Average Molecular Weight Of Polymer Research Articles

Modelling of a continuous kneader reactor for the polymerization of partially neutralized acrylic acid

AbstractA mathematical model and analysis of the continuous polymerization of partially neutralized acrylic acid (AA) in a continuous kneader reactor is presented here as an initial attempt to simulate the synthesis of a superabsorbent polymer. A detailed kinetic model has been used to describe the copolymerization of AA and sodium acrylate (NaA) in aqueous medium. This model is used to describe batch and continuous operations. The polymerization is initiated by a mixture of potassium persulphate (K2S2O8, KPS) and hydrogen peroxide (H2O2) as oxidizing agent and ascorbic acid (AsA) as reducing agent. A novel set of kinetic parameters has been estimated by fitting experimental data from different literature sources. The operation of a continuous kneader reactor modelled as a plug‐flow reactor with axial dispersion is theoretically investigated to predict temperature profile, total and individual monomer conversion, consumption of KPS, H2O2, and AsA, and polymer average molecular weights. The simulation results show the presence of a hot spot close to the reactor entrance that could be potentially severe during startup and could have a detrimental impact on polymer quality. This model is a first step in the direction of achieving optimal operating protocols and exploring improved polymerization reactor designs.

Study on polymer mechanical degradation in core plugs versus in capillary tubes

Polymer flooding has been recognized as an effective technology to improve oil recovery. While synthetic polymers have been widely used in this process, mechanical degradation tends to occur at near-wellbore regions where flow rate is high. In this paper, we evaluated the polymer mechanical degradation in both core samples and capillary tubes. Results showed that the degradation tended to be severer when the polymer solution flowing through tighter core samples or through capillary tubes with smaller diameter. After mechanical degradation, the polymer average molecular weight was lower and its distribution became wider, indicating the irreversible fragmentation of polymer molecules. The critical shear rate, beyond which evident polymer degradation occurred, tended to be lower for sandstone cores than that for carbonate cores in the same permeability range. On the other hand, the critical shear rates obtained from capillary tubes were significantly higher than those from the core samples. Correlations between the polymer degradation in core samples and in capillary tubes were established, which can be used to estimate the polymer mechanical degradation in reservoir rocks from the more convenient measurement using capillary tubes. This study provides a robust technique for polymer evaluation, and the results are also helpful for better understanding of the polymer flow in porous media.

Hot melt extruded PLGA implants loaded with ibuprofen: How heat exposure alters the physical drug state

Hot melt extrusion offers an interesting potential for the manufacturing of poly(lactic-co-glycolic acid) (PLGA)-based implants. However, the heat treatment might substantially alter the polymer, drug and degree of drug-polymer mixing. The aim of this study was to better understand the impact of varying the exposure time to 105 °C in the case of ibuprofen-loaded PLGA implants. In vitro drug release was measured in phosphate buffer pH 7.4. Optical and scanning electron microscopy, DSC, GPC, X-ray diffraction as well as gravimetric analysis were used to monitor dynamic changes of the implants’ morphology, dry & wet mass and average polymer molecular weight. Interestingly, increasing the exposure time from 3 to 15 min led to a decrease in the amount of crystalline drug present in the system, resulting in a slight decrease in the initial burst release. The average PLGA molecular weight also slightly decreased during the heat treatment. In contrast, the relatively rapid penetration of water into the implant and subsequent polymer degradation throughout the device did not seem to be affected to a noteworthy extent. Also the onset of substantial implant swelling after about 1 week and the subsequent beginning of the final rapid drug release phase (accounting for about 80% of the total drug dose) were not significantly altered. Thus, in this study, the changes in the physical state of the drug in the implant induced by prolonged heat exposure had only a limited impact on system performance. However, for different drugs and polymers, changes in their physical state as a function of the heat exposure time might have more importance consequences. Careful monitoring of these kinetic aspects is recommended to assure desired product quality.

Free-radical polymerization of methacrylic acid: From batch to continuous using a stirred tank reactor

In the last years important efforts have been made to convert the traditional batch polymer production to continuous. This transition allows to overcome most of the limitations of discontinuous or semi-continuous processes, such as environmental and safety issues and inadequate product quality. In this work we propose a model–based strategy to convert the solution free-radical polymerization of non-ionized methacrylic acid (MAA) from semibatch to continuous while preserving the product average molecular weight and polymer content. First, a purely kinetic model for the polymerization of MAA was validated for batch, semibatch and continuous stirred tank reactors (CSTR). Then, a basic optimization approach was applied to guide the transition of a selected semibatch process to a CSTR. This strategy results in a substantial productivity increase (5.1 times higher than in the original semibatch) while preserving the selected polymer average molecular weight and dry content. Finally, in order to reduce the residual monomer in the product leaving the CSTR, we simulated the addition of a tubular reactor. This was modelled introducing a small plug flow reactor in series to the CSTR. This approach represents an effective and robust tool for polymer manufacturers to assist switching their productions to continuous preserving their product portfolio.

Effect of Na- and Organo-Modified Montmorillonite/Essential Oil Nanohybrids on the Kinetics of the In Situ Radical Polymerization of Styrene.

The great concern about the use of hazardous additives in food packaging materials has shown the way to new bio-based materials, such as nanoclays incorporating bioactive essential oils (EO). One of the still unresolved issues is the proper incorporation of these materials into a polymeric matrix. The in situ polymerization seems to be a promising technique, not requiring high temperatures or toxic solvents. Therefore, in this study, the bulk radical polymerization of styrene was investigated in the presence of sodium montmorillonite (NaMMT) and organo-modified montmorillonite (orgMMT) including thyme (TO), oregano (OO), and basil (BO) essential oil. It was found that the hydroxyl groups present in the main ingredients of TO and OO may participate in side retardation reactions leading to lower polymerization rates (measured gravimetrically by the variation of monomer conversion with time) accompanied by higher polymer average molecular weight (measured via GPC). The use of BO did not seem to affect significantly the polymerization kinetics and polymer MWD. These results were verified from independent experiments using model compounds, thymol, carvacrol and estragol instead of the clays. Partially intercalated structures were revealed from XRD scans. The glass transition temperature (from DSC) and the thermal stability (from TGA) of the nanocomposites formed were slightly increased from 95 to 98 °C and from 435 to 445 °C, respectively. Finally, better dispersion was observed when orgMMT was added instead of NaMMT.

Comparative Study of the Mucoadhesive Properties of Polymers for Pharmaceutical Use

BACKGROUND: In recent years, mucoadhesive dosage forms due to their advantages have attracted the interest of researchers and developers. Polymeric excipients are included into the drug composition to give adhesion to the mucous membrane.
 AIM: The aim of this research was to select a specific brand of pharmaceutical quality polymer that is promising for inclusion in the drug formulation.
 METHODS: The article presents the results of studying the mucoadhesive properties of polymers on two models using mucin: By measuring the amount of adhesion and by the evaluation the sample movement speed.
 RESULTS: According to the combination of two indicators, the highest mucoadhesive properties were shown by the brands of hydroxypropylmethylcellulose and xanthan gum. In addition, it was noted that hydroxyethylcellulose (HEC), sodium alginate, and hydroxypropylmethylcellulose (HPMC) also have good mucoadhesive properties. Polyethylene glycols proved to have the weakest mucoadhesive properties. The negative relationship between the average molecular weight and the sample movement speed of the HEC and HPMC was established. Obtained data showed no direct influence of the polymer average molecular weight on the amount of adhesion. It was also noted that there is no strong correlation between the amount of adhesion and the sample movement speed of the experimental samples.
 CONCLUSION: Based on the results of the study, it was suggested that the complex influences of the physical and chemical properties of the polymer on its mucoadhesive properties.

Nitroxide-mediated polymerization of styrene and limonene in the framework of synthesis of potentially functional polymers using naturally occurring terpenes

In the framework of synthesis of potentially functional macromolecules based on commodity polymers with naturally occurring compounds, the nitroxide-mediated polymerization of styrene with limonene was investigated here. Various ratios of styrene and limonene were used, and the incorporation of limonene in the final polymer was monitored. Results from benzoyl peroxide/TEMPO-initiated polymerization showed small incorporation of limonene in the polystyrene chains, while it was also involved in forming oligomers (such as dimers or trimers). The presence of limonene resulted in a reduction in polymer average molecular weight through chain transfer reactions. From the kinetic analysis, limonene was found to inhibit styrene thermal auto-polymerization at high temperatures, acting as a radical scavenger. Using TEMPO-functionalized polystyrene macroinitiators to initiate the polymerization, no limonene oligomers in the final product were observed. Finally, when polystyrene macroinitiators and limonene were reacted in the absence of styrene monomer, limonene moieties were identified in the final polymer, resulting thus in polystyrene functionalization. This functionalization can be extended to the synthesis of novel materials based on naturally occurring terpenes, considering the variety of structures that can be obtained by applying NMP.

Hierarchically porous monoliths based on low-valence transition metal (Cu, Co, Mn) oxides: gelation and phase separation.

Hierarchically porous monoliths based on copper (Cu), cobalt (Co) and manganese (Mn) oxides with three-dimensionally (3D) interconnected macropores and open nanopores were prepared using metal bromides as precursors via a sol–gel process accompanied by phase separation. The difficulty of gelation for low-valence metal cation was overcome by introducing a highly electronegative Br atom near to the metal atom to control the rates of hydrolysis and polycondensation. The 3D interconnected macropores were obtained using appropriate polymers to induce phase separation. The domain sizes of macropores and skeletons can be controlled by reaction parameters such as concentration and/or average molecular weight of polymers, and the amount of hydrochloric acid. The crystalline metal oxide monoliths with their 3D interconnected macroporous structure preserved were obtained after heat treatment in air.

Method of Moments Applied to Most-Likely High-Temperature Free-Radical Polymerization Reactions

Many widely-used polymers are made via free-radical polymerization. Mathematical models of polymerization reactors have many applications such as reactor design, operation, and intensification. The method of moments has been utilized extensively for many decades to derive rate equations needed to predict polymer bulk properties. In this article, for a comprehensive list consisting of more than 40 different reactions that are most likely to occur in high-temperature free-radical homopolymerization, moment rate equations are derived methodically. Three types of radicals—secondary radicals, tertiary radicals formed through backbiting reactions, and tertiary radicals produced by intermolecular chain transfer to polymer reactions—are accounted for. The former tertiary radicals generate short-chain branches, while the latter ones produce long-chain branches. In addition, two types of dead polymer chains, saturated and unsaturated, are considered. Using a step-by-step approach based on the method of moments, this article guides the reader to determine the contributions of each reaction to the production or consumption of each species as well as to the zeroth, first and second moments of chain-length distributions of live and dead polymer chains, in order to derive the overall rate equation for each species, and to derive the rate equations for the leading moments of different chain-length distributions. The closure problems that arise are addressed by assuming chain-length distribution models. As a case study, β-scission and backbiting rate coefficients of methyl acrylate are estimated using the model, and the model is then applied to batch spontaneous thermal polymerization to predict polymer average molecular weights and monomer conversion. These predictions are compared with experimental measurements.

Experimental Design and Statistical Analysis of AGET ATRP of MMA in Emulsion Polymer Reactor

AbstractThis study investigates atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using activators generated by electron transfer (AGET) as the initiation technique in an emulsion well‐mixed 2L stirred tank reactor. The performance of the AGET ATRP of MMA is analyzed for five key independent variables, namely temperature, catalyst complex (CuBr2/dNbpy), initiator (EBiB), reducing agent (ascorbic acid), and surfactant (Brij 98). The reaction is carried out based on a two‐step polymerization procedure. A resolution 5 fractional factorial design technique is employed to assess the influence of the five independent variables on the monomer conversion, polymer average molecular weights, and polydispersity index (PDI). An input–output model is constructed from the data of 21 designed experimental tests. A statistical analysis of the results shows that the temperature is the most influential variable for the three output process responses. The initiator strongly affects the poly(methyl methacrylate) (PMMA) molecular weights. It is the least important key variable affecting MMA conversion and PDI, and the surfactant is the least one affecting PMMA Mn. On assessing the independent interactions effect, the interactions of temperature‐surfactant on conversion, and temperature‐initiator for PMMA Mn are considered. Process simulation in 3D mapping has demonstrated that model predictions agree well with experimental data.

Polyamide-based pH and temperature-responsive hydrogels: Synthesis and physicochemical characterization

The pH- and temperature-responsive pentablock copolymers that could form in situ hydrogels, composed of pH-responsive polyamide and temperature-responsive poly(e-caprolactone)-b-poly(ethylene glycol)-b-poly(e-caprolactone) (PCL-b-PEG-b-PCL), have been synthesized. The pH-responsive polyamide blocks containing diamide linkages were synthesized using condensation polymerization of adipic acid dihydrazide and phthalic anhydride; whereas, temperature-responsive PCL-b-PEG-b-PCL was synthesized by ring-opening polymerization of e-caprolactone in the presence of bifunctional PEG macroinitiator. Pentablock copolymer was then synthesized by the chemical conjugation of carboxylic acid-terminated pH-responsive copolymer to the chain end of temperature-responsive triblock copolymer through ester bond formation. The pKa values of pH-sensitive polyamide, measured using titration method, varied depending on the average molecular weight of polymers. In aqueous solutions, the pentablock and triblock copolymers formed spherical micelles and their particle sizes were found to be 55 to 100 nm. The pentablock copolymer exhibited pH- and temperature-induced sol-to-gel phase transition. At high pH and low temperature, the copolymers were freely soluble even at 20 wt% concentration and form stable hydrogel at the physiological condition (pH 7.4, 37 °C). Furthermore, the sol-to-gel window of the pentablock copolymers was controlled by varying the composition of polyamide to PCL/PEG and covers the physiological region. Overall, these results suggest that the sharp physicochemical change of the pentablock copolymers may be exploited in controlled delivery applications.

Poly(azomethine-epoxy-ether) containing phenyl and etoxy moieties: synthesis, characterization and fluorescence property

The design and synthesis of poly(azomethine-epoxy-ether) (PAZ-EP) containing epoxide moiety was described. The purpose of the research was the improvement of poly(azomethine-ether) containing epoxide by introduction of Schiff base moiety. PAZ-EP was synthesized using epichlorohydrin (EP). The structure of the Schiff base (SB) and PAZ-EP were verified by FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic analyses. Further characterization was employed using photophysical, electrochemical and fluorescence (PL) measurements. Application of TGA and differential scanning calorimetry analyses revealed thermal stability and thus propose a thermal processibility, which makes them potential materials for many contemporary practices. The number of average molecular weight of polymer with a polydispersity index of 1.14 was found to be 6750 Da using a gel permeation chromatography instrument. The highest occupied–lowest unoccupied energy levels and electrochemical ( $$E_{\text{g}}^{'}$$ ) band gap values of PAZ-EP were determined by cyclic voltammetry (CV) measurement. Scanning electron microscopy (SEM) images were illustrated at different magnifications to study the morphologic property of PAZ-EP.

Micellar polymerization: Computer simulations by dissipative particle dynamics.

Nowadays, micellar polymerization is widely used in different fields of industry and research, including modern living polymerization technique. However, this process has many variables and there is no comprehensive model to describe all features. This research presents simulation methodology which describes key properties of such reactions to take a guide through a variety of their modifications. Dissipative particle dynamics is used in addition to Monte Carlo scheme to simulate initiation, propagation, and termination events. Influence of initiation probability and different termination processes on final conversion and molecular-weight distribution are presented. We demonstrate that prolonged initiation leads to increasing in polymer average molecular weight, and surface termination events play major role in conversion limitation, in comparison with recombination. © 2018 Wiley Periodicals, Inc.

Polyolefins Made with Dual Metallocene Catalysts: How Microstructure Affects Polymer Properties

AbstractSlow crack growth resistance correlates with the lifetime of polyethylene pipes. Since this measurement may take considerable time, alternative ways to estimate it help expedite the development of new polyethylene resins. The primary structural parameter (PSP2), calculated from the distribution of molecular weight and short chain branching of polyethylenes, can predict the stress crack growth resistance of polyethylene resins without needing to measure it over long periods of time. In this investigation, a model is developed to calculate PSP2 of ethylene homopolymers and ethylene/1‐hexene copolymers made with two metallocene catalysts. For each metallocene, the effect of the following parameters on PSP2 is investigated: (1) polymer mass fraction, (2) polymer average molecular weight, and (3) average comonomer fraction. The simulation trends agree with previously published experimental results. The generated 3D surface response plots are useful guides for the design of polyethylenes having optimized slow crack growth resistance.

Fluorescence Enhancement of a Cationic Fluorene-Phenylene Conjugated Polyelectrolyte Induced by Nonionic n-Alkyl Polyoxyethylene Surfactants.

The modulation of conjugated polyelectrolyte fluorescence response by nonionic surfactants is dependent on the structures of the surfactant and polymer, polymer average molecular weight, and polyelectrolyte-surfactant interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CiEj) with different alkyl chain lengths (CiE5 with i = 6, 8, 10, and 12) and number of oxyethylene groups (C12Ej with j = 5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide-water 4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains tend to approach as the simulation evolves. However, the minimum distance between the polymer centers of mass increases upon addition of the surfactant and grows with both the surfactant alkyl chain length and the number of oxyethylene groups, although there are no specific polymer-surfactant interactions. A significant increase in the polymer emission intensity has been observed at surfactant concentrations around their critical micelle concentrations (cmcs), which is attributed to polymer aggregate disruption. However, an increase in the solution conductivity for concentrations above the C12E5 cmc has only been observed for the HTMA-PFP/C12E5 system. The enhancement of fluorescence emission intensity and conductivity upon surfactant addition increases with polymer average molecular weights and seems to be controlled by the polymer-surfactant proximity, which is maximum for C10E5 and C12E5.

Synthesis, characterization, and gas permeation properties of adamantane‐containing polymers of intrinsic microporosity

ABSTRACTA new bis(catechol) monomer, namely, 4,4′‐((1r,3r)‐adamantane‐2,2‐diyl)bis(benzene‐1,2diol) (THADM) was synthesized by condensation of 2‐adamantanone with veratrole followed by demethylation of the formed (1r,3r)‐2,2‐bis(3,4 dimethoxyphenyl)adamantane. Polycondensation of THADM and various compositions of THADM and 5,5,6′,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane was performed with 2,3,5,6‐tetrafluoroterephthalonitrile (TFTPN) to obtain the homopolymer and copolymers. These polymers demonstrated good solubility in common organic solvents such as dichloromethane, chloroform, and tetrahydrofuran and could be cast into tough films from their chloroform solutions. GPC analysis revealed that number average molecular weights of polymers were in the range 48,100–61,700 g mol−1, suggesting the formation of reasonably high molecular weight polymers. They possessed intrinsic microporosity with Brunauer‐Emmett‐Teller (BET) surface area in the range 703–741 m2 g−1. Thermogravimetric analysis of polymers indicated that 10% weight loss temperature was in the range 513–518 °C demonstrating their excellent thermal stability. THADM‐based polymer of intrinsic microporosity (PIM) showed P(CO2) = 1080, P(O2) = 232 and appreciable selectivity [α(CO2/CH4) = 22.6, α(CO2/N2) = 26.7, and α(O2/N2)= 5.7]. The gas permeability measurements revealed that with increase in the content of adamantane units in PIMs, selectivity increased and permeability decreased, following the trade‐off relationship. The gas separation properties of PIMs containing adamantane units were located close to 2008 Robeson upper bound for gas pairs such as CO2/CH4, CO2/N2, H2/N2, and O2/N2. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 16–24

On the modeling of number and weight average molecular weight of polymers

The modeling of the molecular weight distribution of polymers is critical in polymerization modeling. Moment-based models and kinetic Monte Carlo are two methods used to calculate the number and weight average molecular weight during simulation of polymerization. While these two methods are commonly considered to yield equivalent results in the molecular weight distribution, we show that there can be significant differences between these two methods when copolymerization of multiple monomers is modeled. In particular, clear differences in results exist for low molecular weight polymers where the molar mass of one monomer is two or more times greater than the others. Detailed analysis is provided for the cause of the difference, and we demonstrate the importance of tracking the exact number of each type of monomer in every polymer chain when calculating the moments of molecular weight.

Effect of rheological and physical properties on mitigation of melt fracture instability during extrusion of polymer melts through a radial flow die

This study examines the role of both a radial flow created at the entrance of the die and the average molecular weight of polymer on the appearance and development of the helical defect. To do so, three linear polydimethylsiloxanes (PDMSs) of different viscosities and molecular weights were considered. A convergent radial flow is created at the entrance zone when a radial geometry is generated upstream the extrusion die. As for the influence of the considered radial flow, extrudate photographs show that helical instability can be mitigated since its frequency is higher and its amplitude is smaller than what they are when radial flow geometry is not installed. However, it is possible to relate the observed effects to the establishment of the radial flow at the die entrance where the shear deformations are enhanced with respect to the elongational ones. In fact, the development of the helical defect is shaped with amplitude, which is sensitive to the gap width of the radial flow and a frequency imposed by both the entrance geometry and the molecular weight of the polymer. It has also been shown that the ratio of frequencies of the onset of helical instability and the ratio of the Newtonian viscosities, for two given polymers, are inversely equal. Moreover, results obtained confirm that the frequency of the instabilities at their onset is inversely proportional to a mean characteristic time τ M as to the plateau viscosity of the considered PDMS.

Metallocene Catalytic Insertion Polymerization of 1-Silene to Polycarbosilanes.

Metallocene of zirconium were used as a catalyst for an insertion polymerization of 1-methylsilene directly into pre-ceramic precursor polyzirconocenecarbosilane (PZCS) during dechlorination of dichlorodimethylesilane by sodium, which exhibits high catalytic effectiveness with the maximum conversion ratio of polycarbosilane up to 91%. The average molecular weights of polymers synthesized are less than 1400, all with very narrow polymolecularities. The mechanism of catalytic polymerization was assumed to be similar to a coordination insertion polymerization of 1-olefins by metallocenes. The obtained PZCS show high ceramic yields with formation of composite ceramics of ZrC-SiC, which are novel polymeric precursors of ultra-high temperature ceramic (UHTC) fiber and composite.

A Chromatographic Study of Shear Stability of Poly(styrene-co-alkyl methacrylate) Viscosity Modifier for Lubricating Oils

Shear stability of styrene, dodecyl methacrylate, and octadecyl methacrylate terpolymer of various molecular weights, as the rheology modifier of improved solubility, thermal and oxidation stability in mineral base oil, was investigated. Viscosity loss of the 5 wt% solutions caused by scission of macromolecules subjected to the high shear forces ranges between 15% and 27% for weight average molecular weights from 156000 to 252000. After the shear tests the number average molecular weights of polymer increases while weight and Z-average molecular weights decrease. As macromolecules of molecular weights above 700000 fully break the molar-mass dispersity decreases significantly, from starting at 2.34–2.79 down to below 1.8. A linear dependence between viscosity loss of terpolymer solutions and molecular weights was observed. The advantage of using the size exclusion chromatography to determine the stability of the polymer against mechanical shear directly and the viscosity loss indirectly was established.