[PDF]    https://doi.org/10.3952/physics.v62i4.4821

Open access article / Atviros prieigos straipsnis
Lith. J. Phys. 62, 243–253 (2022)

SOLID-STATE NMR STUDY OF SPIN DYNAMICS AND LOCAL DISORDER IN SMART POLYMERS: PDMAEMA
Vytautas Klimavičiusa, Vaidas Klimkevičiusb, Laurynas Dagysc, Kęstutis Aidasa, Ričardas Makuškab, and Vytautas Balevičiusa
a Institute of Chemical Physics, Vilnius University, Saulėtekio 9, 10222 Vilnius, Lithuania
b Institute of Chemistry, Vilnius University, Naugarduko 24, 03225 Vilnius, Lithuania
c NVision Imaging Technologies GmbH, D-89081 Ulm, Germany
Email: vytautas.balevicius@ff.vu.lt

Received 28 September 2022; accepted 3 October 2022

The solid-state 1H and 13C NMR spectra as well as the 1H–13C cross-polarization upon magic angle spinning (CP MAS) kinetics were studied for poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), i.e. a smart pH- and thermo-responsive polymer. The stereochemical content of PDMAEMA was determined from the  complex shaped 13C MAS signal of CH3 group. The  kinetic data were processed using the Hirschinger and Raya spin dynamics model that includes the complete scheme of rotating frame spin-lattice relaxation pathways. The  general solution was adapted for the  spin cluster treatment. The  earlier studied experimental CP MAS kinetics data of poly [2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. one of its quaternized form, were revisited and newly processed applying this model. The spin-lattice relaxation of protons in the rotating frame in PDMAEMA and PMETAC occurs in the same scale from one to tens of milliseconds. Very high anisotropy of spin-diffusion was found for both polymers. However, the local disorder of various spin sites in PDMAEMA is significantly higher than in PMETAC. It is characterized by the order parameters 0.71–0.77 and 0.87–0.91, respectively. The main chain in PDMAEMA is also more disordered and more flexible than in PMETAC.
Keywords: solid-state NMR, cross-polarization, smart polymers, poly[2-(dimethylamino)ethyl methacrylate]

SUKINIŲ DINAMIKOS IR LOKALIOSIOS NETVARKOS IŠMANIUOSIUOSE POLIMERUOSE TYRIMAS KIETOJO KŪNO BMR METODU: PDMAEMA
Vytautas Klimavičiusa, Vaidas Klimkevičiusb, Laurynas Dagysc, Kęstutis Aidasa, Ričardas Makuškab, Vytautas Balevičiusa

a Vilniaus universiteto Cheminės fizikos institutas, Vilnius, Lietuva
b Vilniaus universiteto Chemijos institutas, Vilnius, Lietuva
c NVision Imaging Technologies GmbH, Ulmas, Vokietija
Ištirti kietojo kūno 1H ir 13C BMR spektrai bei 1H–13C CP („kryžminės poliarizacijos“) MAS („magiško kampo sukimo“) kinetika poli[2-(dimetilamino)-etilmetakrilate] (PDMAEMA), t. y. išmaniajame polimere, kuris pasižymi jautrumu pH ar temperatūros pokyčiams. Stereocheminė PDMAEMA sudėtis buvo nustatyta iš CH3 grupių 13C MAS signalo kontūro formos, atliekant persiklojusių smailių atskyrimą ir aproksimuojant jas Voigt funkcijomis. Eksperimentiniai CP MAS kinetikos duomenys buvo apdoroti taikant Hirschinger ir Raya sukinių dinamikos modelį, kuriame įtraukta pilnoji sukinių ir gardelės relaksacijų schema. Bend­roji kinetinė lygtis buvo adaptuota sukinių spiečių nagrinėjimui. Siekiant palyginti, buvo peržiūrėti eksperimentiniai anksčiau tirtos CP MAS kinetikos poli[2-(metakriloiloksi)etiltrimetilamonio chloride] (PMETAC), t. y. vienoje iš kvaternizuotų PDMAEMA formų, duomenys ir apdoroti pritaikius šį modelį. Nustatytos ir palygintos sukinių difuzijos bei sukinių ir gardelės relaksacijų spartos, taip pat 1H ir 13C sukinių sąveikos konstantos. Pastarieji duomenys buvo naudojami dinaminiams lokaliosios tvarkos parametrams įvertinti. Aptikta anomaliai didelė sukinių difuzijos anizotropija; ji didžiausia CH2 grupėms, esančioms šalia azoto atomų. Tai būdinga sukinių sistemoms, kuriose dominuoja Ising tipo sąveika. Nustatyta, kad protonų sukinių ir gardelės relaksacijos spartos abiejuose polimeruose yra panašios, ir šie vyksmai yra milisekundžių eilės. Lokalioji netvarka PDMAEMA yra žymiai didesnė. Ji apibūdinama lokaliosios tvarkos parametrais 0,71–0,77 PDMAEMA fragmentams ir atitinkamai 0,87–0,91 PMETAC fragmentams. Nustatyta, kad pagrindinė PDMAEMA grandinė taip pat labiau netvarki ir lankstesnė nei PMETAC.


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