The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied.It was shown the variation of transition metal compound in the MgCl_2-...The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied.It was shown the variation of transition metal compound in the MgCl_2-supported catalyst affect of MWD of PE produced in broad range:Vanadium-magnesium catalyst(VMC)produce PE with broad and bimodal MWD(M_w/M_n=14-21).MWD of PE,produced over titanium-magnesium catalyst(TMC)is narrow or medium depending on Ti content in the catalyst(M_w/M_n=3.1-4.8).The oxidati...展开更多
Thin-wall injection molded parts have been paid much attention to the lightweight saving from viewpoints of natural resources saving. In the injection molding, skin-core structure can be found in the parts. This skin-...Thin-wall injection molded parts have been paid much attention to the lightweight saving from viewpoints of natural resources saving. In the injection molding, skin-core structure can be found in the parts. This skin-core structure affects the property of completed injection molding parts (bulk property) even if in thin-wall injection molding. However, there is a few research about the relationship between bulk property and internal property distribution in the injection molding specimen. In this study, thin-wall injection molded parts of polypropylene (PP) were prepared by 4 different molecular weight and molecular weight distribution to reveal the relationship between bulk property and property distribution. These characteristics were investigated by using tensile test, fracture toughness characterized by Essential Work of Fracture (EWF) method for bulk property and film tensile test by sliced sample for tensile property distribution. The property distribution test results revealed that the highly bulk property sample had thicker highly mechanical property layer on its surface.展开更多
Polymer dispersity (Đ) or molecular weight distribution (MWD) is a basic but vital parameter for the properties of polymeric materials. Developing new methodologies for controlling polymer MWD is emerging as a researc...Polymer dispersity (Đ) or molecular weight distribution (MWD) is a basic but vital parameter for the properties of polymeric materials. Developing new methodologies for controlling polymer MWD is emerging as a research hotspot. However, the methods to tune polymer MWD in cationic polymerization are still not well explored. Herein, we present a simple method to control the dispersity of poly(isobutyl vinyl ether) (PIBVE) by mixing two different chain transfer agents in batch visible light induced cationic RAFT polymerization. A broad dispersity range (Đ ≈ 1.16—1.80) was successfully achieved while maintaining monomodal MWD. Moreover, chain extension of PIBVE through both cationic polymerization and radical polymerization has been studied, which also provides a method to tune polymer MWD in mechanism transformation polymerization.展开更多
Controlled and homogeneous free-radical polymerization of acrylamide(AM) in aqueous phase was realized by using S,S'-bis(α,α'-dimethyl-α''-acetic acid)-trithiocarbonate as a reversible addition-frag...Controlled and homogeneous free-radical polymerization of acrylamide(AM) in aqueous phase was realized by using S,S'-bis(α,α'-dimethyl-α''-acetic acid)-trithiocarbonate as a reversible addition-fragmentation transfer(RAFT) agent. Linear increases in molecular weight with conversion and narrow molecular weight distribution were observed for polyacrylamide(PAM) throughout the polymerization. By this method, PAMs with controlled molecular weight(up to 1.0 × 10~6) and narrow molecular weight distribution(M_w/M_n < 1.2) were prepared. This study provides an effective method for synthesis of PAMs with narrow molecular weight distribution under environmentally friendly conditions.展开更多
Molecular weight distribution(MWD)is fundamental for polymer analysis,which influences many important properties of polymeric materials.In this work,we demonstrate the development of a computer-aided droplet-flow syst...Molecular weight distribution(MWD)is fundamental for polymer analysis,which influences many important properties of polymeric materials.In this work,we demonstrate the development of a computer-aided droplet-flow system that combines photo-mediated reversible-deactivation radical polymerization(RDRP)and chain transfer agent(CTA)diffusion strategy to enable facile MWD control for the first time.Synthetic advantages of this photo-flow polymerization allow controlled chain-growth to yield a variety of polymers of tunable MWDs in a broad range(Ð≈1.1—1.9)with predetermined molecular weights(Mn≈4—30 kDa)and good chain-end fidelity.Notably,the computer-aided platform has streamlined an automatic and high-throughput pathway to prepare polymer libraries of tunable MWDs.For copolymers,chemical compositions could be readily regulated besides MWDs with the droplet-flow platform.We believe that this work should be attractive for polymer engineering,and informative to create more flow polymerization techniques toward on-demand control of diverse polymer characters.展开更多
In this study, the relationship between skin structure and shear strength distribution of thin-wall injection molded polypropylene (PP) molded at different molecular weight and molecular distribution was investigated....In this study, the relationship between skin structure and shear strength distribution of thin-wall injection molded polypropylene (PP) molded at different molecular weight and molecular distribution was investigated. Skin-core structure, cross-sectional morphology, crystallinity, crystal orientation, crystal morphology and molecular orientation were evaluated by using polarized optical microscope, differential scanning calorimeter, X-ray spectroscopic analyzer and laser Raman spectroscopy, respectively, while the shear strength distribution was investigated using a micro cutting method called SAICAS (Surface And Interfacial Cutting Analysis System). The results indicated that the difference of molecular weight and molecular weight distribution showed own skin layer thickness. Especially, high molecular weight sample showed thicker layer of the lamellar orientation and molecular orientation than low molecular weight sample. In addition, wide molecular distribution sample showed large crystal orientation layer.展开更多
Hydroxypropyl methylcellulose acetate succinate(HPMCAS)was successfully synthesized from the reaction of hydroxypropyl methylcellulose with succinic anhydride and acetic anhydride in an acetone/pyridine system.Product...Hydroxypropyl methylcellulose acetate succinate(HPMCAS)was successfully synthesized from the reaction of hydroxypropyl methylcellulose with succinic anhydride and acetic anhydride in an acetone/pyridine system.Products with different contents of succinyl groups and acetyl groups were prepared by varying the reaction conditions.In the acetone/pyridine system,equipment corrosion does not occur,the product is easy to wash,and the solvent can be recycled.By varying the concentration of the esterifying agents,products with different ratios of acidic groups can be obtained.Under the optimum conditions,the obtained products had an average molecular weight between 5.39×104 and 5.41×104,a number average molecular weight from 4.97×104 to 5.13×104,and a polydispersity index from 1.05 to 1.08.The products dissolved well in acetone and methanol,and formed films on a mold.The films had good pH-sensitivity,tensile strength,and thermal stability.The formed films could dissolve in solutions with a pH value ranging from 5.4 to 6.4,and are therefore suitable for use as an enteric coating for pharmaceutical dosage forms.展开更多
The aim of this study was to obtain a better understanding of the range of organic molecular weight(MW)causing membrane fouling through the comparison between direct UF and in-line coagulation(without settling)/UF pro...The aim of this study was to obtain a better understanding of the range of organic molecular weight(MW)causing membrane fouling through the comparison between direct UF and in-line coagulation(without settling)/UF process.The experimental results indicated that,when raw water with organics was treated and the MW of more than half of the organics was less than 1 kDa,membrane fouling was rather serious by only UF and coagulation could improve the fouling for the treatment of raw water.Besides,coagulation/UF could remove organics in each region,and organics with MW greater than 30 kDa were the most possible matters causing membrane fouling,while organics with MW less than 1 kDa were impossibly responsible for membrane fouling due to few organics removed.Therefore,organics with MW greater than 30 kDa were the major factor of membrane fouling.展开更多
In this work, homopolymerization of propylene for synthesis of different molecular weights polypropylene was done using an isospecific metallocene catalyst by changing the polymerization conditions such as Al/Zr (Alum...In this work, homopolymerization of propylene for synthesis of different molecular weights polypropylene was done using an isospecific metallocene catalyst by changing the polymerization conditions such as Al/Zr (Aluminium/Zirconium) ratio, temperature, pressure and polymerization time. The effects of the polymerization conditions on the molecular weight and other polymer properties have been discussed according to the results obtained. The results indicate that the activity of polymerization increased with increasing the Al/Zr mole ratio and reached a maximum value at a ratio of 2000. In relation to the mole ratio, the molecular weight also followed the same trend. The activity was also seen to increase with increase in temperature. The molecular weight increased with increasing the polymerization time at both 0°C and 25°C, but reduced with increase in time at 40°C. The increase of pressure also increased activity but lowered the molecular weight, indicating β-H elimination to the monomer.展开更多
On-demand regulation of molecular weight distribution(MWD)is crucial to influence the properties of polymers.In this work,we reported an organocatalyzed photo-controlled radical polymerization(photo-CRP)from the tosyl...On-demand regulation of molecular weight distribution(MWD)is crucial to influence the properties of polymers.In this work,we reported an organocatalyzed photo-controlled radical polymerization(photo-CRP)from the tosyl chloride initiator by combining two disulfides as chain transfer agents.This novel synthetic protocol allows facile access toward well-defined polymers with tunable MWDs and predetermined molecular weights.Experiments including structural characterization,kinetic investigation and chain-extension polymerization exhibited good chain-growth control for polymers of different dispersities.Given the easy accessibility of the initiating site(sulfonyl chloride)on many aromatic sources,this work presents a promising avenue to modify such substances with polymers of tailored MWDs,chain lengths and repeating units under metal-free and mild conditions driven by light.展开更多
Objective To clarify the influence on component and pharmacological action of Astragalus polysaccharides(APS) as complementary therapeutic agents prepared by different extraction and purification techniques.Methods Co...Objective To clarify the influence on component and pharmacological action of Astragalus polysaccharides(APS) as complementary therapeutic agents prepared by different extraction and purification techniques.Methods Components of APS prepared by different extraction and purification techniques were analyzed,and these APS were used for synergy and attenuation of chemotherapy,radiotherapy treatment with H22 liver cancer and Lewis lung cancer of tumor-bearing mice,and also used for the regulation of immune function to immunosuppression mice.Results Experimental data were analyzed by means of statistical method to get pharmaco-result:A3(extracted by microwave assistance and purified by membrane separation)>A4(extracted by refluxing and purified by membrane separation)>A1(extracted by refluxing and no purification)≈A2(extracted by microwave assistance and no purification).There were no significant differences on pharmacodynamic action between A1 and A2.However,compared with A1 and A2,it was worth noting that A3 and A4 exhibited good pharmacodynamic action.Then A3-in and A4-in,the samples in dialyzer after dialysis,were separated and purified to get homogeneous APS,which were the principal constituents of APS in dialyzer,with the molecular weight(Mw) of 7669 and 14142 determined by HPGPC,respectively.The average Mw of APS outside of the dialyzer,A3-out was 3102 and A4-out 3256,which were the main compositions of A3 and A4,accounted for 79.63% and 53.92%,respectively.Conclusion APS with Mw about 5000 Da exhibit better antitumor effect and immunological activity.Refluxing,microwave assistance extractions,and membrane enrichment techniques bring different cases on Mw distribution,components and pharmacodynamic action,and obviously exhibit relationship among component,Mw distribution,and pharmacological action.展开更多
Molecules adsorbed or attached on a surface is a quite basic phenomenon in numerous chemical or biological systems.Grafting-onto is considered as a feasible way to achieve it.The grafting reaction is essentially contr...Molecules adsorbed or attached on a surface is a quite basic phenomenon in numerous chemical or biological systems.Grafting-onto is considered as a feasible way to achieve it.The grafting reaction is essentially controlled by the diffusion of the molecules,thus it is more likely a physical issue,instead of a chemical issue.Because of the experimental difficulty in measuring the properties of surface-attached molecules(e.g.,the polymeric molecules),the surface-bound molecules are often assumed as with the same properties as that of the start feeding ones in solution.This assumption was even used to guide further characterization,while it is proved to be invalid by different quantifying methods.Consequently,an effective prediction for the properties of surface-bound molecules is still lacking.Based on a microscopic level and a dynamic perspective,the grafting process onto a flat substrate with polydisperse feeding polymeric molecules is investigated in-depth by coarse-grained Brownian dynamics simulation as well as model analysis.We find from simulations that for the final grafting densityσ_(g)and the mean chain length of start feeding molecules<N_(0)>,the dependence ofσ_(g)-<N_(0)>^(γ)with the constant exponential factorγmay be a determined rule for one-end functionalized flexible linear polymer chains grafting on the flat substrate.Since grafting-onto is a multiple interplayed process,our simulation study indicates that there is an optimized initial concentration of start feeding molecules for achieving high grafting density of surface-bound polymers.We also propose a correctional equation to quantitatively predict the molecular weight distribution(MWD)of surface-bound polymeric molecules,which may be effective for predicting the MWD of the surface-bound ones in specific conditions.This simulation study helps to better understand the kinetics of grafting-onto process,and serves as a theoretical guide to achieve the precise design of surface modification materials via grafting-onto strategy.展开更多
The antioxidant and free radical-scavenging activities of black soybean peptides(BSP)fractions(Fra-Ⅰ,Fra-Ⅱ,Fra-Ⅲ)were investigated using reducing power and DPPH·/superoxide/hydroxyl radical-scavenging assay.Th...The antioxidant and free radical-scavenging activities of black soybean peptides(BSP)fractions(Fra-Ⅰ,Fra-Ⅱ,Fra-Ⅲ)were investigated using reducing power and DPPH·/superoxide/hydroxyl radical-scavenging assay.The reducing power activity of Fra-Ⅲwas closer to that of BHT but lower than that of ascorbic acid.Fra-Ⅲshowed the strongest scavenging activity against free radicals.The radical-scavenging effect was in a dose-dependent manner and the IC50 values for DPPH·,superoxide and hydroxyl radicals were found to be 1.873,1.684 and 1.735 mg/mL,respectively.Amino acid analysis showed that Fra-Ⅲhad high hydrophobic amino acids(HAA)content and hydrophobicity.The molecular weight distribution of Fra-Ⅲwas found to vary from 100 to 1,000 Da mainly.The antioxidant activity of Fra-Ⅲis clearly related to the amino acid composition,the content of HAA and the molecular mass.The present study suggests that BSP with low molecular weight are useful nutritional antioxidant and potential functional factor for anti-aging.展开更多
文摘The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied.It was shown the variation of transition metal compound in the MgCl_2-supported catalyst affect of MWD of PE produced in broad range:Vanadium-magnesium catalyst(VMC)produce PE with broad and bimodal MWD(M_w/M_n=14-21).MWD of PE,produced over titanium-magnesium catalyst(TMC)is narrow or medium depending on Ti content in the catalyst(M_w/M_n=3.1-4.8).The oxidati...
文摘Thin-wall injection molded parts have been paid much attention to the lightweight saving from viewpoints of natural resources saving. In the injection molding, skin-core structure can be found in the parts. This skin-core structure affects the property of completed injection molding parts (bulk property) even if in thin-wall injection molding. However, there is a few research about the relationship between bulk property and internal property distribution in the injection molding specimen. In this study, thin-wall injection molded parts of polypropylene (PP) were prepared by 4 different molecular weight and molecular weight distribution to reveal the relationship between bulk property and property distribution. These characteristics were investigated by using tensile test, fracture toughness characterized by Essential Work of Fracture (EWF) method for bulk property and film tensile test by sliced sample for tensile property distribution. The property distribution test results revealed that the highly bulk property sample had thicker highly mechanical property layer on its surface.
基金supported by the National Natural Science Foundation of China(No.22101196)the China Postdoctoral Science Foundation(No.2021M692348).
文摘Polymer dispersity (Đ) or molecular weight distribution (MWD) is a basic but vital parameter for the properties of polymeric materials. Developing new methodologies for controlling polymer MWD is emerging as a research hotspot. However, the methods to tune polymer MWD in cationic polymerization are still not well explored. Herein, we present a simple method to control the dispersity of poly(isobutyl vinyl ether) (PIBVE) by mixing two different chain transfer agents in batch visible light induced cationic RAFT polymerization. A broad dispersity range (Đ ≈ 1.16—1.80) was successfully achieved while maintaining monomodal MWD. Moreover, chain extension of PIBVE through both cationic polymerization and radical polymerization has been studied, which also provides a method to tune polymer MWD in mechanism transformation polymerization.
文摘Controlled and homogeneous free-radical polymerization of acrylamide(AM) in aqueous phase was realized by using S,S'-bis(α,α'-dimethyl-α''-acetic acid)-trithiocarbonate as a reversible addition-fragmentation transfer(RAFT) agent. Linear increases in molecular weight with conversion and narrow molecular weight distribution were observed for polyacrylamide(PAM) throughout the polymerization. By this method, PAMs with controlled molecular weight(up to 1.0 × 10~6) and narrow molecular weight distribution(M_w/M_n < 1.2) were prepared. This study provides an effective method for synthesis of PAMs with narrow molecular weight distribution under environmentally friendly conditions.
基金This research was financially supported by Science and Technology Commission of Shanghai Municipality(STCSM)and the Shanghai Pilot Program for Basic Research--Fudan University 21TQ1400100(No.21TQ007)NSFC(No.21971044)State Key Laboratory of Molecular Engineering of Polymers.
文摘Molecular weight distribution(MWD)is fundamental for polymer analysis,which influences many important properties of polymeric materials.In this work,we demonstrate the development of a computer-aided droplet-flow system that combines photo-mediated reversible-deactivation radical polymerization(RDRP)and chain transfer agent(CTA)diffusion strategy to enable facile MWD control for the first time.Synthetic advantages of this photo-flow polymerization allow controlled chain-growth to yield a variety of polymers of tunable MWDs in a broad range(Ð≈1.1—1.9)with predetermined molecular weights(Mn≈4—30 kDa)and good chain-end fidelity.Notably,the computer-aided platform has streamlined an automatic and high-throughput pathway to prepare polymer libraries of tunable MWDs.For copolymers,chemical compositions could be readily regulated besides MWDs with the droplet-flow platform.We believe that this work should be attractive for polymer engineering,and informative to create more flow polymerization techniques toward on-demand control of diverse polymer characters.
文摘In this study, the relationship between skin structure and shear strength distribution of thin-wall injection molded polypropylene (PP) molded at different molecular weight and molecular distribution was investigated. Skin-core structure, cross-sectional morphology, crystallinity, crystal orientation, crystal morphology and molecular orientation were evaluated by using polarized optical microscope, differential scanning calorimeter, X-ray spectroscopic analyzer and laser Raman spectroscopy, respectively, while the shear strength distribution was investigated using a micro cutting method called SAICAS (Surface And Interfacial Cutting Analysis System). The results indicated that the difference of molecular weight and molecular weight distribution showed own skin layer thickness. Especially, high molecular weight sample showed thicker layer of the lamellar orientation and molecular orientation than low molecular weight sample. In addition, wide molecular distribution sample showed large crystal orientation layer.
基金The authors are grateful for the financial supports of this research from the Science and Technology Program of Guangdong(2019A1515011890)National Key R&D Program of China(2017YFD0601003).
文摘Hydroxypropyl methylcellulose acetate succinate(HPMCAS)was successfully synthesized from the reaction of hydroxypropyl methylcellulose with succinic anhydride and acetic anhydride in an acetone/pyridine system.Products with different contents of succinyl groups and acetyl groups were prepared by varying the reaction conditions.In the acetone/pyridine system,equipment corrosion does not occur,the product is easy to wash,and the solvent can be recycled.By varying the concentration of the esterifying agents,products with different ratios of acidic groups can be obtained.Under the optimum conditions,the obtained products had an average molecular weight between 5.39×104 and 5.41×104,a number average molecular weight from 4.97×104 to 5.13×104,and a polydispersity index from 1.05 to 1.08.The products dissolved well in acetone and methanol,and formed films on a mold.The films had good pH-sensitivity,tensile strength,and thermal stability.The formed films could dissolve in solutions with a pH value ranging from 5.4 to 6.4,and are therefore suitable for use as an enteric coating for pharmaceutical dosage forms.
基金Sponsored by the Tianjin Municipal Science and Technology Commission(Grant No.05FZZDSH00500)
文摘The aim of this study was to obtain a better understanding of the range of organic molecular weight(MW)causing membrane fouling through the comparison between direct UF and in-line coagulation(without settling)/UF process.The experimental results indicated that,when raw water with organics was treated and the MW of more than half of the organics was less than 1 kDa,membrane fouling was rather serious by only UF and coagulation could improve the fouling for the treatment of raw water.Besides,coagulation/UF could remove organics in each region,and organics with MW greater than 30 kDa were the most possible matters causing membrane fouling,while organics with MW less than 1 kDa were impossibly responsible for membrane fouling due to few organics removed.Therefore,organics with MW greater than 30 kDa were the major factor of membrane fouling.
文摘In this work, homopolymerization of propylene for synthesis of different molecular weights polypropylene was done using an isospecific metallocene catalyst by changing the polymerization conditions such as Al/Zr (Aluminium/Zirconium) ratio, temperature, pressure and polymerization time. The effects of the polymerization conditions on the molecular weight and other polymer properties have been discussed according to the results obtained. The results indicate that the activity of polymerization increased with increasing the Al/Zr mole ratio and reached a maximum value at a ratio of 2000. In relation to the mole ratio, the molecular weight also followed the same trend. The activity was also seen to increase with increase in temperature. The molecular weight increased with increasing the polymerization time at both 0°C and 25°C, but reduced with increase in time at 40°C. The increase of pressure also increased activity but lowered the molecular weight, indicating β-H elimination to the monomer.
基金This work was supported by the National Natural Science Foundation of China(No.22171051)the Shanghai Pilot Program for Basic Research-Fudan University 21TQ1400100,China(No.21TQ007)the Project of the State Key Laboratory of Molecular Engineering of Polymers,Fudan University,China。
文摘On-demand regulation of molecular weight distribution(MWD)is crucial to influence the properties of polymers.In this work,we reported an organocatalyzed photo-controlled radical polymerization(photo-CRP)from the tosyl chloride initiator by combining two disulfides as chain transfer agents.This novel synthetic protocol allows facile access toward well-defined polymers with tunable MWDs and predetermined molecular weights.Experiments including structural characterization,kinetic investigation and chain-extension polymerization exhibited good chain-growth control for polymers of different dispersities.Given the easy accessibility of the initiating site(sulfonyl chloride)on many aromatic sources,this work presents a promising avenue to modify such substances with polymers of tailored MWDs,chain lengths and repeating units under metal-free and mild conditions driven by light.
基金The National Key Scientific and Technological Project in 11th Five-year Plan (No:2009ZX09301-007)
文摘Objective To clarify the influence on component and pharmacological action of Astragalus polysaccharides(APS) as complementary therapeutic agents prepared by different extraction and purification techniques.Methods Components of APS prepared by different extraction and purification techniques were analyzed,and these APS were used for synergy and attenuation of chemotherapy,radiotherapy treatment with H22 liver cancer and Lewis lung cancer of tumor-bearing mice,and also used for the regulation of immune function to immunosuppression mice.Results Experimental data were analyzed by means of statistical method to get pharmaco-result:A3(extracted by microwave assistance and purified by membrane separation)>A4(extracted by refluxing and purified by membrane separation)>A1(extracted by refluxing and no purification)≈A2(extracted by microwave assistance and no purification).There were no significant differences on pharmacodynamic action between A1 and A2.However,compared with A1 and A2,it was worth noting that A3 and A4 exhibited good pharmacodynamic action.Then A3-in and A4-in,the samples in dialyzer after dialysis,were separated and purified to get homogeneous APS,which were the principal constituents of APS in dialyzer,with the molecular weight(Mw) of 7669 and 14142 determined by HPGPC,respectively.The average Mw of APS outside of the dialyzer,A3-out was 3102 and A4-out 3256,which were the main compositions of A3 and A4,accounted for 79.63% and 53.92%,respectively.Conclusion APS with Mw about 5000 Da exhibit better antitumor effect and immunological activity.Refluxing,microwave assistance extractions,and membrane enrichment techniques bring different cases on Mw distribution,components and pharmacodynamic action,and obviously exhibit relationship among component,Mw distribution,and pharmacological action.
基金financially supported by the National Natural Science Foundation of China(Nos.22022303 and 21774051)Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciencesthe support from the Alexander von Humboldt Foundation。
文摘Molecules adsorbed or attached on a surface is a quite basic phenomenon in numerous chemical or biological systems.Grafting-onto is considered as a feasible way to achieve it.The grafting reaction is essentially controlled by the diffusion of the molecules,thus it is more likely a physical issue,instead of a chemical issue.Because of the experimental difficulty in measuring the properties of surface-attached molecules(e.g.,the polymeric molecules),the surface-bound molecules are often assumed as with the same properties as that of the start feeding ones in solution.This assumption was even used to guide further characterization,while it is proved to be invalid by different quantifying methods.Consequently,an effective prediction for the properties of surface-bound molecules is still lacking.Based on a microscopic level and a dynamic perspective,the grafting process onto a flat substrate with polydisperse feeding polymeric molecules is investigated in-depth by coarse-grained Brownian dynamics simulation as well as model analysis.We find from simulations that for the final grafting densityσ_(g)and the mean chain length of start feeding molecules<N_(0)>,the dependence ofσ_(g)-<N_(0)>^(γ)with the constant exponential factorγmay be a determined rule for one-end functionalized flexible linear polymer chains grafting on the flat substrate.Since grafting-onto is a multiple interplayed process,our simulation study indicates that there is an optimized initial concentration of start feeding molecules for achieving high grafting density of surface-bound polymers.We also propose a correctional equation to quantitatively predict the molecular weight distribution(MWD)of surface-bound polymeric molecules,which may be effective for predicting the MWD of the surface-bound ones in specific conditions.This simulation study helps to better understand the kinetics of grafting-onto process,and serves as a theoretical guide to achieve the precise design of surface modification materials via grafting-onto strategy.
文摘The antioxidant and free radical-scavenging activities of black soybean peptides(BSP)fractions(Fra-Ⅰ,Fra-Ⅱ,Fra-Ⅲ)were investigated using reducing power and DPPH·/superoxide/hydroxyl radical-scavenging assay.The reducing power activity of Fra-Ⅲwas closer to that of BHT but lower than that of ascorbic acid.Fra-Ⅲshowed the strongest scavenging activity against free radicals.The radical-scavenging effect was in a dose-dependent manner and the IC50 values for DPPH·,superoxide and hydroxyl radicals were found to be 1.873,1.684 and 1.735 mg/mL,respectively.Amino acid analysis showed that Fra-Ⅲhad high hydrophobic amino acids(HAA)content and hydrophobicity.The molecular weight distribution of Fra-Ⅲwas found to vary from 100 to 1,000 Da mainly.The antioxidant activity of Fra-Ⅲis clearly related to the amino acid composition,the content of HAA and the molecular mass.The present study suggests that BSP with low molecular weight are useful nutritional antioxidant and potential functional factor for anti-aging.
