Two commercial ethylene-propylene random copolymers(A and B) for hot water piping of which A has better long term heat stability and slow crack growth resistance performance than B were fractionated with respect to th...Two commercial ethylene-propylene random copolymers(A and B) for hot water piping of which A has better long term heat stability and slow crack growth resistance performance than B were fractionated with respect to the isotactity distribution by preparative temperature-rising elution fractionation(TREF).The molecular weight and distribution of fractions and the original resins were investigated by gel permeation chromatography.The results indicated that both A and B had broad isotacticity distribution and A had fewer portions of high isotacticity than B.At the same time A had broader and more typical double-peak molecular weight distribution.The fractions of A had higher molecular weight and broader molecular weight distribution than those of B’s.All of these results implied the differences between the catalysts or the polymerization processes for the two copolymers.展开更多
A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation（P-TREF）. All fract...A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation（P-TREF）. All fractions are characterized via high-temperature gel permeation chromatography（GPC）, 13 C nuclear magnetic resonance spectroscopy（13C-NMR）, and differential scanning calorimetry（DSC）. The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve（ethylene/1-hexene） of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing（SSA） thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.展开更多
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 ori...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.展开更多
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 s...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.展开更多
文摘Two commercial ethylene-propylene random copolymers(A and B) for hot water piping of which A has better long term heat stability and slow crack growth resistance performance than B were fractionated with respect to the isotactity distribution by preparative temperature-rising elution fractionation(TREF).The molecular weight and distribution of fractions and the original resins were investigated by gel permeation chromatography.The results indicated that both A and B had broad isotacticity distribution and A had fewer portions of high isotacticity than B.At the same time A had broader and more typical double-peak molecular weight distribution.The fractions of A had higher molecular weight and broader molecular weight distribution than those of B’s.All of these results implied the differences between the catalysts or the polymerization processes for the two copolymers.
基金financially supported by the National Natural Science Foundation of China(Nos.20734006 and 50921062)
文摘A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation（P-TREF）. All fractions are characterized via high-temperature gel permeation chromatography（GPC）, 13 C nuclear magnetic resonance spectroscopy（13C-NMR）, and differential scanning calorimetry（DSC）. The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve（ethylene/1-hexene） of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing（SSA） thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.
基金financially supported by the National Basic Research Program of China(No.2005CB623806)the National Natural Science Foundation of China(Nos.20734006 and 50921062)
文摘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.
基金financially supported by the National Basic Research Program of China(No.2005CB623806)the National Natural Science Foundation of China(Nos.20734006 and 50921062)
文摘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.
