Bimodal melting peak

However, there are also aspects of the crystallization process that are particular to statistical copolymers [16, 69, 71-76]. In a series of studies on the crystallization and melting behavior of ethylene-butene statistical copolymers, it was observed that after isothermal crystallization, while polyethylene homopolymer exhibited a single-peak melting endotherm, all the copolymers showed bimodal melting behavior [16,71]. Each melting peak of the copolymer endotherm was determined to represent a distinct crystal population because its shape... 

The addition of bilirubin or uremic toxin CMPF, which are strongly bound to HSA, alters the shape of the melting curve of serum albumin producing a bimodal curve, and causes a shift of the temperature maximum of the first peak to the right (Fig. 29.2) [7,8]. 

The PP exhibits a sharp peak at the maximum on CL intensity whereas the HDPE curve shows a broad bimodal behavior that has been thoroughly described elsewhere [127]. In the CL curves of the blend all these features were observed, which may be a strong indication of the existence of a two-phase system in the molten state [128], although based on peroxide treatment of PP/PE blend melts. It appears that PP oxidises first and the oxidation sites created during this process accelerate, to some extent, the oxidation of the PE phase. The overlap between the PP and PE traces in the blend can be interpreted as the interface of these two phases where the PE starts oxidising. In addition, the shape of the curves confirms that the oxidation mechanisms of the resins are different and that this difference remains during the oxidation of the blend in the molten state. 

Toughness of HDPE was improved by adding polyisobutylene they were not miscible, but formed micro-size morphologies [186]. In blends of HDPE with butyl rubber, plots of properties vs blend ratio were mostly S-shaped, indicating useful two-phase systems [77]. Melt viscosity and ultimate elongation exhibited unusual bimodal peaks at high and low HDPE/butyl ratios, where the morphology was fibrillar or laminar, whereas fairly equal ratios were simply particulate [188]. 

These generally gave two-phase blends with PIB and butyl rubber. Properties vs polyblend ratio usually indicated that these phases were partially miscible solid solutions [77]. Crosslinked phases increased stability of morphology and properties [26]. Intensive studies of HDPE -I- Butyl blends gave bimodal peaks for melt viscosity and ultimate elongation vs blend ratio, which were explained by two continuous laminar/fibrillar phases [188]. 

The mixture of long and short chains also has striking effects on the viscoelastic properties. Thorough experimental studies of polymer melts with sharplv peaked bimodal distribution of polymerization indexes, have shown qualitative discrepancies with the blending law... 

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