New specialty linear polymers (SLP) for power cables

Fouling of nanofiltration membrane by e ffl uent organic matter: Characterization using different organic fractions in wastewater

Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.

In free‐radical olefin polymerizations, the polymer‐transfer reactions could lead to chain scission as well as the formation of long‐chain branches. The Monte Carlo simulation for free‐radical polymerization that involves simultaneous long‐chain branching and random scission is used to investigate detailed branched structure. The relationship between the mean‐square radius of gyration 〈s2〉 and degree of polymerization P as well as that between the branching density and P is the same for both with and without random scission reactions—at least for smaller frequencies of scission reactions. The 〈s2〉 values were larger than those calculated from the Zimm–Stockmayer (Z‐S) equation in which random distribution of branch points is assumed, and therefore, the Z‐S equation may not be applied for low‐density polyethylenes. The elution curves of size exclusion chromatography were also simulated. The molecular weight distribution (MWD) calibrated relative to standard linear polymers is much narrower than the true MWD, and high molecular weight tails are clearly underestimated. A simplified method to estimate the true MWD from the calibrated MWD data is proposed. The MWD obtained with a light scattering photometer in which the absolute weight‐average molecular weight of polymers at each retention volume is determined directly is considered a reasonable estimate of the true MWD. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2960–2968, 2001

Calf-thymus (CT-DNA) is widely used as a binding agent. The commercial samples are known to be "highly polymerized DNA" samples. CT-DNA is known to be fragile in particular upon ultrasonic wave irradiation. Degradation products could have dramatic consequences on its bio-sensing activity, and an accurate determination of the molecular weight distribution and stability of commercial samples is highly demanded. We investigated the sensitivity of charge detection mass spectrometry (CDMS), a single-molecule MS method, both with single-pass and ion trap CDMS ("Benner" trap) modes to the determination of the composition and stability (under multiphoton IR irradiation) of calf-thymus DNAs. We also investigated the changes in molecular weight distributions in the course of sonication by irradiating ultrasonic waves to CT-DNA. We report, for the first time, the direct molecular weight (MW) distribution of DNA sodium salt from calf-thymus revealing two populations at high (~10MDa) and low (~3MDa) molecular weights. We evidence a transition between the high-MW to the low-MW distribution, confirming that the low-MW distribution results from degradation of CT-DNA. Finally, we report also IRMPD experiments carried out on trapped single-stranded linear DNAs from calf-thymus allowing extraction of their activation energy for unimolecular dissociation. We show that single-pass CDMS is a direct, efficient and accurate MS-based approach to determine the composition of calf-thymus DNAs. Furthermore, ion trap CDMS allows us to evaluate the stability (both under multiphoton IR irradiation and in the course of sonication by irradiating ultrasonic wave) of calf-thymus DNAs.

Enzymatic hydrolysis: Sialylated mucin (SiaMuc) glycoprotein of edible swiftlet's nest (ESN) and its molecular weight distribution as bioactive ESN SiaMuc-glycopeptide hydrolysate

Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography

This work investigates the possibility of obtaining the molecular weight distribution (MWD) of linear ultrahigh molecular weight (UHMW) polypropylene (PP) through rheology. To this end, the linear viscoelastic response of a set of UHMWPP samples is measured over the largest possible frequency range. The terminal relaxation is achieved by running creep experiments and converting the compliance in dynamic moduli. A time–temperature concentration principle, recently validated for UHMW polyethylene, is also applied to obtain the terminal relaxation of the sample with the largest molecular weight. The linear rheological response is correlated with gel permeation chromatography (GPC) results by means of the mixing rule based on the relaxation modulus. The implementation of such a rule requires the knowledge of some material parameters governing the stress relaxation of the polymer. Since they are unknown in literature for PP, they are estimated from the comparison between the viscoelastic spectra and the GPC distributions of three lab-made UHMWPPs with narrow polydispersity. Such parameters are then used as a basis to predict the MWDs of two UHMWPP samples with large polydispersity. The variability of the parameters upon molecular weight and polydispersity is assessed by applying the mixing rule to two different PP samples with lower molecular weights, one with narrow polydyspersity and another one with broad polydispersity. As the GPC curves of the samples are available, first the direct problem of estimating the rheological response from MWD and then the inverse problem of obtaining the MWD from the rheological data are solved. An overall satisfactory agreement is found between the calculated and measured MWD for the two samples, with both the direct and inverse approach.

Soluble microbial products (SMP) generated by activated sludge cultures receiving a mixed feed of phenol and glucose were characterized with respect to molecular weight (MW) distribution, octanol-water partition coefficient (K(ow)), and Microtox toxicity. Short-term batch reactor tests using 14C-labeled substrates were performed to collect SMP derived from each substrate, while long-term tests were performed with SMP accumulated over multiple feed cycles using fed-batch reactors receiving non-labeled substrates. Yield of SMP in the batch tests, 10%-20% for phenol and 2%-5% for glucose, differed for each substrate and was independent of initial concentration. The MW distribution (MWD) of SMP was independent of feed composition, and was bimodal in the < 1 kDa and 10-100 kDa MW ranges for phenol-derived SMP and predominantly < 1 kDa for glucose-derived SMP. In the non-labeled tests, the fraction of SMP of MW > 100 kDa increased with the proportion of glucose in the feed. The K(ow) of phenol-derived SMP was higher compared to glucose-derived SMP, indicating that the phenol-derived SMP were more hydrophobic. This was particularly true at an acidic pH, where the K(ow) was 4.2 +/- 1.0 for phenol-derived SMP versus 0.13 +/- 0.13 for glucose-derived SMP. Toxicity testing indicated that phenol-derived SMP, exerting a mean Microtox inhibition of 1%, were less toxic than phenol itself, and showed little correlation between toxicity and concentration. However, glucose-derived SMP were generally more toxic than glucose itself (a non-toxic substrate), and the toxicity increased linearly with the concentration of SMP.

Mesoporous silica nanoparticles/polymer hybrid materials were prepared via metal-free surface-initiated atom-transfer radical polymerization (SI-ATRP). Self-synthesized mesoporous SBA-15 with surface hydroxyl groups was modified with (3-aminopropyl)-triethoxysilane, followed by anchoring of the ATRP initiator α-bromoisobutyryl bromide onto the surface via amide reaction. The SI-ATRP of methyl methacrylate was then carried out with fluorescein (FL) as a photocatalyst and trimethylamine (TEA) as an electron donor under irradiation with blue light. Thus, polymer chains grew directly from mesoporous walls. The hybrid materials were characterized by gel permeation chromatography, N2 adsorption/desorption measurements, and thermogravimetric analysis. The effects of the ligand/photocatalyst molar ratios, solvent, and the monomer/initiator molar ratios on grafting density, molecular weight, and molecular-weight distribution were investigated. The results show that a higher TEA/FL ratio led to a higher reaction rate and better controllability of the polymerization but also to a lower grafting density. These properties were also affected by the solvent. With an increasing monomer/initiator molar ratio, the grafting rate, molecular weight, and grafting density exhibited increasing trends.

A statistical model has been developed for the prediction of molecular weight and molecular weight distribution in transesterification reactions of diols onto polyesters (ideally polycondensated wi...

Asphalt flocculation and deposition. III. The molecular weight distribution

Force-elongation curves of a set of random ethylene-1-alkene copolymers have been studied. The comonomers included 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene. The copolymers all had the most probable molecular weight and narrow composition distributions. A set of hydrogenated poly(butadienes), random ethyl-branched copolymers, that have very narrow molecular weight and composition distributions were also studied as reference. Only ductile type deformations were studied. Several important generalizations resulted from this work. An important finding was that the molecular weight, copolymer composition, and chemical nature of the co-units have to be considered as independent variables in analyzing the tensile behavior. The nominal stress-strain curves of even modest molecular weights are dominated by strain-hardening. This characteristic is similar to that of very high molecular weight linear polyethylenes. However, the effect is not as large for the ethylene-butenes as compared with the other copolymers. The ultimate properties of the ethylene-butene copolymers also differ from the others. An explanation for these differences can be given by postulating that in the melt structure, and thus in the residual liquid-like region, noncrystalline portions are affected by interaction of the side groups. In contrast, the yield stress and initial modulus do not depend on the chemical nature of the co-unit but only on the crystallinity level. In the regions of overlap there is a substantial difference between the yield stress and initial modulus of linear polyethylene and the copolymers. Different portions of the force-elongation curves are governed by different structural and molecular features indicating the complexity of the problem. The wide range of experimental data that are presented, for thoroughly characterized samples, can serve as a basis for the molecular understanding of the ductile deformation of random copolymers.

Chapter 4 - Mechanical analysis of polymers

The polydisperse Mead–Park (MP) “toy” molecular constitutive model developed in Paper I [Mead et al., J. Rheol. 62, 121–134 (2017)] as well as our previously published work [e.g., J. Rheol. 59, 335–363 (2015)] is used in the “forward” direction to study model polydisperse melts of entangled linear flexible polymers in severe, fast shear flows. The properties of our new model are elucidated by way of numerical simulation of a representative model polydisperse polymer melt in step shear rate and interrupted shear flow. In particular, we demonstrate how the MP model simulates the individual molecular weight distribution (MWD) component dynamics as well as the bulk material properties. Additionally, we demonstrate that the polydisperse MP model predicts the phenomenon of “shear modification” for model MWD's with a long, high molecular weight tail. Specifically, the terminal dynamic moduli following cessation of severe, disentangling deformation, are shown to slowly heal/recover on the orientational relaxation time scale of the longest chains in the MWD. This is the first molecular constitutive equation to predict the phenomenon of shear modification. We provide detailed insight into the molecular mechanism responsible for this previously enigmatic and important phenomenon. Additionally, the presence of shear modification is not necessarily associated with the presence of shear stress peak overshoot transients in interrupted shear flow. Specifically, we examine and analyze the interrupted shear experiments reported by Tsang and Dealy [J. Non-Newtonian Fluid Mech. 9, 203–222 (1981)] and demonstrate quantitatively their lack of a relationship to shear modification. We also demonstrate that the new MP model accurately predicts the Cox-Merz rule, Laun's rule and Gleissele's mirror relations in steady shear.

Pretreatment of coal gasification wastewater by adsorption using activated carbons and activated coke