scholarly journals KINETIC HETEROGENEITY OF POLYMER PRODUCTS OBTAINED IN THE PRESENCE OF MICROHETEROGENIC CATALYTIC SYSTEMS BASED ON GEL CHROMATOGRAMS

2021 ◽  
Vol 18 (38) ◽  
pp. 27-37
Author(s):  
Eldar N. MIFTAKHOV ◽  
Svetlana A. MUSTAFINA ◽  
Ildus Sh NASYROV ◽  
Azat Kh DAMINOV
Keyword(s):  
Molecular Weight ◽  
Average Molecular Weight ◽  
Polymerization Process ◽  
Fredholm Integral Equations ◽  
Molecular Characteristics ◽  
Active Centers ◽  
Catalytic Systems ◽  
Polymer Product ◽  
Software Algorithms ◽  
Kinetic Heterogeneity

Background: the polymer product obtained in the presence of microheterogeneous catalytic systems is characterized by fairly molecular weight distribution (MWD), resulted from kinetically nonequivalent active centers (ACs) in the system that initiate the polymerization process. The nature and composition of ACs are determined by setting and solving an inverse problem on the formation of MWD. This problem is acute because revealing the nature of the kinetic heterogeneity explains changes in the molecular and consumer parameters of the product for different catalyst compositions and propagation modes in polymerizations. Aim: This study aimed to develop methods and algorithms for interpreting gel chromatograms to analyze the kinetic heterogeneity of a polymer product obtained industrially in microheterogeneous catalytic systems. Methods: the solution method is based on the assumption that the formed MWD is a superposition of distributions inherent in each type of ACs. Since the problem in the final formulation refers to the Fredholm integral equations of the first kind, the regularization method of A. N. Tikhonov is used for its numerical solution, with the original problem being preliminary discretized. This methodology and the developed software algorithms were used to determine the kinetic heterogeneity of titanium- and neodymium-containing catalytic systems. Results and discussion: The MWD analysis revealed two types of ACs with an average molecular weight of ATi-lnM = 11.3 and BTi-lnM = 13.2 in the titanium catalyst and three types of ACs ANd-lnM = 11.1, BNd-lnM = 12.7 and CNd-lnM = 14 for the neodymium catalyst, respectively. Conclusions: repeated computational experiments under different polymerization conditions and requirements for the preparation of a catalytic system make it possible to reveal a relationship with the resulting heterogeneity of ACs. It allows us to set and solve problems of controlling the molecular characteristics of the resulting polymer product.

Synthesis of Ultra-High Molecular Weight Polyacrylonitrile (UHMWPAN) by Aqueous Suspension Polymerization

2015 ◽  
Vol 1120-1121 ◽  
pp. 615-619
Author(s):  
Hui Yu Jiang ◽  
Mei Hua Zhou ◽  
Ding Pan
Keyword(s):  
Molecular Weight ◽  
Suspension Polymerization ◽  
Aqueous Suspension ◽  
Average Molecular Weight ◽  
Monomer Concentration ◽  
Polymerization Process ◽  
Polymerization Temperature ◽  
Different Temperatures ◽  
Total Monomer Concentration ◽  
Ultra High Molecular Weight

Acrylonitrile (AN) and itaconic acid (IA) were used to synthesize UHMWPAN by aqueous suspension method with 2,2’-azobisisobutyronitrile (AIBN) as the initiator and polyvinylalcohol (PVA) as the disperser at different temperatures (55°C~75°C) for different timings (1.0h~3.0h). The usage amounts of AN, IA, AIBN and PVA were also technical polymerization parameters used to obtain the optimal polymerization process. We found that the conversion and the viscosity average molecular weight both achieved the optimum levels when the conditions were as follows: the total monomer concentration (21wt%), the monomer ratio (AN: IA=98:2), the usage amount of the initiator (AIBN, 0.01wt%), the usage amount of the disperser (PVA, 0.1wt%), the polymerization temperature (70°C) and the polymerization time (2h).

SEARCH FOR KINETIC CONSTANTS IN MODELING THE PROCESSES OF POLYCENTERS NON-BREAK POLYMERIZATION OF DIENES

2020 ◽  
pp. 13-18
Author(s):  
Э.Р. Гиззатова ◽  
С.Л. Подвальный ◽  
С.И. Спивак
Keyword(s):  
Differential Equations ◽  
Rate Constants ◽  
Material Balance ◽  
Kinetic Scheme ◽  
Polymerization Process ◽  
Active Centers ◽  
Catalytic Systems ◽  
Molecular Weights ◽  
Inverse Kinetic Problem ◽  
Kinetic Problem

Приводится методика решения обратной кинетической задачи поиска констант скоростей полимеризационного процесса для кинетически неоднородных каталитических систем Циглера-Натта. Неоднородность катализаторов рассматривается как существование нескольких типов активных центров, параллельно друг другу ведущих процессы роста и обрыва полимерных цепей. Кинетическая схема процесса исключает материальный обрыв цепи, что влечет передачу активности с одного центра на другой. Наблюдаемое условие постоянства концентрации активных центров является уравнением материального баланса полимеризационной системы. Оно соблюдается в математической модели, описывающей процесс в виде автономной системы, содержащей бесконечное число обыкновенных дифференциальных уравнений первого порядка по мономеру, преобразованной методом моментов к конечному виду. Отмечено, что статистические моменты, присутствующие в системе дифференциальных уравнений, являются начальными моментами молекулярно-массового распределения. На их основе даны аналитические зависимости для искомых средних молекулярных масс образующихся полимеров на каждом типе активных центров и всего полимерного образца. Расчетный эксперимент проведен для процесса полимеризации изопрена на 4-центровой ванадийсодержащей каталитической системе с целью получения решения обратной кинетической задачи. Найден совокупный набор констант скоростей элементарных стадий процесса. Показаны графические иллюстрации сравнений расчетов и экспериментов по значениям средних молекулярных масс по каждому типу активных центров и всего полимера в целом We present a technique for solving the inverse kinetic problem of finding the rate constants of the polymerization process for kinetically inhomogeneous catalytic systems of the Ziegler-Natta. We consider inhomogeneity of catalysts as the existence of several types of active centers, parallel to each other leading processes of growth and termination of polymer chains. The kinetic scheme of the process excludes material breaking of the chain, which entails the transfer of activity from one center to another. The observed condition for the constancy of the concentration of active centers is the material balance equation for the polymerization system. It is observed in a mathematical model that describes the process in the form of an autonomous system containing an infinite number of ordinary differential equations of the first order in monomer, transformed by the method of moments to a finite form. We note that the statistical moments present in the system of differential equations are the initial moments of the molecular weight distribution. On their basis, we give analytical dependences for the desired average molecular weights of the resulting polymers on each type of active centers and the entire polymer sample. We carried out a computational experiment for the process of isoprene polymerization on a 4-center vanadium-containing catalytic system in order to obtain a solution to the inverse kinetic problem. We found a cumulative set of rate constants for elementary stages of the process. We show graphical illustrations of comparisons of calculations and experiments on the values of the average molecular weights for each type of active site and the entire polymer as a whole

scholarly journals Extract Methods, Molecular Characteristics, and Bioactivities of Polysaccharide from Alfalfa (Medicago sativa L.)

Nutrients ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 1181 ◽  
Author(s):  
Chen Zhang ◽  
Zemin Li ◽  
Chong-Yu Zhang ◽  
Mengmeng Li ◽  
Yunkyoung Lee ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Medicago Sativa ◽  
Biological Activities ◽  
Average Molecular Weight ◽  
Molar Ratio ◽  
Molecular Characteristics ◽  
Ionization Mass ◽  
Potential Candidate ◽  
Dependent Manner ◽  
Medicago Sativa L

The polysaccharide isolated from alfalfa was considered to be a kind of macromolecule with some biological activities; however, its molecular structure and effects on immune cells are still unclear. The objectives of this study were to explore the extraction and purifying methods of alfalfa (Medicago sativa L.) polysaccharide (APS) and decipher its composition and molecular characteristics, as well as its activation to lymphocytes. The crude polysaccharides isolated from alfalfa by water extraction and alcohol precipitation methods were purified by semipermeable membrane dialysis. Five batches of alfalfa samples were obtained from five farms (one composite sample per farm) and three replicates were conducted for each sample in determination. The results from ion chromatography (IC) analysis showed that the APS was composed of fucose, arabinose, galactose, glucose, xylose, mannose, galactose, galacturonic acid (GalA), and glucuronic acid (GlcA) with a molar ratio of 2.6:8.0:4.7:21.3:3.2:1.0:74.2:14.9. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) of APS were calculated to be 3.30 × 106, 4.06 × 105, and 1.43 × 108 g/mol, respectively, according to the analysis by gel permeation chromatography-refractive index-multiangle laser light scattering (GPC-RI-MALS). The findings of electron ionization mass spectrometry (EI-MS) suggest that APS consists of seven linkage residues, namely 1,5-Araf, galactose (T-D-Glc), glucose (T-D-Gal), 1,4-Gal-Ac, 1,4-Glc, 1,6-Gal, and 1,3,4-GalA, with molar proportions of 10.30%, 4.02%, 10.28%, 52.29%, 17.02%, 3.52%, and 2.57%, respectively. Additionally, APS markedly increased B-cell proliferation and IgM secretion in a dose- and time-dependent manner but not the proliferation and cytokine (IL-2, -4, and IFN-γ) expression of T cells. Taken together, the present results suggest that APS are macromolecular polymers with a molar mass (indicated by Mw) of 3.3 × 106 g/mol and may be a potential candidate as an immunopotentiating pharmaceutical agent or functional food.

Simulation for Polymerization Process of Styrene Butadiene Rubber (SBR)

2010 ◽  
Vol 148-149 ◽  
pp. 1661-1667
Author(s):  
Kai Gu ◽  
Xiao Di Xu ◽  
Ming Zhao
Keyword(s):  
Molecular Weight ◽  
Process Model ◽  
Average Molecular Weight ◽  
Polymerization Process ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Weight Average Molecular Weight ◽  
Sensitivity Analysis Method ◽  
Increasing Temperature ◽  
Styrene Butadiene

In this paper, Polymer Plus of Aspen Tech Inc. is used to establish a styrene-butadiene rubber (SBR) polymerization process model; the sensitivity analysis method is used to analyze concentration of the initiator, reaction temperature and other factors which influence production and molecular weight of product. It is concluded that increasing amount of initiator can improve production, while the molecular weight would increase at first and then decline; and along with the increasing temperature, weight-average molecular weight would lower and production of polymer PBS would increase; molecular weight of polymer and production of polymer would magnify along with increase of amount of emulsifier and volume of the reactor.

Final Report on the Safety Assessment of Polyethylene1

2007 ◽  
Vol 26 (1_suppl) ◽  
pp. 115-127 ◽  
Keyword(s):  
Molecular Weight ◽  
Solid State ◽  
Adverse Effects ◽  
Average Molecular Weight ◽  
The United States ◽  
Polymerization Process ◽  
Residual Catalyst ◽  
Implant Material ◽  
Physical Form ◽  
Mild Irritant

Polyethylene is an ethylene polymer used for a variety of purposes in cosmetics as an abrasive, adhesive, binder or bulking agent, an emulsion stabilizer, a film former, an oral care agent, and as a nonaqueous viscosity-increasing agent. Polyethylene is also used in food packaging materials and medical products, including prosthetics. The molecular weight of Polyethylene as used in cosmetics varies over a wide range. The lowest reported molecular weight is 198 Daltons and the highest is 150,000. In any given polymer preparation, there can be a broad range of molecular weights. Cellular and tissue responses to Polyethylene, determined as part of implant biocompatibility testing, include fibrous connective tissue build-up around the implant material that varies as a function of the physical form of the implant material. Specific assays for osteoblast proliferation and collagen synthesis demonstrated a reduction as a function of exposure to Polyethylene particles that is inversely related to particle size. The effect of Polyurethane particles on monocyte-derived macrophages, however, had a stimulatory effect, prolonging the survival of these cells in culture. The LD50 for Polyethylene, with an average molecular weight of 450, in rats was > 2000 mg/kg. For Polyethylene with an average molecular weight of 655, the LD50 was > 5.0 g/kg. Toxicity testing in rats shows no adverse effects at Polyethylene (molecular weight not given) doses of 7.95 g/kg or at 1.25%, 2.50%, or 5.00% in feed for 90 days. Dermal irritation studies on rabbits in which 0.5 g of Polyethylene (average molecular weight of 450) was administered in 0.5ml of water caused no irritation or corrosive effects; Polyethylene with an average molecular weight of 655 was a mild irritant. Polyethylene (average molecular weight of 450) did not cause dermal sensitization in guinea pigs tested with 50% Polyethylene ( w/w ) in a rachis oil BP. Polyethylene, with a molecular weight of 450 and a molecular weight of 655, was a mild irritant when tested as a solid material in the eyes of rabbits. Rabbit eyes treated with a solution containing 13% Polyethylene beads produced minimal irritation and no corneal abrasions. No genotoxicity was found in bacterial assays. No chemical carcinogenicity has been seen in implantation studies, although particles from Polyethylene implants can induce so-called solid-state carcinogenicity, which is a physical reaction to an implanted material. Occupational case reports of ocular irritation and systemic sclerosis in workers exposed to Polyethylene have been difficult to interpret because such workers are also exposed to other irritants. Clinical testing of intrauterine devices made of Polyethylene failed to conclusively identify statistically significant adverse effects, although squamous metaplasia was observed. The Cosmetic Ingredient Review (CIR) Expert Panel did not expect significant dermal absorption and systemic exposure to large Polyethylene polymers used in cosmetics. The Panel was concerned that information on impurities, including residual catalyst and reactants from the polymerization process, was not available. The Panel considered that the monomer unit in Polyethylene polymerization is ethylene. In the United States, ethylene is 99.9% pure. The other 0.1% includes ethane, propylene, carbon dioxide, carbon monoxide, sulfur, hydrogen, acetylene, water, and oxygen. The Panel believed that the concentration of these impurities in any final polymer would be so low as to not raise toxicity issues. Safety tests of cosmetic-grade Polyethylene have consistently failed to identify any toxicity associated with residual catalyst. Although it was reported that one process used to cross-link Polyethylene with an organic peroxide, this process is not currently used. In addition, cosmetic-grade Polyethylene is not expected to contain toxic hexanes. The Panel was concerned that the only genotoxicity data available was nonmammalian, but taking this information in concert with the absence of any chemical car-cinogenicity in implant studies suggests no genotoxic mechanism for carcinogenicity. The solid-state carcinogenicity effect was not seen as relevant for Polyethylene as used in cosmetics. The available data support the conclusion that Polyethylene is safe for use in cosmetic formulations in the practices of use and concentrations described.

Solvent effect on molecular characteristics of polybutadiene and on the kinetic heterogeneity of catalytic systems based on TiCl4

2010 ◽  
Vol 83 (3) ◽  
pp. 487-491
Author(s):  
I. R. Mirgalieva ◽  
E. A. Glukhov ◽  
I. A. Ionova ◽  
A. G. Mustafin ◽  
Yu. B. Monakov
Keyword(s):  
Solvent Effect ◽  
Molecular Characteristics ◽  
Catalytic Systems ◽  
Kinetic Heterogeneity

Modelling and numerical study of the physicochemical laws of 1,4-cis-polyisoprene obtained in the presence of modified catalytic systems

2020 ◽  
pp. 7-17
Author(s):  
Эльдар Наилевич Мифтахов ◽  
Светлана Анатольевна Мустафина ◽  
Семен Израилевич Спивак
Keyword(s):  
Mathematical Model ◽  
Numerical Study ◽  
Continuous Process ◽  
Kinetic Equations ◽  
Molecular Characteristics ◽  
Batch Reactors ◽  
Active Centers ◽  
Catalytic Systems ◽  
Continuous Mixing ◽  
The Mathematical Model

Построена математическая модель, описывающая процесс получения полиизопрена в присутствии микрогетерогенных титансодержащих каталитических систем с учетом динамики активных центров. Построение модели носило поэтапный характер, при котором модель, описывающая периодический процесс, была дополнена рекуррентными соотношениями с целью описания процесса в каскаде реакторов идеального перемешивания. Численное решение прямой задачи позволило провести анализ молекулярно-массового распределения получаемого продукта в зависимости от исходной загрузки. The aim of this work is building a mathematical model that describes the process of producing polyisoprene in the presence of microheterogeneous titanium-containing catalytic systems, taking into account the dynamics of active centers and numerical calculation of the main physicochemical properties of the resulting product. The main methodology for compiling the mathematical model is the application of the kinetic approach, which consists of compiling and numerically solving the kinetic equations for all types of particles involved in the process. Previously, the distribution of active centers of the applied catalytic system was studied. The confirmed polycentricity of the used catalyst, represented by two types of active centers, is reflected in the nature of the description of the mathematical model. To reduce the system of differential equations to the final form, the method of moments was applied, which allows evaluating the complex properties of the obtained product by its averaged molecular characteristics. A model that permits describing the scale of batch reactors was modified by a macrokinetic module that takes into account possible energy and hydrodynamic laws of the process. For this, recurrence relations were introduced that are valid for the description of continuous mixing reactors. The software package developed by the authors of the work allows carring out a computational experiment for various technological conditions for conducting a continuous process. Based on the results of its launch, the dependences of conversion and averaged molecular characteristics on time in the context of each polymerizer were obtained. Thus, the numerical solution of the direct problem is capable analyzing the molecular weight distribution of the obtained product depending on various parameters of the initial load, for both the batch and continuous modes of the process. The dependences obtained by calculation showed satisfactory agreement with experimental data

Simulation and Analysis of Propylene Coordination Polymerization Process Based on Aspen (polymer) plus

2020 ◽  
Vol 42 (1) ◽  
pp. 62-62
Author(s):  
Jinjin Wang Jinjin Wang ◽  
Wangbin Chen Wangbin Chen ◽  
Manlin Zhang Manlin Zhang ◽  
Bin Pan Bin Pan ◽  
Xiaorong Wang Xiaorong Wang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Performance Index ◽  
Average Molecular Weight ◽  
Degree Of Polymerization ◽  
Average Degree ◽  
Polymerization Process ◽  
Polymerization Degree ◽  
Coordination Polymerization ◽  
Actual Production ◽  
Coordination Process

Based on the industrial conditions of coordination polymerization of polypropylene, Polymer plus was used to simulate and analyze the coordination process of propylene. The effects of the amount of propane, main catalyst (TiCl4), chain transfer agent (hydrogen), shielding gas (nitrogen), and monomer (propylene) on the number average degree of polymerization (DPN), the weight average degree of polymerization (DPW), the number average molecular weight (MWN), the weight average molecular weight (MWW), the polydispersity index (PDI), and the throughput of polypropylene were explored to guide actual production in this paper. Through analysis, the polymerization degree and molecular weight of polypropylene could be adjusted by hydrogen in actual production. The monomer (propylene) should be purified as much as possible to reduce the feed amount of propane. The increase of the propylene contributed to the molecular weight and polymerization degree of the product. The increase in the nitrogen feed amount had no effect on the product performance index. The feed amount of nitrogen could be adjusted as needed according to the actual equipment specifications. The catalyst has the greatest influence on the comprehensive performance index of the product, thus the amount of main catalyst TiCl4 must be strictly controlled.

The Catalytic Polymerization of Isoprene with Butyllithium

1960 ◽  
Vol 33 (3) ◽  
pp. 610-622 ◽  
Author(s):  
A. S. Korotkov ◽  
N. N. Chesnokova ◽  
L. B. Truchmanova
Keyword(s):  
Molecular Weight ◽  
Catalyst Concentration ◽  
Narrow Range ◽  
Average Molecular Weight ◽  
Polymerization Temperature ◽  
Polymer Content ◽  
Active Centers ◽  
Saturated Hydrocarbons ◽  
Polymer Molecules ◽  
A Chain

Abstract 1. The kinetics for the polymerization of isoprene with butyllithium in a solution of saturated hydrocarbons were determined. 2. The reaction has the mechanism of a chain catalytic reaction, in which active centers appear that are involved complexes formed from metallorganic compounds and monomer-polymer molecules. 3. Deactivation of growing chains takes place as a result of the reaction of active centers with each other or with metallorganic compounds. With this there are formed new metallorganic compounds of high molecular weight capable of becoming new polymerization centers. 4. The polymer possesses a narrow range of molecular fractions, closely approximating the Gaussion distribution, but the value of the average molecular weight of the polymer after completion of polymerization is inversely proportional to the catalyst concentration. 5. The polymerization temperature, and also the concentrations of the monomer and catalyst, do not affect the microstructure of the polymer (content of 1,2 and 3,4 isoprene units).

scholarly journals Regression Methods Based on Nearest Neighbors with Adaptive Distance Metrics Applied to a Polymerization Process

Mathematics ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 547
Author(s):  
Silvia Curteanu ◽  
Florin Leon ◽  
Andra-Maria Mircea-Vicoveanu ◽  
Doina Logofătu
Keyword(s):  
Molecular Weight ◽  
Adaptive Sampling ◽  
Chemical Engineering ◽  
Average Molecular Weight ◽  
Monomer Conversion ◽  
Polymerization Process ◽  
Support Vector ◽  
Distance Metrics ◽  
Sampled Data ◽  
Regression Methods

Empirical models based on sampled data can be useful for complex chemical engineering processes such as the free radical polymerization of methyl methacrylate achieved in a batch bulk process. In this case, the goal is to predict the monomer conversion, the numerical average molecular weight and the gravimetrical average molecular weight. This process is characterized by non-linear gel and glass effects caused by the sharp increase in the viscosity as the reaction progresses. To increase accuracy, one needs more samples in the areas with higher variation and this is achieved with adaptive sampling. An extensive comparative study is performed between three regression algorithms for this chemical process. The first two are based on the concept of a large margin, typical of support vector machines, but used for regression, in conjunction with an instance-based method. The learning of problem-specific distance metrics can be performed by means of either an evolutionary algorithm or an approximate differential approach. Having a set of prototypes with different distance metrics is especially useful when a large number of instances should be handled. Another original regression method is based on the idea of denoising autoencoders, i.e., the prototype weights and positions are set in such a way as to minimize the mean square error on a slightly corrupted version of the training set, where the instances inputs are slightly changed with a small random quantity. Several combinations of parameters and ways of splitting the data into training and testing sets are used in order to assess the performance of the algorithms in different scenarios.

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