Molar Mass Range Research Articles

Origin of Melt Memory Effects in Poly(ethylene oxide): The Crucial Role of Entanglements.

The melt memory effect on crystallization is an intriguing phenomenon displayed by semicrystalline polymers, as opposed to low molar mass molecules. It concerns the effect of melt temperature on nucleation upon recrystallization. Typically, polymer crystals must be considerably superheated to erase the effect of previous morphology on the subsequent crystallization, avoiding an acceleration of the process. Despite being known for decades, its origin is still not fully understood. Investigating model poly(ethylene oxide) covering a wide range of molar mass, it is demonstrated that melt memory originates from topological constraints among the chains, i.e., entanglements, for PEO in which weak intermolecular interactions are present due to the ether groups. In fact, no memory is observed for samples below the critical molar mass for the formation of entanglements (about 1 kg mol-1). The increase in molar mass raises the number of entanglements and induces the formation of folded chains crystals, both factors leading to a topologically complex amorphous phase, enhancing the melt memory effect. The molecular origin of the melt memory effect in polymers with weak intermolecular interactions is thus ascribed to a slower isotropization in the melt of the chain segments originally contained in the crystals, due to the presence of entanglements among the chains. This study defines the distinction between small molecules and polymers from the point of view of melt memory.

Rigid Rod-like Viscoelastic Behaviors of Methyl Cellulose Samples with a Wide Range of Molar Masses Dissolved in Aqueous Solutions.

The viscoelastic behaviors of aqueous solutions of commercially available methyl cellulose (MC) samples with a degree of substitution of 1.8 and a wide range of weight average molar masses (Mw) were investigated over a wide concentration (c) range at some temperatures from -10 to 25 °C. The viscoelastic parameters useful to discuss the structure and dynamics of MC-forming particles in aqueous solutions were precisely determined, such as the zero-shear viscosity (η0), the steady-state compliance (Je), the average relaxation time (τw), and the activation energy (E*) of τw. Because previously obtained scattering and intrinsic viscosity ([η]) data revealed that the MC samples possess a rigid rod-like structure in dilute aqueous solutions over the entire Mw range examined, the viscoelastic data obtained in this study were discussed in detail based on the concept of rigid rod particle suspension rheology. The obtained Je-1 was proportional to the number density of sample molecules (ν = cNAMw-1, where NA means the Avogadro's constant) over the ν range examined irrespective of Mw. The reduced relaxation time (4NAτw(3νJe [η]ηmMw)-1), where ηm means the medium viscosity, was proportional to (νL3)2, L; the average particle length depending on Mw for each sample was determined in a previous study; and the reduced specific viscosity (ηspNAL3(Mw [η])-1), where ηsp means the specific viscosity, was proportional to (νL3)3 in a range of νL3 < 3 × 102. These findings were typical characteristics of the rigid rod suspension rheology. Therefore, the MC samples behave as entangling rigid rod particles in the νL3 range from rheological points of view. A stepwise increase in E* was clearly observed in a c range higher than the [η]-1 value irrespective of Mw. This observation proposes that contact or entanglement formation between particles formed by MC molecules results in an increase in E*.

Molar mass determination via linear regression from SEC measurements: The case of polylactide, polycaprolactone and poly(2,2‐dimethylthrimethylene carbonate)

AbstractMolar mass correction coefficients (cc) were determined for calculating the absolute molar masses of polylactide (PLA), polycaprolactone (PCL), and poly(2,2‐dimethyltrimethylene carbonate) (PDTC) in the range of 2,5–190 kg/mol, using calibration based on polystyrene standards (PS). Linear PLAs, PCLs, and PDTCs with a wide range of molar masses were synthesized using tin (II) octoate and diol as a catalyst/initiator system. Size Exclusion Chromatography (SEC) coupled with a Refractive Index detector (SEC‐RI) or a Multi‐Angle Laser Light Scattering detector (SEC‐MALLS) was utilized to determine the relative molar mass or absolute molar mass of the samples under investigation. Additionally, for comparison, the absolute molar mass of low molar mass PLA, PCL, or PDTC was calculated based on end‐group analysis using the 1H NMR method. Correction coefficients were subsequently calculated by comparing the molar mass obtained from SEC‐MALLS and SEC‐RI. The calculated correction coefficients ranged from 0.40 to 0.87 and increased with the rising molar mass of the polymers. The derived equation could be used to evaluate the absolute molar masses from PS standards over a broad range for the analyzed polymers.

Molecular characterization of a galactomannan extracted from Tara (Caesalpinia spinosa) seeds

Tara gum (TG) is a polysaccharide extracted from the seeds of a South American tree called Tara (Caesalpinia spinosa). TG is a galactomannan with many applications in the food industry, mainly as an emulsifier and stabilizer agent. In addition, it is also used in the paper and cosmetic industries. In the present study, we performed a molecular characterization based on chemical composition and physicochemical properties to understand the properties behind TG applications. TG was extracted and purified from Tara seeds distributed in different ecoregions of Bolivia. The monosaccharide composition analysis was determined by high-performance anion-exchange chromatography/pulsed amperometric detection (HPAEC-PAD). At the same time, their molecular characteristics, such as molar mass, root-mean-square radius, hydrodynamic radius, conformation, and densities, were studied by asymmetrical flow field-flow fractionation coupled to multi-angle light scattering refractive index (AF4-MALS-dRI), also the specific refractive index increment (dn/dc) was determined for the first time using AF4 for TG. The results revealed that the gum samples are galactomannans composed of mannose (Man) and galactose (Gal) in a ratio of 3.37 (Man/Gal), with an average molar mass range from 2.460 × 107 to 3.699 × 107 Da, distributed in a single population. The root-mean-square radius range from 260.4 to 281.6 nm, and dn/dc is 0.1454. The Kratky plots based on 14 scattering angles indicated that the conformation of all samples corresponds to random coil monodisperse, while their gyration radius/hydrodynamic radius ratio (ρ) is high. All these results suggest that the chains have a low branched density, consistent with the Gal/Man composition. To the best of our knowledge, we report for the first time an integrated physicochemical study of TG relevant to developing emulsifier and stabilizer formulations.

Waxes from Long-Chain Aliphatic Difunctional Monomers.

Petrochemical polyethylene waxes (Mn = 800-8000 g/mol for commercial Ziegler waxes) as additives, lubricants, and release agents are essential to numerous products and production processes. The biodegradability of this class of compounds when unintentionally released to the environment is molar mass dependent and subject to ongoing discussions, and alternatives to conventional polyethylene waxes are desirable. By employing bottom-up and top-down approaches, that is nonstoichiometric A2 + B2 polycondensation and chain scission, respectively, linear waxes with multiple in-chain ester groups as biodegradation break points could be obtained. Specifically, waxes with 12,12 (WLE-12,12, WLE = waxes linear ester) and 2,18 (WLE-2,18) carbon atom linear ester repeat unit motifs were accessible over a wide range of molar masses (Mn ≈ 600-10 000 g/mol). In addition to the molar mass, the type of end group functionality (i.e., methyl ester, hydroxy, or carboxylic acid end groups) significantly impacts the thermal properties of the waxes, with higher melting points observed for carboxylic acid end groups (e.g., Tm = 83 °C for carboxylic acid-terminated WLE-12,12 with Mn,NMR = 1900 g/mol, Tm = 92 °C for WLE-2,18 with Mn,NMR = 2200 g/mol). A HDPE-like orthorhombic crystalline structure and rheological properties comparable to a commercial polyethylene wax suggest WLE-12,12 and WLE-2,18 are viable biodegradable and biosourced alternatives to conventional, petrochemical polyethylene waxes.

Heterotelechelic Silicones: Facile Synthesis and Functionalization Using Silane-Based Initiators.

The synthetic utility of heterotelechelic polydimethylsiloxane (PDMS) derivatives is limited due to challenges in preparing materials with high chain-end fidelity. In this study, anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D3) monomers using a specifically designed silyl hydride (Si-H)-based initiator provides a versatile approach toward a library of heterotelechelic PDMS polymers. A novel initiator, where the Si-H terminal group is connected to a C atom (H-Si-C) and not an O atom (H-Si-O) as in traditional systems, suppresses intermolecular transfer of the Si-H group, leading to heterotelechelic PDMS derivatives with a high degree of control over chain ends. In situ termination of the D3 propagating chain end with commercially available chlorosilanes (alkyl chlorides, methacrylates, and norbornenes) yields an array of chain-end-functionalized PDMS derivatives. This diversity can be further increased by hydrosilylation with functionalized alkenes (alcohols, esters, and epoxides) to generate a library of heterotelechelic PDMS polymers. Due to the living nature of ring-opening polymerization and efficient initiation, narrow-dispersity (Đ < 1.2) polymers spanning a wide range of molar masses (2-11 kg mol-1) were synthesized. With facile access to α-Si-H and ω-norbornene functionalized PDMS macromonomers (H-PDMS-Nb), the synthesis of well-defined supersoft (G' = 30 kPa) PDMS bottlebrush networks, which are difficult to prepare using established strategies, was demonstrated.

Reaction kinetics of chitosan nanogels crosslinked by genipin

Crosslinking of chitosan chains in dilute solution by natural crosslinker genipin leads to biocompatible nanogels. Here we investigated the reaction kinetics between chitosan and genipin in a 200 mM acetate buffer at 37 °C, and the structural and conformational evolutions of the nanogels during the crosslinking reaction by multi detection asymmetric flow field-flow fractionation (AF4). Upon crosslinking by genipin, the z-average hydrodynamic radius Rhz of the chitosan chains increased from 26 nm to 130 nm, while the weight average molar mass Mw increased from 2.0 × 105 g/mol to 1.8 × 107 g/mol. The crosslinking reaction appeared to be first-order and size-dependent. In particular, the intrachain crosslinking reaction was preferentially for nanogels having the larger size, leading to formation of branched chains/nanogels having a wide range of molar masses between 106 and 108 g/mol but a similar radius of gyration Rg ∼ 40 nm. For the largest nanogel fractions with M > 2.0 × 108 g/mol, both Rg and Rh showed a scaling relation with exponent 1/3 and a structure parameter Rg/Rh = 0.74, as expected for the hard sphere particle. The reaction was accompanied by a reduction of charge density and an increase in hydrophobicity of chitosan nanogels, which plays a key role in the formation of uniform size nanogels with chain density ρ(Rh) up to 0.45 g/cm3.

Structure and Conformation of Hydroxypropylmethyl Cellulose with a Wide Range of Molar Masses in Aqueous Solution─Effects of Hydroxypropyl Group Addition.

The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses (Mw) from 23 to 5000 kg mol-1, a controlled degree of substitution (DS) of 1.9 by methyl groups, and a molar substitution number (MS) of 0.25 by hydroxypropyl groups dissolved in aqueous solution was examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide angle neutron scattering (S-WANS) techniques, and intrinsic viscosity ([η]) measurements. The determined Mw and the radius of gyration (Rg) showed the relationships Rg ∝ Mw1.0 and [η] ∝ Mw1.7 in a range of Mw < 100 kg mol-1, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing Mw and reached ∼0.5 in a high Mw region, which is a typical value of flexible chain molecules for both Rg and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (lp). The ratios of the hydrodynamic radius via DLS measurements to Rg also supported semiflexible rod behavior. Particle form factors and the average lengths (L) resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of Mw < 100 kg mol-1 and semiflexible rods with lp ∼ 100 nm in Mw > 100 kg mol-1. Because the average contour length (lc) calculated from Mw is approximately twice as long as L in the Mw range < 100 kg mol-1, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the lc/L value increases gradually in the range Mw > 200 kg mol-1, where the formed HpMC particles behave as semiflexible rods. The formed particle structure was substantially different from that found in methyl cellulose samples with a similar DS value, which showed rod-like behavior over a wide Mw range. The addition of hydroxypropyl groups only at MS = 0.25 effectively changed the formed particle structure.

Conformational approach to the crystallization mechanisms of organosilicon liquids of PMS brand in a non-uniform temperature field

The possibility of using the conformational approach to describe the crystallization kinetics during melt-crystal phase transitions in an inhomogeneous temperature field and to determine the molar mass range corresponding to a change in the crystallization mechanism is shown using the example of PMS brand organosilicon liquids. It is established that the curve of dependence of the mean square of the dipole moment of a macromolecule on the average molar mass of an organosilicon polymer contains three sections, each of which has its own crystallization mechanism.

Thermoresponsive and co-nonsolvency behavior of poly(N-vinyl isobutyramide) and poly(N-isopropyl methacrylamide) as poly(N-isopropyl acrylamide) analogs in aqueous media

Sets of the nonionic polymers poly(N-vinyl isobutyramide) (pNVIBAm) and poly(N-isopropyl methacrylamide) (pNIPMAm) are synthesized by radical polymerization covering the molar mass range from about 20,000 to 150,000 kg mol−1, and their thermoresponsive and solvent-responsive behaviors in aqueous solution are studied. Both polymers feature a lower critical solution temperature (LCST) apparently of the rare so-called type II, as characteristic for their well-studied analogue poly(N-isopropyl acrylamide) (pNIPAm). Moreover, in analogy to pNIPAm, both polymers exhibit co-nonsolvency behavior in mixtures of water with several co-solvents, including short-chain alcohols as well as a range of polar aprotic solvents. While the cloud points of the aqueous solutions are a few degrees higher than those for pNIPAm and increase in the order pNIPAm < pNVIBAm < pNIPMAm, the co-nonsolvency behavior becomes less pronounced in the order pNIPAm > pNVIBAm > pNIPMAm. Exceptionally, pNIPMAm does not show co-nonsolvency in mixtures of water and N,N-dimethylformamide.Graphical

Catalyst-Free Single-Step Solution Polycondensation of Polyesters: Toward High Molar Masses and Control over the Molar Mass Range

Catalyst-Free Single-Step Solution Polycondensation of Polyesters: Toward High Molar Masses and Control over the Molar Mass Range

Rigid rod particle like viscoelastic responses of poly(vinylidene fluoride) in N-methylpyrrolidone solution

A systematic study was performed on the dynamic viscoelastic properties of N-methylpyrrolidone (NMP) solutions of poly(vinylidene fluoride) (PVDF) samples with a wide range of weight average molar masses (Mw) from 140 to 3300 kg mol−1 over a temperature range of −24 to 35 °C in the dilute to semidilute concentration (c) regime in this study. In previous studies under extremely dilute conditions, it was confirmed that PVDF molecules behave as isolated highly elongated rigid rods, and the average particle length (⟨L⟩) and diameter (⟨d⟩) for different PVDF samples were precisely determined. The fundamental viscoelastic parameters used to analyze the dynamics of PVDF molecules dissolved in NMP were precisely determined, including the zero-shear shear viscosity (η0), the steady state compliance (Je), the average relaxation time (τw), and the activation energy (E*v) of τw in this study. E*v increased stepwise above c values corresponding to the reciprocal of the intrinsic viscosity ([η]−1) for different solutions, independent of Mw, showing that contact or the formation of entanglements between PVDF molecules causes the increase in E*v. Je−1 was found to be proportional to the number density of PVDF molecules (ν = cNAMw−1, where NA denotes the Avogadro constant) over the entire investigated v range, irrespective of Mw and the presence of entanglements between PVDF molecules. The reduced specific viscosities, ηspNA⟨L⟩3(Mw[η])−1, were reasonably described as a universal function in the parameter ν⟨L⟩3 over the entire investigated range, and ηspNA⟨L⟩3(Mw[η])−1 ∝ (ν⟨L⟩3)3 was found over the region 102 &amp;lt; ν⟨L⟩3 &amp;lt; 103, irrespective of Mw.

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range.

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn-Mark-Houwink-Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M-0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG.

Novel epoxy-terminated macromonomers and their polymerization for synthesis of bottle-brush type amphiphilic block copolymers.

Architecture of polymers has vital implications for their physical properties and applications. In this study, synthesis of a series of novel epoxy-terminated macromonomers namely Ep-DEGMME, Ep-TEGMME, Ep-EGMEE, Ep-EGMBE, and Ep-EGMHE is reported. The synthesized macromonomers vary in number of ethylene oxide units and length of the alkyl group. These macromonomers are first homopolymerized by anionic ring-opening polymerization for synthesis of homopolymers of a molar mass range. Subsequently, these macromonomers with different lengths of two segments (alkyl group and ethylene oxide units) are copolymerized with other monomers for synthesis of bottle-brush type architectures. In the first case, di- and tri-block copolymers of Ep-EGMBE are synthesized while using MeO-PEG or PEG as a macroinitiator; the resulting block copolymers have hydrophilic handle and hydrophobic brush. On the same lines, block copolymers of Ep-TEGMME with ε-caprolactone have hydrophobic handle and hydrophilic brush. The synthesized block copolymers are comprehensively characterized by SEC and liquid chromatography at critical conditions. The analysis reveals the successful synthesis of block copolymers while providing information on relative total molar mass, and individual block lengths of the block copolymers, along with amount of unwanted homopolymers in the sample.

Conformation and Structure of Hydroxyethyl Cellulose Ether with a Wide Range of Average Molar Masses in Aqueous Solutions

The solution properties of a water-soluble chemically modified cellulose ether, hydroxyethyl cellulose (HeC), were examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide-angle neutron scattering (S-WANS), small-to-wide-angle X-ray scattering (S-WAXS) and viscometric techniques at 25 °C. The examined HeC samples had average molar substitution numbers ranging from 2.36 to 2.41 and weight average molar masses (Mw) that fell within a wide range from 87 to 1500 kg mol-1. Although the relationship between the determined radius of gyration (Rg) and Mw was described as Rg ∝ Mw~0.6, as is observed usually in flexible polymer solutions in good solvents, the observed scattering vector (q) dependencies of excess Rayleigh ratios were well interpreted using a rigid rod particle model, even in high-Mw samples. Moreover, the ratios of the formed particle length (L) evaluated assuming the model for rigid rods to the determined Rg showed the relationship LRg-1 ~ 3.5 irrespective of Mw and were close to those theoretically predicted for rigid rod particle systems, i.e., LRg-1 = 12. The observed SLS behavior suggested that HeC molecules behave just like rigid rods in aqueous solution. As the L values were not simply proportional to the average molecular contour length calculated from the Mw, the chain conformation or structure of the formed particles by HeC molecules in aqueous solution changed with increasing Mw. The q dependencies of excess scattering intensities observed using the S-WANS and S-WAXS experiments demonstrated that HeC molecules with Mw less than 200 kg mol-1 have a diameter of ~1.4 nm and possess an extended rigid rod-like local structure, the size of which increases gradually with increasing Mw. The observed Mw dependencies of the translational and rotational diffusion coefficients and the intrinsic viscosity of the particle suspensions strongly support the idea that the HeC molecules behave as rigid rod particles irrespective of their Mw.

Pyrolysis and thermal degradation studies of silane-carbosilane transformation using hyphenated thermal analysis

Pyrolysis process accompanying polydimethylsilane to polycarbosilane transformation and the decomposition behaviors of polydimethylsilane (PDMS), polycarbosilanes (PCS Mk-I/II and III) were investigated applying evolved gas analysis and pyrolysis–gas chromatography-mass spectrometry. Volatile fractions evolved during the reactions were recorded as specific pyrograms. The degradation of the polymer skeleton under argon leads to the evolution of methyl silane and higher linear oligomers in the molar mass range 42 ̶ 348 Da; the escape of hydrogen starts simultaneously. Based on the results, specific pyrolysis patterns and decomposition behavior of PDMS, PCS Mk-III were established. Mass spectral data revealed the structural and compositional identification of molecular moieties evolved during the pyrolysis reactions. Thermal data confirmed and complemented the pyrolysis data.

Dynamics of Poly(cyclohexene carbonate) as a Function of Molar Mass

Stereoregular poly(cyclohexene carbonate) (PCHC) homopolymers were prepared via copolymerization of cyclohexene oxide and carbon dioxide (CO2) using (R,R)-(salcy)-CoCl and bis(triphenylphosphine)iminium chloride as a catalyst. The homopolymers had molar masses in the range of 4800–33,000 g mol–1 and relatively narrow dispersity after careful fractionation, as required for the molecular dynamics investigation. We employed differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, for investigating the thermal properties and the molecular dynamics, respectively. The segmental dynamics in the vicinity of the liquid-to-glass temperature was very complex. The dual segmental processes were inseparable by decreasing the temperature or by increasing the pressure. Based on DFT calculations of the dipole moment, they were ascribed to different stereo sequences of the PCHC backbone. The limiting glass temperature, Tg, for very high molar masses was ∼125 °C. The high Tg value obtained herein well justifies its application as a CO2-based alternative for polystyrene (PS) in a variety of materials based on block copolymers. Moreover, fragility increased with increasing molar mass with values intermediate to poly(styrene) and poly(cyclohexyl methacrylate). The flexible cyclohexyl group in PCHC undergoing intramolecular chair-to-chair conversion increases the packing ability and consequently decreases the fragility. PCHC is a brittle material because it lacks entanglements even for the higher molar masses investigated herein, which is relevant for application as a PS substitute. Within the investigated range of molar masses, the dependences of the terminal relaxation times, τΝΜ, and of the zero-shear viscosity, ηο, on the molar mass, M, are τΝΜ/τSM ∼ M3.2 and ηο ∼ M1.4, revealing an intermediate behavior between Rouse and entangled chains.

Comparative Hydrodynamic Study on Non-Aqueous Soluble Archaeological Wood Consolidants: Butvar B-98 and PDMS-OH Siloxanes.

Butvar B-98 and PDMS-OH both have a demonstrable ability as consolidants for archaeological wood. This makes them both potential treatment options for the Oseberg collection, which is one of the most important archaeological finds from the Viking era. Both Butvar B-98 and PDMS-OH are soluble in organic solvents, offering a useful alternative to aqueous-based consolidants. Extensive characterisation studies were carried out on both of these polymers, with the use of analytical ultracentrifugation and viscometry, for the benefit of conservators wanting to know more about the physical properties of these materials. Short column sedimentation equilibrium analysis using SEDFIT-MSTAR revealed a weight-average molar mass (weight-average molecular weight) Mw of (54.0 ± 1.5) kDa (kg · mol−1) for Butvar B-98, while four samples of PDMS-OH siloxanes (each with a different molar mass) had an Mw of (52.5 ± 3.0) kDa, (38.8 ± 1.5) kDa, (6.2 ± 0.7) kDa and (1.6 ± 0.1) kDa. Sedimentation velocity confirmed that all polymers were heterogeneous, with a wide range of molar masses. All molecular species showed considerable conformational asymmetry from measurements of intrinsic viscosity, which would facilitate networking interactions as consolidants. It is anticipated that the accumulated data on these two consolidants will enable conservators to make a more informed decision when it comes to choosing which treatment to administer to archaeological artefacts.

Determination of ultrahigh molar mass of polyelectrolytes by Taylor dispersion analysis

Taylor dispersion analysis (TDA) was successfully applied to obtain broadly distributed, ultrahigh molar masses of industrial anionic polyacrylamides (IPAMs) up to 25×106g/mol, far beyond the limits of Size Exclusion Chromatography (SEC) (about 7.3×106g/mol for anionic polyacrylamides standards (APAM)). Two protocols of TDA differing in capillary surface and rinsing procedure were employed: (i) bare fused silica capillaries under intensive between-run rinsing with 1M NaOH, and (ii) fused silica capillaries coated with polyelectrolyte multilayers composed of polydiallyldimethylammonium chloride polycation and sodium polystyrenesulfonate polyanion under simple rinsing with background electrolyte. Both cases led to similar results and in agreement with those obtained by static light scattering, the rinsing capillary step being much shorter in the second case (8min instead of 30min). The data processing of the obtained taylorgrams was realized using multiple-Gaussian fitting of the overall taylorgrams, by separating the contribution of low molar mass impurities from the polymeric profiles, and by determining the mean hydrodynamic radii and diffusion coefficients of the polymers. The molar masses of ultra-high molar mass industrial anionic polyacrylamides (IPAM) were derived from the hydrodynamic radii according to logRh versus logMw linear correlation established with APAM standards. Compared to capillary gel electrophoresis for which the size separation was only feasible up to Mw ∼ 10×106g/mol due to field induced polymer aggregation, TDA largely extended the range of accessible molar mass with easy-to-run and time saving assays.

UPLC‐ESI‐TOF‐MS Analysis of the Effect of Dendrimers Core Lengths on Their Molecular Profiles and Purity

The effect of core length of Polyamidoamine (PAMAM) dendrimers on their physicochemical properties and hence their purity was studied by ultraperformance liquid chromatography‐electrospray ionization‐time of flight‐mass spectrometry (UPLC‐ESI‐TOF‐MS). Seven consecutive generations Gn = (G0-6) of both Ethylenediamine core (C2) and Diaminobutane core (C4) dendrimers were tested. The separation and detection of each generation of dendrimers (covering a molar mass range of 517‐58,076 Da and a radius range of 15‐67 Å) were performed within 10 min. Increasing the length of the core by the C2H4 group significantly changed the morphological characteristics of the dendrimers. For example, the general morphology of C4 dendrimers becomes less compact than C2 dendrimers. This facilitates the influx of impurities from the inner nanocavities of these molecules, even at higher generations, during the UPLC run providing C4 dendrimers of higher purity than C2 dendrimers. These results reveal that the toxicity found by some researchers due to the application of dendrimers may be mostly due to leakage of the encapsulated starting materials, which can be eliminated by using optimized dendritic molecules.12