Narrow Molecular Mass Distribution Research Articles

Synthesis of Polymers with Narrow Molecular Mass Distribution through Interface-Initiated Room-Temperature Polymerization in Emulsion Gels.

Homopolymers of n-butyl acrylate, methyl methacrylate, styrene, and their random copolymers were prepared via interface-initiated polymerization of emulsion gels at 20 °C. The polymerization was conducted in a free radical polymerization manner without inert gas protection. Compared with the polymers synthesized at 60 °C, the polymerization of emulsion gels at 20 °C produced homo- and copolymers with a higher molecular mass and a narrower molecular mass distribution. The polydispersity indices for the polymers synthesized at 20 °C were found to be between 1.12 and 1.37. The glass transition temperatures for the as-synthesized butyl acrylate copolymers agree well with the prediction from the Gordon-Taylor equation. Interface-initiated room-temperature polymerization is a robust, energy-saving polymerization technique for synthesizing polymers with a narrow molecular mass distribution.

Preparation and Characterization of PAM‐b‐DOPOAA by ATRP

AbstractPolyacrylamide has been a hot topic of research in recent years, however, the preparation of block copolymers of polyacrylamide using ATRP method has been little studied. In this paper, polyacrylamide with reactive group bromine (PAM−Br) was synthesized by atom transfer radical polymerization (ATRP) using acrylamide (AM) as the monomer and water as the solvent, and polyacrylamide was used as the macromolecular initiator for the next reaction step. Then 9,10‐dihydro‐9‐oxa‐10‐phosphafi‐10‐oxide (DOPO) was organically modified to obtain acrylate monomers with DOPO functional groups (DOPOAA), and a mixture of water and N, N‐dimethylformamide (DMF) was used as the solvent to obtain PAM‐b‐DOPOAA block copolymers with controllable molecular mass and narrow molecular mass distribution. The effects of the molecular mass of the macromolecular initiator, polymerization time, and the molar ratio of catalyst to the ligand on the polymerization process were investigated. The structure and properties of the products were also characterized by 1H‐NMR, FTIR, XPS, DSC, TG, etc. The PAM‐b‐DOPOAA prepared by ATRP method can artificially design the length and ratio of the two chain segments, realizing one additive with two functions and the permanent existence of the function of polymer additives.

Influence of Hollander beater refining on xylan extraction from hardwood paper pulp by cold caustic extraction and xylanase treatment

Cellulose fibers’ complex and compact structure hinders the quantitative extraction of residual hemicelluloses from the fiber wall. In this study, hardwood kraft paper pulp was subjected to refining with a Hollander beater at different refining loads (3, 4.5, and 5.5 kg) in order to assess the impact of refining load on xylan removal by cold caustic extraction. The refined pulp showed high water retention values and specific surface area, which increased accessibility and a correspondingly high degree of xylan removal. Coupling refining and cold caustic extraction (100 g/L soda) achieved over 50% more xylan removal than the unrefined pulp (3% against 7%, respectively). Furthermore, an improvement in xylan removal (79%) was achieved by implementing a one-pot simultaneous refining and cold caustic extraction treatment at half the time required for the sequential treatment and low soda concentration (60 g/L). Finally, the benefit of beating was also observed for xylanase treatment. Overall, the combined extractions made it possible to remove 85% of xylan from a conventional hardwood paper pulp giving rise to a high purity cellulose pulp with unimodal and narrow molecular mass distribution.

Design of High-Relaxivity Polyelectrolyte Nanocapsules Based on Citrate Complexes of Gadolinium(III) of Unusual Composition.

Through nuclear magnetic relaxation and pH-metry, the details of the complexation of gadolinium(III) ions with citric acid (H4L) in water and aqueous solutions of cationic polyelectrolytes are established. It is shown that the presence of poly(ethylene imine) (PEI) in solution affects magnetic relaxation behavior of gadolinium(III) complexes with citric acid (Cit) to a greater extent than polydiallyldimethylammonium chloride (PDDC). A large increase in relaxivity (up to 50 mM−1s−1) in the broad pH range (4–8) is revealed for the gadolinium(III)–citric acid–PEI system, which is particularly strong in the case of PEI with the molecular weight of 25 and 60 kDa. In weakly acidic medium (pH 3–7), the presence of PEI results in the formation of two tris-ligand associates [Gd(H2L)3]3− and [Gd(H2L)2(HL)]4−, which do not exist in aqueous medium. In weakly alkaline medium (pH 7–10), formation of ternary complexes Gd(III)–Cit–PEI with the Gd(III)–to–Cit ratio of 1:2 is evidenced. Using transmission electron microscopy (TEM) and dynamic light scattering techniques (DLS), the formation of the particles with the size of 50–100 nm possessing narrow molecular-mass distribution (PDI 0.08) is determined in the solution containing associate of PEI with tris-ligand complex [Gd(H2L)2(HL)]4−.

Analysis of glycidyl nitrate polymerization reaction

Poly(glycidyl nitrate) (PGN) is a high-energetic polymer whose properties are determined by the presence of an –ONO2 explosophoric group. PGN can be obtained by polymerization of glycidyl nitrate (GN) monomers. The preferred polymerization route is via the activated monomer mechanism, due to its two main advantages: narrow molecular mass distribution of the obtained polymer and ability to control the heat generated during the reaction. The study allowed the GN monomer to be obtained as a product of nitration of epichlorohydrin. A series of GN polymerization reactions was conducted under different conditions (temperature, time and reactant amounts). The analysis showed that the lower the catalyst to initiator ratio, the higher the molecular mass of the obtained polymer (PGN). A temperature between 0-10 °C is the optimum temperature for GN polymerization. The longer the GN polymerization time the higher the molecular mass of the PGN. The GN polymerization reaction was scaled up without affecting the molecular mass or other properties of the obtained polymers. The following tests were carried out to determine the basic properties of PGN: GPC, 1H NMR, FTIR, DSC, TG, calorific value, viscosity, sensitivity to friction and impact.

Nickel(II) Complexes with Mono(imino)pyrrole Ligands: Preparation, Structure, and MMA Polymerization Behavior

A simplified synthetic method was initiated to prepare the corresponding nickel complexes NiL2 (I–III) with direct condensation of mono(imino)pyrroles (L1–L3) and nickel dichloride, the structures and methyl methacrylate (MMA) catalytic polymerization behavior of this series of mono(imino)pyrrole nickel complexes were presented. The mono(imine)pyrrole ligands and the corresponding nickel complexes were determined by 1H NMR, 13C NMR, IR and MS, etc. Complexes I and III were further characterized by X-ray crystal diffraction (CIF files CCDC nos. 1890965 (I), 1890964 (III)). Both of the structures showed that the ligand chelated to nickel with 2 : 1 molar ratio. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for MMA polymerization and catalyst structure, reaction time, reaction temperature, and ratio of monomer with catalyst. The optimum reaction conditions of the molar ratio of monomer to catalyst is of 1200 : 1, the polymerization temperature of 100°C, time of 10 h, the nickel complex with two bulky substituents on the o-position of phenyl ring linked with imine showed excellent catalytic activities for MMA polymerization (4.791 × 104 g mol–1 h–1), high molecular weight (Mn = 65.873 × 103 g mol–1), and narrow molecular mass distribution (polymer dispersity index = 3.9877), and azodiisobutyronitrile acted as co-catalyst during MMA polymerization.

Исследования по подбору отечественной вязкостной присадки для всесезонных гидравлических масел уровня HVLP

At the present time, imported viscosity additives purchased abroad are used to produce premium multi-grade hydraulic oils in Russia. The high technology production such oils is entirely dependent on the import of these additives. At the JSC "MidVolgaNIINP" conducted research on the development and selection of domestic viscosity additives is not inferior to foreign analogues in the composition of hydraulic oils of the HVLP. For select the domestic viscous additive of optimal quality were studied three laboratory samples of polyalkyl methacrylate additives in physicochemical and operational properties in base oil. The results obtained were selected a domestic viscosity additive with a narrow molecular-mass distribution (2.19 Р) and a minimal weighted average molecular weight (34983 Da) that allows hydraulic oils to meet the requirements DIN 51524-3 and OEM. Studies had found that the quality of thickened oils is affected by the content viscous additive. The optimal contents of domestic additives for obtaining oils of viscosity levels ISO VG 32 and ISO VG 46 have been determined. The results are used in further research on the development of multi-grade hydraulic oils HVLP.

Synthesis of Polyester-graft-Polyoxazolines on the Basis of Macroinitiators of Sulfonyl Chloride Type

Comb-shaped thermosensitive polymers have been synthesized on macroinitiators of sulfochloride type via cationic polymerization of 2-ethyl-2-oxazoline. It has been proved that, on sulfochloride macroinitiators, the polymerization proceeds in the “living” chain mode and allows one to obtain polymers with a narrow molecular mass distribution, in particular, without the intermediate isolation of the macroinitiator.

Molecular Mass-Dependent Resorption and Bone Regeneration of 3D Printed PPF Scaffolds in a Critical-Sized Rat Cranial Defect Model.

The emergence of additive manufacturing has afforded the ability to fabricate intricate, high resolution, and patient-specific polymeric implants. However, the availability of biocompatible resins with tunable resorption profiles remains a significant hurdle to clinical translation. In this study, 3D scaffolds are fabricated via stereolithographic cDLP printing of poly(propylene fumarate) (PPF) and assessed for bone regeneration in a rat critical-sized cranial defect model. Scaffolds are printed with two different molecular mass resin formulations (1000 and 1900 Da) with narrow molecular mass distributions and implanted to determine if these polymer characteristics influence scaffold resorption and bone regeneration in vivo. X-ray microcomputed tomography (µ-CT) data reveal that at 4 weeks the lower molecular mass polymer degrades faster than the higher molecular mass PPF and thus more new bone is able to infiltrate the defect. However, at 12 weeks, the regenerated bone volume of the 1900 Da formulation is nearly equivalent to the lower molecular mass 1000 Da formulation. Significantly, lamellar bone bridges the defect at 12 weeks with both PPF formulations and there is no indication of an acute inflammatory response.

Non-Innocent Methylene Linker in Bridged Lewis Pair Initiators.

Deprotonation usually occurs as an unwanted side reaction in the Lewis pair polymerization of Michael acceptors, for which the conjugated addition of the Lewis base to the acid-activated monomer is the commonly accepted initiation mechanism. This has also been reported for B-P-based bridged Lewis pairs (BLPs) that form macrocyclic addition products. We now show that the formerly unwanted deprotonation is the likely initiation pathway in the case of Al-P-based BLPs. In a detailed study of a series of Al-P-based BLPs, using a combination of single-crystal diffraction experiments (X-ray and neutron) and mechanistic investigations (experimental and computational), an active role of the methylene bridge was revealed, acting as a base towards the α-acidic monomers. Additionally, the polymerization studies proved a living behavior combined with significantly high activities, narrow molecular mass distributions, and the possibility of copolymerization.

Controlled ATRP Synthesis of Novel Linear-Dendritic Block Copolymers and Their Directed Self-Assembly in Breath Figure Arrays.

Herein, we report the formation and characterization of novel amphiphilic linear-dendritic block copolymers (LDBCs) composed of hydrophilic dendritic poly(ether-ester), PEE, blocks and hydrophobic linear poly(styrene), PSt. The LDBCs are synthesized via controlled atom transfer radical polymerization (ATRP) initiated by a PEE macroinitiator. The copolymers formed have narrow molecular mass distributions and are designated as LGn-PSt Mn, in which LG represents the PEE fragment, n denotes the generation of the dendron (n = 1–3), and Mn refers to the average molecular mass of the LDBC (Mn = 3.5–68 kDa). The obtained LDBCs are utilized to fabricate honeycomb films by a static “breath figure” (BF) technique. The copolymer composition strongly affects the film morphology. LDBCs bearing acetonide dendron end groups produce honeycomb films when the PEE fraction is lower than 20%. Pore uniformity increases as the PEE content decreases. For LDBCs with hydroxyl end groups, only the first generation LDBCs yield BF films, but with a significantly smaller pore size (0.23 μm vs. 1–2 μm, respectively). Although higher generation LDBCs with free hydroxyl end groups fail to generate honeycomb films by themselves, the use of a cosolvent or addition of homo PSt leads to BF films with a controllable pore size (3.7–0.42 μm), depending on the LDBC content. Palladium complexes within the two triazole groups in each of the dendron’s branching moieties can also fine-tune the morphology of the BF films.

Mechanism of Catalytic Polymerization of 2-Hydroxyethyl Methacrylate under the Influence of Vanadium(IV) Oxo Complex

An oxovanadium(IV) complex with dimethyl sulfoxide exhibits a substantial catalytic activity for the reaction of polymerization of 2-hydroxyethyl methacrylate (HEMA) with high selectivity for monomer. The complex does not catalyze polymerization of other monomers, including other methacrylates. A carbo-chain structure of polymeric HEMA is established by 13 C NMR. The resulting poly-HEMA has a narrow unimodal molecular mass distribution. It is found that the polymerization is catalytic in nature. A coordination mechanism for this polymerization is proposed.

INVESTIGATION THE OLIGOMERIZATION PROCESS OF HEXENE-1

In article for oligomerization and alkylation processes, to obtain a useful and highly stable active catalyst, New Catalytic Complex (NCC) synthesized which is based on aluminum metal using C2H4Cl2 and this complex has shown high stability in alkylation, oligomerization processes compared to other aluminum-containing catalysts. It is difficult to regulate the molecular mass distribution of received products during oligomerization, either Intensificate the oligomerization process of olefins that is why this process take place in presence of obtaining of bimetal catalytic complex with a highly stable activity from the modification of the New Catalytic Complex(NCC) with transition metal chloride. Comparatively studied oligomerization of Hexen-1 in present of new bimetallic catalytic complex which was modified by NCC and chromium salt (NCC/CrCl3), effect of temperature, reaction time, concentration of the catalyst and the proportion of catalyst components (Al:Cr) in the process was investigated.It was determined that at the initial time (10 min) conversion hexene-1 and the yield of purposeful oil fraction were low. Increasing time, conversion rate of Hexen-1 increases and the optimal time for the process is considered as 60 minutes. In low concentrations of catalyst (0,1-0,3) oligomerization of hexene-1 is low but in high concentrations(>1%) reaction goes with high rate, at optimal concentration 0,5% mass both the yield of oil fraction and its chemical-physical properties were high.In oligomerization process investigated ratio effect of catalyst components Al: Cr that was used Al: Cr=(4-32):1 mol.It has been revealed that oligomerization of Hexen-1, at low mol ratio of components (4:1), received yield of oligomer fraction decreases while mol ratio increases (16:1, 32:1).Studies determined that bimetallic complex at 8:1 mole has shown the maximal activity in oligomerization process of Hexen-1.The effect of the temperature on the oligomerization process was studied in the range of 30-60ºC, increasing the temperature up to 50 °C has a positive effect on the course of the process and despite providing complete oligomerization of hexene-1 its also providing increasing the amount of oil fractions with high viscosity. According to the researches, the optimal conditions for the oligomerization process of hexene-1 with the participation of the bimetallic catalytic complex: reaction time – 60 min., concentration of catalyst – 0,5 % by wt., mol ration of components Al:Cr = 8:1, temperature – 50 °C. In known optimal condition its possible to obtain oligomers with physical indications, characterized by narrow molecular mass distribution, by new catalytic complex that was modified by chromium salt.Such products have special importance, as low-freezing, high viscosity index qualitative engine oils.Synthesis of bimetallic catalytic complexes, with their presence in oligomerization of olefins and fractions, opens wide range perspectives in synthesis of different high-molecular compounds in industry

Products of hydrothermal treatment of lignin and the importance of ortho-directed repolymerization reactions

Alkaline hydrothermal treatment (HTT) of Protobind 1000 lignin was studied to improve the understanding of lignin conversion paths. HTT was performed at 300°C using NaOH as base catalyst. Product separation by acidification and solvent fractionation resulted in a liquid product of low molecular mass and narrow molecular mass distribution and two high molecular mass solid fractions. Twenty volatile compounds accounted for about 36wt% of the liquid product, however, the analysis by liquid injection GC–MS was estimated to detect only about 12wt% of the total products. Analytical pyrolysis was applied to investigate the pyrolyzable fraction of the liquid product and the high molecular mass fractions. The pyrolyzable mass accounted for 49wt% of the total products. The liquid product was quantitatively pyrolyzed at 500°C (91±10wt%) while less than half of the high molecular mass fractions were pyrolyzed. Several chemical features of the pyrolysates suggested that ortho-directed alkylation and condensation reactions of phenolate ions were important for the production of oligomeric and polymeric aromatic compounds during HTT. Increased abundancy of hydroxyphenyl and o-alkyl aromatic pyrolysates in the high molecular mass fractions suggested that the syringyl units of the raw lignin were less affected by repolymerization reactions than hydroxyphenyl and guaiacyl units. These results suggest that the monolignol composition of lignin is an important factor for the valorization of lignin by alkaline hydrothermal treatment.

Synthesis of multiarm star block copolymers via simplified electrochemically mediated ATRP

Star-shaped polymers were received using β-cyclodextrin (β-CD) as core, and methyl methacrylate (MMA) arms via a simplified electrochemically mediated ATRP (seATRP). To demonstrate the living nature of the seATRP, star multiblock copolymers were successfully prepared by chain extension of the ω-functional PMMA arms with a tert-butyl acrylate (tBA), and respectively, n-butyl acrylate (BA). Novelty of this work is that the β-CD-PMMA-b-PtBA-b-PBA multiarm star block copolymers were synthesized for the first time via seATRP procedure, utilizing 4 × 10−6 mol% of CuII complex. The results from 1H NMR spectral studies support the formation of 21-arm star (co)polymers. Furthermore, the GPC traces of the arms detached from synthesized star-like (co)polymers confirms the absence of star–star coupling reactions during seATRP. It was shown as an advantage over other ATRP methods–low catalyst concentrations and narrow molecular mass distributions, while maintaining well-defined composition.

Enzymatic production of specifically distributed hyaluronan oligosaccharides

High-molecular-mass hyaluronan (HA) was controllably depolymerized in pure aqueous solution with recombinant leech hyaluronidase (HAase). The HAase concentration per unit HA and hydrolysis time played important roles in molecular mass distribution. By modulating the concentrations of HAase and controlling the hydrolysis time, any molar-mass-defined HA oligomers could be efficiently and specifically produced on a large scale (40g/L), such as HA oligosaccharides with weight-average molar mass of 4000, 10,000, and 30,000Da and end hydrolysates containing only HA6 and HA4. High performance liquid chromatography-size exclusion chromatography, polyacrylamide gel electrophoresis, capillary zone electrophoresis, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry confirmed low polydispersity of the produced molar-mass-defined HA oligosaccharides. Therefore, large-scale production of defined HA oligosaccharides with narrow molecular mass distribution will significantly promote progress in related research and its potential applications.

Purification and characterization of kraft lignin

AbstractTo upgrade the utilization of kraft lignin (KL) for high-performance lignin-based materials (e.g., carbon fiber), the purity, molecular mass distribution (MMD), and thermal properties need to be improved and adjusted to target values. Therefore, different methods, such as ultrasonic extraction (UE), solvent extraction, dialysis, and hot water treatment (HWT), were applied for the purification of KL. The chemical and thermal properties of purified lignin have been characterized by nuclear magnetic resonance, Fourier transform infrared, gel permeation chromatography, elemental analysis, differential scanning calorimetry, and thermogravimetric analysis. The lignin fractions obtained by UE with ethanol/acetone (E/A) mixture (9:1) revealed a very narrow MMD and were nearly free of inorganic compounds and carbohydrates. Further, the E/A-extracted lignin showed a lower glass transition temperature (Tg) and a clearly detectable melting temperature (Tm). Dialysis followed by HWT at 220°C is an efficient method for the removal of inorganics and carbohydrates; however, lignin was partly forming condensed structures during the treatment.

Synthesis of Polyisoprene with Narrow Relative Molecular Mass Distribution Using Nd(OiPr)3-based Catalytic System

The effects of chloride donor and aging temperature of neodymium isopropoxide /diisobutylaluminum hydride / chloride donor( Nd( OiPr)3/ Al( iBu)2H / RCl) catalyst on isoprene polymerization were investigated. The resulting polymer was fully assessed by NMR,IR and GPC. Chloride donors greatly influenced the relative molecular mass distribution( MWD) of plyisoprene and only Nd( OiPr)3/ Al( iBu)2H / Me2SiCl2catalytic system could afford polyisoprene with a narrow MWD. In the Nd( OiPr)3/ Al( iBu)2H / Me2SiCl2catalytic system,the polymerization results showed that MWD of polyisoprene kept around 1. 5 when the catalyst was aged at 0 ~ 50 ℃ and became much broader( MWD 6. 0) when the aging temperature was above 50 ℃. Additionally,the yield and 1,4-content of polyisopere increased with the aging temperature.

Controlled copolymerization of acrylonitrile in bulk via the reversible addition-fragmentation chain-transfer mechanism

The pseudoliving radical binary copolymerization of acrylonitrile with methyl acrylate, styrene, n-butyl acrylate, and tert-butyl acrylate in bulk in the presence of the reversible addition-fragmentation chain-transfer agent dibenzyl trithiocarbonate is performed for the first time. The addition of trithiocarbonate makes it possible to prepare a narrowly dispersed visually optically transparent copolymer in a wide range of monomer-feed compositions even at limiting conversions. Conditions for the synthesis of acrylonitrile copolymers with controlled molecular masses and narrow molecular-mass distributions are ascertained. In the above copolymers, the trithiocarbonate group is shown to be located within the chain.

Enzyme-catalyzed ring-opening polymerization of ε-caprolactone using alkyne functionalized initiators

Well-defined poly(caprolactone)s were generated using alkyne-based initiating systems catalyzed by Candida antarctica Lipase B (CALB). Propargyl alcohol and 4-dibenzocyclooctynol (DIBO) were shown to efficiently initiate the polymerizations under metal free conditions and yielded 4 to 24 KDa polymers with relatively narrow molecular mass distribution. The alkyne bonds in the strained and unstrained initiating systems survived the polymerization conditions and the purification process. The resulting bonds can be sequentially functionalized post-polymerization using metal free and copper catalyzed click chemistry conditions.