Synthesis and characterization of thermally degradable polymer networks

Diacrylate and dimethacrylate monomers containing thermally cleavable tertiary ester linkages with different spacer lengths were synthesized and studied. The photopolymerization rates of diacrylates were much higher than those of dimethacrylates. Glass transition temperatures of the prepared networks increased from 55 to 180 degrees C with decreasing spacer length for diacrylate networks and from 135 to 185 degrees C for dimethacrylate networks. Isothermal thermogravimetric analyses revealed that the networks were thermally stable up to 150 degrees C and decomposed smoothly between 180 and 200 degrees C to form partially dehydrated linear poly(acrylic acid) or poly(methacrylic acid). It was observed that decomposition reactions were dominated by an autoacceleration mechanism. The rate of weight loss was dependent on temperature and spacer length. Although the resulting decomposition products were insoluble in dimethylformamide, methanol, and water due to the presence of intermolecular acid anhydride groups, they were completely soluble in dilute sodium hydroxide and ammonium hydroxide solution accompanied by hydrolysis or ammonolysis of the anhydride units.