Neural Network Modeling Applied to Polyacrylamide Based Hydrogels Synthetized By Single Step Process

This paper presents a series of experimental data obtained from the synthesis of polyacrylamide-based hydrogels and a general neural network methodology that accomplishes the modeling and optimization of the polymerization process.

Using direct neural network modeling, the variation of the main parameters in the synthesis of polyacrylamide-based hydrogels (polymerization yield and maximum swelling degree) was modeled in correlation with reactant concentrations, temperature, and reaction time. The predictions of the network, verified against initial training data and other testing data in the domain of the reaction conditions, were quite precise.

Inverse neural modeling determines, in a facile manner and with good results, the initial reaction conditions, which lead to a preestablished reaction yield and maximum swelling degree. This optimization method is more advantageous compared to a difficult classical procedure that requires a good mathematical model and an optimization solving technique.     

在微波作用下正交设计合成丙烯酸十六酯

利用正交设计法研究由丙烯酸和十六醇为原料,对甲苯磺酸为催化．剂,采用微波加热法合成丙烯酸十六酯。通过方差分析,探讨了催化剂用量、微波功率和辐射时间以及它们之间的交互作用对合成丙烯酸十六酯产率的影响。结果表明,辐射时间的改变对产率的影响高度显著,催化剂用量和微波功率的改变对产率影响显著,并且这三个因素之间存在交互作用,当催化剂用量、微波功率和辐射时间分别为质量分数0.8％、260W和15min时,合成丙烯酸十六酯的产率在96％以上。     

响应面法优化N-氨基甲酰谷氨酸的合成工艺

关于N-氨基甲酰谷氨酸的合成国内外已有许多报道,通过以L-谷氨酸和尿素为原料,研究了N-氨基甲酰谷氨酸的合成工艺。在单因素实验的基础上,采用响应面分析法的Box-Behnken设计方法,利用软件Design-Expert 10考察了反应温度、反应时间、物料比等因素以及因素之间的交互作用对合成N-氨基甲酰谷氨酸产率的影响。建立了N-氨基甲酰谷氨酸产率的二次线性回归方程,获得了最优工艺条件:反应时间2.05 h、反应温度119.83℃、n(L-谷氨酸)∶n(尿素)=1∶2.2,在此条件下N-氨基甲酰谷氨酸产率为82.47%,并进行了3次验证性实验,得到N-氨基甲酰谷氨酸的产率为81.76%,与理论预测值相对误差较小,与响应面模型预测值非常吻合,说明采用响应面优化方案有效、可靠。     

Lipase‐catalyzed production of medium‐chain triacylglycerols from palm kernel oil distillate: Optimization using response surface methodology

Optimization of lipase‐catalyzed esterification for the production of medium‐chain triacylglycerols (MCT) from palm kernel oil distillate and glycerol was carried out in order to determine the factors that have significant effects on the reaction system and MCT yield. Novozyme 435 from Candida antarctica lipase was found to have the highest activity at 52.87 ± 0.03 U/g. This lipase also produced the highest MCT yield, which is 56.67%. The effect of different variables on MCT synthesis was studied with a two‐level five‐factor fractional factorial design. The various variables include (1) reaction temperature, (2) enzyme load, (3) molecular sieves concentration, (4) reaction time and (5) molar substrate ratio. Reaction temperature, reaction time and molar substrate ratio strongly affect MCT synthesis (p <0.05). However, enzyme load and molecular sieve concentration did not have a significant (p >0.05) influence on MCT yield. Therefore, the significant variables such as reaction temperature, reaction time and molar substrate ratio were further optimized through central composite rotatable design (CCRD). Comparisons between predicted and experimental values from the CCRD optimization procedures revealed good correlation, implying that the quadric response model satisfactorily expressed the percentage yield of MCT in the lipase‐catalyzed esterification. The optimum MCT yield is 73.3% by using 2 wt‐% enzyme dosage, a molecular sieves concentration of 1 wt‐%, a reaction temperature of 90 °C, a reaction time of 10 h and a molar substrate ratio of 4 : 1 (medium‐chain fatty acid/glycerol). Experiments to confirm the predicted results using the optimal parameters were conducted and an MCT yield of 70.21 ± 0.18% (n = 3) was obtained.     

Hydroxyl-terminated polybutadiene. I. A study of the polymerization of butadiene in the presence of hydrogen peroxide

The polymerization of butadiene in a solution of 1-butanol as a solvent and in the presence of hydrogen peroxide as an initiator was studied. The influence of four factors—polymerization temperature, concentration of the initiator, polymerization time, and stirring rate—on the yield, molecular weight characteristics, and the number-average functionality of the hydroxyl-terminated polybutadienes (HTPBs) were determined. Regression models which adequately fit the experimental data were obtained. On this basis, the optimum values of the most significant factors—polymerization temperature and concentration of the initiator for obtaining maximum yield of HTPB—were evaluated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2491–2496, 1997     

Optimization of Microwave-Assisted Extraction of Puerarin from Radix Puerariae using Response Surface Methodology

Statistical experimentical designs were applied to optimize microwave-assisted extraction of puerarin from Radix Puerariae. The most important factors affecting the extraction procedure were determined using a Plackett-Burman design. Results indicated that the concentration of ethanol, solvent-material ratio, extraction time, and microwave power were the main factors affecting the extraction yield. These factors were further optimized using a central composite design and response surface methodology. The optimal extraction parameters were ethanol concentration of 52.36%, microwave irradiation time of 60 s, microwave power of 184.8 W and solvent-material ratio of 25:1(mL/g). The average experimental puerarin yield under the optimum conditions was found to be 11.97 mg/g, which agreed with the predicted value of 11.8 mg/g. The proposed method shows high degree of reproducibility.     

微波促进对甲苯磺酸催化合成肉桂酸甲酯

进行了微波辐射对甲苯磺酸催化合成肉桂酸甲酯的合成研究,结果表明微波辐射对催化剂的催化效果有促进作用,但微波辐射本身没有催化作用;微波加热法比常规加热法合成肉桂酸甲酯要快52．5倍,产率提高4％;优化条件下：对甲苯磺酸0．1000g,肉桂酸0．5000g,微波辐射温度为120℃,反应时间为4min,产率达93．07％,产物经红外光谱表征。     

Block copolymerization of vinyl ester monomers via RAFT/MADIX under microwave irradiation

Well-defined homopolymers and block copolymers of vinyl esters were synthesized under microwave irradiation via reversible addition-fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthates (MADIX) polymerization without the significant inhibition or retardation often observed under conventional heating conditions. Poly(vinyl acetate) (PVAc) with molecular weights of 1000−10 000 g/mol was prepared in less than 15 min under microwave irradiation at an apparent temperature of 70 °C in the presence of the commercially available chain transfer agent ethylxanthogenacetic acid. The polymerizations were well-controlled, leading to polymers with narrow molecular weight distributions and excellent agreement between theoretical and experimental number average molecular weights. Despite the high rates of polymerization, the resulting PVAc homopolymers retained a high degree of thiocarbonylthio end group functionality that allowed the synthesis of block copolymers by chain extension with vinyl benzoate and vinyl pivalate. The rates of polymerization during the addition of the second blocks were also high, and the resulting block copolymers were obtained in good yield with excellent blocking efficiencies.     

非腈复合引发剂用于乙酸乙烯溶液聚合

以生物乙烯法生产的乙酸乙烯为单体、过氧化月桂酰-十二烷基二甲基叔胺为非腈复合引发剂、甲醇为溶剂进行溶液聚合反应的研究。实验考察了反应温度、反应时间、甲醇用量、引发剂用量对反应产物聚合率和聚合度的影响,采用正交试验优化了乙酸乙烯溶液聚合的反应条件,确定反应因素对聚合率和聚合度影响的相对大小。结果表明,最优的乙酸乙烯溶液聚合条件为:反应温度65℃,反应时间3h,甲醇用量10%,引发剂用量0.010%,获得聚乙烯醇产品的聚合度为3776,聚合率为45.29%。直观分析确定影响聚合率的因素主次顺序为引发剂用量> 反应时间> 甲醇用量> 反应温度;影响聚合度的因素主次顺序为甲醇用量 >引发剂用量 >反应温度 >反应时间。     

Optimization of microwave-assisted synthesis of cyclodextrin nanosponges using response surface methodology

The reaction of polymerization of cyclodextrins with suitable polyfunctional agents leads to highly cross linked porous structures, referred to as cyclodextrin nanosponges. The conventional heating approach for the synthesis of nanosponges can lead to nonuniform reaction conditions caused by sharp thermal gradients in the bulk solution. In this work, we present a facile method for the synthesis of cyclodextrin nanosponges by microwave irradiation with significant reduction in reaction time. Response surface methodology and Box–Behnken design were used for the optimization of the process parameters including microwave power level (A), reaction time (B) and stirring speed (C). Two dependent variables practical yield and particle size were measured as responses. Mathematical equations and response surface plots were used to relate the dependent variables with independent variables. The optimization model predicted a yield of 96.5287 % and particle size of about 152.355 nm with A, B and C levels of 508.22, 83.55 and 1,471.55 respectively. The observed responses of the optimized process were in close agreement with the predicted values. Three confirmation batches of cyclodextrin nanosponges were synthesized under optimized conditions. The Fourier transformed infrared spectra of nanosponges showed a characteristic peak of the carbonate group at around 1,750 cm^?1 which confirms the formation of nanosponges. TGA revealed the stability of obtained nanosponges up to 325 °C. The nanosponges obtained by microwave irradiation exhibited a higher degree of crystallinity. Dimension of the crystal lattice was found to be equal to 0.70 nm. TEM image confirmed the spherical shape and the particle size range of about 153 nm. Compared to conventional heating method, microwave method resulted in four folds reduction in reaction time and provided with particles of homogeneous size distribution and uniform crystallinity.     

Factorial design optimization of polystyrene microspheres obtained by aqueous dispersion polymerization in the presence of poly(2‐ethyl‐2‐oxazoline) reactive stabilizer

The present study highlights the use of statistical design to establish an effective model for the synthesis of polystyrene microspheres by aqueous dispersion polymerization using poly(2‐ethyl‐2‐oxazoline) reactive stabilizer. The significant parameters (e.g. solvent polarity, stabilizer and initiator concentration) influencing the characteristic responses of the process such as yield, particle size and size distribution, as well as the interactions between the variables, were identified. The macromonomer concentration and solvent polarity influence both particle size and size distribution, whereas initiator concentration influences the yield. Analysis of the variance of process variables indicates that the models can be successfully used to describe the dispersion polymerization process. Moreover, the factorial design allows the development of microspheres with optimal properties with respect to size and size distribution. The experimental data regarding yield, particle size and size distribution of the optimized dispersion polymerization shows less than 7% difference compared with the predicted responses. In view of these results, the implementation of statistical design models represents an efficient solution for optimizing microparticle synthesis while aiming for industrial applications. © 2020 Society of Chemical Industry     

Improved synthesis of poly(MAA)–starch graft copolymers

Graft copolymerization of methacrylic acid (MAA) onto starch using a potassium persulfate/sodium thiosulfate redox initiation system was investigated. Emphasis was placed on the promotion of graft formation while minimizing homopolymerization. This could be achieved through a thorough investigation into the major factors affecting the polymerization reaction such as the state of the starch, redox ratio of the initiator, monomer and initiator concentrations, time and temperature of polymerization, and material-to-liquor ratio. The results obtained imply that the magnitude of the polymer yield including total conversion, graft yield, and homopolymer are determined by these factors. The yield is favored under the influence of higher temperature, longer time, short liquor, and increased monomer and initiator concentrations. A poly-(MAA)–starch graft copolymer is the main product of the polymerization reactions only when starch was preswelled (through cooking prior to grafting). Moreover, this grafted product could be precipitated by more dilution with water and easily separated by filtration. Hence, the results of the current work formed the basis of a novel method for the synthesis of poly(MAA)–starch graft copolymers. The mechanisms involved in the synthesis are reported. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1709–1715, 1998     

Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation

Diethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry     

回归正交优化头孢菌素中间体7-DTMC合成工艺

7-对甲苯硫亚氨基-3-（1-甲基-1H-四唑-5-硫甲基）-3-头孢烯-4-羧基酸二苯甲酯（7-DTMC）是合成甲氧头孢菌素关键中间体7β-氨基-7α-甲氧基-3-（1-甲基-1H-四唑-5-硫甲基）-3-头孢烯-4-羧酸二苯甲酯（7-MAC）的重要中间体。采用7β-氨基-3-（1-甲基-1H-四唑-5-硫甲基）-3-头孢烯-4-羧酸二苯酯（7-DAMC）为原料,以对甲基苯硫氯（TSC）为氨基保护试剂,二氯甲烷为溶剂,1,2-环氧丙烷为催化剂和4分子筛为脱水剂剂反应制备得到7-DTMC。本文主要探讨了反应温度、反应时间、物料配比、催化剂用量等因素对反应的影响,并通过二次回归建立了数学模型,确定了合成7-DTMC的最佳工艺条件。在此基础上合成的产品收率89.71%,HPLC纯度99.34%。产品结构经1H-NMR和FT-IR表征确认。     

甲基丙烯酰氯制备方法的改进

对甲基丙烯酸与三氯化磷反应制备标题化合物的方法作了改进,简化了反应操作,缩短了反应时间,产率约78%。最佳反应条件:氯化亚铜为阻聚剂,反应温度为体系沸点,反应时间为70min,甲基丙烯酸与三氯化磷的进料比为2.9。     

水溶性丙烯酸树脂的制备研究

用于水性油墨的水溶性丙烯酸树脂由丙烯酸丁酯(BA)、甲基丙烯酸甲酯(MMA)、丙烯酸(AA)三种单体采用传统的自由基溶液聚合方式合成,通过大量的对比实验筛选了各种不同的反应条件,获得了最佳合成工艺,包括引发剂、溶剂、加料方式、聚合时间和温度。对影响树脂性能的指标如共聚物组成、玻璃化转变温度Tg等各种因素,采用DSC、IR等分析方法进行了详尽的分析和表证。     

一步法合成烯丙基缩水甘油醚的研究

烯丙基缩水甘油醚是一种脂肪族缩水甘油醚,可以用作聚合单体和有机合成中间体,是合成硅烷偶联剂KH560的主要原料。实验研究了以环氧氯丙烷和烯丙醇为原料,在一定的相转移催化剂条件下,直接合成烯丙基缩水甘油醚。考察了反应温度、反应时间、物料物质的量比、催化剂体系、带水剂体系对反应产率的影响,确定了最佳的合成工艺条件。     

低聚合度多聚甲醛制备工艺的优化

考察了制备低聚合度多聚甲醛(PF)的适宜助剂、加入质量分数和效果,并研究了反应时间、反应温度和热空气线速度对制备的PF中醛质量分数和醛收率的影响规律。采用二次回归正交组合设计实验方法,建立了甲醛质量分数、甲醛收率与反应温度、反应时间和热空气线速度之间的经验数学模型,模型计算值与实验值较吻合,平均相对偏差均小于3.44%。结果表明:影响PF中甲醛质量分数的因素主次顺序为热空气线速度>温度>聚合时间;影响甲醛收率的因素主次顺序为温度>聚合时间>热空气线速度。确定了制备PF质量分数为95%同时甲醛收率达到60%—70%的适宜工艺条件。     

Nanohybrid polymer prepared by successive polymerization of methacrylate monomer containing silver nanoparticles in situ prepared under microwave irradiation

The well-dispersed silver nanoparticles were prepared in reactive methacrylate monomers under microwave irradiation without polymerization. In contrast to conventional heating, the synthesis of Ag nanoparticles proceeded uniformly throughout the reaction vessel only under microwave irradiation, reaching the completion of the reaction simultaneously in the whole reaction solution. Successive polymerization of the monomer containing the resulting nanoparticles has successfully produced a monohybrid of the silver nanoparticles dispersed in polymer matrix.     

Polymerization of ethylene induced by fractured metallic oxides. III. Factors affecting the polymerization

Mechanochemical polymerization of ethylene was found to be induced by fracture of γ-alumina under quite low pressure and room temperature. The factors to control the polymerization yield, for example, calcination temperature of the alumina, spin concentration after ball milling, milling time, and changes of acidity before and after the fracture, were investigated in order to know the polymerization mechanism. It was found that the polymerization yield did correlate not with the spin concentration responsible to paramagnetic species produced by the fracture, but the calcination temperature of the γ-alumina and the milling time. The resultant polymeric material on the fractured alumina was extracted alumina was extracted with solvents, and the fraction extracted with petroleum ether was characterized using GC and GC mass spectrometer. The results indicated that odd-numbered linear hydrocarbons were produced, although the major products of this polymerization were even-numbered. It is concluded from the accumulated experimental results that a carbonium ion mechanism rather than radical mechanism is probable for the mechanochemical polymerization induced by fracture of γ-alumina.