Polymer Molar Mass Research Articles

Lignin Nanoparticle Morphology Depends on Polymer Properties and Solvent Composition: an Experimental and Computational Study

Kraft lignin is an underutilized sideproduct from the pulp and paper industry that can be used as a feedstock for various bio-based products. In particular, microstructured lignin particles are used as functionalized materials in applications such as the controlled release of active substances and the absorption of contaminants and as polymer additives. Gaps in our understanding of lignin molecular interactions and morphology in various solvents limit our ability to tailor processes to produce particles with desired properties. We empirically demonstrate that the dispersity and aqueous phase polarizability influence lignin polymer chain conformation and thus the resulting nanoparticle morphology. Our complementary experimental and computational studies investigate lignin dynamics and indicate that a high molar mass polymer with a low polydispersity index, which contains numerous aromatic structures, will aggregate via hydrophobic interactions and form compact globules in an aqueous environment. Even in the presence of a sacrificial negatively charged surfactant sodium dodecyl sulfate, electronic interactions of aromatic units predominate, resulting in a compact globule after the surfactant is removed. Additionally, the number of inter-lignin contacts, solvent–polymer hydrogen bonds, and radius of gyration for a high molar mass, low polydispersity index lignin polymer remained almost constant in water and in the mixed (water/ethanol) solvent system containing the surfactant. We also report dendritic lignin nanoparticles obtained experimentally from low molar mass, high polydispersity index lignin, in a water/ethanol mixed aqueous phase. Molecular simulation results suggest that the intermolecular forces driving this morphology are stable inter-lignin contacts over time and enhanced lignin-solvent hydrogen bonding in the mixed solvent. Our results demonstrate the controlled behavior of lignin nanoparticle morphologies in aqueous solvents. This work contributes toward establishing property–performance correlations for lignin and advances knowledge for the synthesis of shape-specific lignin nanoparticles.

The future of poly(2-oxazoline)s

Poly(2-oxazoline)s have gained significant interest in the past decade, especially driven by their high potential for biomedical applications, amongst others to substitute poly(ethylene glycol). Within this perspective article the emerging trends in the area of poly(2-oxazoline)s are discussed with a focus on synthetic advances, including the development of high molar mass polymers, the broadening of the cyclic imino ether monomer range, and the development of degradable poly(2-oxazoline) derivatives. Furthermore, emerging trends in the use of poly(2-oxazoline)s will be highlighted, including their use to study basic fundamental polymer properties, specific biomedical applications, including drug delivery and 3D scaffolds, as well as other applications as interlayers in organic devices and polymer gel electrolytes. Finally, this perspective article provides a discussion on the future vision for the area of poly(2-oxazoline)s.

Branching analysis of β-cyclodextrin-based poly(N-isopropylacrylamide) star polymers using triple detection SEC

For the first time, poly(N-isopropylacrylamide) (PNIPAAm) star polymers with a β-cyclodextrin core are characterized in detail by size-exclusion chromatography (SEC) with triple detection to experimentally verify the number of arms. A combination of a refractive index detector, multi-angle laser light scattering detector, and an online-viscosimeter was used for branching analysis. At first, the SEC system was calibrated and the detector setup was validated using linear polystyrene reference polymers. The applicability of the established triple detection SEC for branching analysis was shown by the analysis of two commercially available polystyrene star polymers. Due to the high molar masses of the star polymers, both the contraction ratio g and g′ could be determined independently, thus allowing the calculation of the viscosity shielding ratio ε. Finally, the branching analysis of the PNIPAAm star polymers could experimentally confirm the assumed arm number of up to 21 arms. Moreover, an increasingly compact molecular structure and the influence of the arm number on the viscosity shielding ratio could be shown.

Mechanism and Kinetics of Lipase-Catalyzed Polycondensation of Glycerol and Sebacic Acid: Influence of Solvent and Temperature.

The mechanism for theCandida antacticalipase B (CALB)-catalyzed polycondensation of glycerol and sebacic acid in polar solvents was proposed based on the profile of formation and consumption of the glyceridic species in the reaction media and on the occurrence of the acyl migration reaction. The acyl migration is mainly responsible for the esterification of the secondary hydroxyl of glycerol and in an opposite way to the regioselective CALB-catalyzed esterification of primary hydroxyls. The enzymatic esterification of glycerol primary hydroxyls occurs preferentially up to carboxylic acid conversions of approximately 0.60-0.75 with rate constants in the range of 0.07-1.44 L mol-1 h-1, depending on the solvent. Above carboxylic acid conversions of 0.60-0.75, acyl migration occurs in parallel to enzymatic esterification with rate constants of approximately 0.04-0.12 h-1 and is the rate-limiting step of the polymerization. The hydrogen bonding accepting ability of the solvents is the main parameter that dictates the enzymatic catalysis rate. However, the magnitude of the polymer-solvent interaction governs the polymer chain growth. Acetonitrile has a lower hydrogen bonding accepting ability and a less favorable polymer-solvent interaction compared with the other polymer-solvent pairs, and polycondensation achieves the highest enzymatic rate constant of approximately 0.84-1.44 L mol-1 h-1; however, low molar mass polymers with Mn = 1.4 kDa were formed. On the other hand, acetone has intermediate hydrogen bonding accepting ability and optimal intermediate polymer-solvent interactions and, therefore, an intermediate enzymatic rate constant of approximately 0.41-0.52 L mol-1 h-1, and the highest molar mass polymers with Mn = 4.9-9.4 kDa were obtained.

Chemically Recyclable CO2 -Based Solid Polyesters with Facile Property Tunability.

Synthesizing chemically recyclable solid polymeric materials is a significant strategy to potentially achieve carbon neutral production of new polymers and alleviate plastic pollution, especially when the synthesis is based on CO2 and inexpensive co-feedstocks available in large scales. Additionally, polymeric materials should have high enough molecular weight to exhibit distinguished properties from low molar mass polymers to serve for a broader range of application scenarios. However, up to now, strategies for developing solid-state CO2 -based chemically recyclable polyesters with both high molecular weight and facile property tunability are still unprecedented. Herein, a brand-new synthetic route is developed to synthesize chemically recyclable CO2 -based solid polyesters with high molecular weight (Mn up to 587.7kg mol-1 ) and narrow dispersity (Đ <1.2), which should further broaden the potential application scenarios of new CO2 -based polyesters. Additionally, complete monomer recovery from poly(δLH2 ) material is also achieved. The preserved terminal alkene groups allow facile property tuning of the polyesters via photo-initiated thiol-ene click reactions, enabling more potential utilities and further functionalizations.

Membrane-active diacylglycerol-terminated thermoresponsive polymers: RAFT synthesis and biocompatibility evaluation

Well-defined diacylglycerol end-functionalized poly(N-isopropylacrylamide)s (PNIPAAm) and poly(N-vinylcaprolacam)s (PNVCL) with number-average molar masses (Mn) ranging from 1260 to 19 350 g·mol−1 were synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization from xanthate-functionalized diacylglycerols (DAGs) containing palmitic or oleic acid moieties. The formation of polymeric nanoparticles (PNPs) and their thermoresponsive properties was studied. Phase separation temperature dependence on polymer molar mass and hydrophilic/hydrophobic ratio was investigated in phosphate buffer saline (PBS). Biological tests showed that the particles are non-hemolytic and highly compatible with representatives of immune cells - monocyte/macrophage THP-1 cells. The biocompatibility combined with the potential ability to modulate the cell membrane environment make the proposed polymers a promising foundation for drug carriers.

Tuneable thermal properties of PTHF-based copolymers by incorporation of epoxide units

In order to decrease the crystallinity of polytetrahydrofuran (PTHF), statistical copolymerizations with 1,2-butylene oxide (BO) and 3,3-dimethyl-1,2-butylene oxide (DMBO) epoxides as comonomer were investigated in a process compatible with an easy scaling up. Difunctionnal poly(tetrahydrofuran-stat-1,2-butylene oxide)s (PTHF-stat-PBO) and poly(tetrahydrofuran-stat-3,3-dimethyl-1,2-butylene oxide)s (PTHF-stat-PDMBO) were synthesized in the range of 0–20 °C using different operating conditions. The reactivity ratios showed a homogeneous distribution of the epoxide units all along the copolymer chains by using BO, while an alternation of several THF and DMBO monomer units sequences was obtained in the DMBO-based copolymers. Still, both copolymerizations fit well with an ideal copolymerization behavior. A slow addition of BO during the propagation step or the introduction of BO or DMBO at the beginning of the polymerization were investigated. Whatever the comonomer used, its insertion in the polymer chain reduced the melting temperature of the copolymers and the impact of the THF polymerization equilibrium on the yields. As a consequence, higher polymerization yields were obtained. A fairly good control of the polymer molar masses was observed, although elimination reactions were highlighted. However, operating conditions were determined to limit the content of the resulting alkene chain ends to about 10%, providing guaranties for further macromolecular architectures developments.

Energetic analysis of the liquid–liquid equilibrium of systems containing polyethylene glycol (4000 g.mol−1 or 6000 g.mol−1) and salts (Na2SO4 or Na3C6H5O7) at different temperatures and their application in the bovine serum albumin and α-lactalbumin partitioning

This work aims to determine the interaction parameters and the energetic analysis of the aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG 4000 g.mol−1 or PEG 6000 g.mol−1), salt (Na2SO4 or Na3C6H5O7) and water at different temperatures T = (293.2, 298.2, 303.2 and 308.2) K. Partition assays of bovine serum albumin (BSA) and α-lactalbumin in the different systems studied were also performed in order to demonstrate the application of the two-phase aqueous systems studied. The temperature had no effect on the ATPS phase equilibrium compositions while the polymer molar mass had an influence, presenting a greater biphasic region in the systems formed by PEG 6000. The systems composed by Na2SO4 showed greater biphasic region. The salting-out capacity and the effective excluded volume (EEV) of the systems were also determined. It was observed that the salting-out effect was greater in the systems composed of Na2SO4. The EEV was higher in the systems formed by PEG 6000 for both salts. In addition, the equilibrium data of the systems were thermodynamically modelled using UNIFAC model and it was found that the water-salt interaction was greater than the water-PEG interaction, thus proving the higher water concentration in the systems bottom phase. It was also verified that the UNIFAC model presented low values of the global deviations (2.970%), being considered adequate to predict the new parameters of interaction between the contribution groups of the studied systems. This study shows that the values found in thermodynamic modelling can be used to predict other systems that have these same contribution groups evaluated. It was also found that α-lactalbumin and BSA migrated preferentially to the bottom phase in most systems. It was observed lower kp in the systems formed by Na2SO4. Such behavior may be related due to the greater interaction of α-lactalbumin and BSA with the bottom phase of the system formed by Na2SO4. For the systems formed by sodium citrate, the partition coefficient for α-lactalbumin and BSA increased with the increase in the molar mass of the polymer (4000 to 6000). The salt type effect had more effect on the partition than the polymer molar mass, but both influenced.

Hybrid polymer/lipid vesicles: Influence of polymer architecture and molar mass on line tension

Hybrid polymer/lipid vesicles are self-assembled structures that have been the subject of an increasing number of studies in recent years. They are particularly promising tools in the development of cell membrane models because they offer the possibility to fine-tune their membrane structure by adjusting the distribution of components (presence or absence of “raft-like” lipid domains), which is of prime importance to control their membrane properties. Line tension in multiphase membranes is known to be a key parameter on membrane structuration, but remains unexplored, either experimentally or by computer modeling for hybrid polymer/lipid vesicles. In this study, we were able to measure the line tension on different budded hybrid vesicles, using a micropipette aspiration technique, and show the influence of the molar mass and the architecture of block copolymers on line tension and its consequences for membrane structuration.

Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s.

The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with Mw of 120 and 245 kg/mol, 4-arm with Mw of 123 kg/mol, and three linear PLLAs with Mw of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 °C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 °C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with Mw of 240 kg/mol was more intense than that of the 6-arm polymer with similar Mw, most possibly due to its higher Mz. However, the influence of shear on the crystallization of the star polymers with Mw close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling.

Revealing Electrical and Mechanical Performances of Highly Oriented Electrospun Conductive Nanofibers of Biopolymers with Tunable Diameter.

The present study outlines a reliable approach to determining the electrical conductivity and elasticity of highly oriented electrospun conductive nanofibers of biopolymers. The highly oriented conductive fibers are fabricated by blending a high molar mass polyethylene oxide (PEO), polycaprolactone (PCL), and polylactic acid (PLA) with polyaniline (PANi) filler. The filler-matrix interaction and molar mass (M) of host polymer are among governing factors for variable fiber diameter. The conductivity as a function of filler fraction (φ) is shown and described using a McLachlan equation to reveal the electrical percolation thresholds (φc) of the nanofibers. The molar mass of biopolymer, storage time, and annealing temperature are significant factors for φc. The Young’s modulus (E) of conductive fibers is dependent on filler fraction, molar mass, and post-annealing process. The combination of high orientation, tunable diameter, tunable conductivity, tunable elasticity, and biodegradability makes the presented nanofibers superior to the fibers described in previous literature and highly desirable for various biomedical and technical applications.

From Single to Multi Mode Lasing: The role of materials revealed in optical simulations

ABSTRACT The comparative study of thin film Cholesteric Liquid Crystal (CLC) lasers made from different materials and optically pumped by an external solid state laser reveals a striking dependence of lasing behaviour (ranging from single mode at the edge of the selective reflection band to multimode lasing) on the morphology and microstructure of CLC films. The materials studied belong to two groups: low molar mass liquid crystals and polymers. It is shown that the orientation of individual chiral domains and fluctuations in helical pitch contribute significantly to the type of lasing displayed by the material. Different ways of preparing CLC cells that lead to predominantly one type of lasing are discussed. The importance of variations of the helical pitch and domain orientation in producing single and multimode lasing is justified by optical simulations (4x4 matrix method) of lasing in multilayered samples.

Lactides and Lactones Yielding Eco-Friendly and Biocompatible Polymers by Metal-Catalyzed Ring-Opening Polymerization

Currently, there is a growing interest in the development of suitable methods for the preparation of eco-friendly and biocompatible materials in order to increase environmental protection and reduce human health risk. Therefore, this mini-review summarizes several studies involving lactides and lactones as monomers for the synthesis of biodegradable and biocompatible polymers via metal-catalyzed Ring-Opening Polymerization (ROP). Hence, synthetic approaches involving mono, bi and trinuclear metallic catalysts, with different catalytic activity, were reviewed. Complexes mostly based on metals such as Na, Mg, Al, Ti, Zn are considered. Generally, from ROP reactions, it has been found that conversion, stereoselectivity, number-average molar mass (Mn) and dispersity of the molar mass (Ð) of polymers are influenced by the type of monomer, the characteristics of the catalyst, the nature of the solvent, temperature and reaction time. Additionally, the polymer properties can also be controlled by varying the molar ratios between the monomer and the initiating system. Thus, this review may be found helpful for the scientific community and students involved in research in different areas of chemistry such as organic chemistry, inorganic chemistry, polymers chemistry, and materials science. The survey covers selected data published between 2017 and 2020; however, previous relevant reports were also studied.

Enhanced Polyester Degradation through Transesterification with Salicylates.

Polyesters constitute nearly 10% of the global plastic market, but most are essentially non-degradable under ambient conditions or in engineered environments. A range of degradable polyesters have been developed as more sustainable alternatives; however, limitations of practical degradability and scalability have hindered their viability. Here, we utilized transesterification approaches, including in situ polymerization-transesterification, between a salicylate and a polyester to incorporate salicylate units into commercial polyester backbones. The strategy is scalable and practically relevant given that high molar mass polymers can be obtained from melt-processing of commercial polyesters using common compounders or extruders. Polylactide containing sparse salicylate moieties shows enhanced hydrolytic degradability in aqueous buffer, seawater, and alkaline solutions without sacrificing the thermal, mechanical, and O2 barrier properties of the parent material. Additionally, salicylate sequences were incorporated into polycaprolactone and a derivative of poly(ethylene terephthalate), and those modified polymers also exhibited facile degradation behavior in alkaline solution, further expanding the scope of this approach. This work provides insights and direction for the development of high-performance yet more sustainable and degradable alternatives to conventional polyesters.

Poly(Butylene Succinate) Molar Mass Calculation by GPC and 1H‐NMR

AbstractThe determination of the molar mass of a polymer is a fundamental characterization. One of the most common techniques used for this purpose is gel permeation chromatography (GPC). However, the most used columns are not appropriate for low molar mass polymers, presenting results that are different from reality. For these cases, it is possible to use the nuclear magnetic resonance (NMR) technique to obtain molar mass values (based on calculations associated with spectra signals and the quantity of the polymer used in the analysis). However, in some cases, the resultant signals of different chain portions can be presented in the same spectral region, hampering calculations. Thus, this paper proposes the use of an external standard. This way, it can correlate to the molar mass of four different samples of poly(butylene succinate) (PBS) with different molar mass values. The results based on NMR spectra were different from those found using GPC, but both increased in the same proportion (R² = 0.8828). Since NMR presents an absolute result, it seems to be the most accurate result. This analysis method also allows us to quantify the experimental percentage of unsaturation, which was lower than the theoretical one due to losses during the PBS synthesis.

The Average Quantities – Molar Mass of Polymers and Molecular Speed in Fluids

The average quantities, molar mass of polymers and molecular speed in fluids, have been treated rigorously to have the general proofs that the weight average molecular weight of a polymer sample is higher than its number average molecular weight, and the rms speed of the molecules of a gas or liquid is higher than their mean speed. The methods work for any distribution.

Interconvertible Living Radical and Cationic Polymerization using a Dual Photoelectrochemical Catalyst

The necessity of well-tuned reactivity for successful controlled polymer synthesis often comes with the price of limited monomer substrate scope. We demonstrate here the on-demand interconversion between living radical and cationic polymerization using two orthogonal stimuli and a dual responsive single catalyst. The dual photo- and electrochemical reactivity of 10-phenylphenothiazine catalyst provides control of the polymer's molar mass and composition by orthogonally activating the common dormant species toward two distinct chemical routes. This enables the synthesis of copolymer chains that consist of radically and cationically polymerized segments where the length of each block is controlled by the duration of the stimulus exposure. By alternating the application of photochemical and electrochemical stimuli, the on-demand incorporation of acrylates and vinyl ethers is achieved without compromising the end-group fidelity or dispersity of the formed polymer. The results provide a proof-of-concept for the ability to substantially extend substrate scope for block copolymer synthesis under mild, metal-free conditions through the use of a single, dual reactive catalyst.

Cationic Polymerization of Hexamethylcyclotrisiloxane in Excess Water.

Ring-opening ionic polymerization of cyclosiloxanes in dispersed media has long been discovered, and is nowadays both fundamentally studied and practically used. In this short communication, we show some preliminary results on the cationic ring-opening polymerization of hexamethylcyclotrisiloxane (D3), a crystalline strained cycle, in water. Depending on the catalyst or/and surfactants used, polymers of various molar masses are prepared in a straightforward way. Emphasis is given here on experiments conducted with tris(pentafluorophenyl)borane (BCF), where high-molar polymers were generated at room temperature. In surfactant-free conditions, µm-sized droplets are stabilized by silanol end-groups of thus generated amphiphilic polymers, the latter of which precipitate in the course of reaction through chain extension. Introducing various surfactants in the recipe allows generating smaller emulsions in size with close polymerization ability, but better final colloidal stability, at the expense of low small cycles’ content. A tentative mechanism is finally proposed.

Polycarbonate/mica extrusion using mixing elements: Improvement of transparency and thermal, mechanical and water and gas barrier properties

Polycarbonate (PC) was loaded with mica fillers by melt mixing process using a twin-screw extruder. The influence of the mica content on the PC properties was analyzed. Also, the presence of mixing elements of grid shape on the mica distribution during the PC extrusion was discussed. These elements allowed us to significantly improve the fillers dispersion in the polymer matrix. As a consequence, the transparency of the PC films was maintained up to 5 wt% of mica due to reducing the aggregates formation and the homogeneous mica dispersion. Despite a slight decrease of the polymer molar mass, a strong improvement of the PC thermal stability, mechanical resistance as well as barrier properties towards water and gases (N2, O2 and CO2) was obtained due to the reinforce and tortuosity effects induced by mica fillers in the PC matrix. The gas and water transport properties of the PC/mica films were well-fitted using a predictive empirical model, that took into account the double tortuosity and immobility effect of mica particles. In addition, mica fillers were found to have specific interactions with water molecules, that led to enhancement of the moisture resistance of PC, thus improving its performance.

Shear Flow and Relaxation Behaviors of Entangled Viscoelastic Nanorod-Stabilized Immiscible Polymer Blends

To blend and process different high molar mass polymers into multiphase materials, predicting/controlling their morphology and rheological behavior is paramount. Herein, a segmental repulsive poten...