Polyethylene multiple melting peaks

Like other crystalline polymers, liquid crystalline polymers can also exhibit multiple melting peaks when studied with DSC. Multi-melting is common to crystalline polymers including single crystals of polyethylene. For example, Bair et al. (1967) found the single crystals of PE grown... 

Kolesov and Radusch prepared peroxide cross-linked binary and ternary blend SMPs from high density polyethylene and two ethylene-l-octene copolymers with medium and high degrees of branching [47]. The blends were prepared by a melt mixing and subsequently are cross-linked with 2 wt% of liquid peroxide 2,5-dimethyl-2,5-di-(tertbutylperoxy)-hexane at 190°C. The blends showed multiple shape memory behavior that appeared only at consequent stepwise application of convenient programming strains and temperatures. Obviously, that is caused by multiple melting behavior of these blends with many poorly separated peaks. 

The Tin values of homo-polyethylene and homo-PMCP (67.6% trans rings) produced using catalyst 7 were 138.0 and 76.7 °C, respectively. The poly(ethylene-co-l,5-HD)s produced by the same catalysts showed multiple melt transitions. As an example, a copolymer containing 16.7 mol% of 1,5-HD units in the main chain showed TmS at 88.6 and 116.4 C, and a copolymer containing 39.6 mol% of 1,5-HD units in the main chain showed TniS at 73.8 and 96.9 C. The crystallinity of the copolymers, as measured by XRD analysis, decreased monotonously as the content of 1,5-HD units in the main chain increased. Poly(propylene-co-l,5-HD)s produced by 7 lost their crystallinity, as evidenced by both XRD and differential scanning calorimetry (DSC) analysis, as the content of 1,5-HD units in the main chain was increased. Thus, when the content of enchained 1,5-HD units reached 6.7%, the copolymer showed no Tm and no characteristic XRD peaks. 

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