Quantitative Influence of Unsaturated End on Thermal Stability of <scp>PMMA</scp>

ABSTRACT Poly(methyl methacrylate) (PMMA) with different content of unsaturated end (UE, 42.6%–56.6%) structure was prepared by high‐temperature free radical polymerization. The influence of UE structure on the thermal stability of PMMA was quantitatively elucidated. The innovative method of bromine addition‐iodometric titration with 1 H‐NMR complementary validation system was used for the precise quantification of UE. Thermogravimetric analysis results showed that under nitrogen atmosphere, the increasing content of UE significantly decreased the thermal stability of PMMA, and for every 1% increasing content of UE, the initial degradation temperature (T i ) decreased by 3.14°C ± 0.38°C, the low‐temperature peak temperature (T d1 ) decreased by 2.38°C ± 0.16°C, the apparent activation energy (Ea) decreased by 4.18 ± 0.49 kJ mol −1 ; under air atmosphere, oxygen showed a stabilization effect in the initial stage by inhibiting the “unzipping” degradation triggered by UE with a positive correlation between ΔT i and UE (ΔT i = 3.05UE–125.15). The dual role of oxygen (stabilization at low temperature and promotion at high temperature) and modulation of stabilization effect by UE resolved the controversy in the literature. This study provided a quantitative framework for the optimization of PMMA thermal stability.