Narrow Molecular Weight Distribution Research Articles

High-Yield Synthesis of Molecular Bottlebrushes via PISA-Assisted Grafting-from Strategy.

To prepare molecular bottlebrushes with high yield via a grafting-from strategy using a reversible deactivation radical polymerization (RDRP) technique has always been a big challenge due to the intra- and intermolecular radical-radical coupling. Herein, a polymerization-induced self-assembly (PISA)-assisted grafting-from strategy based on reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization was developed to synthesize the Janus molecular bottlebrushes with a well-defined structure and high yield using polynorbornene-g-(poly(ethylene glycols)-branch-RAFT agent) (PNB-g-(PEG-branch-CTA)) as a solvophilic multifunctional macro-CTA. The results indicated the biradical coupling terminations of propagating side chains could be significantly suppressed due to the nanoconfinement effect in the PISA of the generated Janus molecular bottlebrushes. Janus molecular bottlebrushes with a narrow molecular weight distribution (Mw/Mn < 1.25) and negligible intermolecular cross-linking at monomer conversion as high as 84% were prepared, demonstrating the efficiency and versatility of the PISA-assisted grafting-from approach.

Emulsion iodine transfer polymerization of nearly uniform submicrometer‐sized polystyrene particles

AbstractEmulsifier‐free emulsion iodine transfer polymerization (emulsion ITP) of styrene was carried out using unpurified and purified poly(methacrylic acid)–iodine (PMAA‐I). PMAA‐I was previously synthesized by solution ITP in dioxane. The solution ITP of methacrylic acid was completed at 40 °C for 24 h. Unexpectedly, 64% of added CHI3 remained in dioxane even after the polymerization. The emulsion ITP was carried out at pH ∼ 9 with unpurified or purified PMAA‐I. The number‐average diameter (dn) of the polymer particles obtained using purified PMAA‐I (148 nm at 93% conversion) was much smaller than that using unpurified PMAA‐I (710 nm at 68% conversion). In both cases, in the early stage of the polymerization, polystyrene (PS) particles stabilized by some PMAA‐b‐PS copolymer chains were formed. This indicates that PMAA‐I worked not only as a macro chain transfer agent but also as a colloidal stabilizer. In the unpurified system, the remaining CHI3 also operated as a chain transfer agent. It resulted in PS‐I homopolymers having controlled molecular weight in the PS particles. On the other hand, many high molecular weight PS homopolymers were formed in the purified system by emulsion conventional radical polymerization in the PS particles. To depress emulsion conventional radical polymerization, the CHI3 was post‐added after 90 min. Nearly uniform submicrometer‐sized (82 nm) PS particles with narrow molecular weight distribution (Mw/Mn = 1.24) were achieved. These polymerization behaviors were reasonably explained from the results obtained by gel permeation chromatography and diffusion ordered spectroscopy 1NMR. © 2021 Society of Industrial Chemistry.

Cis-1,4 Selective Coordination Polymerization of 1,3-Butadiene and Copolymerization with Polar 2-(4-Methoxyphenyl)-1,3-butadiene by Acenaphthene-Based α-Diimine Cobalt Complexes Featuring Intra-Ligand π-π Stacking Interactions.

Highly cis-1,4 selective (up to 98%) coordination–insertion polymerization of 1,3-butadiene (BD) has been achieved herein using acenaphthene-based α-diimine cobalt complexes. Due to the presence of intra-ligand π-π stacking interactions, the complexes revealed high thermostability, affording polybutadiene products in high yields. Moreover, all of the obtained polymers possessed a relatively narrow molecular weight distribution as well as high molecular weight (up to 92.2 × 104 Dalton). The molecular weights of the resultant polybutadienes could be finely tuned by varying polymerization parameters, including temperature, Al/Co ratio, etc. Moreover, the copolymerization of butadiene with polar monomer 2-(4-methoxyphenyl)-1,3-butadiene (2-MOPB) was also successfully realized to produce a type of polar cis-1,4 polybutadiene (cis-1,4 content: up to 98.1%) with a range of 2-MOPB content (0.46–1.83%). Water contact angle measurements indicated that the insertion of a polar monomer into a polymer chain could significantly improve the polymer’s surface property.

Preparation of Quaternary Amphiphilic Block Copolymer PMA-b-P (NVP/MAH/St) and Its Application in Surface Modification of Aluminum Nitride Powders.

Poly(methyl acrylate)-b-poly(N-vinyl pyrrolidone/maleic anhydride/styrene) (PMA-b-P (NVP/MAH/St)) quaternary amphiphilic block copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) was used to improve the anti-hydrolysis and dispersion properties of aluminum nitride (AIN) powders that were modified by copolymers. Its structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and Hydrogen nuclear magnetic spectroscopy (1H-NMR). The results demonstrate that the molecular weight distribution of the quaternary amphiphilic block copolymers is 1.35–1.60, which is characteristic of controlled molecular weight and narrow molecular weight distribution. Through charge transfer complexes, NVP/MAH/St produces a regular alternating arrangement structure. After being treated with micro-crosslinking, AlN powder modified by copolymer PMA-b-P(NVP/MAH/St) exhibits outstanding resistance to hydrolysis and can be stabilized in hot water at 50 °C for more than 14 h, and the agglomeration of powder particles was improved remarkably.

2D Porphyrinic Metal-Organic Framework Nanosheets as Multidimensional Photocatalysts for Functional Materials.

Ultrathin porphyrinic 2D MOFs, ZnTCPP nanosheets (TCPP: 5,10,15,20-(tetra-4-carboxyphenyl) porphyrin) were employed as heterogeneous photocatalysts to activate PET-RAFT polymerization under various wavelengths ranging from violet to orange light. High polymerization rates, oxygen tolerance, and precise temporal control were achieved. The polymers showed narrow molecular weight distributions and good chain-end fidelity. The 2D ZnTCPP nanosheets were applied as photocatalysts in stereolithographic 3D printing in an open-air environment under blue light to yield well-defined 3D printed objects. Apart from providing an efficient catalytic system, 2D ZnTCPP nanosheets reinforced the mechanical properties of the 3D printed materials. The presence of ZnTCPP embedded in the materials conferred effective antimicrobial activity under visible light by production of singlet oxygen, affording 98 % and 93 % anti-bacterial efficiency against Gram-positive and Gram-negative bacteria, respectively.

2D Porphyrinic Metal–Organic Framework Nanosheets as Multidimensional Photocatalysts for Functional Materials

AbstractUltrathin porphyrinic 2D MOFs, ZnTCPP nanosheets (TCPP: 5,10,15,20‐(tetra‐4‐carboxyphenyl) porphyrin) were employed as heterogeneous photocatalysts to activate PET‐RAFT polymerization under various wavelengths ranging from violet to orange light. High polymerization rates, oxygen tolerance, and precise temporal control were achieved. The polymers showed narrow molecular weight distributions and good chain‐end fidelity. The 2D ZnTCPP nanosheets were applied as photocatalysts in stereolithographic 3D printing in an open‐air environment under blue light to yield well‐defined 3D printed objects. Apart from providing an efficient catalytic system, 2D ZnTCPP nanosheets reinforced the mechanical properties of the 3D printed materials. The presence of ZnTCPP embedded in the materials conferred effective antimicrobial activity under visible light by production of singlet oxygen, affording 98 % and 93 % anti‐bacterial efficiency against Gram‐positive and Gram‐negative bacteria, respectively.

Steric Hindrance Drives the Boron-Initiated Polymerization of Dienyltriphenylarsonium Ylides to Photoluminescent C5-Polymers.

A series of alkyl‐subsituted dienyltriphenylarsonium ylides were synthesized and used as monomers in borane‐initiated polymerization to obtain practically pure C5‐polymers (main‐chain grows by five carbon atoms at a time). The impact of triethylborane (Et3B), tributylborane (Bu3B), tri‐sec‐butylborane (s‐Bu3B), and triphenylborane (Ph3B) initiators on C5 polymerization was studied. Based on NMR and SEC results, we have shown that all synthesized polymers have C5 units with a unique unsaturated backbone where two conjugated double bonds are separated by one methylene. The synthesized C5‐polymers possess predictable molecular weights and narrow molecular weight distributions (M n,NMR=2.8 −11.9 kg mol−1, Ð=1.04–1.24). It has been found that increasing the steric hindrance of both the monomer and the initiator can facilitate the formation of more C5 repeating units, thus driving the polymerization to almost pure C5‐polymer (up to 95.8 %). The polymerization mechanism was studied by 11B NMR and confirmed by DFT calculations. The synthesized C5‐polymers are amorphous with tunable glass‐transition temperatures by adjusting the substituents of monomers, ranging from +30.1 °C to −38.4 °C. Furthermore, they possess blue photoluminescence that changes to yellow illuminating the polymers for 5 days with UV radiation of 365 nm (IIE, isomerization induced emission).

Steric Hindrance Drives the Boron‐Initiated Polymerization of Dienyltriphenylarsonium Ylides to Photoluminescent C5‐Polymers

AbstractA series of alkyl‐subsituted dienyltriphenylarsonium ylides were synthesized and used as monomers in borane‐initiated polymerization to obtain practically pure C5‐polymers (main‐chain grows by five carbon atoms at a time). The impact of triethylborane (Et3B), tributylborane (Bu3B), tri‐sec‐butylborane (s‐Bu3B), and triphenylborane (Ph3B) initiators on C5 polymerization was studied. Based on NMR and SEC results, we have shown that all synthesized polymers have C5 units with a unique unsaturated backbone where two conjugated double bonds are separated by one methylene. The synthesized C5‐polymers possess predictable molecular weights and narrow molecular weight distributions (Mn,NMR=2.8 −11.9 kg mol−1, Ð=1.04–1.24). It has been found that increasing the steric hindrance of both the monomer and the initiator can facilitate the formation of more C5 repeating units, thus driving the polymerization to almost pure C5‐polymer (up to 95.8 %). The polymerization mechanism was studied by 11B NMR and confirmed by DFT calculations. The synthesized C5‐polymers are amorphous with tunable glass‐transition temperatures by adjusting the substituents of monomers, ranging from +30.1 °C to −38.4 °C. Furthermore, they possess blue photoluminescence that changes to yellow illuminating the polymers for 5 days with UV radiation of 365 nm (IIE, isomerization induced emission).

Visible Light-Regulated Heterogeneous Catalytic PET-RAFT by High Crystallinity Covalent Organic Framework.

Covalent organic frameworks (COFs) are a class of promising photocatalysts for conversing light energy into chemical energy. Based on the tunable building blocks, COFs can be well-designed as photocatalyst for mediating reversible addition-fragmentation chain-transfer (RAFT) polymerization. Herein, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2″-bipyridine-5,5″-diamine (Bpy) are chosen to construct imine-based TFPPy-Bpy-COFs for catalyzing RAFT polymerization of methacrylates under white light irradiation. The well-defined polymers with precise molecular weight and narrow molecular weight distribution are obtained. The switch on/off light experiments suggest excellent temporal control toward RAFT polymerization system and the chain-extension reaction indicates high chain-end fidelity of macro-initiators. Mechanism study clarifies that the electron transfer between excited state of TFPPy-Bpy-COFs and RAFT agent can form living radicals to mediate polymerization. This methodology provides a novel platform for reversible-deactivation radical polymerization using COFs as heterogeneous catalysts.

Block copolymer self-assembly: Polydisperse corona-forming blocks leading to uniform morphologies

<h2>Summary</h2> Bottom-up block copolymer (BCP) self-assembly involving crystallization of the core-forming block can lead, via a multistep protocol, to a range of uniform structures. One normally works with polymers of narrow molecular weight distribution, at low concentrations, and several steps are necessary because one has to separate the nucleation and growth steps. Here, we show that BCPs with polydisperse corona chains enable one to obtain a broad range of uniform structures in a single pot via a single heating-cooling-aging process, in which the nature of the structures is determined by the solvents and the annealing temperature. Most of the sample dissolves upon heating, but a fraction of the components in the mixture with the smallest corona/core block ratio persists as crystallites and, upon cooling, nucleates the growth of the more soluble components. Remarkably, this one-pot self-assembly can be scaled up to a concentration of 12% w/w, opening the door to useful applications.

CFD modeling for the prediction of molecular weight distribution in the LDPE autoclave reactor: Effects of non-ideal mixing

A commercial Low-density polyethylene (LDPE) reactor was modeled to investigate the effects of highly nonlinear hydrodynamics in an industrial-scale autoclave reactor on the polymer Molecular weight distribution (MWD). To reduce the extremely high computational burden of Computational fluid dynamics (CFD) runs and detailed MWD calculations, a combination of the CFD multicompartment model and probability generating function transformation is proposed. The validity of the proposed model was verified by a comparison with experimental data on industrial equipment. The computation time was shown to be only 37% of the actual operation time. The proposed model showed that strong downflow and weak reverse-flow coexisted to form circulation flow between the disks in the autoclave. Polymerization mainly occurred in the strong downflow region of the tubular regime. The circulation flow increased the accumulation of dead polymers to enhance the chain transfer to polymer, which produces long-branched living polymer chains and termination by recombination for a broad MWD with bimodality. Further analysis based on the simulation without the circulation flow showed a narrow MWD and no bimodality. These results indicate that the flow pattern must be properly controlled to produce polymers with desired properties in large-scale polymerization reactors.

Syndiospecific Polymerization of Styrene Catalyzed by Half‐titanocenes Containing Monodentate Anionic Nitrogen Ligands

Main observation and conclusionStyrene polymerization catalyzed by the half‐titanocenes CpTiCl2[1,3‐R2(CH2N)2C=N] (6b: R= 2,6‐Me2C6H3, T4: R = 2,4,6‐Me3C6H2; T5: R = 2,6‐iPr2C6H3) was carried out in the presence of methylaluminoxane (MAO). Compared to the styrene conversion (31%) and syndiospecific index (45%) using reported 6b as precatalyst, T5 bearing ligand with isopropyl substitutes on the N‐aryl‐rings exhibits much higher styrene conversion (61%) and syndiospecific index (99%), indicating that the catalytic behavior could be improved obviously by the introduction of electronic donating and steric bulky substituents. One N atom in imidazolin‐2‐iminato ligand was replaced by O atom, affording half‐titanocenes CpTiCl2[3‐C6H5(CH2N)(CH2O)C=N (T1) and CpTiCl2[2,6‐Me2(C6H3O)(NiPr2)C=N] (T2). Compared to 6b, both higher styrene conversion and syndiospecific index are afforded by using half‐titanocene T1 containing 2‐imino‐3‐phenyloxazolidine ligand. All the results illustrate that both the chemical structure and the nature of substituents of the ligand have obvious influence on the styrene conversion and syndiospecific index in the polymerization of styrene. All the resulting syndiotactic polystyrenes (sPSs) are highly syndiospecific (rrr &gt; 99%). Correspondingly, the sPS prepared using T5/MAO catalytic system exhibits high melting point and narrow molecular weight distribution. The results might show new light on designing more efficient half‐titanocenes for styrene polymerization with both high styrene conversion and high syndiospecific selectivity.

Immunopharmacological Properties of Methacrylic Acid Polymers as Potential Polymeric Carrier Constituents of Anticancer Drugs.

Cytostatic chemotherapeutics provide a classical means to treat cancer, but conventional treatments have not increased in efficacy in the past years, warranting a search for new approaches to therapy. The aim of the study was, therefore, to obtain methacrylic acid (MAA) (co)polymers and to study their immunopharmacological properties. 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CDSPA) and 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) were used as reversible chain transfer agents. Experiments were carried out in Wistar rats. The MTT assay was used to evaluate the cytotoxic effect of the polymeric systems on peritoneal macrophages. An experimental tumor model was obtained by grafting RMK-1 breast cancer cells. Serum cytokine levels of tumor-bearing rats were analyzed. The chain transfer agents employed in classical radical polymerization substantially reduced the molecular weight of the resulting polymers, but a narrow molecular weight distribution was achieved only with CDSPA and high CPDT concentrations. Toxicity was not observed when incubating peritoneal macrophages with polymeric systems. In tumor-bearing rats, the IL-10 concentration was 1.7 times higher and the IL-17 concentration was less than half that of intact rats. Polymeric systems decreased the IL-10 concentration and normalized the IL-17 concentration in tumor-bearing rats. The maximum effect was observed for a MAA homopolymer with a high molecular weight. The anion-active polymers proposed as carrier constituents are promising for further studies and designs of carrier constituents of drug derivatives.

Progress and challenges in the synthesis of sequence controlled polysaccharides.

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure–properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Retrogradation of sweet potato amylose and amylopectin with narrow molecular weight distribution

AbstractRetrogradation of sweet potato amylose and amylopectin with narrow molecular weight distribution at different temperatures was investigated by X‐ray diffraction (XRD). Atomic force microscope (AFM), scanning electron microscope (SEM) and light microscopy were combined to study the morphology of the molecular assemblies during retrogradation. Avrami equation was used to the retrogradation kinetics the of above starches by determining the crystallinity and the ratio of peak area of two distinctive peaks. It was found that only the ratio of peak area/total area at 2θ = ~16.3° could represent the crystallinity of retrograded starch‐containing amorphous regions. Considering the crystallinity as retrogradation rate, only the retrogradation kinetics of sweet potato amylose could be analysed by Avrami equation, but not the amylopectin’s. All Avrami exponents n of amyloses at any temperatures were less than 1.0, indicating instantaneous nucleation and rod‐like growth. AFM results showed that the maximum heights of layered structure for sweet potato amylose, amylopectin and blending of both were approximately 4800, 180 and 200 nm, respectively. The height of the former two decreased during storage, but the height of blending remained unchanged. Amylose served as nuclei of amylopectin during starch retrogradation.

Oligomerization of ethylene to linear α-olefins in the presence of complex catalytic systems based on zirconium carboxylates

The study considers the process of ethylene oligomerization in a medium of aliphatic and aromatic solvents in the presence of complex catalytic systems based on zirconium carboxylates, which were obtained from the fractions of naphthenic acids recovered from Baku oils and individual carboxylic acids. It was found that the catalytic activity and the molecular weight distribution (MWD) of the produced oligomeric products depend mostly on the solvent nature and the composition of zirconium complex. The ethylene oligomerization rate in the presence of catalytic systems based on zirconium carboxylates is 2–3 times lower in a medium of aliphatic solvents as compared to aromatic solvents; the obtained product has a narrow MWD and consists predominantly of С4-С10 fractions. Oligomeric products obtained in a medium of aromatic solvents have a broad MWD and in the presence of zirconium carboxylates comprise mostly С4-С18, while in the presence of zirconium naphthenates, С12-С18 and С20 fractions.

Synthesis of a lignin-based alcohol ether carboxylate surfactant and its application as cotton fiber detergent

Alkyl glycidyl ether and 3-chloropropionic acid were grafted onto alkaline lignin (KL) to obtain lignin-based alcohol ether carboxylate surfactant (KLS) and its structure, surface tension, emulsifying ability and detergency of cotton fiber were investigated. Then, the alkaline lignin was pretreated by using ultrasound to activate the KL molecular. The pretreated KL showed lower Mn and narrow molecular weight distribution. The absorbance ratio of A1125/A1600 and A1047/A1600 of pretreated KL increased as the time of the ultrasound increased, indicating that new phenolic hydroxyl groups were formed. Further study revealed that the Mn, surface tension and emulsifying ability were significantly affected by the reaction temperature and ultrasound treatment. The sample (KLSU) obtained at 70 °C with ultrasound pretreatment had a good surface activity and emulsifying ability. The critical micelle concentration of KLSU was 3.1 g/L and the corresponding surface tension was 29.1 mN/m. The KLSU was used as a novel surfactant for detergent and exhibited significant detergency property. The effect of different types of surfactant on the detergency, zeta potential, surface tension and particle distribution of mixture solution containing KLSU were investigated. The KLSU solution mixed with sodium dodecyl benzene sulfonate showed good detergency, surface tension and stability. This article highlighted the potential usage of lignin-based alcohol ether carboxylate surfactant in detergent.

Photocontrolled RAFT Polymerization Catalyzed by Conjugated Polymers under Aerobic Aqueous Conditions.

Photocontrolled polymerization offers a convenient way to direct the reaction progress and tailor the polymer structures. Nevertheless, conjugated polymers are yet to be utilized as the photocatalyst in associated reactions. Herein, we employed poly(boron dipyrromethene-alt-fluorene) (PBF), a conjugated polymer with better photostability than eosin Y, as the photocatalyst for photo-RAFT polymerizations of acrylic monomers, and the polymers were obtained with moderately narrow molecular weight distributions. The reaction progress was effectively controlled by switching irradiation conditions, and the block copolymers were prepared from chain extension of a macroinitiator. As electron spin resonance (ESR) and optical spectra results suggested, the reductive quenching of PBF* by ascorbate was the key step leading to the reduction of a chain transfer agent (CTA), whereas the hydroxyl radical derived from superoxide was considered as a byproduct of deoxygenation.

Withdrawal: Quantitative Synthesis of Temperature-responsive Polymersomes by Multiblock Polymerization.

The current challenge for polymersomes is to prepare amphiphilic block polymers with not only well-defined molecular weight, but also precisely high-order multiblock structure in terms of the distribution of monomeric units along the chain. Here, we describe a synthesis of temperature-responsive polymersomes with precisely defined membrane structures using high-precision amphiphilic multiblock polymer via aqueous single electron transfer living radical polymerization (SET-LRP) in which poly(ethylene glycol) (PEG) macromolecules are used as initiators. We develop a one-pot, rapid and multistep sequential polymerization process with yields >99% within 30 min for each block, giving access to a wide range of high-precision multiblock polymers with very narrow molecular weight distributions (Ð ≤ 1.14). Synthesized multiblock polymers are used to form nano-sized polymersomes which are highly promising as smart carriers for high loading and triggered release of biopharmaceutics such as pharmaceutical proteins and peptides. This synthesis approach is environmentally friendly, fully translation and thus represents a significant advance in the design and synthesis of a new generation of polymer nanomaterials with precisely defined structures, which is highly attractive for applications in nanotechnology.

Monomer effect on the chain transfer by diethyl zinc in olefin polymerization by metallocene catalysts

The present paper systematically studies the homo- and copolymerization of ethylene or propylene using metallocene as catalyst and diethyl zinc as chain transfer agent to obtain the polyolefin waxes with narrow molecular weight distribution and with a high activity. The molecular weight of the resultant polymer could be controllable by the concentration of diethyl zinc quantitatively. The introduction of a-olefin into the ethylene polymerization system would shield the chain transfer action, and the shielding effect in propylene (co) polymerization is more serious, due to the mass transfer resistance of the substituents on the monomers. Branched comonomer and long chain comonomer provide stronger shielding effect. The regression results show that the order of the chain transfer reaction of propylene polymerization is smaller than that of ethylene polymerization, and the order of the chain transfer reaction of copolymerization is less than that of homopolymerization. It indicates that the substituent on the monomer would result in the deviation of the regression data from the ideal primary reaction order.