High Molecular Weight Copolymers Research Articles

Flexible Axial Shielding Strategy for Improving Ethylene (Co)polymerization with 8-Cycloalkylnaphthyl α-Diimine Catalysts.

8-aryl or alkyl-naphthyl substituents are widely used as an effective axial shielding strategy for the suppression of chain transfer in late-transition metal-catalyzed ethylene (co)polymerization to yield high molecular weight polyethylene and copolymers. In this study, two 8-cycloalkylnaphthyl acenaphthene-based α-diimine ligands and the corresponding four nickel and palladium complexes were designed and synthesized to explore the effect of axial flexible shielding on ethylene (co)polymerization. In ethylene polymerization, the nickel complexes displayed high activities (up to 1.99 × 106 g mol-1 h-1) and generated lightly branched (34-54/1000 C) polyethylenes with high molecular weights (up to Mn = 1075 kg/mol), whereas the corresponding palladium complexes exhibited moderate activities (level of 104 g mol-1 h-1), producing highly branched (111-125/1000 C) polyethylenes with high molecular weights (up to Mn = 37.6 kg/mol). Highly branched (110-123/1000 C) E-MA copolymers with moderate insertion ratios (1.97-5.56 mol %) were produced by these palladium complexes in ethylene/methyl acrylate (MA) copolymerization. In addition, the size of the 8-cycloalkyl ring in these α-diimine catalysts strongly influences the ethylene (co)polymerization. Compared to cyclopentyl groups, cyclohexyl groups are more effective in suppressing chain transfer reactions in the polymerization of ethylene and the copolymerization of ethylene and MA, leading to higher molecular weight polyethylene and E-MA copolymers. Most interestingly, compared to the reported rigid planar 8-arylnaphthyl catalysts, the flexible 8-cyclohexylnaphthyl catalysts exhibited higher activity and produced higher molecular weight polyethylene in ethylene polymerization. Moreover, in nickel-catalyzed ethylene polymerization, the cyclohexyl catalyst produced significantly reduced branched polyethylene, while in palladium-catalyzed ethylene (co)polymerization, the cyclohexyl catalyst produced more highly branched polyethylene and copolymers. In contrast to the previously reported flexible 8-butylnaphthyl nickel catalysts, the 8-cycloalkylnaphthyl catalysts reported in this work yielded polyethylene with narrow unimodal molecular weight distributions.

Synthesis of water soluble ionic liquid copolymers based on acrylamide and investigation of their properties in flocculating of clay suspensions

To overcome water absorption and swelling by clay mineral layers, it is very important to develop stabilizing additives for water-based drilling fluids, where organic polymers are used as raw materials. Acrylamide copolymers, acting as flocculating agents, have the potential to separate minerals such as montmorillonite. In this study, three water-soluble copolymers containing acrylamide-amphoter, acrylamide-amphoter-anion, and acrylamide-amphoter-cation were synthesized and characterized using various analytical techniques, including Fourier-transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, and derivative thermal gravimetric techniques. These copolymers were employed as flocculants to treat water suspensions containing montmorillonite particles, and a range of analytical methods, such as sedimentation volume measurement, scanning electron microscopy analysis, X-ray diffraction analysis, and contact angle measurement, were employed to identify the relationship between inhibitive performance. The flocculation of montmorillonite plates was attributed to the electrostatic attractions between montmorillonite and the synthesized copolymers. High molecular weight copolymers offer greater thermal stability and better flocculation characteristics for water-based drilling fluids. Among the tested copolymers, the acrylamide-amphoter-anion sample, with the highest molecular weight, exhibited the best performance as a coagulant when compared to the other copolymers.

Synthesis of Si‐O‐Si bridged diamido Group 4 complexes and the applications to polymerization of olefins

Titanium, zirconium, and hafnium complexes O[Me2Si(Dip)N]2MCl2 [Dip = 2,6‐iPr2C6H3; M = Ti (1), Zr (2), Hf (3)], O[Me2Si(tBu)N]2ZrCl2 (4), and O[iPr2Si(Dip)N]2ZrCl2 (5) supported by Si‐O‐Si bridged diamido ligands were synthesized. X‐ray diffraction analysis disclosed that complex 2 displays a distorted trigonal bipyramidal geometry. Complexes 1–5, upon the activation with sMAO, exhibited diverse catalytic performance for the polymerization of ethylene and copolymerization of ethylene with norbornene or 1‐octene. For ethylene homopolymerization, both complexes 1–2 are good catalysts giving polymer with high molecular weight and narrow polydispersities. Complex 2 catalyzed copolymerization of ethylene with 1‐octene exhibiting high catalytic activity but with norbornene showing moderate activity, affording corresponding high molecular weight copolymers with relatively high comonomer incorporations of 11% and 29%, respectively.

Improvement of the self‐assembly of low χABA triblock copolymers with the addition of an ionic liquid

AbstractSelf‐assembly of high molecular weight commercially available low χ ABA triblock copolymers with ionic liquids (ILs) was observed after solvent casting without the implementation of an additional annealing step. Here, the addition of an IL to a triblock copolymer poly(methyl methacrylate‐b‐butyl acrylate‐b‐methyl methacrylate) (MAM) with an elastomeric central block and rigid end blocks is proposed to tune the self‐assembled morphology. Two different compositions of this copolymer with different initial microstructures (ill‐defined morphology without long‐range order and a lamellar morphology) were selected. The selectivity of the IL addition in one of the block phases was studied through the evolution of the glass transition of both blocks. The impact of the IL weight concentration on the morphology as well as the domain spacing is presented. Adding IL to the first copolymer detected a lyotropic disorder–order transition towards a gyroid morphology, observed even for a high molecular weight copolymer due to the low χ parameter, and for higher IL content a second transition to a lamellar morphology was observed. For the second copolymer, only an order–order transition (lamellae to cylinders) could be detected at high IL content. IL also enhanced the long‐range ordering of the MAM morphology obtained through solvent casting without additional annealing steps, compared with the same composition without IL. © 2022 Society of Industrial Chemistry.

Polymerization of butadiene, isoprene and 1-substituted dienes using cobalt catalysts

Cobalt complexes carrying 6-(N-di-tert-butylphosphinoxide)-2-(2′-R-2H’-benzoimidazole)- aminepyridine (R = H, Co1; ethyl, Co2 and benzyl, Co3) ligand were prepared and characterized by FT-IR, UV–vis and elemental analysis. Single crystal X-ray diffraction analysis revealed that Co2 displayed a distorted trigonal bipyramid configuration via N, N, O-tridentate coordination to cobalt center. Activated with AlEt2Cl or MAO, all cobalt complexes are notably active in butadiene and isoprene polymerization, affording cis-1,4 polybutadiene and cis-1,4/3,4 polyisoprene, respectively. The formed catalysts are also efficient for 1-phenyl-1,3-butadiene and 1-(4′-methoxylphenyl)-1,3-butadiene polymerizations, but surprisingly result in partially cyclic product probably arising from Friedel-Craft reaction of formed internal olefin with pending aryl group. Copolymerization of isoprene with 1-substituted-1,3-butadiene is able to afford a series of high molecular weight copolymers with 1.4–8.7 mol-% incorporation rate that free of cyclization. The effects of the substitution pattern of monomer on the polymerization reactivity are also evaluated.

Promoting Ethylene (co)Polymerization in Aliphatic Hydrocarbon Solvents Using tert‐Butyl Substituted Nickel Catalysts

Comprehensive SummaryIn the past few decades, the development of high‐performance catalysts has been a key driving force and a center of research efforts in the field of olefin polymerization. However, a major discrepancy exists between industrial researches which utilize aliphatic hydrocarbon solvents, and academic researches which predominantly focus the catalytic properties in aromatic solvents. In this contribution, a novel diaryl‐methyl aniline bearing eight tert‐butyl groups was prepared and subsequently transformed to four different kinds of imine‐type ligands. The corresponding nickel complexes as well as their counterparts derived from diphenyl‐methyl aniline without the tert‐butyl groups were prepared and investigated in ethylene polymerization. The multiple tert‐butyl groups enable great solubility of the metal complexes in aliphatic hydrocarbon solvents, leading to similar polymerization properties comparing with aromatic solvents. In contrast, their counterparts without tert‐butyl groups demonstrate significant solvent effect. Moreover, the ligand electronic and steric effects induced by the tert‐butyl groups lead to nickel catalysts with great thermal stability (up to 140 oC) and capabilities of generating high molecular weight polymer and copolymer products. This tert‐butyl strategy can be potentially applied to many different polymerization catalyst systems and help to bridge academic studies with practical applications.

Salt endurable and shear resistant polymer systems based on dynamically reversible acyl hydrazone bond

The macromolecule systems constructed via dynamic covalent bonds may exhibit high viscosity and elasticity. The ketone-based copolymers were prepared via free radical copolymerization of acrylamide (AM) with diacetone acrylamide (DAAM). And the cross-linked copolymer based on dynamic acyl hydrazone bond was formed by ketone-based copolymer and adipic dihydrazide (ADH). The optimum conditions for the construction of the cross-linked copolymer and its salt endurance, shear resistance and temperature tolerance were investigated by viscosity analysis, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Moreover, the viscoelasticity behavior of copolymers in aqueous solution was explored by rheology measurements. The results showed that the system had excellent viscosity with a 1 M ratio of hydrazide at 3000 mg/L. Furthermore, the cross-linked copolymer still maintained a large hydrodynamic radius and considerable viscosity at high salinity, even after high-speed shear. The combination of high molecular weight copolymer and dynamic covalent bond makes the copolymer exhibit excellent salt and shear resistance, which provides an alternative thought of enhancing oil recovery.

Membrane properties of trisulfonated hydrophilic and partially fluorinated hydrophobic multiblock copolymer

A multiblock copolymer with increased charge density in the hydrophilic phase was synthesized by utilizing a trisulfonated poly(arylene ether sulfone) backbone (SHQS100). To achieve a balance of membrane properties a partially fluorinated poly(arylene ether benzonitrile) hydrophobic phase (6FPAEB) was used in uneven block lengths to form the hydrophilic-hydrophobic multiblock copolymer. Multiblock copolymers were synthesized via nucleophilic aromatic substitution to achieve high molecular weight copolymers and corresponding ductile membranes. Combination of the shorter increased charge density hydrophilic phase and longer partially fluorinated hydrophobic phase resulted in superior proton conductivity and mechanical properties while limiting water uptake and swelling, despite high ion-exchange capacity. The trifunctional SHQSH hydrophilic phase is proposed to produce a more concentrated charge region in the hydrophilic phase, while swelling of the membrane was limited by a longer partially fluorinated hydrophobic phase.

Anion exchange membranes containing no β-hydrogen atoms on ammonium groups: synthesis, properties, and alkaline stability.

Novel anion conductive polymer membranes have been designed and synthesized to investigate whether the absence of β-hydrogen atoms of ammonium groups affects the membranes' properties and chemical stability. The hydrophilic monomer, 2,2-bis(4-chlorobenzyl)-2-phenyl-ethylamine (3), was obtained via a two-step reaction with an overall yield of 98% under mild reaction conditions. Ni(0)-promoted copolymerization of 3 with 2,2-bis(4-chlorophenyl)hexafluoropropane (1) afforded high molecular weight copolymers (Mn = 12.8–19.6 kDa, Mw = 82.1–224.6 kDa). After quaternization with iodomethane, QBAF-BS polymers formed bendable, robust membranes from solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.50 to 2.44 mequiv. g−1. The membranes exhibited high hydroxide ion conductivity in water (up to 191 mS cm−1 at 80 °C for IEC = 2.25 mequiv. g−1), suggesting that the newly designed hydrophilic structure was effective in improving the ion conductivity. Based on small-angle X-ray scattering (SAXS) analyses and transmission electron microscopy (TEM) images, all membranes featured nano-phase separated morphology with a large dependence on the copolymer composition. The strain properties were improved on increasing the content of the hydrophilic component up to IEC = 2.25 mequiv. g−1, above which the strain became smaller due to the larger water absorption. The membranes were not stable under harsh alkaline conditions (in 8 M KOH at 80 °C) gradually losing the hydroxide ion conductivity. Compared to our previous AEMs which contained typical aliphatic ammonium groups, the lack of β-hydrogen atoms did not practically improve the alkaline stability of AEMs possibly due to the main chain degradation but contributed to higher ion conductivity.

Extremely high gas permeability of naphthyl group-containing diarylacetylene copolymers

Gas separation using separation membranes is highly advantageous as they consume less energy and are environmentally friendly and inexpensive. Substituted poly(diarylacetylene)s are potential materials for gas-separation membrane owing to the excellent permeation performance. Herein, 1-β-naphthyl-2-(4-trimethylsilyl)phenylacetylene (NS) was copolymerized with 1-phenyl-2-(4-tert-butyl)phenylacetylene (TB) and 1-(4-trimethylsilyl)phenyl-2-(4-trimethylsilyl)phenylacetylene (BS) with the TaCl5/n-Bu4Sn catalyst, which afforded high-molecular weight copolymers [poly(NS-TB) and poly(NS-BS)]. The poly(NS-TB) and poly(NS-BS) membranes showed high oxygen permeability (PO2: 3600–6500 barrers). Desilylation of poly(NS-TB) and poly(NS-BS) was carried out using a CF3COOH/hexane mixture to obtain the corresponding desilylated membranes [Dpoly(NS-TB) and Dpoly(NS-BS)]. Desilylation significantly enhanced the gas permeability. The PO2 values of Dpoly(NS-TB) were extremely large (10800–12100 barrers), owing to the large fractional free volume (ca. 0.40). All the membranes maintained a fairly high gas permeability after 150 days of aging. The study results may help in designing better gas separation membranes.

Synthesis and self-assembly of brush-shaped block copolymer structure via ATRP and ROP

Well-controlled brush-shaped block copolymers (BBCPs) of high molecular weight with polystyrene (PS) and polylactic (PLA) side chains, (poly (cis-5-norbornene-exo-2,3-dicarboximide-end poly (styrene)))-block-(poly (cis-5-norbornene-exo-2,3-dicarboximide-end poly (lactide))) (PNB- g -PS)- b -(PNB- g -PLA) were synthesized by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). The synthesis of the (PNB- g -PS)- b -(PNB- g -PLA) was well-controlled with molecular weight and polydispersity index ( M n, GPC = 1310000 g mol - 1 and M w / M n (GPC) = 1.16). The SEM, XRD and DSC reveal that there are two immiscible cis-5-norbornene-exo-2,3-dicarboximide-end poly(styrene) (NB-PS) and cis-5-norbornene-exo-2,3-dicarboximide-end poly(lactide) (NB-PLA) phases in BBCP after self-assembly, which leads to partial crystallization. Moreover, the effect of the self-assembly temperature on morphology and reflectance of (PNB- g -PS)- b -(PNB- g -PLA) has been investigated. These (PNB-g-PS)-b-(PNB-g-PLA) exhibit obvious pearlescent appearance and wide band reflection after heat-treated at different temperatures (120 °C, 130 °C, 140 °C and 150 °C). Besides, with the increase of the self-assembly temperature, the domain spacing of (PNB- g -PS)- b -(PNB- g -PLA) decreases and the reflectance in visible range of (PNB- g -PS)- b -(PNB- g -PLA) increases. However, the self-assembly temperature does not significantly influence the reflection wavelength range of (PNB- g -PS)- b -(PNB- g -PLA). • A brush-shaped block copolymer was synthesized via ATRP and ROP. • The BBCP after self-assembly shows crystallization behavior. • The temperature of self-assembly can tune the domain spacing of BBCP. • The BBCPs exhibit obvious pearlescent appearance and wide band reflection after heat-treated at different temperatures.

Preparation and effectiveness of a high-temperature anti-settling agent for well cement slurries

A high molecular weight copolymer consisting of 2-acrylamido-2-tert butyl sulfonic acid (ATBS) and N,N-dimethyl acrylamide (NNDMA) was encapsulated in a natural rubber latex matrix and evaluated relative to its functionality as thermally activated, delayed release anti-settling agent in well cementing. Successful incorporation of CaATBS-co-NNDMA was confirmed via scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that the composite material has only minor influence on the viscosity during slurry mixing at the surface, whereas starting at 80 °C the viscosifying polymer is gradually released and thermal thinning of cement slurry is suppressed. Thereby preventing the sedimentation of cement particles which can result in a failed cement job. The effectiveness of the composite material is owed to the release of CaATBS-co-NNDMA when the rubber matrix softens at elevated temperatures. High-temperature/high-pressure (HT/HP) consistometer testing including off/on-cycles demonstrated that the polymer successfully prevents the settling of cement at temperatures up to 180 °C. The encapsulated product presented here delivers a solution to mitigate high surface rheology of the cement slurry during mixing and counteract the effect of thermal thinning at elevated temperatures, thus making cementing operations more successful and safer under such conditions. The method introduced in this paper might be suitable to encapsulate any other additive which is to be released at increased temperatures.

Ethylene homopolymerization and copolymerization with 1-hexene and 1-octene catalyzed by titanium(IV) dichloride TADDOLate complex activated with MAO

The synthesis and olefin polymerization behavior of a new TADDOL-based Ti(IV) complex, (4R,5R)-2,2-dimethyl-??,??,?????,?????-tetrakis[bis-(3,5-trifluoromethyl)phenyl]-1,3-dioxolane-4,5-dimethanolato-titanium(IV) dichloride, are described. Upon activation with MAO, this complex polymerized ethylene, producing ultra-high molecular weight linear polyethylene (UHMWPE) with activities up to 4500 kg mol (Ti)???1 [C2H4]???1 h???1 atm???1 and molecular weights up to 3.25????????106. The optimal temperature for UHMWPE synthesis was 50 ??C. This complex is also capable of copolymerizing ethylene with 1-hexene and 1-octene, giving high molecular weight copolymers with ??-olefin incorporation up to 7.8%. The copolymers, obtained with a different ratio of comonomers, are statistical, according to the analysis of the 13C NMR spectra. The reaction parameters that influenced the copolymerization behavior, such as comonomer concentration, reaction temperature and [Al]/[Ti] molar ratio, are examined in detail. Furthermore, high catalytic activities up to 12,531 kg mol(Ti)???1 [C2H4]???1 h???1 atm???1 were observed in copolymerization of ethylene and 1-hexene or 1-octene with the 2/MAO catalytic system. The obtained copolymers possess high molecular weights (Mw???=???1.4????????106???ethylene/1-hexene and 1.86????????106???ethylene/1-octene) with broad MWD (Mw/Mn???=???3.04???8.23) and high comonomer incorporation degrees (up to 6.2 mol% of 1-hexene and 7.8 mol% of 1-octene). Depending on the synthesis conditions, it is possible to form both a statistical copolymer and a block copolymer.

Quinolinyl Imidazolidin-2-imine Nickel Catalyzed Efficient Copolymerization of Norbornene with para-Chlorostyrene

A series of novel quinolinyl imidazolidin-2-imine nickel complexes with different substituents on the imidazolidin-2-imine ligand were synthesized and characterized. The complexes in the presence of methylaluminoxane (MAO) as a cocatalyst catalyzed the copolymerization of norbornene (N) and styrene (S) or para-chlorostyrene (CS) with high activity (up to 1070 kg·mol−1·h−1). The installation of sterically bulky substituents on the imidazolidine-2-imine ligand was effective for the increase of the molecular weight and the comonomer content, affording high molecular weight copolymers with tunable CS content (0.57 mol%–11.7 mol%), in which the existence of Cl group can provide reaction site for the further functionalization of copolymers as well as the synthesis of graft or cross-linked polymers. The linear relationship between the comonomer content and the glass transition temperature of the copolymers and the monomer reactivity ratios in the copolymerization indicated the formation of the expected functionalized cyclic olefin copolymers (COC).

Dual asymmetric centrifugation as a novel method to prepare highly concentrated dispersions of PEG-b-PCL polymersomes as drug carriers.

Polymersomes are vesicles formed by self-assembly from block copolymers. A widely studied biodegradable diblock copolymer that forms polymersomes is poly(ethylene-glycol)-block-poly(ε-caprolactone) (PEG-b-PCL). Polymersomes from this copolymer have been prepared by various methods. Major drawbacks are either the use of organic solvents, the need for post-preparation steps or low polymer concentration in resulting dispersions. Here, we studied the use of dual asymmetric centrifugation (DAC) as alternative and innovative preparation method by which these disadvantages can be overcome. We investigated the influence of process parameters on the size of resulting particles and their morphology. Additionally, the ability of this method to encapsulate both hydrophilic and hydrophobic drugs into polymersomes was assessed to evaluate its usefulness in the manufacture of nano-therapeutics. We found, that depending on process parameters, formation of nanosized vesicles with considerable drug encapsulation is achievable. Interestingly, with DAC polymersomes could also be prepared from a high molecular weight copolymer that was not able to generate vesicles by conventional methods. In addition, no organic solvents are used, no postprocessing is necessary and preparation is done quickly in a single vessel, minimizing product loss. DAC leads to highly concentrated, drug-loaded polymersome dispersions and therefore represents a major step towards their applicability in nanomedicine.

Differences in the Synthetic Method Affected Copolymer Sequence and Membrane Properties of Sulfonated Polymers

Abstract The versatility of the synthesis of sulfonated aromatic polymers using NiBr2 was investigated. The copolymerization of sulfo-dichlorobenzene protected with a neopentyl group was carried out with chlorine-terminated oligomer (1) or three different comonomers (2, 3, 4). The copolymerization proceeded well to obtain high molecular weight copolymers (Mn = 4.83–60.1 kDa, Mw = 24.9–133 kDa) and provided flexible membranes, comparable to those obtained with Ni(0) as a polymerization promoter. 1H NMR spectra suggested differences in the comonomer sequence between the copolymers synthesized with Ni(II) and Ni(0). The sequence was quantified as a “randomness of sulfophenylene (SP) unit” and correlated with the membrane properties. The randomness of SP unit in the sulfonated polyphenylene copolymer (SPP-QP) did not affect the phase-separated morphology under the dry-state as suggested by TEM images. SAXS analysis under humidified conditions revealed that the SPP-QP with lower randomness of SP unit formed higher periodicity in the self-assembling structures (i.e., the uniform-sized ionic clusters). The increase of the randomness of SP unit from 19% to 47% in SPP-QP caused decrease of the proton conductivity (at 80 °C and 20% RH) by a factor of 1/1.7 and decrease of the elongation (at 80 °C and 60% RH) by a factor of 1/27. Similar tendency was observed for other series of the sulfonated copolymer membranes.

Synthesis of super high molecular weight copolymer of AM/NaA/AMPS by oxidation\u2013reduction and controlled radical polymerization

Super high molecular weight copolymers of AM/NaA/AMPS were prepared by oxidation–reduction [OR-P(AM/NaA/AMPS)] and controlled radical polymerization [CR-P(AM/NaA/AMPS)]. The resulting copolymers were fully characterized, and the reaction conditions for their preparation were optimized. OR-P(AM/NaA/AMPS), CR-P(AM/NaA/AMPS), and conventional partially hydrolyzed polyacrylamide (HPAM) in brine solution were comprehensively characterized by thermogravimetric analysis, scanning electron microscopy, atomic force microscopy, and dynamic light scattering. OR-P(AM/NaA/AMPS) and CR-P(AM/NaA/AMPS) containing AMPS monomer showed better salt resistance, temperature tolerance, and viscosification property than the conventional HPAM polymer, making them more promising for enhanced oil recovery. Through comprehensive comparison and analysis, it was found that OR-P(AM/NaA/AMPS) was more conducive for high-temperature condition due to the existence of xanthone in OR-P(AM/NaA/AMPS). On the other hand, CR-P(AM/NaA/AMPS) was more suitable for high-mineral atmosphere, which could be attributed to its higher intrinsic viscosity.

Lithium Cycling, Limiting Current, and Electrochemical Characterization in Solid Polymer Electrolytes

Successful prevention of lithium dendrite growth would enable the use of lithium metal as an anode material in next-generation secondary batteries. Mechanically stiff solid polymer electrolytes have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth. A series of diblock copolymers of high modulus and molecular weight were synthesized, and their nanostructures and electrochemical properties were characterized as a function of polymer composition and lithium salt concentration, including measurements of the limiting current. X-ray tomography was used to observe lithium metal plating and cycling through these solid polymer electrolyte membranes under a range of electrochemical conditions. Insight into the interplay between electrochemical and mechanical properties, polymer microstructure, and lithium electrodeposition morphology will aid in the design of next-generation electrolytes.

Synthesis of water-soluble grafted chitosan copolymers by atom transfer radical polymerization

Chitosan acylation with 2-bromoisobutyryl bromide in dimethylformamide was studied to obtain a macroinitiator for the subsequent synthesis of graft copolymers of chitosan with trimethyloxyethylmethacryloylammonium methyl sulfate using Atom Transfer Radical Polymerization. The acylation reaction under heterophase conditions is a distinctive feature of the proposed approach. The advantages of this approach are the ease of obtaining a macroinitiator and zero destruction of chitosan samples. This will allow to obtain high molecular weight copolymers of chitosan. In this work, chitosan samples with different molecular weight (ranging from 110 to 260 kDa) and degree of deacetylation (80–92%) were studied. Elemental analysis, IR spectroscopy, and energy-dispersive analysis have shown that the acylation reaction proceeds via the NH2 group, because it is most reactive. Regardless of the molecular weight and degree of deacetylation, the degree of acylation is 76–99% with the optimal synthesis time of 1 day. Due to the extremely high sensitivity to contamination of the reaction and of the subsequent polymerization reaction, special attention is paid to the preparation of initial chitosan samples (i.e., purification from unreacted chitin and various impurities). The presented results on obtaining chitosan macroinitiator are novel and serve as the basis for the synthesis of graft copolymers of chitosan using Atom Transfer Radical Polymerization with a variable hydrophilic–lipophilic balance.

Cationic indium complexes for the copolymerization of functionalized epoxides with cyclic ethers and lactide.

We report the first example of discrete cationic indium complexes for the copolymerization of epoxides, cyclic ethers, and lactide. [SalenIn][SbF6] in particular proved to be a highly active catalyst for the homo-polymerization of functionalized epoxides and their copolymerization with other cyclic ethers THF, oxetane and oxepane. This catalyst also proved competent in the polymerization of epichlorohydrin and lactide, forming copolymers with good activity and control. Investigation of the role of counteranions and solvent donors on the kinetics of polymerization of epoxides revealed a subtle effect of solvents on initiation rates.