Polymorphism and Phase Transformation of Poly 1-Butene Hydrogenated Oligo Cyclopentadiene

7 Polymorphism and Phase Transformation of Poly (1-Butene)/Hydrogenated Oligo (Cyclopentadiene) 

The PB-1 crystallizes from the melt in the tetragonal crystal modihcation (form II), and then transforms into the hexagonal crystal modihcation (form I). This transformation, which is affected by time, temperature, atmospheric pressure, and mechanical deformation, changes the thermal, mechanical, and physical properties of the polymer (49-55). The thermal behavior of PB-I is strongly influenced by the presence of HOCP. The variations of the kinetics of PB-I crystal transformation from form II to form I were considered to be a consequence of the crystallization of PB-1 in the presence of HOCP. The samples were crystallized from the melt at different temperatures, (Table 6.4), chosen so as to provide the same undercooling according to the relation = T — AT, in which values are reported in Table 6.3 and AT = 46°C was kept constant for all isothermal crystallizations. The crystallized samples were kept for different periods of time, at the following different temperatures, Ta. 4, 20, 40, and 69°C. 

The presence of HOCP considerably slows down the melt crystallization process of PB-1. Therefore, the adopted values, lowered by increasing the HOCP fraction, provided similar rates of crystallization for pure PB-1 and blends. Previous calculations from the spherulite growth rate and from the overall kinetic rate constant showed that the number of nuclei per unit volume was similar for samples crystallized at equal undercoolings. Had we used a constant value of T, there would have 

During the conversion process, the melting temperatures (I m) of the two crystalline forms were quite constant at all the aging temperatures. The mean values for I m are reported in Table 6.4. The values decreased as the HOCP fraction increased in the blends due to the different values adopted and the interference by HOCP. The apparent enthalpies of fusion (A//n) were calculated from the area under the endothermic peaks of form II, obtained by DSC. The crystalline weight fractions of form II, am, referred to the amount of PB-1 present in the blends, were calculated from the relation  

It can be seen that the isothermal conversion process became increasingly slower when the form II of PB-1 was crystallized from the melt in the presence of increasing amounts of HOCP. This trend was observed at all aging temperatures except 69°C. It was also noted in the slow phase transformation curves that complete conversion of residual small amount of form II into form I was exceedingly slow. This might have been due to continuous supplies of form II from the amorphous phase by secondary crystallization of the PB-1 (51). 

---