1H NMR study of thermotropic phase transitions in D2O solutions of poly(N-isopropylmethacrylamide)/poly(vinyl methyl ether) mixtures

Structures and interactions in collapsed hydrogels of thermoresponsive interpenetrating polymer networks

“…While for the hydrogel of PNIPMAm/PNIPAm IPN containing 54 mol% of PNIPAm monomer units, two different transitions were detected by NMR and DSC in our previous study [33], a single transition was observed in PNIPMAm/PNIPAm IPN samples with a larger amount of PNIPAm component, thus showing enhanced mutual intertwining of both types of polymer chains in these samples. Such behavior resembles the LCST behavior of aqueous solutions of random copolymers [31,58], while two separate transitions of both components are typical for mixtures of two thermoresponsive homopolymers [30][31][32]. In our opinion, network structures of IPNs PVCL/PNIPAm and PNIPMAm/PNIPAm with~50 mol% of PNIPAm monomer units contain microregions where single components collapse independently.…”

“…In the last decade, in addition to various thermoresponsive homopolymers, we also applied NMR spectroscopy to aqueous solutions of polymer mixtures and random copolymers with thermosensitive components [30][31][32] with the aim to control and tune temperature responsivity of these systems for possible applications. The solutions of linear polymers and copolymers can be considered as model systems for corresponding hydrogels.…”

1H NMR study of temperature-induced phase transitions in D2O solutions of poly(N-isopropylmethacrylamide)/poly(N-isopropylacrylamide) mixtures and random copolymers

“…Though phase transitions especially in PIPAAm aqueous solutions were extensively studied by various methods (cloud point, viscometric, calorimetric, diffusion, viscoelastic, infrared and Raman measurements), the application of NMR spectroscopy to investigations of the phase separation in aqueous solutions of PIPAAm and its copolymers was rather seldom [4][5][6][7][8]. Together with cited papers, we have also shown that 1 H NMR spectroscopy can be a suitable method to follow the temperature-induced phase separation on molecular level and applied this method to D 2 O solutions and gels of poly(N,N-diethylacrylamide), poly(vinyl methyl ether) (PVME) and PIPMAm [9][10][11][12][13][14][15], as well as to PIPMAm/PVME mixtures [16].…”

“…where I is the integrated intensity of the certain polymer line in the spectrum of partly-separated system and I 0 is the integrated intensity of this line if no phase separation occurs [10][11][12][13][14][15][16]. For I 0 we took values based on integrated intensities below the phase-transition, using the expected 1/T temperature dependence.…”

“…For this purpose, D 2 O solutions (polymer concentration cZ0.1, 1 and 5 wt%) of PIPMAm/PIPAAm mixtures and statistical copolymers P(IPMAm/IPAAm) (cZ1 wt%) of various composition (molar ratio of monomeric units was 3/1, 1/1 and 1/3 both for mixtures and copolymers) were prepared. In comparison with recently studied PIPMAm/PVME mixtures in D 2 O solutions [16] there is important difference for systems investigated in the present study: while LCST is for PVME at least 60 K above the temperature of the glass transition T g of PVME in bulk, for PIPAAm the LCST is well below the respective T g Z403 K [18]. From the methodical point of view, we used an approach based on measurements of temperature dependences of 1 H NMR spectra (integrated intensities), used by us already in the past [10][11][12][13][14][15][16], that makes it possible to determine the temperature dependences of the phase separated fraction.…”