| Abstract: | The influence of annealing on mechanical αc‐relaxation of isotactic polypropylene (i PP) is investigated. In the sample without annealing, polymer chains in the intermediate phase are constrained by crystallites with a broad size distribution, leading to one αc‐relaxation peak with activation energy (E a) of 53.39 kJ mol−1. With an annealing temperature between 60 and 105 °C imperfect lamellae melting releases a part of the constraining force. Consequently, two αc‐relaxation peaks can be observed (αc1‐ and αc2‐relaxation in the order of increasing temperature). Both relaxation peaks shift to higher temperatures as annealing temperature increases. E a of αc1‐relaxation decreases from 38.43 to 35.55 kJ mol−1 as the intermediate phase thickness increases from 2.0 to 2.2 nm. With an annealing temperature higher than 105 °C, a new crystalline phase is formed, which enhances the constraining force on the polymer chains. So the αc1‐relaxation peak is broadened and its position shifts to a higher temperature. Moreover, the polymer chains between the initial and the newly formed crystalline phase are strongly confined. Therefore, the αc2‐relaxation is undetectable. E a of αc1‐relaxation decreases from 23.58 to 13.68 kJ mol−1 as the intermediate phase thickness increases from 2.3 to 3.0 nm. |
