Solid state NMR study of segmented polymer networks: fine-tuning of phase morphology via their molecular design |
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Authors: | Wouter Lequieu Filip E Du Prez Peter Adriaensens Jan Gelan |
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Affiliation: | a Polymer Chemistry Research Group, Department of Organic Chemistry, Ghent University, Krijgslaan 281 S4bis, B-9000 Ghent, Belgium b Division Chemistry, Limburgs Universitair Centrum, Institute for Materials Research (IMO), Universitaire Campus, Building D, B-3590 Diepenbeek, Belgium |
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Abstract: | Segmented polymer networks (SPNs) based on thermo-sensitive poly(N-isopropyl acryl amide) (PNIPAA) and poly(tetrahydrofuran) (PTHF) have been synthesized by free radical copolymerization of PTHF bis-macromonomers with N-isopropyl acrylamide. The nature of the polymerizable end group on the bis-macromonomer has been varied, respectively from acrylate to acrylamide end groups. The multiphase behaviour of the corresponding SPNs has been examined as a function of the nature of the end group by making use of solid-state 13C CP/MAS NMR relaxometry, 1H wideline NMR relaxometry and dynamic mechanical analysis (DMA). When PTHF with acrylate end groups was used during the SPN formation, analysis of proton spin-lattice relaxation times (T1H) and proton spin-lattice relaxation times in the rotating frame (T1ρH) revealed phase separation with domain sizes larger than 5 nm when the PTHF fraction exceeds 10 wt%. Only for lower PTHF-amounts, the SPNs were homogeneous on the nanometer scale. On the other hand, when PTHF with acrylamide end groups was used as macromolecular cross-linker, the NMR results showed the absence of any domain formation for SPNs with PTHF fractions up to 50 wt%. The major impact of the molecular design on the ultimate phase morphology of bicomponent polymer networks has been confirmed in all cases by DMA-analysis. |
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Keywords: | Segmented polymer network Phase morphology Solid-state NMR |
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