Broad Molecular Weight Distribution Research Articles

Shear induced crystallization of bimodal and unimodal high density polyethylene

In-situ step-shear experiments by synchrotron X-ray techniques were performed to study shear-induced crystallization of bimodal (BM1) and unimodal (UM1) high-density polyethylene (HDPE). The BM1 sample consisted of a bimodal molecular weight (MW) and composition distribution with the low MW components having less short chain branches (SCBs), or hexene co-monomer, and the high MW components having more SCBs. The average molecular weight of BM1 was higher than that of UM1, where both BM1 and UM1 covered the same molecular weight range. The UM1 sample contained a unimodal but broad molecular weight distribution (MWD) with a constant SCB value between those of the low and high MW components in BM1. Discrete primary and secondary lamellae were found in BM1 and UM1, whereas UM1 exhibited faster secondary lamellar growth. Shear-induced crystallization resulted in higher lamellar orientation in UM1, but higher crystallinity in BM1. The large fraction of medium high MW components in UM1 was found to be effective in crystallization under deformation, leading to stronger shear-induced crystalline orientation.

Pseudo-Homopolymerization Approach To Predict the Molecular Weight Distribution in the Copolymerization via Activator Regenerated by Electron Transfer Atom Transfer Radical Polymerization

An efficient kinetic model based on the pseudo-homopolymerization (PHP) and reduced stiffness by quasi-steady state approximation (RQSSA) methodology is presented to compute the molecular weight distribution (MWD) in the activator regenerated by electron transfer via atom transfer radical copolymerization. The copolymerization of butyl methacrylate and butyl acrylate is taken as basis of the study; validation with the experimental data results in good agreement, and a deviation between the prediction of the Mayo–Lewis equation and the model estimation is presented. The MWD is dependent on the fed monomer composition. A semibatch process with an extra addition of reduced agent resulted in an increased polymerization rate; however, this affects the process control, and a broader MWD is obtained. The computational time expended to compute the MWD is on the order of seconds or minutes, which can be reduced by using a new expression to calculate the bounds of the MWD.

Differences between ab initio emulsion and miniemulsion polymerization of styrene mediated by an alkenyl-functionalized amphiphilic RAFT agent

An alkenyl (butene)-functionalized amphiphilic macromolecular reversible addition fragmentation chain transfer (macro-RAFT) agent was designed as both surfactant and polymerization mediator for ab initio emulsion and miniemulsion polymerization of styrene (St), intending to synthesize polymer nanoparticles with alkenyl-enriched surfaces. However, the pendent alkenyl units exhibited unexpectedly higher reactivity in ab initio emulsion polymerization than they did in solution polymerization. Their copolymerization with St resulted in depletion of alkenyl groups, positive deviation of molecular weights, broad molecular weight distributions, and limiting conversions. Miniemulsion polymerization was superior to ab initio emulsion polymerization in its ability to prepare alkenyl-functionalized nanoparticles. Consumption of alkenyl groups happened, but only within the nucleation period. In spite of positive deviation of molecular weights and broad molecular weight distributions, the final particles were characteristics of alkenyl functionalities confined to the particle surfaces. Thus, PSt nanoparticles with alkenyl-enriched surface were obtained via miniemulsion polymerization.

Ring-opening cryo-polymerization of N-carboxy-α-amino acid anhydride of γ-benzyl l-Glutamate

Ring-opening polymerization (ROP) of N-carboxy-α-amino acid anhydride (NCA) of γ-benzyl l-glutamate (BLG) was investigated under frozen condition for the first time. This cryo-ROP was performed in DMSO or 1,4-dioxane below the freezing point of polymerization mixture. The kinetics was monitored with proton nuclear magnetic resonance spectroscopy and gel permeation chromatography, disclosing the well control over molecular weight, living polymerization features and considerable polymerization rate. Compared with the polymerization proceeded at 30 °C, which showed weak linearity regarding the reaction kinetics and relatively broad distribution of molecular weight, the cryo-ROP exhibited excellent first-order kinetics as well as narrow molecular distribution.

Living Supramolecular Polymerization of DNA.

Recently there have been notable synthetic successes in supramolecular polymerization. By contrast, it has long been known that DNA can undergo supramolecular polymerization (concatemerization). Concatemerization is a step-like polymerization and consequently suffers from broad molecular weight distributions and generally undesirable cyclization reactions. Here we demonstrate that another supramolecular polymerization of DNA, hybridization chain reaction (HCR), is in fact a living polymerization. After consumption of initial monomer, the polymerization can be continued with further addition of monomer, and the molecular weight can be varied by the ratio of monomer to initiator. In contrast to concatemerization, HCR produces polymers with narrow dispersity while avoiding cyclization. Identification of the living character of this supramolecular polymerization presents new opportunities in structural DNA nanotechnology and molecular biology.

A Simple Monte Carlo Method for Modeling Arborescent Polymer Production in Continuous Stirred Tank Reactor

AbstractA dynamic model is developed to simulate arborescent polyisobutylene (arbPIB) production via self‐condensing vinyl copolymerization in a continuous stirred tank reactor (CSTR). A kinetic Monte Carlo algorithm is proposed that discretizes inflow and outflow separately from reaction steps. The model predicts dynamic changes in monomer and inimer (IM) concentrations, as well as , , and molecular weight distribution (MWD). The CSTR produces arbPIB with broader MWD, compared to a batch reactor using the same recipe and operation time. Predictions of and agree with a previous deterministic model. CSTR operation with high [IM] is unstable because large molecules tend to become even larger as time increases.

Fractals in crystallizing food systems

The present paper reviews and discusses the possible influences of irregular random fractal formation on crystallizing food systems, such as triacylglycerols (fats) and inulin (oligofructoses). In both cases the crystallization process is driven by selective processes. Triacylglycerols consist of three different fatty acids, mostly of different length and saturation degree, inulin of oligofructose molecules of a broad molecular weight distribution. The structure formation, which can be at several stages `fractal’, determines part of the processes in chocolate preparation and in the use of inulin gels, for providing nice mouthfeel during oral processing. The common physics during crystallization is also relevant for using inulin as fat replacer.

Improved aqueous solubility and stability of wool and feather proteins by reactive-extraction with H2O2 as bisulfide ([sbnd]S[sbnd]S[sbnd]) splitting agent

With the aim of developing new bioplastics from wool and chicken feather proteins three different protein extracting methodologies were explored, aiming to split its characteristic intermolecular bisulfide (SS) bond: one reductive, using thioglycolate (HSCH2COO−) as reducing agent, and two oxidative routes, one using H2O2 and the other NaClO as oxidative agents. The resulting proteins were characterized by FTIR, SDS-PAGE, solubility tests, and by SAXS and WAXS. Treatment with NaClO destroyed completely the proteins due to strong oxidation which led to severe molecular weight reduction. In comparison with the classical thioglycolate reductive method, the oxidative H2O2 treatment lead to proteins with broader molecular weight distribution, lower isoelectric point, lower fractions of β-sheet structures and lower capability of bisulfide reformation, presumably due to the introduction of stable SO species such as sulfenic (RSOH), sulfinic (RSO2H) or sulfonic (RSO3H) acids. For these reasons this type of proteins presented higher water solubility. In addition, aqueous/isopropanol solutions of wool proteins obtained through H2O2 oxidation presented excellent film forming capability.

Lignin from Hardwood and Softwood Biomass as a Lubricating Additive to Ethylene Glycol.

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants.

Synthesis of Waterborne Polyurethane by the Telechelic α,ω-Di(hydroxy)poly(n-butyl acrylate).

A key for the preparation of polyacrylate-based polyurethane is the synthesis of hydroxyl-terminated polyacrylate. To our knowledge, exactly one hydroxyl group of every polyacrylate chain has not been reported. The hydroxyl-terminated poly(butyl acrylate) (PBA) has been successfully synthesized by degenerative iodine transfer polymerization (DITP) of the n-butyl acrylate (n-BA) using 4,4′-azobis(4-cyano-1-pentanol) (ACPO) and diiodoxylene (DIX) as initiator and chain transfer agent, respectively, and subsequently substituted reaction of the iodine-terminated PBA with β-mercaptoethanol in alkaline condition. The latter reaction was highly efficient, and the terminal iodine at the end of polymer chains were almost quantitatively transformed to a hydroxyl group. 2,2′-Azobis(isobutyronitrile) (AIBN) and ACPO were used as initiators in the DITPs of n-BA. The results demonstrated that they had a significant influence on the terminal groups of the formed polymer chains. The structure, molecular weight, and molecular weight distribution of the hydroxyl-terminated PBA have been studied by 1H, 13C NMR, and GPC results. The components of hydroxyl-terminated PBA were determined by MALDI-TOF MS spectra, and their formation is discussed. The broad molecular weight distribution of the PBA and the difference in the polymerization behaviors from typical living radical polymerization are explained based on the results of 1H NMR and MALDI-TOF MS spectra. The hydroxyl-terminated PBA has been successfully used in the preparation of PBA-based polyurethane dispersions (PUDs). The aqueous PUDs were stable, and based on the DSC results it can be said that the miscibility of hard segments with PBA chains was improved.

Characterization of broad molecular weight distribution polyethylene with multi-detection gel permeation chromatography

High temperature gel permeation chromatography (GPC) equipped with differential refractive index, light scattering and viscometer is used to characterize polyethylene with broad molecular weight distribution (MWD). Methods are discussed through the measurement of broad MWD polyethylene PE52K and 4731B, including Mark-Houwink calibration, universal calibration, triple-detectors and light scattering dual-detectors calibrations. As the broadness of MWD increases, the two fitting curve calibrations with first order equations are chosen, despite a slight inaccuracy within molecular weight range of standards. More reliable polymer dispersity indexes (PDI) are obtained by triple-detectors and light scattering dual-detectors calibrations. From the Mark-Houwink plot of 4731B, branching information can only be obtained from triple-detectors calibration, indicating the validity of triple-detectors calibration on the characterization of branched polyethylene with broad MWD. The triple detectors calibration upon 4731B provides a weight average molecular weight of 313 kg/mol, a PDI of 47 and a branching of 0.30 per chain.

Zn(II) and Cu(II) unsymmetrical formamidine complexes as effective initiators for ring‐opening polymerization of cyclic esters

A series of Zn(II) and Cu(II) complexes were synthesized using unsymmetrical N,N′‐ diarylformamidine ligands, i.e. N‐(2‐methoxyphenyl)‐N′‐2,6‐dichorophenyl)‐formamidine (L1), N‐(2‐methoxyphenyl)‐N′‐phenyl)‐formamidine (L2), N‐(2‐methoxyphenyl)‐N′‐(2,6‐dimethylphenyl)‐formamidine (L3) and N‐(2‐methoxyphenyl)‐N′‐(2,6‐diisopropylphenyl)‐formamidine (L4). The complexes, [Zn2(L1)2(OAc)4] (1), [Zn2(L2)2(OAc)4] (2), [Zn2(L3)2(OAc)4] (3), [Zn2(L4)2(OAc)4] (4), [Cu2(L1)2(OAc)4] (5), [Cu2(L2)2(OAc)4] (6), [Cu2(L3)2(OAc)4] (7) and [Cu2(L4)2(OAc)4] (8), were prepared via a mechanochemical method with excellent yields between 95 ‐ 98% by reacting the metal acetates and corresponding ligands. Structural studies showed that both complexes are dimeric with a paddlewheel core structure in which the separation between the two metal centres are 2.9898 (8) and 2.6653 (7) Å in complexes 3 and 7, respectively. Complexes 1 – 8 were used in ring‐opening polymerization of ε‐caprolactone (ε‐CL) and rac‐lactide (rac‐LA). Zn(II) complexes were more active than Cu(II) complexes, with complex 1 bearing electron withdrawing chloro groups being the most active (kapp = 0.0803 h‐1). Low molecular weight poly‐(ε‐CL) and poly‐(rac‐LA) ranging from 1720 to 6042 g mol‐1, with broad molecular weight distribution (PDIs, 1.78 – 1.87) were obtained. Complex 2 gave reaction orders of 0.56 and 1.52 with respect to ε‐CL and rac‐LA, respectively.

Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process

Emulsion polymerization process provides a unique polymerization locus that has a confined tiny space with a higher polymer concentration, compared with the corresponding bulk polymerization, especially for the ab initio emulsion polymerization. Assuming the ideal polymerization kinetics and a constant polymer/monomer ratio, the effect of such a unique reaction environment is explored for both conventional and living free-radical polymerization (FRP), which involves chain transfer to the polymer, forming polymers with long-chain branches. Monte Carlo simulation is applied to investigate detailed branched polymer architecture, including the mean-square radius of gyration of each polymer molecule, <s2>0. The conventional FRP shows a very broad molecular weight distribution (MWD), with the high molecular weight region conforming to the power law distribution. The MWD is much broader than the random branched polymers, having the same primary chain length distribution. The expected <s2>0 for a given MW is much smaller than the random branched polymers. On the other hand, the living FRP shows a much narrower MWD compared with the corresponding random branched polymers. Interestingly, the expected <s2>0 for a given MW is essentially the same as that for the random branched polymers. Emulsion polymerization process affects branched polymer architecture quite differently for the conventional and living FRP.

Truxillic and truxinic acid-based, bio-derived diesters as potent internal donor in Ziegler-Natta catalyst for propylene polymerization

In this study, novel α-truxillic and β-truxinic acid-based, bio-derived diesters have been developed as internal donors for preparing Ziegler-Natta (ZN) catalysts. Impacts of these bio-derived diesters were investigated on the chemical composition, the morphology, the mode of adsorption, and the propylene polymerization performance of the catalysts in comparison to the most widely used fourth-generation catalyst containing dibutyl phthalate. The molecular structures of the diesters and the particle morphology of the catalysts were preserved in the catalyst preparation. The bio-derived diesters afforded ZN catalysts with a reasonable activity and stereospecificity in propylene polymerization along with similarly broad molecular weight distribution (MWD) as the phthalate-based catalyst. Another promising feature of the catalysts was an opposite hydrogen response in terms of expansion of MWD upon the addition of H2.

Preparation of polydisperse polystyrene-block-poly(4-vinyl pyridine) synthesized by TEMPO-mediated radical polymerization and the facile nanostructure formation by self-assembly

This article reports a successful nanostructure formation from block copolymer having broad distribution of molecular weight. The block copolymer synthesis and the nanosphere formation are facile; therefore, it is promising for fabrication of nanostructure materials in large-scale manufactory. The polydisperse diblock copolymer of polystyrene-block-poly(4-vinyl pyridine) (PSVP) was prepared by the nitroxide-mediated radical polymerization that contains the fraction of poly(4-vinyl pyridine) block of 45 mol% and the overall polydispersity index of 2.08. The phase separation of PSVP was induced by the simple evaporation of co-solvent DMF:THF (70:30 v/v) of the PSVP solution. The SEM images of the self-assembled polydisperse PSVP display the spherical morphology with the diameter of ~ 50 nm, which is larger than that of block copolymer having narrow molecular weight distribution. By simply immersing the self-assembled film into iron chloride solution, the transformation from the spherical structure to the porous structure occurred directly without sacrificing the block copolymer component indicating the advantage of stimuli-response properties of the self-assembled PSVP. The results demonstrated that the polydisperse block copolymer could be used for the nanostructure formation by simple synthesis and evaporation procedures and, therefore, it is suitable for industrial applications.Graphical

Synthesis and characterisation of highly branched polyisoprene: exploiting the "Strathclyde route" in anionic polymerisation.

This work aimed at developing a synthetic route towards highly branched poly(isoprene) from commercially available raw materials, in good yield and devoid of microgelation, i.e., to prepare a completely soluble polymer via the versatile technique anionic polymerisation. The polymerisations were conducted under high vacuum conditions using sec-butyllithium as initiator at 50 °C in toluene. Toluene served both as a solvent and as a chain-transfer agent. The polar modifier used was tetramethylethylenediamine (TMEDA), and a commercial mixture of divinylbenzene (DVB) was employed as the branching agent for the “living” poly(isoprenyl)lithium anions. The nature of the reaction was studied on the TMEDA/Li ratio as well as the DVB/Li ratio. The obtained branched polymers were characterised by triple detection size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC) and melt rheology. Broad molecular weight distributions have been obtained for the highly branched polymer products. 1H NMR spectroscopy reveals the dominance of 3,4-polyisoprene microstructure. It was found that the complex viscosities and dynamic moduli of the branched samples were much lower compared to their linear counterparts. The results conform with earlier findings by the “Strathclyde team” for radical polymerisation systems. This methodology has the potential of providing soluble branched vinyl polymers at low cost using the readily available raw materials.

Binuclear aluminum complexes supported by linked bis(β-diketiminate) ligands for ring-opening polymerization of cyclic esters

Binuclear aluminum alkyl complexes 2a–4g supported by linked bis(β-diketiminate) ligands were synthesized via the reaction of AlEt3 or AlMe3 and the corresponding proligand in a 2:1 molar ratio with moderate yields. The isolated complexes were well-characterized by 1H-NMR, 13C-NMR and elemental analysis. The binuclear nature of aluminum complex 2b was further confirmed by an X-ray diffraction study. All complexes 2a–4g could efficiently initiate the ring-opening polymerization (ROP) of e-caprolactone in toluene. The substituents at the aromatic rings and the linker unit in the auxiliary ligands exerted significant influence on the catalytic behavior of the investigated aluminum complexes. Complex 4g (R1 = R2 = Cl) containing propylenyl bridging unit exhibited the highest catalytic activity among these complexes, which might be attributed to the increased electrophilicity of the metal center as well as more opened coordination sphere. The molecular weights of obtained poly(e-caprolactone)s deviating considerably from the theoretical values indicated that the ROP of e-caprolactone by complexes 2a–4g was not well-controlled, which was also judged from the broad molecular weight distributions (MWD = 1.47–2.47) of produced poly(e-caprolactone)s. These complexes proved to be inactive toward the polymerization of rac-lactide alone. In the presence of alcohol the polymerization occurred, which was actually initiated by the decomposition species of the aluminum complex upon the treatment with isopropanol.

Asphaltenes subfractions extracted from Brazilian vacuum residue: Chemical characterization and stabilization of model water-in-oil (W/O) emulsions

Asphaltenes were obtained from a Brazilian vacuum residue (VR) by precipitation with different ratios of n-heptane/VR to give three asphaltene subfractions. The behavior of these different subfractions in relation to the stability of water-in-oil (W/O) emulsions were evaluated. The whole asphaltene subfraction (AH) was obtained with the addition of n-heptane/VR in a 40:1 ratio (v/v) followed by filtration. Two more asphaltene subfractions (A4 and A10) were obtained by precipitation with n-heptane/VR ratios of 4:1 and 10:1, respectively. The properties of the precipitated asphaltene subfractions were analyzed by atmospheric pressure photoionization (APPI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in positive-ion mode, ultraviolet–visible (UV–Vis) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. The FT-ICR MS results showed that the A4 subfraction exhibited a profile with a higher amount of heteroatoms, high polarity and broader molecular weight distribution (Mw). An inverse correlation was observed concerning the degree of aromaticity and solubility in heptane/toluene solutions (onset point). The AH and A10 subfractions were more aromatic than A4, as confirmed by 1H NMR analysis. Also, the asphaltene subfractions promoted greater stability of the emulsions produced. The droplet size distribution and bottle test showed similar results for the stability of the emulsions obtained with the three different subfractions. After the application of centrifugal forces, the formation of a densely packed layer emulsion was observed, containing approximately 85% of water. The stabilization was improved when the W/O interface formed a viscous layer and effectively blocked the water coalescence, which remained stable for two weeks.

One pot synthesis of bimodal UHMWPE/HDPE in‐reactor blends with Cr/V bimetallic catalysts

ABSTRACTBimodal ultra‐high‐molecular‐weight polyethylene (UHMWPE)/high‐density polyethylene (HDPE) in‐reactor blends (IRBs) are produced by the bimetallic catalysts, which are synthesized through co‐supporting silylchromate and vanadium‐oxide‐based catalysts on silica or alumina, zirconia and titania‐modified silica. After support modification, the activities of the catalysts for ethylene polymerization are substantially enhanced. The IRBs produced by the modified catalysts also contain more UHMWPE and low‐molecular‐weight polyethylene (LMWPE) fractions, and have much broader molecular weight distribution (MWD). The homogeneous nature of the IRBs is preliminarily confirmed by the differential scanning calorimetry melting curves, showing unique melting peak in both nascent and recrystallized states. The rheological results reflect that the viscosity of the IRBs is reduced more or less when compared with UHMWPE. The distinct elastic dominance of the IRBs is also observed, implying the UHMWPE characteristics in the IRBs. In addition, the intimate mixing of the IRBs is further verified by the similar slopes of Han curves for the polyethylene (PE) samples. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3404–3412

Self‐Assembly of Amphiphilic Random Copolyacrylamides into Uniform and Necklace Micelles in Water

Amphiphilic random copolyacrylamides bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl pendants induce precision self‐assembly to produce quite small uniform and/or necklace micelles (≈10 nm) in water. The size, structure, and thermoresponsive properties of the micelles are controlled by the primary structure (composition and chain length) of the copolymers. For this, random copolymers with different composition, chain length, and molecular weight distribution are synthesized by iron‐catalyzed living or free radical copolymerization of PEG acrylamide and dodecyl acrylamide (DAAm). The copolymers with controlled molecular weight (degree of polymerization: ≈40) intermolecularly self‐assemble and/or self‐fold to form uniform (multichain or unimer) micelles in water; the size increases with increasing hydrophobic DAAm content (19–57 mol%: Mw = 43 900–191 000). In contrast, random copolymers with relatively small DAAm content (<35 mol%) and broad molecular weight distribution provide both uniform and necklace micelles in water.