The T-l rho C-13 spin-lattice relaxation time of interpenetrating networksby solid state NMR

Poly (2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacry late) interpenetrated with 5% SiO2 (PHEMA-IPN) were studied by C-13 CP/MAS NMR. From these results, the structure of two polymers were verified by C-1 3 NMR. Spin-lattice relaxation times for the polymer carbons in the rotatin g frame, T-1 rho, have been measured as a function of temperature. The T-1 rho spin-lattice relaxation times of the alpha-quarternary and carbonyl in the PHEMA and PHEMA-IPN undergo slow motions, i.e., motions on the slow sid e of the T-1 rho minimum, while those of the 1-,2-, beta-methylene, and 3-m ethyl undergo fast motions, i.e., motions on the fast side of the T-1 rho m inimum. From these T-1 rho spin-lattice relaxation times, we discuss the mo bility, the correlation time, and activation energy for the PHEMA and PHEMA -IPN, respectively. The activation energies for the PHEMA-IPN were found to be generally higher than those of PHEMA. The higher activation energy for the side-chain 2-methylene in the PHEMA-IPN is attributed to bonding betwee n the SiO2 and the hydroxyl group of the PHEMA. (C) 1999 Elsevier Science L td. All rights reserved.