Crystalline polymers melting point

Table 6. Melting point and crystalline structure of the most stereoregular fractions of polymers of some optically active and racemic a-olefins... 

The equilibrium melting temperature, T°m, can be obtained from data for crystals of finite thickness using the Thompson-Gibbs equation. The melting point of crystalline polymers with a well-defined crystal thickness (/c) can be measured and the data extrapolated to 41 = 0 using the Thompson Gibbs equation (Gedde 1995) ... 

Only a polymer that is crystallizable can have a melting point, and crystallinity in a polymer has advantages. In the case of thermoplastics, the... 

Nesterov and Lipatov studied the compatibility of mixtures of crystallizable polymers (77) and the effects of quartz fillers on polymer-solute interactions (78). Information on the compatibility of these systems was obtained via the determination of melting points and crystallinities of the mixed stationary phases. Depending on the polymers considered a single melting transition at an intermediate temperature or distinct melting transitions for each polymer could be detected. 

An empirical rule has been proposed that predicts whether a co-poly(am-ide) is amorphous or crystalline. This rule is based on the stereochemical contributions of the constituent monomers to the overall polymer ehain structure. It turns out that PAs with high melting points are crystalline if more than 80% of the monomer units are S5mimetrical. Thus dissymmetry favors amorphous polymers. 

At temperatures above their melting points, semi-crystalline polymers resemble amorphous polymers. We find the same states as described for crosslinked amorphous materials, provided that there are covalent bonds between the chains. 

MW, MW distribution and side-chain branches in PE influence its material properties, including melting point and crystallinity. Linear low-density PE is more easily processed than high-density PE due to the presence of side-chain branches. The combination of stiffness and stress-crack resistance of the material are improved by the presence of these side chains [6, 7]. To improve processing, polymers with different MW can be melt-blended, but with the resultant problems and cost. 

The true melting points of crystalline polymers can be determined by plotting the differential scanning calorimetry (DSC) melting peak temperatures as a function of the square root of heating rate and linear extrapolations to zero heating rate. 

---