Very Sensitive ¹³C NMR Method for the Detection and Quantification of Long-Chain Branches in Ethylene–Hexene Linear Low-Density Polyethylene

Abstract

Some linear low-density polyethylene (LLDPE) resins are designed to have long-chain branches (LCBs) to improve the viscoelastic properties. While improving the viscoelastic properties, the presence of LCBs can also be detrimental to the LLDPE mechanical properties. Thus, it is crucial to have a reliable, accurate technique to directly measure LCBs, for example, with intrinsically quantitative 13C NMR. We recently reported a method which overcame the “challenge of LCB signal overlap with the ethylene–hexene–ethylene branch (EHE Br) low field 13C satellite signal when using a 1-chloronaphthalene/PDCB-d 4 (9:1, w/w) mixture as a solvent to separate the LCB signal from the EHE Br signal and using a 600–700 MHz NMR 10 mm cryoprobe to boost the 13C sensitivity”. This approach enabled 13C NMR measurement of LCBs in the ethylene–hexene (EH) copolymer LLDPE. However, the method suffers 10% sensitivity loss as compared with the conventional quantitative 13C NMR method. This inspired us to develop a much more sensitive method “refocused insensitive nuclei enhanced by polarization transfer-anti-incredible natural abundance double quantum transfer experiment (RINEPT-anti-INADEQUATE)” for LCB measurement. This new method provides a 4.5 times sensitivity increase compared with the anti-INADEQUATE method, which we reported recently. This means that a single-day NMR measurement duration with the current RINEPT-anti-INADEQUATE method can achieve a similar signal-to-noise ratio as 20 days NMR measurement time with the previous anti-INADEQUATE method. Furthermore, the results are quantitative.

Hafnium and Zirconium Complexes Bearing SNN-Ligands Enhancing Catalytic Performances toward Ethylene/1-Octene Copolymerization

“…Note that long-chain branching (LCB) can be formed during ethylene polymerization using molecular catalysts. However, measuring LCB for copolymers has challenges due to overlapping signals from short-chain branching. − In this study, only C 6 branching was observed in the 13 C NMR spectra (Figures S16–S20) using a 5 mm BBO probe and LCB can be ignored. The T m s of resultant copolymers by differential scanning calorimetry (DSC) analysis were from 119 to 127 °C (Table and Figures S21–S25) depending on different degrees of 1-octene incorporation and suggesting the productions of typical LLDPEs.…”

Catalytic tandem dehydrochlorination–hydrogenation of PVC towards valorisation of chlorinated plastic waste

“…The intense 13 C peak at 29 ppm indicates that sequences of -CH 2groups are now dominant in the polymer backbone, but the observation of a range of other signals (25-42 ppm) indicates that the structure does not resemble much that of pure polyethylene. 19 The peaks around 39 ppm could be ascribed either to (i) -CH 2groups adjacent to isolated secondary -CHClunits, or to (ii) allylic -CH 2groups, in a of newly formed C]C bonds. Finally, while the strong -CH 2signals at ∼27 and ∼33 ppm are clearly of an aliphatic nature, they do not belong to a simple polyethylene chain.…”

Composition analysis of post‐consumer recycled blends of linear low‐ and low‐density polyethylene using a solution‐based technique

“…This occurs mostly at higher LDPE content (LDPE > 50 wt%) and is a function of the comonomer type in LLDPE. 20,33,34 For example, 1-hexene LLDPE has been shown to have the least degree of cocrystallization with LDPE when the LDPE concentration is about 70 wt% or more, while cocrystallization is noticeable when the LDPE concentration is about 20 wt% or more in a blend with 1-octene comonomer LLDPE. 19 Prasad reported that the origin of the additional third peak, or peak splitting effect, in the higher melting temperature of the LLDPE component in the blend is due to the meltrecrystallization of the LLDPE component during the second heating step, rather than cocrystallization between LDPE and LLDPE during the crystallization step.…”

“…Cocrystallization, indicated as a third intermediate peak in DSC melting thermographs, has also been proposed and reported in LDPE/LLDPE blends, where the polymers of each component form a shared lamellae structure in addition to their separate lamellae phases. This occurs mostly at higher LDPE content (LDPE > 50 wt%) and is a function of the comonomer type in LLDPE 20,33,34 . For example, 1‐hexene LLDPE has been shown to have the least degree of cocrystallization with LDPE when the LDPE concentration is about 70 wt% or more, while cocrystallization is noticeable when the LDPE concentration is about 20 wt% or more in a blend with 1‐octene comonomer LLDPE 19 .…”