Low Molecular Weight Polymers Research Articles

Glasshouse study of a sprayable, degradable polymer to reduce water use in cotton establishment

This glasshouse pot experiment demonstrated that a new sprayable and degradable polymer reduced soil water evaporation and promoted cotton seedling emergence and establishment. The polymer was tested on two contrasting soils (sandy loam and clay), representative of those used to grow cotton in Australia. Changes in soil water content in non-treated and polymer-treated pots were monitored over 80 days, after surface or subsurface watering. Plant biomass, soil water content and soil chemical properties were determined at harvest. The polymer reduced soil water evaporation by up to 35% in sandy loam and up to 20% in clay, did not compromise seedling emergence and improved plant growth per unit water applied by up to 26.2%. The polymer underwent extensive degradation after 80 days to produce low molecular-weight polymers or oligomers and water-extractable silicon species that may have implications for plant nutrition.

The matrix of SDS integrated with linear hydrophilic polymer for resolution of high- and low-molecular weight hyaluronic acids in MEKC

Hyaluronic acid (HA), a multi-functional material, has a high dispersion in molecular weight, and the functions of HA are determined through the size. Nevertheless, hyaluronic acid mixtures are not easily separated due to their polydispersity. In this study, a capillary electrophoresis strategy was developed for resolution of different molecular-weight HA without enzymatic digestion. Here, hyaluronic acid mixtures with low molecular weight (380 kD; LHA) and high molecular weight (2180 kD; HHA) were successfully resolved by the SDS integrated with low molecular-weight polymer in capillary electrophoresis. By optimizing experimental conditions, the separation of LHA and HHA was completed within 14 min. The optimal conditions were as follows: the running buffer was 25 mM borate buffer (pH 9.75) containing 30 mM SDS and 10% polyethylene glycol (MW: 8000); applied voltage was 20 kV (detector at cathode side) and separation temperature was set at 25 °C. The data of method validation showed that calibration plots were linear (r ≥ 0.9977) over a range of 10–50 μg/mL for LHA, and 40–200 μg/mL for HHA. In the evaluation of precision and accuracy for this method, the RSD and RE values were all less than 4.2%. This fascinating technique was successfully applied to the quality control of cosmetic and pharmaceutical containing different ratios of LHA and HHA, and it was feasible for serving as a tool to quantitatively analyze different sizes of HA for clinical survey.

Thermal gelation of partially hydrolysed polyacrylamide/polyethylenimine mixtures using design of experiments approach

Polyethylenimine crosslinked polymer gels are gaining a huge interest in conformance control applications in oilfields. They are used to reduce the production of undesirable fluids (water & gas) by blocking the fractures that connect injection and production wells. In this paper, a statistical analysis on the thermal gelation of well characterized reactants namely partially hydrolysed polyacrylamide (PHPA) (Mw = 5.1 million Daltons and hydrolysis degree = 6%) and polyethylenimine (PEI) (Mw = 19.2 kilo Daltons and branching degree = 59%), was conducted using response surface methodology (RSM). A four factor doehlert matrix was employed in designing the experiments and evaluating the gelation time as function of salinity (0–8 g/L NaCl), polymer (PHPA) and crosslinker (PEI) concentrations, temperature (70 °C–90 °C) and their corresponding combinations. As a result, the gelation time was found to strongly vary with salinity, temperature and PHPA concentration following a nonlinear mathematical model. The analysis of variance (ANOVA) of this model revealed its significance in a 95% confidence level against experimental data. In a second part, an experimental investigation was carried out to understand the interaction between PHPA and PEI. To do so, the viscosity variations of analogue mixtures prepared with low molecular weight (Mw) polymers, such as polyacrylamide (PAM) and polyacrylic acid (PAA), were monitored using capillary viscometry at different conditions of temperature, pH and reaction time. The PAM/PEI mixtures showed a remarkable viscosity increase at typical pH of around 10 when cured at 80 °C. While, the PAA/PEI mixtures underwent precipitation at pH of around 6 revealing the strong interaction between PAA and PEI at this condition.

Michael addition in reactive extrusion: A facile sustainable route to developing phosphorus based flame retardant materials

This study addresses three very important aspects of sustainable development of new flame re-tardant material, i.e. in situ solvent free synthesis of flame retardant macromolecules during thermal processing of polymers, their leaching behavior from the polymer matrix and their preliminary toxicity assessment. Polyamide 6 (PA6) was functionalized by a novel reactive extrusion process. In situ synthesis of phosphine oxide based macromolecules was obtained via Michael addition reaction of divinyl phenyl phosphine oxide (DVPPO) and piperazine during the reactive extrusion process. The formation of phosphine oxide macromolecules (oligomers and low molecular weight polymers) were confirmed by NMR study of the modified PA6 polymer and UPLC-MS analysis of extracts from PA6 samples. Elemental analysis of the modified PA6 after the extraction with chloroform and water confirmed retention of majority of phosphorus species, confirming the beneficial effect of large macromolecular additives. This non-leaching behavior of modified PA6 is an important requirement for thin walled substrates like fibers and films where long-term durability is very important. The reactive extruded PA6 was successfully processed into textile fibers via melt spinning process in a laboratory spinning plant. The presence of phosphine oxide macromolecules in PA6 matrix had a lubricating effect, which has influence in the thermal processing and final properties of the fiber. The modified PA6 was evaluated for fire performance in small-scale fire tests where it showed improved fire performance. Moreover, the preliminary toxicity assessment of the relatively unknown DVPPO, via a well-established in vitro platform showed no adverse effects on cell viability.

Possibility of artocarpus heterophyllus latex as an alternative source for natural rubber

Abstract Natural rubber (NR) has much application in rubber product manufacturing industries, which cannot be replaced by synthetic rubber. At present, Hevea rubber tree is the only economical and commercially viable source of NR. Therefore, the objective of the present research was to find alternative source of NR. NR mainly comprise of cis-1,4 polyisoprene. Artocarpus heterophyllus latex (jackfruit latex) was collected and analyzed to investigate if it can be considered as alternative source of NR. It was found from FTIR, 1H NMR and GC-MS study that jackfruit latex contains both cis-1,4 polyisoprene and trans- 1,4 polyisoprene along with few other chemical constituents. However, molecular weight of jackfruit latex is significantly lower than the NR. Because of low molecular weight polymer and presence of several other chemical constituents as impurity, jackfruit latex does not impart significant mechanical properties in vulcanized rubber compound, but it provides additional wet skid resistance (WSR) and aid in better dispersion of carbon black in rubber compound. Therefore, jackfruit latex cannot be used to replace NR, but can be used as low molecular weight natural resin, especially to improve dispersion of carbon black in rubber compound and to enhance WSR for tire.

Factors affecting fractal patterns obtained by electroless deposition in polymer

Electroless deposition of silver has been studied experimentally in a polymer (chitosan) with different molecular weight (∼50 000–190 000 Da and ∼600 000 Da). Transport of ions in polymers involves various dynamical processes having different time scales. The time scale of ion dynamics depends on the number of monomer chains in the polymer, i.e., the molecular weight of the polymer. Polymers of high molecular weight contain regular arrangement of long chains of monomers which generally leads to high crystallinity. Copper, zinc and aluminum wires have been used for different reaction rates in the polymer-Ag salt solution. Anisotropy of the polymer-salt solution varies due to the change in the ion dynamics in high molecular weight polymer as compared to the low molecular weight polymer. Varying anisotropy leads to different aggregation patterns around the reactive metal wires. X-ray diffraction has been performed to determine the crystallinity while the voltage-time measurement has been done to validate the aggregation process. Effect of air exposure/oxidation on the growth patterns has also been considered as the adsorption of oxygen ions changes with the change in the crystallinity of the polymer.

Applications of Algal Polysaccharides and Derivatives in Therapeutic and Agricultural Fields.

Recently, researchers have given more and more consideration to natural polysaccharides thanks to their huge properties such as stability, biodegradability and biocompatibility for food and therapeutics applications. a number of enzymatic and chemical processes were performed to generate bioactive molecules, such as low molecular weight fractions and oligosaccharides derivatives from algal polysaccharides. These considerable characteristics allow algal polysaccharides and their derivatives such as low molecular weight polymers and oligosaccharides structures to have great potential to be used in lots of domains, such as pharmaceutics and agriculture etc. Conclusion: The present review describes the mains polysaccharides structures from Algae and focuses on the currents agricultural (fertilizer, bio-elicitor, stimulators, signaling molecules and activators) and pharmaceutical (wound dressing, tissues engineering and drugs delivery) applications by using polysaccharides and/or their oligosaccharides derivatives obtained by chemical, physical and enzymatic processes.

Thermal, Mechanical Properties and Rheological Behavior of Poly(Propylene Carbonate)/Poly(Ethylene Glycol)/Graphene Oxide Nanocomposites

Graphene oxide (GO) is an efficient nanofiller for polymers and a good dispersion of GO in polymer matrix is most important to enhance properties. Poly(propylene carbonate) (PPC)/GO nanocomposite was prepared by a method with solution blending and melt mixing for improvement of GO dispersion. First, GO was prepared using an improved Hummers method. In the solution blending, GO was well dispersed in water and another low molecular weight polymer, poly(ethylene glycol) (PEG), was also dispersed in water, as a dispersion medium for next melt mixing of PPC and GO. Then PPC and PEG/GO was melt-mixed in a HAAKE mixer. The dispersion of GO in PPC matrix and effect of GO content on properties of PPC/PEG/GO nanocomposites was investigated. Results show that tensile strength of nanocomposites with the content of 0.5 wt% GO increased from 17.51 MPa (pure PPC) to 21.61 MPa and elongation at break can be kept high. The complex viscosity, storage and loss modulus is the highest for nanocomposites with the content of 0.5 wt% GO. This illustrated that a lower content of GO can improve the properties of PPC, owing to the good dispersion of GO in PPC matrix. Based on dispersion of GO and chemical structure of PPC, PEG, and GO, the reinforcement mechanism of GO in PPC was analyzed.

A scientific report on the flow of Maxwell fluid with heat transfer in vertical oscillating cylinder

The nonlinear nature of viscoelastic non-Newtonian fluids, introduce a unique challenge to physicists and mathematicians. By developing and utilizing viscoelastic models can play a special role in saving and treatments of every living species and to describe its particular characteristics. In the past three decades, viscoelastic fluid models are focused to improve its accuracy and reliability. Some rate type viscoelastic fluids include Maxwell fluid which effects in relaxation time. Such effect of relaxation time cannot be predicted by differential-type fluids. The polymers of low molecular weight are usefully described by Maxwell model. However, a keen interest of the researchers is seen in studying rate type fluids due to the fact that they incorporate both the elastic nature and memory behaviour together. In this article, viscoelastic Maxwell fluid is considered in cylindrical tube together with heat transfer due to convection caused by the buoyancy force. This problem is modelled using the classical approach and then solved for exact solution using joint the Laplace and Hankel transforms. Effects of pertinent parameters on Maxwell fluid velocity have been shown graphically. Behaviour of temperature is studied for various values of Prandtl number.

Mechanical formation of micro- and nano-plastic materials for environmental studies in agricultural ecosystems

Release of microplastics (MPs) and nanoplastics (NPs) into agricultural fields is of great concern due to their reported ecotoxicity to organisms that provide beneficial service to the soil such as earthworms, and the potential ability of MPs and NPs to enter the food chain. Most fundamental studies of the fate and transport of plastic particulates in terrestrial environments employ idealized MP materials as models, such as monodisperse polystyrene spheres. In contrast, plastics that reside in agricultural soils consist of polydisperse fragments resulting from degraded films employed in agriculture. There exists a need for more representative materials in fundamental studies of the fate, transport, and ecotoxicity of MPs and NPs in soil ecosystems. The objective of this study was therefore to develop a procedure to produce MPs and NPs from agricultural plastics (a mulch film prepared biodegradable polymer polybutyrate adipate-co-terephthalate (PBAT) and low-density PE [LDPE]), and to characterize the resultant materials. Soaking of PBAT films under cryogenic conditions promoted embrittlement, similar to what occurs through environmental weathering. LDPE and cryogenically-treated PBAT underwent mechanical milling followed by sieve fractionation into MP fractions of 840 μm, 250 μm, 106 μm, and 45 μm. The 106 μm fraction was subjected to wet grinding to produce NPs of average particle size 366.0 nm and 389.4 nm for PBAT and LDPE, respectively. A two-parameter Weibull model described the MPs' particle size distributions, while NPs possessed bimodal distributions. Size reduction did not produce any changes in the chemical properties of the plastics, except for slight depolymerization and an increase of crystallinity resulting from cryogenic treatment. This study suggests that MPs form from cutting and high-impact mechanical degradation as would occur during the tillage into soil, and that NPs form from the MP fragments in regions of relative weakness that possess lower molecular weight polymers and crystallinity.

Monte Carlo simulation of molecular and structural properties of mono- and bi-dispersed poly(ethylene oxide) nanofibers

Molecular and structural properties of poly(ethylene oxide), PEO, nanofibers with different diameters and molecular weights were investigated using Monte Carlo simulation of coarse-grained models on high coordination lattice. PEO nanofibers made up of mono- and bi-dispersed chains of CH3-(OCH2CH2)x-OCH3 where x = 13 to 53, with diameter ranged from 7.4 to 16.4 times the radius of gyration of PEO chains, were analyzed. For mono-disperse chains, as a result of increasing molecular weight, the bulk density increases and the molecular size at the surface is decreased more than the nanofibers composed of shorter chain length. There is higher degree of parallel orientation of the chains and bonds at the surface and a broader region over which this bond orientation pertains. For nanofibers with mixed molecular weight, shorter chains tend to segregate at the surface and the density of short chain component is higher in this region. Compared to mono-disperse nanofibers, the properties of longer chains do not significantly change, whereas the orientation of chains and bonds for low molecular weight polymers become more anisotropic orientation in the presence of longer chains.

The Dispersion Composition of Polymethylmethacrylate Suspensions and Molecular Weights of Polymers Obtained by Suspension Polymerization in the Presence of Acrylic Copolymers as Surfactants

The dispersion composition of polymer suspensions and molecular weights of polymers obtained by suspension polymerization of MMA in the presence of polymer surfactants – methylmethacrylate and methacrylic acid copolymers – were studied. It is shown that a highly dispersed fraction of particles with diameters of 0.02–2.0 µm and a fraction of particles with large diameters (up to 1000 µm) are always present in the polymer suspension. After fractionation of polymer suspensions 3 fractions of particles with different diameters were obtained. For each particle fraction the molecular masses of polymers were determined by viscometry. A significant difference in the values of the molecular masses of polymers obtained as particles of small and large diameters – 105 and 106 Da, respectively – is shown. The presence of a highly dispersed fraction of particles in which a polymer of high molecular weight is formed has a noticeable effect on the average molecular weight of the polymer. In particles of small diameter polymerization takes place according to a mechanism close to the emulsion, due to the fact that the volume of such particles contains a small amount of radicals. The high rate of polymerization leads to the formation of a polymer of high molecular weight, the appearance of a gel effect and a decrease in the termination constant. In most particles, polymerization proceeds by a mechanism close to the solution polymerization, and polymers of low molecular weight are formed. This makes it possible to synthesize polymers of a given molecular weight in drops of certain dispersity.

Dissecting the Dual Nature of Hyaluronan in the Tumor Microenvironment.

Hyaluronan (HA) is a glycosaminoglycan with a simple structure but diverse and often opposing functions. The biological activities of this polysaccharide depend on its molecular weight and the identity of interacting receptors. HA is initially synthesized as high molecular-weight (HMW) polymers, which maintain homeostasis and restrain cell proliferation and migration in normal tissues. These HMW-HA functions are mediated by constitutively expressed receptors including CD44, LYVE-1, and STABILIN2. During normal processes such as tissue remodeling and wound healing, HMW-HA is fragmented into low molecular weight polymers (LMW-HA) by hyaluronidases and free radicals, which promote inflammation, immune cell recruitment and the epithelial cell migration. These functions are mediated by RHAMM and TLR2,4, which coordinate signaling with CD44 and other HA receptors. Tumor cells hijack the normally tightly regulated HA production/fragmentation associated with wound repair/remodeling, and these HA functions participate in driving and maintaining malignant progression. However, elevated HMW-HA production in the absence of fragmentation is linked to cancer resistance. The controlled production of HA polymer sizes and their functions are predicted to be key to dissecting the role of microenvironment in permitting or restraining the oncogenic potential of tissues. This review focuses on the dual nature of HA in cancer initiation vs. resistance, and the therapeutic potential of HA for chemo-prevention and as a target for cancer management.

Universal behavior of the apparent fragility in ultraslow glass forming systems

Despite decades of studies on the grand problem of the glass transition the question of well-defined universal patterns, including the key problem of the previtreous behavior of the primary (structural) relaxation time, remains elusive. This report shows the universal previtreous behavior of the apparent fragility, i.e. the steepness index mP (T > Tg) = d log10τ(T)/d( Tg/T). It is evidenced that mP(T) = 1(T − T*), for T → Tg and T*= Tg − Δ T*. Basing on this finding, the new 3-parameter dependence for portraying the previtreous behavior of the primary relaxation time has been derived: τ(T) = CΩ((T − T*)/T)−Ω × [exp((T − T*)/T)]Ω. The universality of obtained relations is evidenced for glass formers belonging to low molecular weight liquids, polymers (melt and solid), plastic crystals, liquid crystals, resins and relaxors. They exhibit clear preferences either for the VFT or for the critical-like descriptions, if recalled already used modeling. The novel relation can obey even above the dynamic crossover temperature, with the power exponent Ω ranging between ~17 (liquid crystals) to ~57 (glycerol), what may indicate the impact of symmetry on the previtreous effect. Finally, the emerging similarity to the behavior in the isotropic phase of nematic liquid crystals is recalled.

Связь между хроническим воспалением и развитием мастоцитомы у шарпеев

This article is devoted to the study of the connection between autoinflammatory disease and the development of a mast cell tumor on the example of Shar-Pei. The HAS2 gene, which is responsible for the synthesis of hyaluronic acid, in Shar-Pei has an increased expression due to which hyaluronic acid accumulates in the dermis, forming breed-defining skin phenotype — thik skin folds. It became known that hyaluronic acid is involved in immune reactions. Under normal conditions, it is in the high molecular weight fraction, but in abundant it begins to fragment into low molecular weight polymers interacting with the membranes of mast cells, as an antigen, due to chemical similarity with the microbial surface. Thus, mast cells and other immunocompetent cells initiate the inflammatory process. Therefore, the breed predisposition of Shar-Pei to the accumulation of hyaluronic acid can cause self-inflammatory diseases in dogs. The link with mastocytoma can be traced because hyaluronic acid also affects the proliferation and terminal differentiation of mast cells, interacting with the CD44 co-receptor of c-kit receptor. The KIT gene is marked by researchers as the gene responsible for the active proliferation of mast cells. There were found mutations in the same gene in dogs with a mastocytoma. Perhaps the appearance of hyaluronic acid in chronic inflammation, as well as in the development of mastocytoma indicate the presence of a connection between both pathological processes.

Size-exclusion and the void volume of HPLC column

Size-exclusion chromatography (SEC) is the main technique for determination of polymer molecular weight distribution. SEC elution volumes are limited by column void volume and interparticle volume. Measurements of these volumes at actual size-exclusion conditions is discussed together with the relationship of polymer retention to its hydrodynamic volume. We studied the retention of 32 polystyrene standards with polydispersity below 1.05 on 10 different commercial columns. Nine columns had silica based C18 modified packings, and one, polymer-based packing. Pore sizes of packing materials varied from 8 to 35 nm, and 3 packings were poroshell type. Propagation of the retention dependence on the cubic root of the polymer molecular weight to zero mass value was shown to correspond to the column void volume; and was consistent with other methods of void volume measurement. Observed linear dependencies of retention volumes on for low molecular weight polymers on all studied columns suggests a correlation between the product of the polymer hydrodynamic radius and the adsorbent surface area. This correlation is thoroughly discussed.

Improving the molecular weight and synthesis of a renewable biomimetic adhesive polymer

Renewable materials are in demand to replace the petroleum-based glues we use on a daily basis. Such substitutions will not take place until bio-based adhesives can meet or exceed the performance of current materials. Work presented here examines several chemical parameters in order to improve the molecular weight and synthetic strategy for a polymer that combines polylactic acid with mussel mimicking catechol, (“catechol-PLA”). Altering the polymerization time as well as the deprotection time and temperature afforded better control over both molecular weights and yields. Dispersity and molecular weight were shown to both be parameters tunable to improve adhesion strength. Cross-linking with iron improved the adhesion of low molecular weight polymers, bringing performance up to that of the longer chain counterparts. Such cross-linking and molecular weight effects were seen to alter the balance of adhesive and cohesive interactions. Such development and understanding of renewable polymer systems may help to hasten future competition with petroleum-based adhesives.

Polymer nanodiscs: Advantages and limitations.

There is considerable interest in the development of membrane mimetics to study the structure, dynamics and function of membrane proteins. Polymer nanodiscs have been useful as a membrane mimetic by not only providing a native-like membrane environment, but also have the ability to extract the desired membrane protein directly from the cell membrane. In spite of such great potential, polymer nanodiscs have their disadvantages including lack of size control and instability at low pH and with divalent metals. In this review, we discuss how these limitations have been overcome by simple modifications of synthetic polymers commonly used to form nanodiscs. Recently, size control has been achieved using an ethanolamine functionalization of a low molecular weight polymer. This size control enabled the use of polymer-based lipid-nanodiscs in solution NMR and macro-nanodiscs in solid-state NMR applications. The introduction of quaternary ammonium functional groups has been shown to improve the stability in the presence of low pH and divalent metal ions, forming highly monodispersed nanodiscs. The polymer charge has been shown to play a significant role on the reconstitution of membrane proteins due to the high charge density on the nanodisc's belt. These recent developments have expanded the applications of polymer nanodiscs to study the membrane proteins using wide variety of techniques including NMR, Cryo-EM and other biophysical techniques.

Employing Heterocyclic Hypervalent Iodine Compounds with ICl Bonds as Initiators and Chain Transfer Agents in the Synthesis of Branched Polymers

AbstractHeterocyclic hypervalent (HV) iodine(III) compounds with ICl bonds and various substituents at the N atom are synthesized and found to be very efficient chain transfer agents in the polymerization of styrene with transfer coefficients exceeding that of CCl4 by 2–3 orders of magnitude, depending on the structure. The chain transfer rate coefficients are also determined. Due to the presence of thermally labile HV bonds, the compounds degrade homolytically upon heating and can initiate radical polymerization. For instance, 1‐chloro‐2‐hexyl‐1,2‐benziodazol‐3(2H)‐one, is used in the polymerization of styrene, which yields low molecular weight polymers with alkyl chloride groups at the α‐ (initiation) and the ω‐chain ends (transfer). Chain‐end functionalization reactions with azide and chain extension under low‐catalyst‐concentration atom transfer radical polymerization (ATRP) conditions of the prepared telechelic polymers are carried out. The same initiator/chain transfer agent is successfully employed in the synthesis of highly branched polymers with multiple alkyl chloride‐type chain ends when added to mixtures of styrene and 1,4‐divinylbenzene containing 10–80 mol% of the divinyl crosslinker, or even pure crosslinker. In all cases, soluble hyperbranched polymers are obtained up to moderate monomer conversions. The effects of crosslinker and HV iodine(III) compound concentrations on the polymerization outcome are studied systematically.

Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity.

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II) chlorides (aryl = 2,6-Me2C6H3Fe1; 2,6-Et2C6H3Fe2; 2,6-i-Pr2C6H3Fe3; 2,4,6-Me3C6H2Fe4; and 2,6-Et2-4-Me2C6H2Fe5) have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione, FeCl2·4H2O, and the appropriate aniline in acetic acid. All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy. In addition, the structure of Fe3 has been determined by single crystal X-ray diffraction, which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six- and seven-membered carbocycles to be cis-configured. In combination with either MAO or MMAO, Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization (up to 15.86 × 106 g(PE) mol−1 (Fe) h−1 at 40°C (MMAO) and 9.60 × 106 g(PE) mol−1 (Fe) h−1 at 60°C (MAO)) and produced highly linear polyethylene (HLPE, Tm ≥ 128°C) with a wide range in molecular weights; in general, the MMAO-promoted polymerizations were more active. Irrespective of the cocatalyst employed, the 2,6-Me2-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr2Fe3 the least but afforded the highest molecular weight polyethylene (Mw: 65.6–72.6 kg mol−1). Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40°C showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace (Mw/Mn = 13.4). By contrast, using Fe4/MAO at 60°C a vinyl-terminated polymer of lower molecular weight (Mw = 14.2 kg mol−1) was identified that exhibited a unimodal distribution (Mw/Mn = 3.8). Moreover, the amount of aluminoxane cocatalyst employed, temperature, and run time were also found to be influential on the modality of the polymer.