C-13 CP MAS NMR-STUDY ON MISCIBILITY AND DEHYDRATION OF POLY(2-HYDROXYETHYL METHACRYLATE)POLY(METHACRYLIC ACID) BLENDS/

Miscibility and the dehydration process of poly(2-hydroxyethyl methacr ylate)/poly(methacrylic acid) (PHEMA/PMAA) blends were studied by C-13 CP/MAS NMR. The C-13 NMR spectra showed the possibility of hydrogen b onding between the carboxyl groups of PMAA and the hydroxyl groups of PHEMA in the PHEMA/PMAA. blends. The H-1 T-1 and T-1 rho experiments i ndicated that the blends are homogeneous on the T-1 rho scale. Further more the temperature modulated DSC measurements indicated thermodynami c homogeneity of the blends. These results suggest that PHEMA and PMAA are miscible on a scale of 5-10 nm. The TG curve and C-13 CP/MAS spec tra showed that PMAA is dehydrated to form intramolecular six-membered cyclic anhydrides in a few minutes at 573 K. PHEMA does not undergo s uch dehydration at 573 K. In the PHEMA/PMAA blends, however, C-13 spec tra indicated that PHEMA forms intermolecular esters with PMAA. The C- 13 T-1 experiments showed that the molecular motion of heat-treated bl ends becomes slow.