A Study of Annealing of Poly(ethylene-c o-octene) by Temperature-Modulated and Standard Differential Scanning Calorimetry

Annealing of poly(ethylene-co-octene)s with 12−25 mass % 1-octene for 2.5−5250 min was carried out by approaching the annealing temperature through cooling at 10 K min-1. Above the annealing temperature, primary crystallization was initiated. The analysis of the samples was performed during and after the annealing with temperature-modulated and standard differential scanning calorimetry, respectively (TMDSC and DSC). The irreversible annealing process consists of two different, exothermic events which are secondary crystallization and reorganization. The two processes were separated and quantitatively expressed by exponential laws with relaxation times of the order of 5 and 100 min, respectively. The two stages of crystallization and the reorganization produce a temperature-dependent, arrested, metastable, global structure of crystals and amorphous defects. Changing the annealing time can only partially compensate for changes in annealing temperature. Furthermore, TMDSC reveals a small amount of fully reversible melting. This reversible melting exists in addition to the well-known equilibrium of gauche−trans point defects in the crystal. Overall, there are thus at least five latent-heat contributions to the apparent heat capacity between the glass and melting transitions: primary and secondary crystallization, reorganization, locally reversible melting, and the gauche−trans equilibrium. For quantitative analysis of these latent-heat effects, they must be separated from the heat capacity of the melt, extrapolated from above the melting temperature, and the vibrational heat capacities of the crystal or glass.