Short Chain Branching Research Articles

Rheological properties of high-density polyethylene/linear low-density polyethylene and high-density polyethylene/low-density polyethylene blends

In this work, the effect of the linear low-density polyethylene (LLDPE) containing 1-butene or 1-hexene α-olefin short-chain branching (SCB) and low-density polyethylene (LDPE) containing long-chain branching (LCB) on the rheological properties of high-density polyethylene (HDPE)/LLDPE and HDPE/LDPE blends was investigated. The neat polymers and the blends were characterized by torque rheometry and rheological measurements under dynamic oscillatory shear flow. From torque rheometry analysis, an increase in the viscosity of HDPE/LLDPE blends with the increase in LLDPE content was observed. The inverse was observed for HDPE/LDPE blend, where the viscosity decreased with the increase in the LDPE content. Rheological measurements showed an increase in the complex viscosity of the HDPE/LLDPE and HDPE/LDPE blends with the increase in the LLDPE or LDPE content. HDPE/LDPE blends showed a strong shear-thinning behavior due to the presence of LCB in LDPE. Similar rheological behavior was observed for HDPE/LLDPE blends containing 1-butene and 1-hexene SCB. Cole–Cole, Han plots, and van Gurp–Palmen plots indicated miscibility between HDPE and LLDPE and immiscibility between HDPE and LDPE.

Organic Versus Inorganic Supports for Metallocenes: The Influence of Rigidity on the Homogeneity of the Polyolefin Microstructure and Properties

A procedure to obtain very uniform polyolefin copolymers by supported metallocenes is presented. Conventional metallocene or Ziegler–Natta catalysts, both immobilized on inorganic supports, yield only copolymers with inhomogeneous comonomer incorporation and broad short-chain branching distribution. The main reasons are diffusional limitations of the monomers or the multisite character of the catalysts. By comparing inorganic and organic supports, we demonstrate that metallocenes immobilized on organic supports solve these problems. In this regard, organic and soft nanosized polystyrene particles (nPS) versus industrially used, hard, and inorganic SiO₂ were used to support [Me₂Si(Ind)₂ZrCl₂/MAO (I) and Me₂Si(Benz[e]-Ind)₂ZrCl₂/MAO (BI)] catalysts for ethylene/1-hexene copolymerization. In the inorganic case, the catalyst systems show a substantial inconsistency in the copolymers’ branching distribution, resulting in phase separation. One phase is hexene-poor with high melting temperature (Tₘ) and high molecular weight (MW). The second, hexene-rich phase, however, shows lower Tₘ and MW. By using organic supports, comonomers are uniformly inserted into the polymer chain and homogeneous microstructured copolymers are obtained. These findings are mainly attributed to diffusion processes of the monomers into the soft organic material. To prove this conclusion and to elucidate the structure of the catalyst system, various characterization techniques such as time-of-flight secondary ion mass spectrometry and scanning electron microscopy–energy-dispersive X-ray were performed.

Modeling short-chain branched polyethylenes in dilute solution under variable solvent quality conditions: Basic configurational properties

We perform molecular dynamics (MD) simulations of a coarse-grained model of linear low-density polyethylenes (LLDPEs) having short-chain branching in an implicit solvent and calculate basic configurational properties (radius of gyration Rg, hydrodynamic radius Rh, and intrinsic viscosity [η]) using the path-integration program ZENO. Solvent quality effects in our model are accounted for through the introduction of an attractive polymer-polymer interaction potential with solvent quality “strength” λ that is tuned from a “good” solvent limit, where the inter-polymer interactions are purely repulsive, to a “very poor” solvent regime, where the polymers collapse due to their self-attractive intermolecular interactions. We also identify a compensation condition or “θ point” in our model between these limits, where the polymers are “ideal” in the sense in which attractive interactions effectively nullify inter-polymer repulsions so that the chains behave akin to Gaussian polymer chains in their average conformational properties. In order to compare with experiments performed under variable solvent conditions, we define a dimensionless measure of excluded volume interaction parameter δ in terms of the mass scaling exponent ν for Rg or νh for Rh, which can be determined from both experiment and simulation. We illustrate our variable solvent approach to estimate polymer solution properties in the case of polyethylenes (PEs) and evaluate the δ value that corresponds to the experimental solvent conditions. Our combined use of MD and ZENO allows for the numerical estimation of polymer solution properties for polymers having general monomer structures and solvent qualities in a computationally tractable fashion and should be useful as a general computational tool for polymer structural characterization.

Molecular dynamics simulation of extension-induced crystallization of branched bimodal HDPE: Unraveling the effects of short-chain branches.

Bimodal HDPE models were designed for extension-induced crystallization imitating the architecture of industrial bimodal HDPE copolymerized with ethylene and 1-butene, 1-hexene, or 1-octene. Crystallites of bimodal HDPE experienced the emergence of precursors, shish nuclei, and lamellae. The compact conformation of branched polymers impeded the rolling-over, deposition, and folding of chains on the substrate, and thus the formation of nuclei and lamella. Moreover, this retardation was intensified with the rising branch density and length, causing a depression of crystallinity and an increment of tie-chains concentration. Besides, when branches were all located on long chains, the compact conformation enlarged the resistance to the disentanglement of main chains, thus relatively fewer branched long chains were involved in the precursors or nuclei, resulting in the attenuation of lamella formation. Furthermore, for ethyl branched polymers, the coexistent orthorhombic and monoclinic crystallites were built up, and a few expanded monoclinic cells occurred for butyl branches because of the larger butyl reeling into lamella, while hexagonal crystals were created for ethyl/1-hexyl copolymers because of cocrystallization. Additionally, relative to ethyl, larger butyl and hexyl were preferential to be repelled outside crystals to form tie-chains, and hexyl branched polymers acquired relatively fewer tie-chains because of hexagonal eutectoid.

Cr[CH(SiMe3)2]3/SiO2 catalysts for ethene polymerization: The correlation at a molecular level between the chromium loading and the microstructure of the produced polymer

Several spectroscopic techniques have been applied in a concerted way to investigate the local structure and the function of the chromium sites in a series of Cr[CH(SiMe3)2]3/SiO2 catalysts for ethene polymerization that differ in chromium loading and to correlate them with the microstructure of the produced polyethylene (PE). According to previous studies, the density of the produced PE is proportional to the Cr loading: the higher the Cr loading, the lower the PE density, because of an increase in the content of short-chain branching. Here, the nature of the branches and their enchainment in the polymer have been further investigated to determine the different properties of the produced polymers, and the differences detected have been traced back by spectroscopic analysis to the presence of two different types of Cr sites working in tandem: monografted SiOCr[CH(SiMe3)2]2 species that are responsible for ethene oligomerization, and bis-grafted (SiO)2CrCH(SiMe3)2 species that account for ethene homo- and co-polymerization. The relative abundance of the two species depends on the chromium loading. Moreover, we have also found that carbon monoxide selectively poisons the sites responsible for ethene oligomerization, indicating a possible strategy for the fine regulation of the properties of the produced PE.

Structural and Dynamical Characteristics of Short-Chain Branched Ring Polymer Melts at Interface under Shear Flow

We present a detailed analysis of the interfacial chain structure and dynamics of confined polymer melt systems under shear over a wide range of flow strengths using atomistic nonequilibrium molecular dynamics simulations, paying particular attention to the rheological influence of the closed-loop ring geometry and short-chain branching. We analyzed the interfacial slip, characteristic molecular mechanisms, and deformed chain conformations in response to the applied flow for linear, ring, short-chain branched (SCB) linear, and SCB ring polyethylene melts. The ring topology generally enlarges the interfacial chain dimension along the neutral direction, enhancing the dynamic friction of interfacial chains moving against the wall in the flow direction. This leads to a relatively smaller degree of slip () for the ring-shaped polymers compared with their linear analogues. Furthermore, short-chain branching generally resulted in more compact and less deformed chain structures via the intrinsically fast random motions of the short branches. The short branches tend to be oriented more perpendicular (i.e., aligned in the neutral direction) than parallel to the backbone, which is mostly aligned in the flow direction, thereby enhancing the dynamic wall friction of the moving interfacial chains toward the flow direction. These features afford a relatively lower and less variation in in the weak-to-intermediate flow regimes. Accordingly, the interfacial SCB ring system displayed the lowest among the studied polymer systems throughout these regimes owing to the synergetic effects of ring geometry and short-chain branching. On the contrary, the structural disturbance exerted by the highly mobile short branches promotes the detachment of interfacial chains from the wall at strong flow fields, which results in steeper increasing behavior of the interfacial slip for the SCB polymers in the strong flow regime compared to the pure linear and ring polymers.

Influence of Metal-Alkyls on Early-Stage Ethylene Polymerization over a Cr/SiO2 Phillips Catalyst: A Bulk Characterization and X-ray Chemical Imaging Study.

The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co‐catalysts are required to attain activity. Nonetheless, co‐catalysts in the form of metal‐alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring polymer characteristics. The activation mechanism and related polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal‐alkyl co‐catalyst, we can tailor polymer properties around a single Cr/SiO2 Phillips catalyst formulation. Furthermore, we show that these different polymer properties exist in the early stages of polymerization. We have used conventional polymer characterization techniques, such as size exclusion chromatography (SEC) and 13C NMR, for studying the metal‐alkyl co‐catalyst effect on short‐chain branching (SCB), long‐chain branching (LCB) and molecular weight distribution (MWD) at the bulk scale. In addition, scanning transmission X‐ray microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early‐stage PE within one particle cross‐section with high energy resolution and nanometer scale spatial resolution.

Rheology of Crystallizing LLDPE.

Polymer crystallization occurs in many plastic manufacturing processes, from injection molding to film blowing. Linear low-density polyethylene (LLDPE) is one of the most commonly processed polymers, wherein the type and extent of short-chain branching (SCB) may be varied to influence crystallization. In this work, we report simultaneous measurements of the rheology and Raman spectra, using a Rheo-Raman microscope, for two industrial-grade LLDPEs undergoing crystallization. These polymers are characterized by broad polydispersity, SCB and the presence of polymer chain entanglements. The rheological behavior of these entangled LLDPE melts is modeled as a function of crystallinity using a slip-link model. The partially crystallized melt is represented by a blend of linear chains with either free or crosslinked ends, wherein the crosslinks represent attachment to growing crystallites, and a modulus shift factor that increases with degree of crystallinity. In contrast to our previous application of the slip-link model to isotactic polypropylene (iPP), in which the introduction of only bridging segments with crosslinks at both ends was sufficient to describe the available data, for these LLDPEs we find it necessary to introduce dangling segments, with crosslinks at only one end. The model captures quantitatively the evolution of viscosity and elasticity with crystallization over the whole range of frequencies in the linear regime for two LLDPE grades.

Mechanistic insights into the role of starch multi-level structures in functional properties of high-amylose rice cultivars

The multi-level structures of starch (including molecule, crystalline and granular morphology) and functional properties (pasting behavior, gelatinization and in vitro digestion) of starch granules from different rice cultivars were investigated and their relationships were analyzed. At the molecular level, the transgenic rice cultivar RS10 modified by inhibition of starch branching enzyme IIb (SBE IIb) presented significantly higher amylose content (46.7%), longer amylose chains, smaller whole molecular size and higher amount of amylopectin long B3 branch-chains compared to its wild-type line RS10W and the other two regular cultivars. All the rice cultivars showed A-type crystalline structure but the relative crystallinity varied significantly with the lowest in RS10 and the highest in the low-amylose cultivar Chang5. Pearson correlation analysis indicated that the gelatinization temperature and RS content showed significantly positive correlation with amylose content and average amylopectin chain length, but were negatively correlated with short branch-chains in amylopectin (A chains). The gelatinization enthalpy, relative crystallinity, pasting viscosity, and digestion rate and extent were observed showing significantly negative correlation with amylose content and B3 chains. The structure-functionality relationships illustrated the variations in the functional properties among the rice cultivars could be largely attributed to the different starch molecular and crystalline structures. Nonetheless, the highly aggregated compound voluminous granules could also be responsible for the remarkable lower digestion rate and improved RS content in the native starch as observed in the transgenic high-amylose RS10. This work is meaningful for plant breeders to develop rice cultivars with tailored starch functionality and enriched RS content.

Characterization of Polyethylene Branching by Thermal Analysis-Photoionization Mass Spectrometry.

The rising demand for more and more specialized polyethylene represents a challenge for synthesis and analysis. The desired properties are dependent on the structure, but its elucidation is still intricate. For this purpose, we applied thermal analysis hyphenated to single photon ionization mass spectrometry (STA-SPI-MS). The melting and pyrolysis behavior of different types of polyethylene were tracked by DSC and mass loss. Crystallinity and melting point give hints about the branching but are also influenced by the molecular weight distribution. The evolving gas analysis patterns obtained by SPI-MS however, contain specific molecular information about the samples. Shifts in the summed spectra, which can be clearly observed with our technique, result from differently favored degradation reactions due to the respective structure. Pyrolysis gas chromatography mass spectrometry (Py-GC-EI-MS) was used to support the assignment of pyrolysis products. Principal component analysis was successfully applied to reduce the complexity of data and find suitable markers. The obtained grouping is based on the molecular fingerprint of the samples and is strongly influenced by short-chain branching. Short and medium alkenes and dienes have the strongest impact on the first four principal components. Thus, two marker ratios could be defined, which also give a comprehensible and robust grouping. Butene and pentene were the most abundant signals in our set of samples. With STA-PI-MS, a broad range of pyrolysis products can be measured at the same time, possibly extending the range for quantifiable short-chain branches to more than six carbon atoms for PE. Unfortunately, no clear trend between long-chain branching and any grouping was observed. The quite universal and soft single photon ionization enables access to many different compound classes and hence other polymers can be studied.

Long-term mechanical performance of polyethylene pipe materials in presence of carbon black masterbatch with different carriers

In this paper, two types of carbon black (CB) masterbatch with different carriers, i.e. HDPE and LDPE, are used to produce black compounds using three PE100 resins with various short chain branching distributions. Due to difference in short chain branch (SCB) distribution, the used polyethylene resins behave differently in microstructure development and long-term creep behavior. The microstructural analysis using different DSC techniques and rheological measurements revealed more sensitivity of the polyethylene resin with uniform comonomer distribution to the carbon black aggregates and their polymeric carriers. The Full Notched Creep Test (FNCT) was performed to determine the long-term creep performance of the black compounds; it is shown that the sample having more uniform comonomer distribution is more resistant compared to other samples. On the other hand, by addition of carbon black masterbatch, resistance to slow crack growth in samples decreases since carbon black aggregates can act as stress concentration spots in the structure. However, with addition of the masterbatch with LDPE carrier polymer, the reduction of this value in samples is lower compared to one with HDPE carrier. The reason for this observation is that long branches of LDPE polymer enter the structure of lamellae in the PE100 resins, making them more coherent and increasing the number of tie molecules. The samples that are blended with LDPE polymer have a rougher surface, which means linkage between two sides of crack was stronger due to higher entanglement density in these samples. The impact test confirms the same trend as FNCT test, with the sample containing LDPE carrier having higher impact strength.

Mapping the Structure–Property Space of Bimodal Polyethylene Using Response Surface Methods. Part 2: Experimental Investigation of Polymer Microstructure and Yield Estimations

AbstractA proof of concept for a quick and easy determination of polymer microstructure and yield estimations made with dual catalyst systems through optimally designed experiments and response surface methodology has been experimentally established. Acceptable accuracy (predicted R2 > 0.9780) has been achieved on all the primary target responses (blend molar masses and short chain branching). These primary responses are further deconvoluted into underlying Flory distributions for resolution into component properties and subsequently modeled and predicted accurately (predicted R2 = 0.7440 to 0.9897) for a given set of polymerization conditions. These models are also used to explore their ability to be used for polymerization kinetics evaluation using uptake curves for yield responses. Reasonable predictive ability for yield estimation is also observed (predicted R2 = 0.9346). This methodology has the makings of a new simplified exploratory pathway for inexpensive kinetic investigation and product prediction for dual metallocene catalyst systems.

Using Artificial Intelligence Techniques to Design Ethylene/1‐Olefin Copolymers

AbstractFour global optimization techniques, genetic algorithm, particle swarm, improved ant colony, and modified artificial bee colony, are compared to find alternative polymerization conditions to make ethylene/1‐olefin copolymers with targeted microstructures and polymerization yields. The polymer microstructure targets are divided in three groups: 1) molecular weight distribution, chemical composition distribution, and polymer yield; 2) number and weight average molecular weights, average comonomer content, and polymer yield; and 3) molecular weight distribution, short chain branching distribution, and polymer yield. The modified artificial bee colony optimization generated the fewest number of incorrect solutions, while the polymer microstructure target group 1 generated the most successful solutions.

Molecular Structure, Phase Composition, Melting Behavior, and Chain Entanglements in the Amorphous Phase of High-Density Polyethylenes

A methodology for estimating the entanglement density in the amorphous phase of semicrystalline polyolefins was developed. The method is based on the analysis of the density of physical network junctions in the amorphous phase by 1H NMR T2 relaxation experiments. The density of the entanglement network was estimated for melt- and high-pressure-crystallized high-density polyethylenes (HDPEs) at temperatures close to and gradually approaching melting. Its value is lower for high-pressure-crystallized HDPE than for the same melt-crystallized polymer. The network of entanglements is characterized by the fraction of entangled network chains, the weight-average molecular weight of the network chains between apparent chain entanglements, Me, and the volume average density of apparent chain entanglements. The entanglement network was studied in a series of low- and high-molecular-weight HDPEs and bimodal HDPE samples with different molecular weight characteristics and densities controlled by different contents of the 1-butene comonomer. It turns out that the molecular weight characteristics of the HDPEs influence the entanglement network. The fraction of network chains and the average density of apparent chain entanglements decrease with decreasing molecular weight Mn due to the “dilution” effect caused by disentangled chain-end segments increasing the Me. The current methodology is of interest for studying the effect of crystallization conditions, molecular structures, and short-chain branches on phase composition, melting behavior, and chain entanglements in the amorphous phase of polyolefins. The method allows estimation of the fraction of network chains, which potentially can form tie-chain segments during deformation. The effect of short-chain branches and molecular weight characteristics on the creep response of polyolefins is discussed.

Co‐Monomer Type Influence on the Physical and Optical Properties of High Density Polyethylene Synthesized by Chrome Catalyst

AbstractHigh‐density polyethylene (HDPE) with similar density and Melt Index (MI) is synthesized by using a chrome‐based catalyst with different co‐monomers, 1‐hexene (HDPE‐H) and 1‐butene (HDPE‐B). Both samples have a density of 0.955 g cm−3 and MI of 0.1 g per 10 min. The same density and MI have been chosen to minimize the variable that can affect the test result. Different co‐monomers will generate different short‐chain branching (SCB) which will affect the microstructure of polymer, as well as both physical and optical properties. Physical properties are evaluated such as dart drop impact, film impact, tensile strength, and elongation. Optical properties such as gloss and haze are also evaluated. Physical properties tend to have a better result along with the length of SCB. Meanwhile, the optical properties have a better result when the SCB is shorter. The result of the study exhibits that the type of co‐monomer in HDPE affects the quality of the film in terms of physical and optical properties.

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

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 1H 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 1H 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.

Effects of nitrogen fertilizer on structure and physicochemical properties of ‘super’ rice starch

Nitrogen fertilizer is an essential nutrient for rice (Oryza sativa L.), especially, for newly bred ‘super’ rice cultivars with great yield potential. The effects of nitrogen fertilizer (0, 100, 200, 300, 400 kg N ha−1) on the physicochemical properties of two high yielding ‘super’ rice Yongyou 2640 and Lianjing 7 were investigated in this study. The application of nitrogen fertilizer affects the structure of rice starch, thus changing its functional properties, which ultimately leads to a change in the quality of both rice cultivars. There were dose effects of nitrogen fertilizer on grain quality. Grain quality was improved under moderate nitrogen inputs (100 & 200 kg N ha−1), but deteriorated at excessive nitrogen levels (300 & 400 kg N ha−1). With moderate N application, starch granule size increased and the surface of starch granule became smoother; there were higher proportion of short branch-chain of amylopectin and lower proportion of long branch-chain of amylopectin with low relative crystallinity, lower degree of order of structure and higher content of amorphous structure at the outer region of the starch granules; peak viscosity, hot viscosity, breakdown value were increased while setback and pasting temperature were decreased; gelatinization temperature, gelatinization enthalpy, retrogradation enthalpy, retrogradation percentage, hardness were decreased while viscosity were increased. At excessive nitrogen inputs, the grain quality was deteriorated and the opposite results of structure and physicochemical properties of rice starch were observed. These results indicate that nitrogen fertilizer significantly affected the structure and physicochemical properties of rice starch, and appropriate fertilization would improve rice grain quality.

A New Monte Carlo Simulation of Low-Density-Polyethylene Polymerization for Prediction of its Microstructure as a Result of Various Process Conditions

In the petrochemical industries, a variety of low density polyethylene (LDPE) grades are produced from a single reactor line with changes in process conditions and/or materials. Herein the microstructure parameters, for example, monomer conversion, average molecular weight (), long chain branches (LCB) and short chain branches (SCB), are calculated for various process conditions in the polymerization process such as chain transfer agent (CTA) type and concentration, CTA feed position, initiator feed position, temperature profile, and residence time in the reactor, all based on industry data. Our results showed the CTA with a high rate constant makes three times more LCB but decreases the SCB by 13% relative to the CTA with a low rate constant. Also, for the same CTA type, decreased if the CTA concentration was increased. Injection of initiators at the beginning of the process had no significant effect on the SCB but increased the LCB by 54%. The new equations presented here to predict the microstructure of LDPE produced in tubular reactors resulted in good agreement with reported experimental values. The equations advantage is that the industrial data of the LDPE polymerization can be analyzed with high accuracy and speed to obtain the LDPE microstructure.

A Short‐Chain Branching Distribution Determination Technique for Polyethylene Using IR5‐Detected GPC

AbstractIn this paper, a robust short‐chain branching (SCB) determination technique recently developed using IR5‐detected GPC (GPC‐IR5) for polyethylene resins is reported, wherein the IR5 detector is an infrared detector equipped with five filters set at different frequency ranges and a mercury‐cadmium‐telluride detector with thermoelectric cooling capability. Both intensity ratios of methyl/methylene and methyl/all C─H groups have very good linear relationship with the SCB content. Based on these relationships, an excel spreadsheet method is developed to deduce the SCB distribution across the molecular weight distribution using in‐house developed algorithms. The uncertainty of SCB determination using the GPC‐IR5 technique is found to be chromatographic signal‐to‐noise ratio dependent and can be explicitly expressed and calculated slice by slice. The SCB uncertainty is also found to be a function of experimental conditions and environment, which can affect not only the signals but also the noise levels at different IR bands. At a given polymer concentration, the higher the SCB content, the smaller the relative error bars. The SCB detection limit of this GPC‐IR5 technique is found to be at ≈0.5–1.0 SCB per 1000 TC for all samples tested. Some practical aspects for application of this technique are also discussed in this paper.

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

AbstractPolyethylene 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 13C NMR analysis if the short‐chain branch (SCB) content of the LDPE could be determined accurately. But unambiguous assignment of all peaks in the 13C 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 13C NMR on a routine basis. In this paper, a robust 13C NMR method to determine the LDPE content in LDPE/LLDPE blends is presented. By identifying unique LDPE peaks in the 13C 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.