Abstract: In this paper, the molecular structure of polymethacrylimide (PMI) was studied. Based on the Fourier transform infrared (FR-IR) analysis in situ heating, it was found that the Casecell IH PMI foam prepolymer began the reaction of -COOH and -CN groups turning hexahydric imide ring in the condition of 160 ℃/2 h. The -NH stretching vibration peak type and area were no longer changed, and -C=N stretching vibration peak appeared after treatment at 200 ℃/2 h. The results of ¹³C NMR showed that the adjacent -COOH groups were not included in Casecell IH PMI prepolymer. PMI foam prepolymer only underwent ring formation of the imidization reaction and trapezoidal reaction at high temperature. The molecular weight and distribution of Casecell IH were measured by laser light scattering (LLS) and gel permeation chromatography (GPC). The results showed that the weight average molecular weight appeared double peaks, indicating that the molecular weight of Casecell IH perpolymer was larger and the distribution wide, consistent with the characteristics of free radical copolymerization.

Key words: polymethacrylimide, infrared spectroscopy (IR), laser light scattering (LLS), gel permeation chromatography (GPC), nuclear magnetic resonance (NMR)