Differential scanning calorimetry molecular fractionation

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

Temperature-rising elution fractionation (tref) is a technique for obtaining fractions based on short-chain branch content versus molecular weight (96). On account of the more than four days of sample preparation required, stepwise isothermal segregation (97) and solvated thermal analysis fractionation (98) techniques using variations of differential scanning calorimetry (dsc) techniques have been developed. 

Random copolyesters based on bromoterephthalic acid, methyl hydroquinone, and hexane diol have been synthesized. Their mesophase properties were studied by differential scanning calorimetry, optical microscopy, realtime X-ray diffraction and melt rheology. At low molecular weight these copolymers exhibit triphasic behavior, where two mesomorphic phases coexist with an isotropic phase. Fractionation based on solubility in THF enables the identification of two components. Simple statistical arguments are employed to model the polymerization reaction and account for the observed phase behavior. 

Besides the cross-fractionation of molecular weight and comonomer composition, another group of cross-fractionation techniques focus on the crossfractionation of comonomer composition and chain sequence length. This group includes a combination of P-Tref and differential scanning calorimetry (DSC) with successive nucleation/annealing (SNA) [45,46]. 

Some of the principles as well as problems involved in the melting of random copolymers are found in olefin type copolymers. The melting temperatures of a large number of random type ethylene copolymers, as determined by differential scanning calorimetry, are plotted as a function of the mole percent branch points in Fig. 5.11. The samples represented in this figure are either molecular weight and compositional fractions or those with a narrow composition distribution with a most probable molecular weight distribution.(74) These samples were crystallized and heated rapidly. In this set of data there are two different copolymers that contain ethyl... 

Similar results have been found upon analysis of the crystallization kinetics by differential scanning calorimetry [151, 152] of polyethylene fractions encompassing a very wide range of molecular masses, from 2900 to 8 X 10 . This is the widest range in molecular masses to have been reported for the crystallization kinetics of this polymer. The influence of molecular mass on regime formation has been explored. 

H. Ali, K. El-Sayed, P.W. Sylvester, S. Nazzal, Molecular interaction and localization of tocotrienol-rich fraction (TRF) within the matrices of lipid nanoparticles Evidence studies by Differential Scanning Calorimetry (DSC) and Proton Nuclear Magnetic Resonance spectroscopy (IHNMR), Colloids Surf., B. 77 (2010) 286-297. 

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