Quantum Mechanical Computations and Microkinetic Modeling to Obtain Mechanism and Kinetics of Oxidative Degradation of a Polyimide

Abstract

Improving the high-temperature long-term thermo-oxidative stability of high-performance polymers is crucial for their applications in aerospace industry. For designing novel polymers with improved oxidative stability, it is vital to identify the most reactive moiety of the polyimide toward oxidation and understand the mechanism of oxidation. Quantum chemical calculations and microkinetic analysis have been carried out here to obtain the molecular level details of the oxidative degradation of a commercially important polyimide, PMR-15, at high temperatures. This study identifies the most vulnerable moiety of PMR-15 toward oxidation. Moreover, the rate-determining step in the oxidative degradation is also scrutinized. Mechanistic understanding of the reaction leads us to propose new modifications of PMR-15 with a better thermo-oxidative stability.

Preparation of polyimide films via microwave-assisted thermal imidization

“…However, during the thermal imidization process, both imidization and crystallization happen simultaneously at 150-350 C, resulting in the brittleness of materials, 6,7 and side effects including oxidation and degradation tend to occur at high temperatures. [8][9][10] In addition, high energy cost and insuf-cient utilization of resources should be considered with elevated temperature. Due to these limitations, it is meaningful to exploit novel imidization method to obtain highperformance PI products efficiently.…”

Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer

“…Computational quantum mechanical studies combined with microkinetic analysis is an ideal tool to probe the molecularlevel details of degradation of polymers. 33 In this study, quantum mechanical calculations and microkinetics analysis are used to explore the mechanism and kinetics of the degradation of HFPE. The cross-linked HFPE polymer is divided into four components (PETI, BNS, 6FDA and BTD), as shown in Figure 1a, and the oxidation mechanisms for each of these fragments in the presence of O 2 , O ̇H, and H 2 O are explored.…”

“…In order to understand the mechanism and factors affecting the degradation of such polymers, various experimental and theoretical studies were performed. ,,,− Many of these studies were focused on the improvement of thermo-oxidative stability of the existing polymers by chemical modifications of different molecular fragments of the polymer. ,,− , Among various possible chemical modifications, fluorination of the polymer backbone is identified as a good strategy to improve the thermo-oxidative stability of the polymer. ,,,− In addition to the improved thermo-oxidative stability fluorination of the polymer backbone can also increase the T g of the polymer . Improved properties of fluorinated polymers is attributed to the high bond strength, low polarizability of the C–F bond and small size of the fluorine atom …”

“…Chuang et al compared physical, mechanical and thermo-oxidative stabilities of composites of two fluorinated polymers, PMR-II-50 and HFPE, and found that HFPE has better thermo-oxidative stability among the two . The observed thermo-oxidative stability of HFPE compared to PMR-II-50 composites can be attributed to the presence of stable phenylethynyl (PETI) end-cap in HFPE, whereas in PMR-II the end-cap is nadic, which is known to undergo thermo-oxidative degradation at experimental conditions (600 K) used here. ,,, High thermo-oxidative behavior of HFPE was also reported by Adamczak et al based on their weight loss studies . They showed that HFPE can withstand a temperature of 700 K and degradation starts thereafter.…”

“…Though chemical modifications like fluorination of polymers help to improve mechanical properties and thermo-oxidative stability up to 700 K, it is beneficial for the space and aerospace applications to have materials that can withstand temperature more than 800 K. Toward developing such materials, it is important to have deep understanding of the chemical reactions undergoing during the oxidative degradation of the polymer. Computational quantum mechanical studies combined with microkinetic analysis is an ideal tool to probe the molecular-level details of degradation of polymers …”