Despite their mass production and large applications, polyolefins' stability and durability toward the air, moisture, and weather resistance is a challenge for the ecosystem. After long-term exposure to ultraviolet (UV) radiation or high-temperature or erosion, polyolefins undergo degradation generating microplastics (MPs). The MPs generated after the degradation of these polyolefins are hazardous for the ecosystem. In the present work, we have carried out density functional theory (DFT) studies to investigate the photodegradation of six different polyolefins ranging from polyethylene to polydecene, differing in side-chain. Herein, we have investigated photooxidized derivatives of different polyolefins and analyzed their relative stability, conformations, UV–visible spectral behavior, and carbonyl index. The photooxidized derivatives of various polyolefins formed during degradation are examined. The time-dependent density functional theory analysis confirms that the carbonyl groups of photooxidized products show absorption peak in Infrared (IR) and visible region, acting as light-absorbing species. The relative stabilities of hydroperoxide formed during photo/thermal oxidation of different polyolefins have been evaluated to explain the degradation behavior. The oligomerization and stabilization energies of their corresponding hydroperoxide's were computed and analyzed to explain the degradation behavior of the polyolefins. The computed results suggest that polyolefins in their pristine state are stable toward photooxidation, but chemical impurities like carbonyl, unsaturated carbonyl, carboxylic acid, and hydroperoxide derivatives make them prone to undergo degradation, a fundamental process leading to generation of MPs. The comparative results confirmed that the side-chain length affects the stability and degradation of different polyolefins toward photooxidation.

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基于第一性原理的聚烯烃结构对光氧化行为影响的理论研究

尽管可以大规模生产和大量应用，但聚烯烃对空气、水分和耐候性的稳定性和耐久性对生态系统来说是一个挑战。长期暴露于紫外线 (UV) 辐射或高温或侵蚀后，聚烯烃会发生降解，产生微塑料 (MPs)。这些聚烯烃降解后产生的 MP 对生态系统是有害的。在目前的工作中，我们进行了密度泛函理论 (DFT) 研究，以研究从聚乙烯到聚癸烯的六种不同聚烯烃的光降解，这些聚烯烃的侧链不同。在此，我们研究了不同聚烯烃的光氧化衍生物，并分析了它们的相对稳定性、构象、紫外-可见光谱行为和羰基指数。研究了降解过程中形成的各种聚烯烃的光氧化衍生物。瞬态密度泛函理论分析证实，光氧化产物的羰基在红外 (IR) 和可见光区显示出吸收峰，作为吸光物质。在不同聚烯烃的光/热氧化过程中形成的氢过氧化物的相对稳定性已被评估以解释降解行为。计算并分析了它们相应氢过氧化物的低聚和稳定能，以解释聚烯烃的降解行为。计算结果表明，原始状态的聚烯烃对光氧化是稳定的，但化学杂质如羰基、不饱和羰基、羧酸、和氢过氧化物衍生物使它们易于降解，这是导致 MP 生成的基本过程。比较结果证实，侧链长度影响不同聚烯烃对光氧化的稳定性和降解。