Number-average Molecular Weight Research Articles

Efficient non-catalytic depolymerization of lignin in hydrogen donor solvent for monomeric phenols and its pathways

Thermal degradation of lignin in hydrogen donor solvent (HDS) has been reported to be an efficient method to generate aromatics and phenols. High pressure H2 and catalyst are not required which simplifies this degradation method. This work aims to advance the knowledge of reaction pathway with depolymerization of enzymatic hydrolysis lignin (EHL) in 9,10-dihydroanthracene (DHA) as an example. For this purpose, the liquid products were characterized in detail by GC, GPC, 31P NMR and 2D-HSQC NMR. Results indicate that the yield of monomeric phenols is up to 20.2 wt% at 375–400 °C. This yield is comparable to literature results with high-pressure H2 and catalysts at 220–320 °C. The depolymerization starts with the cleavage of ether linkages and decarboxylation of acrylate linkages, which are followed by the removal of aliphatic-OH, hydrogenation of Cal = Cal, decarbonylation of Cal = O, dealkylation of alkyl substituents and demethylation of aromatic-methoxy groups. The amount of phenolic-OH is about 2.78 mmol/g in the liquid product obtained at 400 °C: 36% from the cleavage of β-O-4 and α-O-4 linkages and about 16% from the demethylation of aromatic-methoxy group. The number-average molecular weight is roughly inversely proportional to the amount of bond cleavage.

Resource utilization of polystyrene waste by preparation of high performance dispersant for coal‒water slurry

ABSTRACT In present paper, structures and properties of degradation products of polystyrene (PS) waste were characterized by gel permeation chromatography (GPC), thermogravimetric (TG) analysis, Fourier transform infrared (FT-IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), and thus the degradation conditions including temperature, time, and assistant type and dosage were investigated and optimized. It is suitable to use 1.0 wt% K2S2O8 as an assistant to degrade PS waste at 300°C for 24 h. Subsequently by sulfonation and neutralization reactions, the degraded PS was prepared into sodium polystyrene sulfonate (PSS), a common dispersant for coal‒water slurry (CWS). The performance of PSS with different molecular weights and sulfonation degrees was studied. Experimental results showed that the PSS with the sulfonation degree of more than 75%, prepared from the degraded PS having number average molecular weight (M n) of about 9000, was appropriate for dispersion and stabilization of CWS suspensions. Additionally, compared with commercial dispersant NSF, the obtained PSS had a better performance for CWS. CWSs prepared with dispersant PSS exhibited pseudo-plastic or shear-thinning rheological behaviors. Combined with coal‒water slurry technology, a new approach is provided for resource utilization of PS waste.

Effects of thermo-oxidative aging on the macrophysical properties and microstructure of asphalt

To study the effect of thermo-oxidative aging on the physical properties and microstructure of base and modified asphalts, conventional index tests, dynamic shear rheology (DSR), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and gel permeation chromatography (GPC) were performed. The macro-physical indexes and microstructural changes in the asphalt before and after aging were analyzed. The results show that with an increase in the thermal-oxidative aging degree, the penetration degree of asphalt decreases; the softening point increases, and the high-temperature performance improves. Simultaneously, the asphalt consistency and hardness increase. This results in a significant increase in the initial modulus and glass transition temperature, decrease in the shear resistance, and degradation of the low-temperature performance. Rubber-modified asphalt exhibited the highest anti-aging performance, followed by styrene–butadiene–styrene-modified and 70# asphalts. Thermal-oxidative aging did not change the original functional group species; however, the peak area ratio of the sulfoxide and carbonyl functional groups increased significantly. After aging, the overall molecular weight of the asphalt shifted in the macromolecular direction. Weight-average and number-average molecular weights and polydispersity increased.

Triggering Degradation of Cellulose Acetate by Embedded Enzymes: Accelerated Enzymatic Degradation and Biodegradation under Simulated Composting Conditions.

A green strategy that significantly accelerates the biodegradation rate of cellulose acetate (CA) by triggering deacetylation was demonstrated. Lipase isolated from Candida rugosa was immobilized on CA particles (immobilized lipase (IL)) by a physical entrapment method and further incorporated in CA films. After 40 days of aging in contact with external enzymes (lipase and cellulase), the number-average molecular weight (Mn) of CA/IL 5% decreased by 88%, while the Mn of CA only exhibited a 48% reduction. Fourier transform infrared and nuclear magnetic resonance spectroscopy of CA/IL 5% indicated significant deacetylation, which was further supported by the decrease of the water contact angle from 59 to 16°. These drastic changes were not observed for CA. Similar differences in the degradation rate were observed during aging under simulated composting conditions. After 180 days of simulated composting, traces of CA/IL 5% were barely observable, while large pieces of CA still remained. This could open the door to modified lignocellulose materials with retained biodegradability, also reducing the requirements for the degradation environment as the process is initiated from inside of the material.

Enhanced Copolymer Characterization for Polyethers Using Gel Permeation Chromatography Combined with Artificial Neural Networks.

Gel permeation chromatography (GPC) is a generally applied method for the mass analysis of various polymers and copolymers, but it inherently fails to provide additional important information such as the composition of copolymers. However, we will show that GPC measurements using different solvents can yield not just the correct molecular weight but the composition of the copolymer. Accordingly, artificial neural networks (ANNs) have been developed to process the data of GPC measurements and determine the molecular weight and the chemical composition of the copolymers. The target values of the ANNs were obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nuclear magnetic resonance (NMR) spectroscopy. Our GPC-ANN method is demonstrated by the analysis of various poloxamers, i.e., poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO) block copolymers. Two ANNs were constructed. The first one (ANN_1) works in a wider mass range (from 900 to 12,500 dalton), while the second one (ANN_2) produces more output values. ANN_2 can thus predict seven characteristic copolymer parameters, namely, two average molecular weights, the average weight fraction of the EO unit, and four average numbers of the repeat units. The correlation between the experimentally obtained outputs and the predicted ones is high (r > 0.98). The accuracy of the ANNs is very convincing, and both ANNs predict the number-average molecular weight (Mn) with an accuracy below 5%. Furthermore, this work is the first step for creating an open database and applications extending the use of the GPC-ANN method for the analysis of copolymers.

Interfacial Photopolymerization: A Method for Light-Based Printing of Thermoplastics.

Ultraviolet (UV) printing of photopolymers is a widely adopted manufacturing method because of its high resolution and throughput. However, available printable photopolymers are typically thermosets, resulting in challenges in postprocessing and recycling of printed structures. Here, we present a new process called interfacial photopolymerization (IPP) which enables photopolymerization printing of linear chain polymers. In IPP, a polymer film is formed at the interface between two immiscible liquids, one containing a chain-growth monomer and the other containing a photoinitiator. We demonstrate the integration of IPP in a proof-of-concept projection system for printing of polyacrylonitrile (PAN) films and rudimentary multi-layer shapes . IPP shows in-plane and out-of-plane resolutions comparable to conventional photoprinting methods. Cohesive PAN films with number-average molecular weights greater than 15 kg mol-1 are obtained, and to our knowledge this is the first report of photopolymerization printing of PAN. A macrokinetics model of IPP is developed to elucidate the transport and reaction rates involved and evaluate how reaction parameters affect film thickness and print speed. Last, demonstration of IPP in a multilayer scheme suggests its suitabiliy for three-dimensional printing of linear-chain polymers.

Biobased polyesters and crosslinked polyester films derived from 10-hydroxy-2-decenoic acid: Synthesis and characterization

In this study, we optimized the melt polycondensation of 10-hydroxy-2-decenoic acid (10-HDA) to produce poly(10-hydroxy-2-decenoate) (PHDA) and used it to form crosslinked polyester films of PHDA via thermal- or photocuring. The physical properties of PHDA depended greatly on the polymerization conditions, particularly the temperature. The reaction conditions were optimized to achieve polymers with high weight- and number-average molecular weights of 4.182 × 104 (±0.324%) and 1.588 × 104 (±1.737%) Da. Structural, thermomechanical, and mechanical characterization revealed that the crosslinked polyester films exhibited comparable tensile properties to existing biobased plastics, with a maximum tensile strength of 29.3 MPa and an elongation at break of 331.0%. The films also demonstrated excellent thermal stability, making PHDA a promising alternative to traditional petrochemically derived polymers.

Doxorubicin-loaded mPEG-pPAd-mPEG triblock polymeric nanoparticles for drug delivery systems: Preparation and in vitro evaluation

Conventional methods in chemotherapy and radiotherapy do not target tumor sites treating breast cancer. Therefore, they cause some extra adverse effects on healthy tissues and cells, which bring fatal results. In recent applications, drug delivery systems have been used to target tumors directly or their environment indirectly. The new approach has attracted considerable interest due to its promise to overcome breast cancer with little adverse effect. Synthetic or natural polymer shell capsules are generally used to deliver therapeutic agents due to their biocompatibility and biodegradability. Doxorubicin (DOX), a convenient chemotherapeutic agent, was encapsulated using produced monomethyl ether ended poly(ethylene glycol)-poly(propylene adipate)- monomethyl ether ended poly(ethylene glycol) (mPEG-pPAd-mPEG) triblock copolymers in this study. The nanoparticle form of the prepared mPEG-pPAd-mPEG tri-block copolymer system was produced by a double emulsion-solvent evaporation method. To prepare triblock copolymer, firstly, poly (propylene adipate) (pPAd) was synthesized and characterized by using Fourier Transform Infrared (FT-IR) spectroscopy structurally and end-group analysis method to determine the number average molecular weight. The nanoparticle's size characteristics were measured by the Dynamic Light Scattering (DLS) method, while encapsulation efficacy and DOX-release profile were determined by spectrofluorometer instrument. Following the production of the nanoparticles, the antiproliferative effect and cellular uptake efficiency of the mPEG-pPAd-mPEG nanoparticles (PANPs), the doxorubicin-loaded mPEG-pPAd-mPEG nanoparticles (DPANPs), ICG-loaded mPEG-pPAd-mPEG nanoparticles (IPANPs), free-DOX, and free-ICG were tested on MCF-7 and MDA-MB-231 breast cancer cell line. The cytotoxicity analysis revealed that the DPANPs exhibited low toxicity compared to free-DOX. The physical and chemical analysis showed that the nanoparticles produced within this study's scope could be used as new drug delivery systems for breast cancer treatment.

Preparation and characteristics of pumpkin polysaccharides and their effects on abnormal glucose metabolism in diabetes mice

Oxidative stress is frequently implicated in the pathogenesis of various diseases, including diabetes mellitus resulting from uncontrolled glucose metabolism. Pumpkin polysaccharides have been shown to have a hypoglycemic effect, but their impact on abnormal glucose metabolism under oxidative stress is still unclear. We dried pumpkin flesh by far-infrared radiation, extracted and separated pumpkin polysaccharides from the dried flesh, and found that they were heteropolysaccharides primarily composed of galacturonic acid, glucose, galactose, and arabinose, with a molar ratio of 31.68:31.81:20.18:9.752. The number average (Mn) and weight average molecular weight (Mw) of pumpkin polysaccharides were 33.72 kDa and 70.88 kDa, respectively. The hemiacetal hydroxyl group forming the glycosidic bond in polysaccharides was mainly β-configuration. Additionally, we utilized streptozotocin (STZ) to induce oxidative stress and replicate an acute diabetic mouse model to study the effects of pumpkin polysaccharides on abnormal glucose metabolism. Our findings demonstrated pumpkin polysaccharides significantly reduced the levels of blood glucose, triglycerides (TG), and total cholesterol (TC) in diabetic mice (p < 0.05). Additionally, pumpkin polysaccharides significantly increased the activities of superoxide dismutase (SOD), catalase (CAT) and the level of the antioxidant glutathione (GSH) (p < 0.05), and decreased the content of the lipid peroxide malondialdehyde (MDA) in the liver (p < 0.05). Pumpkin polysaccharides also increased the activity of pyruvate kinase (PK) and decreased the activity of phosphoenolpyruvate carboxykinase (PEPCK) in the liver (p < 0.05). In conclusion, our study demonstrated pumpkin polysaccharides alleviate hyperglycemic symptoms in mice by mitigating oxidative stress damage and improving glucose metabolism disorders.

Synthesis of Ultrahigh Molecular Weight Poly(methyl Methacrylate) via the Polymerization of MMA Initiated by the Combination of Palladium Carboxylates with Thiols.

A novel synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) using organosulfur compounds combined with a catalytical amount of transition metal carboxylates as an initiator has been developed. The combination of 1-octanethiol with palladium trifluoroacetate (Pd(CF3COO)2) was found to be a very efficient initiator for the polymerization of methyl methacrylate (MMA). An ultrahigh molecular weight PMMA with a number-average molecular weight of 1.68 × 106 Da and a weight-average molecular weight of 5.38 × 106 Da has been synthesized at the optimal formulation of [MMA]:[Pd(CF3COO)2]:[1-octanethiol] = 94,300:8:23 at 70 °C. A kinetic study showed that the reaction orders with respect to Pd(CF3COO)2, 1-octanethiol, and MMA are 0.64, 1.26, and 1.46, respectively. A variety of techniques such as proton nuclear magnetic resonance spectroscopy (1H NMR), electrospray ionization mass spectroscopy (ESI-MS), size exclusion chromatography (SEC), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron paramagnetic resonance spectroscopy (EPR) were employed to characterize the produced PMMA and palladium nanoparticles (Pd NPs). The results revealed that Pd(CF3COO)2 was firstly reduced by the excess of 1-octanethiol to form Pd NPs at the early stage of the polymerization, followed by the adsorption of 1-octanethiol on the surface of nanoparticles and subsequent generation of corresponding thiyl radicals to initiate the polymerization of MMA.

Effects of aging degradation and reactive reconstruction on the structure and properties of styrene–butadiene–styrene block copolymer

Achieving high-performance recycling of aged SBS modified asphalt will help promote the sustainable development of transportation infrastructure. The destruction of the SBS cross-linking network is an important reason for the deterioration of the performance of aged SBS modified asphalt. Scientific reconstruction of aged SBS cross-linked network is the key to achieving the performance recovery of aged modified asphalt. In this research, the evolution of chemical structure, molecular weight, thermodynamic properties, multiple stress creep recovery capability and rheological property of SBS during the process of aging degradation and reactive reconstruction were systematically investigated. The results showed that the molecular weight and creep recovery capability of SBS decreased sharply, and its complex modulus and phase angle exhibited a strong temperature and frequency dependence after aging. While the number average molecular weight of aged SBS increased by over 70% after reactive reconstruction, and its thermal-oxygen stability shown better performance as compared with that of fresh SBS. Meanwhile, the glass transition temperature of aged SBS was restored to −43.8℃ and −54.9℃ after reactive reconstructed by toluene diisocyanate (TDI) and isocyanate pre-polymer. Therefore, isocyanate pre-polymer with flexible long chain structure was more benefit for improving the low-temperature performance of reactive reconstructed aged SBS. Furthermore, the creep recovery ability and complex modulus of aged SBS were all significantly improved, and exhibited dramatically high-elastic properties after reactive reconstruction. And as compared with isocyanate pre-polymer, TDI with benzene ring rigid structure was more conducive to restoring the medium–high temperature rheological properties of aged SBS. Therefore, effective restoration of molecular weight and performance of aged SBS can be achieved by using reaction reconstruction method. This study would provide inspiration and ideas for the high-value recycling of waste polymer modified asphalt.

Comparison of Eco-friendly Ti-M Bimetallic Coordination Catalysts and Commercial Monometallic Sb- or Ti-Based Catalysts for the Synthesis of Poly(ethylene-co-isosorbide terephthalate).

Sustainable development greatly benefits from the effective synthesis of bio-based copolymers that are environmentally friendly. To enhance the polymerization reactivity for the production of poly(ethylene-co-isosorbide terephthalate) (PEIT), five highly active Ti-M (M = Mg, Zn, Al, Fe, and Cu) bimetallic coordination catalysts were designed. The catalytic activity of Ti-M bimetallic coordination catalysts and single Sb- or Ti-based catalysts was compared, and the effects of catalysts with a different type of coordination metal (Mg, Zn, Al, Fe, and Cu) on the thermodynamic and crystallization properties of copolyesters were explored. In polymerization, it was found that Ti-M bimetallic catalysts with 5 ppm (Ti) had higher catalytic activity than traditional antimony-based catalysts or Ti-based catalysts with 200 ppm (Sb) or 5 ppm (Ti). The Ti-Al coordination catalyst showed the best-improved reaction rate of isosorbide among the five transition metals used. Utilizing Ti-M bimetallic catalysts, a high-quality PEIT was successfully synthesized with the highest number-average molecular weight of 2.82 × 104 g/mol and the narrowest molecular weight distribution index of 1.43. The glass-transition temperature of PEIT reached 88.3 °C, allowing the copolyesters to be used in applications requiring a higher Tg, like hot filling. The crystallization kinetics of copolyesters prepared by some Ti-M catalysts was faster than that of copolyesters prepared by conventional titanium catalysts.

Structural Properties of Lotus Seed Starch Nanocrystals Prepared Using Ultrasonic-Assisted Acid Hydrolysis.

This study provides a novel method of preparing lotus seed starch nanocrystals (LS-SNCs) using acid hydrolysis combined with ultrasonic-assisted acid hydrolysis (U-LS-SNCs) and evaluates the structural characteristics of starch nanocrystals using scanning electron microscopy; analysis of particle size, molecular weight, and X-ray diffraction patterns; and FT-IR spectroscopy. The results showed that the preparation time of U-LS-SNCs could be reduced to 2 days less than that for LS-SNCs. The smallest particle size and molecular weight were obtained after a 30 min treatment with 200 W of ultrasonic power and 5 days of acid hydrolysis. The particle size was 147 nm, the weight-average molecular weight was 3.42 × 104 Da, and the number-average molecular weight was 1.59 × 104 Da. When the applied ultrasonic power was 150 W for 30 min and acid hydrolysis was applied for 3 days, the highest relative crystallinity of the starch nanocrystals was 52.8%. The modified nanocrystals can be more widely used in various applications such as food-packaging materials, fillers, pharmaceuticals, etc.

Biosynthesis of Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) from Different 4-Hydroxybutyrate Precursors by New Wild-Type Strain Cupriavidus necator IBP/SFU-1

The study addresses the growth of the new wild-type strain Cupriavidus necator IBP/SFU-1 and the synthesis of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB) on media containing fructose and three different precursors of 4HB (ε-caprolactone 1,4-butanediol and 1,6-hexanediol). It was found that ε-caprolactone is the best precursor for the synthesis of P(3HB-co-4HB) copolymers. By varying the concentration and number of doses of ε-caprolactone added into the bacterial culture, it was possible to find conditions that ensured the synthesis of P(3HB-co-4HB) copolymers with different contents of 4HB (from 3–5 to 22.4 mol.%). The physicochemical properties of the copolymers were investigated depending on the proportions of 4HB monomers. The effect of 4HB monomers was manifested in a certain decrease in the weight-average molecular weight (Mw) (272–353 kDa), number-average molecular weight (Mn) (47–67 kDa) of the samples, and an increase in polydispersity (5.09–6.71) compared with P(3HB). The crystallinity degree decreased with an increasing fraction of the 4HB units (from 72 to 59%, as the 4HB content increased from 0 to 22.4 mol.%). In addition, the increase in 4HB content affected the temperature parameters (melting point, glass transition temperature, crystallization temperature, and thermal degradation temperature).

Efficient Transesterification Preparation of Polycarbonate Diol with High Molecular Weight Using TiO2/SiO2 Solid Acid Catalysts

AbstractA series of TiO2/SiO2 catalysts were prepared by hydrolysis and used in the transesterification of diphenyl carbonate (DPC) and 1,4‐butanediol (BDO) to produce polycarbonate diol (PCDL). The physical properties of TiO2/SiO2 solid acid catalysts were characterized, and the relationship between their structural features and catalytic transesterification reaction was analyzed. The effects of various reaction conditions such as hydrolysis procedure, transesterification temperature, catalyst amount, and the mole ratio of the starting materials on the catalytic synthesis of PCDL were investigated. The maximum catalytic activity was based on the TiO2 : SiO2=3 : 1 with hydrolysis procedure of adding the Ti/Si mixture (A) to deionized water and anhydrous ethanol (B). The as‐synthesized TiO2/SiO2‐A‐to‐B catalyst exhibits rough surface with the average pore size of 6.75 nm, and the total acid amount of 1.07 mmol/g. The PCDL yield of transesterification reached 89.8 %, and the number average molecular weight reached 9074 g/mol under the optimal reaction conditions, and the molecular weight of the PCDL product could be adjusted.

Enhancing the enrichment of conjugated polymer at surfaces of its elastomer blend film via increasing molecular weight to induce desired nanofibril network for highly stretchable polymer film

The vertical phase separation in conjugated polymer-elastomer blend systems plays a critical role in inducing desired film morphology of interconnected polymer nanofibrils for high-performance stretchable electronics. However, the precise control of vertical component distribution remains a great challenge due to the complex interactions among solutes, solvent and substrate in the blend system. Herein, we proposed a strategy to enhance the enrichment of polymer at film surfaces in the conjugated polymer-elastomer blend via increasing polymer molecular weight and systematically investigated the microstructural transition of blends under strain. For this purpose, a number of N2200 polymers with the number-average molecular weight (Mn) below (28, 57, 96 kDa) and above (143 kDa) the critical molecular weight (Mc) were used to blend with SEBS. With the increase of Mn, the phase separation between N2200 and SEBS along depth direction occurred at a greater extent due to the reduced polymer solubility and miscibility of the two components. Film-depth-dependent light absorption spectroscopy (FLAS) measurement shows that the content of N2200 concentrated at the film surfaces is dramatically increased from 66% to 85% as the Mn increases from 28 to 143 kDa, leading to the change of morphology from isolated aggregates to continuous and entangled nanofibril network within SEBS matrix. Under deformation, these nanofibrils formed in the 143 kDa blend film are able to maintain sufficient connections and the crystallites are seldom destroyed, thus guarantee efficient charge transport channels. The mobility of the 143 kDa blend film is 0.188 cm2 V−1 s−1, much higher than that of 28 kDa blend film (0.043 cm2 V−1 s−1) and does not decrease during stretching up to 150% strain.

Polymerization of butadiene and isoprene using α-diimine cobalt catalysts bearing electron donor at the N-aryl of imine

Cobalt dibromide supported by α-diimine ligand ortho-positioned with sulfur and oxygen donor are synthesized and characterized. Single X-ray diffraction result shown the oxygen donor is connected with the metal center in complex Co4, resulting in a triangle bipyramidal configuration. With AlEt2Cl as an activator, the formed catalysts are able to efficiently catalyze butadiene polymerization following in an essential cis-1,4 chemoselectivity at 1/2000–1/6000 catalyst feeding. These catalysts are more active and robust for isoprene polymerization under identical conditions, affording polyisoprene rich in cis-1,4 fraction randomly incorporated with 3,4 units. The number average molecular weights (Mns) of the formed polymers are determined to be 1.1–7.8 × 105, higher than those found for polybutadiene (0.4–9.3 × 104). The O-Me donor in the N-Aryl impacts positively on the activity and the molecular weight of the resultant polymer. The catalysts show a stable chemoselectivity despite the activator and catalyst feeding, applied temperature, even the catalyst structure are varied.

Active Learning as a Tool for Optimizing “Plug‐n‐Play” Electrochemical Atom Transfer Radical Polymerization

AbstractA recently reported “plug‐n‐play” approach to simplified electrochemical atom transfer radical polymerization (seATRP) is investigated using machine learning. It is shown that Bayesian optimization via an active learning (AL) algorithm accelerates optimization of the polymerization of oligo(ethylene glycol methyl ether acrylate)480 (OEGA480) in water. Molecular weight distribution (Mw/Mn; dispersity; Ɖm) is the output selected for optimization targeting poly(oligo[ethylene glycol methyl ether acrylate]) (POEGA480) with low dispersity (Ɖm &lt; 1.30). Input variables included applied potential (Eapp), [M] and [M]/[I], which led to a potential space of 275 possible reaction conditions. From a training data set of seven reactions, selected to yield uncontrolled POEGA480 with higher dispersities (Ɖm &gt; 1.5), ten iteration loops are performed. During each iteration the algorithm suggests the next reaction conditions. The reactions are then performed and the conversion, number average molecular weight (Mn) and Ɖm values are recorded and the Ɖm values fed back into the algorithm. Overall, 80% of the experiments yield POEGA with Ɖm &lt; 1.30. Conversely, only 30% of experiments performed using reaction conditions selected at random from the possible reaction space yield POEGA with Ɖm &lt; 1.30. This study suggests that adopting AL methods can improve the efficiency of optimizing a given seATRP reaction.

Effect of solvation and concentration on F8BT chain solution behavior and film condensed structure

Chain behavior of semi-rigid conjugated polymer in solution, correlation with condensed structure of the films and dynamic evolution in the process from solution to film are hot questions that have received close attention but have not yet solved. In this study, the scaling law obtained by laser light scattering and rheology was combined with fluorescence emission spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The chain behavior of the semi-rigid conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT, the number-average molecular weights (Mn) was 19.8 kg/mol) in solution and the condensed structure of the film were studied, the intrinsic physical relationship between the chain behavior in solution and condensed structure of the film and its dynamic evolution from solution to film were revealed. According to the concentration-dependent scaling relationship by rheology, some important parameters and chain motion characteristics in solution were revealed, such as toluene solvent was just θ solvent of F8BT, and the critical contact concentration between F8BT dilute solution and semidilute unentangled solution was found to be at 7.9 mg/mL, it firstly revealed the precursor solution concentration for film-forming (usually 10–20 mg/mL) was basically in the semidilute unentangled concentration range. The above results enrich the understanding of chain behavior in solution and the formation mechanisms of thin films condensed structure to semi-rigid conjugated polymers. The research is significant to manipulate the chain behavior in solution to construct condensed structures of the film to establish the structure-function relationship between solution state and photoelectronic device performance based on polymer physics.

Preparation and Structural Behavior of High-Performance PBO Fibers

To improve the dispersion ability of monomers in the high-viscosity PBO pre-polymerization system, a new large-capacity mixing paddle for PBO pre-polymerization reaction was designed. Through simulated calculation, it was found that the new mixing paddle has good dispersion effect and produced PBO polymer whose intrinsic viscosity was 37.5 dL/g, number-average molecular weight was 92700, and degree of polymerization was 396. Then the PBO fibers were prepared by the dry jet wet spinning technique. The morphology analysis showed that the PBO fibers were well formed, with a diameter of 14 µm. The infrared spectrum analysis verified the structure of PBO fibers. The mechanical test showed that the tensile strength of PBO fibers was 5.04-5.76 GPa and the elongation at break was 3.93% - 4.54%, which means they have good mechanical properties.