Complementary Multiple Hydrogen-Bonding Interactions Increase the Glass Transition Temperatures to PMMA Copolymer Mixtures

We have prepared a series of poly(methyl methacrylate) (PMMA)-based copolymers through free radical copolymerizations of methyl methacrylate in the presence of the either 2-vinyl-4,6-diamino-1,3,5-triazine (VDAT) or vinylbenzylthymine (VBT). Using H-1 nuclear magnetic resonance (NMR) spectroscopy, solid state C-13 NMR spectroscopy, differential scanning calorimetry (DSC), one- and two-dimensional Fourier transform infrared (FTIR)spectroscopy, and viscosity measurements, we investigated the thermal properties of and hydrogen-bonding interactions within blends of the two copolymers poly(2-vinyl-4,6-diamino-1,3,5-triazine-co-methyl methacrylate) (PVDAT-co-PMMA) and poly(vinylbenzylthymine-co-methyl methacrylate) (PVBT-co-PMMA). A large positive deviation in the behavior of the glass transition temperature-determined using the Kwei equation and DSC analyses-indicated that strong multiple hydrogen-bonding interactions existed between the two copolymers. The FTIR and solid-state NMR spectroscopic analyses provided positive evidence for the presence of three hydrogen bonds between the diamino-1,3,5-triazine groups of PVDAT and thymine groups of PVBT. Furthermore, the proton spin-lattice relaxation time in the rotating frame [T-1 rho(H)] for the copolymer blends had a single value that was less than those of the pure copolymers, indicating that the degree of homogeneity or the D-PMMA/T-PMMA blend was relatively higher than those of the blends.