR are in very good agreement with the complex SEC multidetector analysis.
EXPERIMENTAL SECTIONSamples. Two series of polyisoprenes of different molar masses were used (Table 1). One series consists of samples containing predominantly 1,4-isoprene units with a small content of 3,4-isoprene units (samples 1-5), and the other series is samples containing predominantly 3,4-isoprene units and additionally 1,2-and 1,4-isoprene units (samples 6-10). The corresponding structures are drawn in Scheme 1. LCCC.The LCCC experiments were performed with an Agilent 1100 HPLC system (Agilent Technologies GmbH, B€ oblingen, Germany)
The determination of molecular weight and correlated chemical composition is of major interest for the advanced analysis of copolymers, blends, or unknown samples. In this work, we present a new way of online coupling IR spectroscopy and SEC to achieve a chemically sensitive, universally applicable SEC detector. Our method overcomes the limitations of existing spectroscopy-SEC combinations. We solved the major problems, like huge intensity of solvent signals (polymer concentration in detector <1 g L(-1) ) and short measuring time (<30 s), by recording the IR spectra with fully optimized sensitivity and by following mathematical solvent suppression. The measuring time for a certain S/N was reduced in several optimization steps by a factor of more than 70 000. The resulting sensitivity allows online coupled IR-SEC measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.