Molecular Weight Oligomers Research Articles

Polyacrylate epoxide oligomers with robust photo‐crosslinked and thermomechanical properties enabled by controlling copolymerizing molecular weight distribution

AbstractPhoto‐triggering curing coatings have advantages of improving production efficiency, reducing pollution emissions, and contributing to green environmental protection. However, making the trade‐off between appropriate viscosity and UV‐curing properties in a high‐performing polymer system remains a formidable challenge. In this paper, firstly, a series of acrylate copolymer oligomers (named as PAAR) were synthesized using methyl methacrylate (MMA), butyl acrylate (BA), and glycidyl methacrylate (GMA), then methacrylic acid (MAA) was grafted utilizing the reaction between carboxyl group in MAA with epoxy group in oligomer to introduce double bonds. By adjusting the oligomer molecular weight to control the viscosity and changing the GMA ratio to obtain suitable double bonds content. As a result, the number molecular weight (Mn) of the thus‐obtained PAAR oligomers were less than 3000 Da, and the polymer dispersity indexes (PDI) were lower than 1.8. Photo‐polymerization kinetics revealed that the coating prepared using the oligomers could be fully cross‐linked by UV light triggering within 60 s, achieving a high transparency of 90% along with favorable thermal and mechanical properties. Furthermore, it was confirmed that the water resistance on the surface of the cured films and hydrophobicity were more influenced by the presence of hydroxyl groups.

Acylthiourea oligomers as promising reducing agents for dimethacrylate-based two-component dental materials.

Currently used thiourea-based two-component dental materials may release bitter compounds if they are not properly cured. To address this issue, the objective of this study was to evaluate the potential of acylthiourea oligomers as reducing agents for the development of self-cure composites. Acylthiourea oligomers ATUO1-3 were synthesized via cotelomerization of the acylthiourea methacrylate ATU1 with butyl methacrylate. They were characterized by 1H NMR spectroscopy and size exclusion chromatography. Self-cure composites based on the redox initiator system cumene hydroperoxide/acylthiourea oligomer/copper(II) acetylacetonate were formulated. The flexural strength and modulus were measured using a three-point bending setup. The double bond conversions were determined using NIR spectroscopy. The working time of each self-cure composite was measured using an oscillating rheometer. Leaching experiments using light-cure composites were performed in DMSO-d6. Acylthiourea oligomers ATUO1-3 were successfully synthesized in good yields. Both the oligomer molecular weight and the amount of thiourea groups were varied. Self-cure composites containing ATUO1 or ATUO2 as reducing agents exhibited excellent mechanical properties and high double-bond conversions. The amounts of reducing agent, cumene hydroperoxide and copper(II) acetylacetonate were shown to have a significant impact on the working time. Moreover, a correlation between flexural modulus and the amount of metal salt was clearly established. Self-cure composites containing the oligomer ATUO1 exhibited a longer working time than materials containing ATU1 or acetylthiourea. Contrary to acetylthiourea, ATUO1 was not able to leach out of light-cured composites. Acylthiourea oligomers are promising reducing agents for the formulation of two-component dental materials that do not induce a bitter taste in mouth.

Influence of Phenol–Formaldehyde Resin Oligomer Molecular Weight on the Strength Properties of Beech Wood

The objective of this study was to determine the effects of four phenol–formaldehyde (PF) resin treatments with different molecular weights at four different concentrations (5, 10, 15, and 20%) in treated beech wood. The mechanical properties of untreated and treated beech wood were evaluated. After impregnation with PF resin, all modified beech wood at all PF resin concentrations exhibited an increase in weight percent gain compared with that in untreated beech samples. PF resins with lower molecular weights more easily penetrate the wood cell wall, leading to increased bulking of the wood structure, which in turn improves the dimensional stability of the wood. The PF resin treatment with a molecular weight of 305 g/mol showed better impregnation ability than that of the other PF resins. The impact bending strength of PF-treated wood was considerably reduced because PF-cured resins formed inside the wood and are rigid and brittle. Additionally, PF resin treatments at all concentrations decreased the modulus of elasticity of the wood. Scanning electron microscopy and light microscopy revealed that the PF resins were comparatively well fixed in the wood samples. The results indicate that the large molecular weight PF resins are more uniformly distributed in the fiber lumens.

Improvement of coagulating strength and toughness of alkoxysilanes for conservation of cultural heritage

AbstractThe optimal restoration agent for the brittle walls of Idout's tomb built 4400 years ago in Saqqara, Egypt, which is located underground in a desert area, was investigated. From x‐ray diffraction analysis of the sand collected near the tomb, the main ingredient is silica. Alkoxysilane and its oligomer are used because its alkoxy groups can react readily with silica. The compressive test of solidified model sand its main component is silica was done. The increase of both molecular weight of oligomer and the content of oligomer with higher molecular weight effectively developed the compressive force. When an earthquake occurs, it is desirable that the reinforced wall will be crushed in ductility. The addition of di‐alkoxy type alkoxysilane to oligomers changed the failure mode from brittle to ductile, because the network becomes looser. When a moderate quantity of di‐alkoxy type is added to oligomers, the solidified model sand deforms with greater displacement, while maintaining a high compressive force. From scanning electron microscopic observation of fractured solidified specimen, alkoxysilane was making the sand particles connect as a binder. Many cracks were clearly observed in the binder layer. Whereas, the formed crack was far smaller for di‐alkoxy added system.

Influence of carboxytelechelic oligomer molecular weight on the properties of chain extended polyethylenes

Chain-transfer ring-opening metathesis polymerization (CT-ROMP) previously provided a route to carboxytelechelic polyethylene (PE) of controlled molecular weight; however, the incorporation of oligomeric PE into chain-extended copolymers remains relatively unexplored. Herein, CT-ROMP afforded carboxytelechelic polycyclooctene oligomers of varying molecular weight, and subsequent reduction generated a series of well-defined carboxytelechelic PEs. Melt polycondensation of the telechelic PE oligomers with either 1,6-hexanediamine or 1,6-hexanediol chain extenders generated diester and diamide linked PEs to further understand the influence of linkage structure. The thermomechanical and tensile properties of the step-growth polymers exhibited remarkably similar performance to conventional HDPE independent of PE oligomer molecular weight. The chain extended PEs displayed advantageous physical properties while introducing susceptibility to chemolytic depolymerization, tunable via periodic ester or amide linkages, thus providing valuable fundamental understanding of an alternative route to degradable HDPE. • Chain-transfer ROMP facilitated the synthesis of carboxytelechelic polyethylene of varying molecular weights. • Telechelic PE oligomers underwent chain extension with either a diol or diamine via melt polycondensation. • Chain-extended PEs displayed comparable thermal and mechanical performance to commercial HDPE, while remaining degradable at reactive linkages.

Investigation of the Formation of Squalene Oligomers Exposed to Ultraviolet Light and Changes in the Exposed Squalene as a Potential Skin Model

UV-induced oligomerisation of squalene was undertaken to indicate the potential for squalene-containing biological systems to exhibit rheology changes. DOSY NMR enabled the determination of the molecular weight (MW) range using Stokes–Einstein Gierer–Wirtz Estimation (SEGWE Calculator, University of Manchester). This approach was validated by Atmospheric Solids Analysis Probe Time of Flight Mass Spectrometry (ASAP TOF MS). To demonstrate the principle, both benzoyl peroxide and AIBN were used, separately, to initiate rapid, radical oligomerisation. Subsequent experiments in the absence of initiators compared the influence of UV wavelength and time on the resulting oligomer formation. To further model a relevant biological implication of this potentially chaotic UV oligomerisation, both saturated and unsaturated free fatty acids were added to squalene and exposed to UV at 285 nm and 300 nm to determine if cross oligomerisation could be observed. This representation of sebum evidenced the formation of a distribution of higher MW oligomers. Internal viscosity was normalised using the DMSO solvent, but to confirm that changes in rheology did not affect diffusion, a final experiment where fresh squalene was added to our oligomer mixture, representative of sebum, showed that unchanged squalene possessed the anticipated monomeric diffusion coefficient and hence MW. This work suggests, at least qualitatively, that UV-induced squalene oligomerisation can occur over time and that this may have a role in the behaviour of squalene on the skin.

Mapping the Morphological Landscape of Oligomeric Di‐block Peptide–Polymer Amphiphiles**

AbstractPeptide–polymer amphiphiles (PPAs) are tunable hybrid materials that achieve complex assembly landscapes by combining the sequence‐dependent properties of peptides with the structural diversity of polymers. Despite their promise as biomimetic materials, determining how polymer and peptide properties simultaneously affect PPA self‐assembly remains challenging. We herein present a systematic study of PPA structure–assembly relationships. PPAs containing oligo(ethyl acrylate) and random‐coil peptides were used to determine the role of oligomer molecular weight, dispersity, peptide length, and charge density on self‐assembly. We observed that PPAs predominantly formed spheres rather than anisotropic particles. Oligomer molecular weight and peptide hydrophilicity dictated morphology, while dispersity and peptide charge affected particle size. These key benchmarks will facilitate the rational design of PPAs that expand the scope of biomimetic functionality within assembled soft materials.

Mapping the Morphological Landscape of Oligomeric Di-block Peptide-Polymer Amphiphiles.

Peptide-polymer amphiphiles (PPAs) are tunable hybrid materials that achieve complex assembly landscapes by combining the sequence-dependent properties of peptides with the structural diversity of polymers. Despite their promise as biomimetic materials, determining how polymer and peptide properties simultaneously affect PPA self-assembly remains challenging. We herein present a systematic study of PPA structure-assembly relationships. PPAs containing oligo(ethyl acrylate) and random-coil peptides were used to determine the role of oligomer molecular weight, dispersity, peptide length, and charge density on self-assembly. We observed that PPAs predominantly formed spheres rather than anisotropic particles. Oligomer molecular weight and peptide hydrophilicity dictated morphology, while dispersity and peptide charge affected particle size. These key benchmarks will facilitate the rational design of PPAs that expand the scope of biomimetic functionality within assembled soft materials.

Influence of molecular weight on thermal and mechanical properties of bisphenol A‐based phthalonitrile resins

AbstractThis effort assesses the correlation between chemical structures and performance‐essential thermal, mechanical, and long‐term stability properties of cross‐linked thermosets. Resins of different molecular weights were prepared from the Bisphenol A based PEEK™‐like oligomeric phthalonitrile (BisA). Differential scanning calorimetry, which was used to investigate curing thermodynamics, indicated that BisA resins demonstrated positive correlation between increasing oligomer molecular weight and both resulting melting points and cure initiation conditions. Characterization of thermal properties using thermogravimetric analysis (TGA) indicated a similar molecular weight trend, with char yields ranging between 57% and 73%. Rheological studies of BisA of different molecular weights indicated significant viscosity increases in phthalonitriles that cross‐linked from oligomers with higher molecular weights. Moreover, the n = 1 chain length resin exhibited a gel point at 100°C lower than the n = 25 oligomer. Analysis of hardness of these cured polymers indicated that the resin cross‐linked using the n = 1 oligomer was most brittle, while the thermoset derived from the n = 4 BisA demonstrated highest hardness. Aging of cured phthalonitriles indicated that the n = 10 remained most stable in long‐duration high‐temperature environments. This study suggests the use of preparing BisA thermosets from oligomers with different molecular weights as an effective strategy for improving toughness, albeit at the tradeoff of lower thermal stabilities.

Effect of polymerization conditions on physicochemical properties of gold-like lustrous films of organic solvent soluble 3-methoxythiophene oligomers

Solution-cast films of ClO4−-doped oligo(3-methoxythiophene) exhibit a luster similar to that of metallic gold; however, the effects of synthetic conditions on the physicochemical properties of the above oligomer and its films remain underexplored. To bridge this gap, this study examines how these properties are affected by (i) the time required to add the oxidant solution to the monomer solution (ta) and (ii) the polymerization time (tp) for oligomer synthesis, revealing that oligomer molecular weight, film conductivity, and the amount of edge-on lamellar crystallites increase with decreasing ta and/or increasing tp. Given that the crystallinity of edge-on lamellar structures, together with film surface roughness, strongly influences film specular reflectance, the obtained results are expected to facilitate the fabrication of conductive oligo(3-methoxythiophene) films with tunable color and metal-like luster for diverse applications. The oxidant addition time and polymerization time were varied during the synthesis of oligo(3-methoxythiophene), and the effect of such polymerization conditions on the physicochemical properties of the oligomer and its cast films was investigated. The polymerization conditions changed the oligomer molecular weight and the amount of edge-on lamellar crystallites in the films and, in turn, affected the color and gloss of the films. The obtained results are expected to facilitate the fabrication of conductive oligo(3-methoxythiophene) films with tunable color and metal-like luster for diverse applications.

Elucidation of the mechanism of subunit exchange in \u03b1B crystallin oligomers

AlphaB crystallin (αB-crystallin) is a key protein for maintaining the long-term transparency of the eye lens. In the eye lens, αB-crystallin is a “dynamical” oligomer regulated by subunit exchange between the oligomers. To elucidate the unsettled mechanism of subunit exchange in αB-crystallin oligomers, the study was carried out at two different protein concentrations, 28.5 mg/mL (dense sample) and 0.45 mg/mL (dilute sample), through inverse contrast matching small-angle neutron scattering. Interestingly, the exchange rate of the dense sample was the same as that of the dilute sample. From analytical ultracentrifuge measurements, the coexistence of small molecular weight components and oligomers was detected, regardless of the protein concentration. The model proposed that subunit exchange could proceed through the assistance of monomers and other small oligomers; the key mechanism is attaching/detaching monomers and other small oligomers to/from oligomers. Moreover, this model successfully reproduced the experimental results for both dense and dilute solutions. It is concluded that the monomer and other small oligomers attaching/detaching mainly regulates the subunit exchange in αB-crystallin oligomer.

Isoamylene Oligomerization over Zeolite Catalysts

The study of isoamylene oligomerization over a number of microporous zeolites\t\t\t\t\tsuch as H–Y, H–MOR, H–Beta, H–ZSM-12, and H–ZSM-5 revealed that the isoamylene\t\t\t\t\tconversion rate decreases in the following order: H–MOR > H–Y > H–Beta-40\t\t\t\t\t>> H–ZSM-12 > H–ZSM-5. The maximum yields of isoamylene oligomers were\t\t\t\t\tachieved by using H–MOR (85.0%), H–Y (80.1%), and H–Beta-40 (79.8%). The\t\t\t\t\tpredominant isoamylene oligomers are dimers regardless of the zeolite catalyst\t\t\t\t\tused. The trimer yield reaches its highest when wide-pore zeolites like H–MOR,\t\t\t\t\tH–Y, or H–Beta-40 are employed. An increase in the number of acid sites enhances\t\t\t\t\tmonomer conversion rate, oligomer yield, and oligomer molecular weight.\t\t\t\t\tConditions for producing isopentene dimers and trimers with the maximum possible\t\t\t\t\tyield were determined.

The Catalytic Synthesis of Wholly Aromatic Polyesters Based on 4-hydroxybenzoic Acid via Direct Esterification

The synthesis and properties of wholly aromatic polyesters are of considerable practical importance to create functional and high-performance materials. In the present study, by means of catalytic polyesterification using titanium (IV) butoxide, we’ve synthesized wholly aromatic oligomers derived from 4-hydroxybenzoic acid (HBA), aromatic diacids and dibasic phenols. As revealed by FTIR measurements, the average molecular weight of oligomers has varied from 500 to 1400. The results of DSC have shown endotherm peaks attributed to a phase transition of low-molecular oligomers from crystalline state to mesophase and further isotropization. The synthesized oligomers were resistant to high temperatures up to about 300-320 °C.

Inclusion Complexation between α-Cyclodextrin and Oligo(ethylene glycol) Methyl Ether Methacrylate.

The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.

Highly efficient supported AlCl3‐based cationic catalysts to produce polyα‐olefin oil base stocks

AbstractThe main aim of this research is to decrease the amount of AlCl3 content that is very corrosive and hazardous in the catalytic system, required for the α‐olefin oligomerization without substantial change of final oil features. This was successfully achieved by supporting AlCl3 on different carriers. More precisely, a series of supported bimetallic catalysts was synthesized by immobilization of AlCl3 and TiCl4 onto Al2O3, SiO2, and mixed supports, that is, Al2O3/FeCl3 and SiO2/FeCl3. It was found that silica and alumina‐based catalysts had higher catalytic activities compared to support free AlCl3; however, this enhancement for silica‐based supports was more significant. According to gel permeation chromatography (GPC) results, the use of single supports, that is, Al2O3 and SiO2, increased oligomer's molecular weight, while the application of mixed supports resulted in the decrease of molecular weight of the oligomers. Viscosity characteristics of the synthesized oligomers have also been studied at two different temperatures of 40 and 100°C (KV40 and KV100). The viscosity index (VI) values, derived from KV40 and KV100, of the prepared oligomers were in the range of 126–145. The molecular weight and termination mechanisms of the oligomers were studied by 1H‐NMR spectroscopy. The obtained results disclosed that the employed reaction conditions led to the production of oligomer chains with various structures including vinylidene (Vd), and di and three‐substituted vinylene (2Vn, 3Vn) structures.

Особенности молекулярно-массовых характеристик сополимеров, синтезированных в присутствии системы триэтилбор – кислород, при варьировании времени введения бутилакрилата в кипящий винилбутиловый эфир

The copolymers of butyl acrylate with vinyl butyl ether were synthesized by dosing the active monomer in the presence of an oxidizing agent and triethylboron isolated from the complex with hexamethylenediamine in a solution of vinyl butyl ether by adding methacrylic acid in an amount proportional in moles to the amount of amine before introducing butyl acrylate. The triethylboron was oxidized by the air oxygen remaining in the reaction mixture during the boiling of vinyl butyl ether. The dosing of butyl acrylate was carried out at varying times: 20 minutes, 40 minutes and 60 minutes, and then the reaction mixture was thermostated for some time. At the end of the polymerization, the liquid fraction was distilled off. The obtained samples of copolymers, which were viscous, were dried; their conversion was evaluated by dry residue gravimetrically. Molecular weight parameters were determined for all samples by gel permeation chromatography. A differential refractometer R-403 (Å (Shimadzu) was used as a detector. Tetrahydrofuran was used as the eluent. Narrow-dispersed polystyrene standards were used for calibration. Polystyrene samples were converted to copolymer with the use of standard formulas for polystyrene samples. It has been shown immediately after finishing butyl acrylate dosing that copolymer molecular weight distribution curves are bimodal, oligomeric molecular weight distribution curves have low molecular mass (M n less than 1000) and polydispersity coefficient (M w /M n )=1.1-1.2. Significantly larger low molecular weight modes have a molecular weight value ~30000, in all cases. Similar proportions for these two peaks are observed after thermostating the reaction mixtures after the introduction of butyl acrylate at the boiling point of vinyl butyl ether for another 20 minutes, the oligomeric curve of the molecular weight distribution of the first sample shifts in relation to that for the copolymer sample, selected immediately after dosing butyl acrylate for 20 minutes, and increasing the values of its molecular weight while maintaining polydispersity coefficient of 1.1. At the same time, for the other two samples, no shift in the molecular weight distribution is observed, as well as changes in the molecular weight values. In addition, the proportion of oligomer in relation to the low molecular weight polymer with a molecular weight of ~ 30000 decreases. Longer temperature control of the reaction mixture for two hours and more, after the end of dosing of butyl acrylate for both 40 and 60 minutes, unlike the process with dosing butyl acrylate for 20 minutes, also does not shift the molecular mass distribution curves of both peaks. This decreases the proportion of oligomeric peak in both cases.

Dispersion Media Based on Aqueous Binary Compositions Modified by PEG-Stearox-6 for Abrasive Metalworking

Test results of the dispersive, rheological, and surface active characteristics of aqueous emulsions of the oxyethylated stearic acid derivatives (Stearox-6) and aqueous binary compositions modified by PEG–Stearox-6 are presented. Both synergism and antagonism of the dispersion effect of components being incorporated into the aqueous binary compositions (ABC) during the process of abrasive machining of steel 45 are established. The value of synergism regarding the dispersion action of ABC components is defined by the possibility to form intermolecular complexes between the molecules of amine-based oligomers of different molecular weight (MW) and Stearox-6, and antagonism is determined by their competitive adsorption at the as-formed surface of steel.

In vitro interactions of histones and α-crystallin

The aggregation of crystallins in lenses is associated with cataract formation. We previously reported that mutant crystallins are associated with an increased abundance of histones in knock-in and knockout mouse models. However, very little is known about the specific interactions between lens crystallins and histones. Here, we performed in vitro analyses to determine whether α-crystallin interacts with histones directly. Isothermal titration calorimetry revealed a strong histone–α-crystallin binding with a Kd of 4 × 10−7 M, and the thermodynamic parameters suggested that the interaction was both entropy and enthalpy driven. Size-exclusion chromatography further showed that histone–α-crystallin complexes are water soluble but become water insoluble as the concentration of histones is increased. Right-angle light scattering measurements of the water-soluble fractions of histone–α-crystallin mixtures showed a decrease in the oligomeric molecular weight of α-crystallin, indicating that histones alter the oligomerization of α-crystallin. Taken together, these findings reveal for the first time that histones interact with and affect the solubility and aggregation of α-crystallin, indicating that the interaction between α-crystallin and histones in the lens is functionally important.

Synthesis of semicrystalline poly(guanamine)s based on 2-substituted-4,6-dichloro-1,3,5-triazine with α, ω-alkylene diamines, and the formation of cyclic tetramers

Polycondensation of various 2-substituted-4,6-dichloro-1,3,5-triazine such as N,N-diphenylamino (DCPT), benzylamino (BnDCT) substituents with α, ω - alkylene diamines including hexamethylene (HMDA), octamethylene (OcDA), decamethylene (DcDA), and dodecamethylene diamine (DdDA) was performed, and the resultant polymers were analyzed. Two-phase polymerization in nitrobenzene/aqueous NaHCO3 at 100 °C resulted in a high molecular weight (MW) polymer (Mn = 12,400) with a small fraction (26.7 wt%) of low MW oligomer, whose main component was confirmed as a 4-membered cyclic compound. Polymers prepared with HMDA were crystalline with poor solubility, whereas those with OcDA, DcDA, and DdDA were all amorphous with high MWs (Mn = 40,000–60,000) and good solubility enough to prepare the self-standing transparent films. The polymers show moderate glass transition temperatures from 76 °C to 159 °C. In differential scanning calorimetry measurements, only poly(BnDCT-HMDA) showed a clear endothermic peak (ΔH = 119 J/g), which corresponds to melting at 220 °C.

Thiol-Michael ‘click’ hydrogels as an imageable packing material for cancer therapy

Gynecological cancer treatment strategies commonly employ pelvic brachytherapy, a technique that temporarily locates radioactive materials in or near the source of the tumor. Despite numerous advances in brachytherapy treatment protocols, advances in the required vaginal packing materials lag significantly. This paper describes a packing material for vaginal brachytherapy based on a poly(ethylene glycol) (PEG)-based hydrogel. Commercially available oligomeric starting materials rapidly formed a hydrogel upon action of mild base (NaHCO3) through a thiol-Michael addition reaction. Tuning the base concentration enabled rapid formation of hydrogels with moduli sufficient for effective tissue displacement (>10 kPa). The poly(ethylene glycol) diacrylate oligomer molecular weight exerted minimal influence on the hydrogel modulus. The hydrogels absorbed up to four times their weight in water from the dry state. CT imaging demonstrated distinguishability between hydrogel, water, and metal medical tools. The hydrogels did not induce significant IL-8 upregulation or cytotoxicity when cultured against vaginal macrophage cells, suggesting lack of immunogenicity. Our findings support these hydrogels as ideal candidates for a packing material in pelvic brachytherapy applications.