Long-Chain Branch Measurement in Substantially Linear Ethylene Polymers by <sup>13</sup>C NMR with Halogenated Naphthalenes as Solvents

Zhou, Zhe; Baugh, Dan; Fontaine, Philip P.; He, Yiyong; Shi, Zhengwei; Mukhopadhyay, Shayok; Cong, Rongjuan; Winniford, Bill; Miller, Matt

doi:10.1021/acs.macromol.7b01692

Cited by 16 publications

(23 citation statements)

References 34 publications

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“…[ 8,9 ] NMR is being routinely used for qualitative and quantitative determination of the microstructure of polyethylene for several decades. This method is the ultimate choice in unambiguous identification and quantification of different types of comonomer, [ 10 ] internal olefins, [ 11 ] saturated and vinyl chain‐ends, [ 12 ] and long chain branches [ 13 ] of different types of poly‐α‐olefin resins.…”

Section: Introductionmentioning

confidence: 99%

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Monwar

2020

Macromolecular Symposia

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Polyethylene film properties can be manipulated by blending linear low-density polyethylene (LLDPE) with low density polyethylene (LDPE) resin.The accurate determination of LDPE content in those blends, however, is challenging. Differential scanning calorimetry analysis has been traditionally used to determine the LDPE content, but the result can have significant error due to several limitations. Due to co-crystallization, significant error can also result using temperature rising elution fractionation technique. In principle, the LDPE content would be determined by 13 C NMR analysis if the short-chain branch (SCB) content of the LDPE could be determined accurately. But unambiguous assignment of all peaks in the 13 C NMR spectrum of a LDPE is difficult, if possible. Consequently, the SCB content of LDPE cannot be determined accurately. Therefore, a new approach is required to analyze the LDPE/LLDPE blend composition by 13 C NMR on a routine basis. In this paper, a robust 13 C NMR method to determine the LDPE content in LDPE/LLDPE blends is presented. By identifying unique LDPE peaks in the 13 C NMR spectrum of a LDPE/LLDPE blend compared to that of LLDPE, the blend composition can be determined. The accuracy and precision of this method will also be discussed.

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Section: Introductionmentioning

confidence: 99%

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Monwar

2020

Macromolecular Symposia

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“…Despite being one of the most important LLDPEs, it is impossible to measure saturated chain ends in EO with 1 H NMR as the signals from EO side chain overlap with signals from the chain end. Halogenated naphthalenes were identified as good solvents to separate 13 C NMR signals of EO side chain from saturated chain end . However, sensitivity is an issue as the concentration of polyolefin saturated chain ends is generally very low.…”

Section: Resultsmentioning

confidence: 99%

“…Halogenated naphthalenes were identified as good solvents to separate 13 C NMR signals of EO side chain from saturated chain end. 16 However, sensitivity is an issue as the concentration of polyolefin saturated chain ends is generally very low. It is necessary to further enhance the 13 C sensitivity beyond the 5.5× factor afforded by the cryoprobe itself [compared with a conventional broadband observe (BBO) probe] in order to measure the polyolefin saturated chain ends.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…These products focused on 3–5 mm cryoprobes with an upper temperature limitation of 80 °C and were mainly used in biological research. , In 2007, a high-temperature 10 mm C/H cryoprobe, capable of reaching 135 °C, was developed by Bruker . This type of cryoprobe has been extensively used for 13 C and 1 H NMR characterization of polyolefins, − with over 100 US patents granted using data generated with these cryoprobes. − In order to meet the diversifying needs of polyolefin and hybrid polyolefin studies, a multinuclear (C–Si–N–P/H) 10 mm high-temperature cryoprobe was recently developed.…”

Section: Introductionmentioning

confidence: 99%

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Polyolefin Analyses with a 10 mm Multinuclear NMR Cryoprobe

Zhou¹,

Kuemmerle

Rau³

et al. 2020

Anal. Chem.

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Polyolefins are important and broadly used materials. Their molecular microstructures have direct impact on macroscopic properties and dictate end-use applications. 13 C NMR is a powerful analytical technique used to characterize polyolefin microstructures, such as long-chain branching (LCB), but it suffers from low sensitivity. Although the 13 C sensitivity of polyolefin samples can be increased by about 5.5 times with a cryoprobe, when compared with a conventional broadband observe (BBO) probe, further sensitivity enhancement is in high demand for studying increasingly complex polyolefin microstructures. Toward this goal, distortionless enhancement by polarization transfer (DEPT) and refocused insensitive nuclei enhanced by polarization transfer (RINEPT) are explored. The use of hard, regular, and new short adiabatic 180°1 3 C pulses in DEPT and RINEPT is investigated. It is found that RINEPTs perform better than DEPTs and a sensitivity enhancement of 3.1 can be achieved with RINEPTs. The results of RINEPTs are further analyzed with statistics software JMP and recommendations for optimal usage of RINEPTs are suggested. An example of analyzing saturated chain ends in an ethylene−octene copolymer sample with a hard 180°1 3 C RINEPT pulse is demonstrated. It is shown that the experimental time can be further reduced in half because of faster proton relaxation, where the total experimental time is about 580 times shorter when compared to using a conventional method and a 10 mm BBO probe. A naturally abundant nitrogen-containing polyolefin is analyzed using 1 H− 15 N HMBC and, to our knowledge, is the first 1 H− 15 N HMBC presented in the field of polyolefin characterization. The relative amount of similar nitrogen-containing structures is quantified by two-dimensional integration of 1 H− 15 N HMBC. Two pragmatic technical challenges related to using high-sensitivity NMR cryoprobes are also addressed: (1) A new 1 H decoupling sequence Bi_Waltz_65_256pl is proposed to address decoupling artifacts in 13 C{ 1 H} NMR spectra which contain a strong 13 C signal with a high signal-to-noise ratio (S/N). (2) A simple pulse sequence that affords zero-slope spectral baselines and quantitative results is presented to address acoustic ringing that is often associated with high-sensitivity cryoprobe use.

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“…13 C NMR spectroscopy has been extensively used to characterize polyolefin microstructures, such as SCB and LCB. Such an SCB analysis can typically be done in 20–30 min with 200 mg of polymer when using 10 mm high-temperature cryoprobe technology. − …”

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confidence: 99%

Analyses of Short Chain Branches in Polyolefins with Improved ¹H NMR Spectroscopy

Zhou¹,

Paradkar²,

Cong³

et al. 2020

Anal. Chem.

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Polyolefin microstructures, for example, short chain branching (SCB) and short chain branch distribution (SCBD), have a direct impact on properties and thus ultimately influence end-use applications. The 1 H NMR approach to analyze SCB and SCBD is particularly useful when only a limited amount of sample is available, for example, polyolefin film layers or the fractions from polyolefin separation techniques, such as gel permeation chromatography (GPC), crystallization elution fractionation (CEF), high temperature liquid chromatography (HTLC), and thermal gradient interaction chromatography (TGIC). In this paper, we discuss the best approach to find a good decoupling frequency and propose an improved 1 H pulse sequence with homonuclear decoupling for better measuring SCB. With this new pulse it is possible to reach a S/N of 10 (level of quantification) for the methyl signal from SCB in an ethylene−hexene copolymer (EH, 3.6 mol % H) in 3.5 min with 0.5 μg of sample. We also show an easy method to calculate SCB/1000C and demonstrate the proper use of heteronuclear single quantum coherence (HSQC) to measure SCB in a complicated system. A very quick approach to examine the presence of a small amount of LDPE in a polyolefin sample is also suggested, which can reduce NMR acquisition time from a couple of days to a few minutes.

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Long-Chain Branch Measurement in Substantially Linear Ethylene Polymers by ¹³C NMR with Halogenated Naphthalenes as Solvents

Cited by 16 publications

References 34 publications

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Polyolefin Analyses with a 10 mm Multinuclear NMR Cryoprobe

Analyses of Short Chain Branches in Polyolefins with Improved ¹H NMR Spectroscopy

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Long-Chain Branch Measurement in Substantially Linear Ethylene Polymers by 13C NMR with Halogenated Naphthalenes as Solvents

Cited by 16 publications

References 34 publications

Determination of the Composition of LDPE/LLDPE Blends via 13C NMR

Determination of the Composition of LDPE/LLDPE Blends via 13C NMR

Polyolefin Analyses with a 10 mm Multinuclear NMR Cryoprobe

Analyses of Short Chain Branches in Polyolefins with Improved 1H NMR Spectroscopy

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Product

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Long-Chain Branch Measurement in Substantially Linear Ethylene Polymers by ¹³C NMR with Halogenated Naphthalenes as Solvents

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Determination of the Composition of LDPE/LLDPE Blends via ¹³C NMR

Analyses of Short Chain Branches in Polyolefins with Improved ¹H NMR Spectroscopy