Abstract
The change of tacticity during thermal treatment of commercial poly(methyl methacrylate) (PMMA) at 200 °C in air was studied in detail. The coupling between de‐ and repolymerization is contrasted by NMR analysis. The parameter of tacticity opens up a new perspective in describing the consequences of degradation. The analysis of the configuration of the residue was performed by ^1^H NMR spectroscopy. The ratios of the three characteristic triads – of isotactic (I), syndiotactic (S), and heterotactic (H) sequences – depend on degradation time and approach a constant value of S/H/I = 0.3:0.4:0.3 at about 80% of mass loss when starting with an initial ratio of S/H/I = 0.5:0.4:0.1. A two‐parameter two‐state model is proposed to calculate the transition from the initial to the final stereo‐sequence distribution generated by de‐ and repolymerization. The correlation between the evaluated parameters and the degradation processes leads to information on repolymerization, which is dominant after about 50% weight loss, i.e., from about 20 h on, and afterwards in two consecutive steps with a rapid change in tacticity, when 50% of the residual material is converted into a new sequence distribution. This type of tacticity conversion has its maximum speed at about 80% weight loss in the second of the consecutive steps.
Triad portions during degradation determined by ^1^H NMR spectroscopy: • syndio‐, ♦ hetero‐, ▴ isotactic triads.
magnified imageTriad portions during degradation determined by ^1^H NMR spectroscopy: • syndio‐, ♦ hetero‐, ▴ isotactic triads.