Comparison of Chain Structures between High-speed Extrusion Coating Polyethylene Resins by Preparative Temperature Rising Elution Fractionation and Cross-fractionation

Two polyethylene（PE） resins（samples A and B） are synthesized as high-speed extrusion coatings with similar minimum coating thickness and neck-in performance but different maximum coating speeds. Both samples are separated into seven fractions using preparative temperature rising elution fractionation. The microstructures of the original samples and their fractions are studied by high-temperature gel permeation chromatography, Fourier transform infrared spectroscopy, 13 C nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and successive self-nucleation/annealing thermal fractionation. Compared with sample B, sample A has a broader MWD, more LCB contents, and less SCB contents. Moreover, sample A contains slightly more 30 ℃ and 50 ℃ fractions with lower molecular weights, and more fractions at 75 ℃ and 85 ℃ with higher molecular weight. The chain structure and its distribution in the two PE resins are studied in detail, and the relationship between the chain structure and resin properties is also discussed.

Microstructure Characterization of a Complex Branched Low-density Polyethylene

A low-density polyethylene （LDPE） resin with excellent processing and film-forming properties is fractionated through temperature rising elution fractionation （TREF） technique. The chain structures of both the original resin and its fractions are further analyzed using high-temperature gel permeation chromatography （GPC） coupled with triple detectors （refractive index （RI）-light scattering （LS）-viscometer （VIS））, ^13C-nuclear magnetic resonance spectroscopy （^13C-NMR）, Fourier transform infrared spectroscopy （FTIR）, differential scanning calorimetry （DSC） and successive self- nucleation/annealing （SSA） thermal fractionation. The ^13C-NMR results show that the original resin has both short chain branch （SCB） （2.82 mol%） and long chain branch （LCB） （0.52 mol%） structures. The FTIR results indicate that the methyl numbers （per 1000 C） of the fractions gradually decrease from 81 to 46 with increasing elution temperature from 25 ℃ to 75 ℃. The TREF-GPC cross-fractionation results show that the main component is collected at around 68 ℃. The molecular weight of the components in the high elution temperatures of 60 ℃ to 75 ℃ is from 2.0× 10^3 g/mol to 2.0 × 10^6 g/mol, and the relative amount is more than 80%. In the low elution temperature region below 50 ℃, the molecular weights of the components range from 1.0 × 10^3 g/mol to 1.6 × 10^4 g/mol, and the relative amount is less than 10%. In the DSC results, the melting peaks of the fractions gradually increase from 80.1℃ to 108.8 ℃ with elution temperature. In the SSA thermal fractionation, each resin fraction shows a broad range of endotherm with multiple melting peaks （more than eight peaks）. The melting peaks shift toward high temperatures with the elution temperature. The characteristic chain microstructure for the resin is also discussed in detail.