Dead Polymer Research Articles

A Model for Molecular Weight Prediction in Acrylonitrile Polymerization

The number and weight-average molecular weights in acrylonitrile polymerization have been calculated previously by Peebles[ 2 ]. However, the foundations for the two critically important expressions leading to the calculation of molecular weights were not disclosed in detail, no dynamics were presented, and predictions were not in good agreement with the experimental data, particularly in terms of polydispersity index. The present work focuses on the same issue, and brings a new rigorous dynamic model, based on the kinetics given by Peebles[ 2 ]. The new, more detailed model defines the chain lengths in terms of the leading moments of active and dead polymer, provides the prediction of reactor dynamics in compliance with the practice in industry, and estimates the polydispersity index of the polymer with better agreement to the experimental data.

Novel Approach to Tailoring Molecular Weight Distribution and Structure with a Difunctional RAFT Agent

This work has demonstrated that for the first time a single RAFT agent (i.e., difunctional) can be used in conjunction with a radical initiator to obtain a desired Mn and PDI with controlled rates of polymerization. Simulations were used not only to verify the model but also to provide us with a predictive tool to generate other MWDs. It was also shown that all the MWDs prepared in this work could be translated to higher molecular weights through chain extension experiments with little or no compromise in the control of end group functionality. The ratio of monofunctional to difunctional SC(CH2Ph)S− end groups, XPX and XP (where X = SC(CH2Ph)S−), can be controlled by simply changing the concentration of initiator, AIBN. Importantly, the amount of dead polymer is extremely low and fulfils the criterion as suggested by Szwarc (Nature 1956) that to meet “living” requirements nonfunctional polymeric species formed by side reactions in the process should be undetectable by analytical techniques. In addition, this novel methodology will allow the synthesis of AB, ABA, and statistical multiblock copolymers with predetermined ratios to be produced in a one-pot reaction.

Facile atom transfer radical homo and block copolymerization of higher alkyl methacrylates at ambient temperature using CuCl/PMDETA/quaternaryammonium halide catalyst system

Controlled polymerization of higher alkyl methacrylates, e.g. lauryl methacrylate (LMA) and stearyl methacrylate (SMA) has been successfully achieved by atom transfer radical polymerization (ATRP) at ambient temperature using CuCl/ N, N, N′, N′, N″-pentamethyldiethylenetriamine (PMDETA)/tricaprylylmethylammonium chloride (Aliquat ®336) as the catalyst system and ethyl 2-bromoisobutyrate or 2,2,2-trichloroethanol as the initiator. Although the bulk polymerization gives satisfactory control, the latter becomes better when anisole or THF is added into the system. Without AQCl the control was lost. A large deviation of molecular weight from theory has been observed which has been attributed to the very high-molecular weight of the dead polymers formed during the building-up of the persistent radical. The controlled polymers have been used as macroinitiators for block (di, tri and penta) ATR copolymerization with several methacrylates.

Effect of Quasi-nanometer zirconium carbide on the physical characterization of zirconium carbide/polyurethane composite films irradiated under ultraviolet light

We used quasi-nanometer zirconium carbide (ZrC) and a polyurethane (PU) resin under roller pressure to form a composite film and found that the tensile strength at break, elongation at break, and modulus gradually decreased with increasing ultraviolet (UV)-irradiation time for films of both PU and the PU/ZrC composite. However, this phenomenon was significantly higher for the PU film than for the ZrC/PU composite film. The construction of the PU film changed after UV irradiation, but that of the PU/ZrC composite film was almost unchanged. The degradation of PU molecules occurred in the absence of ZrC particles after irradiation with UV light but almost did not occur in the presence of ZrC particles. This was confirmed with Fourier transform infrared spectroscopy and gel permeation chromatography analyses. It was suggested that polymer radicals which formed through the photooxidation of UV irradiation and free radicals which formed through the photoreduction of nanometer ZrC/UV irradiation interacted to form a dead polymer to stop the degradation; simultaneously, the chemical bonding between polymer molecules could be re-formed from free radicals created by photooxidation and photoreduction and thus reduce the mobility of PU molecules, thereby raising the glass-transition and melting temperatures of the soft segment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4842–4849, 2006

Separation of living and dead polymers in synthetic polypeptide mixtures by nonaqueous capillary electrophoresis using differences in ionization states

The complexity in the mechanisms of polymerization of N-carboxyanhydrides requires the development of new analytical techniques able to separate mixtures of synthetic polypeptides. This work focuses on the separation of poly(N(epsilon)-trifluoroacetyl-L-lysine) (PTLL) mixtures by nonaqueous capillary electrophoresis (CE). The main goal of this work was to find electrophoretic conditions that permit the separation and the quantification of the dead polymer families that were previously identified in the samples. The influence of the pH of the electrolyte on the selectivity of the separation was carefully investigated. The mechanisms of separation of the PTTLs are discussed as a function of their ionization state. The separations obtained on a noncovalently coated capillary were compared with those obtained on a fused-silica capillary. Finally, using two different electrolytes, it is possible to quantify the three families of PTLLs, namely, the living PTLLs, the dead PTLLs with N-formyl end group and the dead PTLLs with a carboxylic end group. These results confirm the importance of CE for the separation of synthetic organic polymers in nonaqueous electrolytes.

Analysis of an industrial continuous slurry reactor for ethylene–butene copolymerization

This work presents the analysis of a slurry polymerization stirred tank reactor for the production of high-density polyethylene. A coordination mechanism is adopted including initiation, propagation, first order deactivation, hydrogen transfer, ethylene transfer, transfer to co-catalyst and β-hydride elimination. Two site types are considered each one with its own kinetic constants. A non-uniform solid phase is considered and in the particle there is a radial distribution of chemical species such as the living and dead polymer chains. In this sense, a general local balance is proposed, providing state equations for the moments of chain length distribution and for the active site concentrations that are treated together with all others modeling scales. The multigrain model approach was adopted, combined with a simulation strategy applying orthogonal collocation. The simulation procedure handles all the equations simultaneously and the model is capable of predicting the behavior of operation variables and variables associated with the polymer properties.

Modeling, Simulation and Optimal Control of Ethylene Polymerization in Non-Isothermal, High-Pressure Tubular Reactors

Low-density polyethylene (LDPE) is a very important polymer, which is usually produced through a free radical polymerization process in high-pressure tubular reactors. In this study, the mathematical model of this process is developed on the basis of a comprehensive reaction mechanism to accurately determine polymerization rate, and polymer properties under extreme temperature conditions. The model comprises of (i) the mass balances of monomer, initiator, solvent, live radicals and dead polymer chains, and (ii) the energy balances of a tubular LDPE reactor, and its jacket under steady state condition. The model considers the variations in the density and viscosity of reactants along reactor length. Computer simulation of the model is successfully carried out to accurately describe the performance of a non-isothermal, high-pressure, industrial LDPE reactor with multiple initiator injections. Based on the developed non-linear model, the optimal control of the industrial reactor is carried out using genetic algorithms to maximize monomer conversion using jacket temperature as a control function of reactor length. The application of optimal control leads to significant improvements in the final monomer conversion, and capacity utilization of the reactor.

Parameter Estimation of Differential-Algebraic Systems Using Accessible Measurement

Hybrid differential evolution is applied to estimate the kinetic parameters of batch polymerization described by differential-algebraic equations. The dynamic behavior of the system consisted of the concentrations of the first and second initiators, the monomer conversion, the zeroth, first and second moments of dead polymer distributions and the total concentration of live polymer. The moments of dead polymer distributions and the total concentration of live polymer were in general difficult to measure in a real process. In this study, we considered that the estimation criterion consisted of some measurable data such as the concentrations of the first and second initiators, the monomer conversion, and the degree of polymerization and polydispersity. We used the worst observed error for all experiments as an objective function so that the parameter estimation problem becomes a min-max estimation problem. Several techniques were also employed to handle the estimation of kinetic parameters for comparison. Hybrid differential evolution could use five individuals to obtain a more satisfactory solution.

Nitroxide-mediated radical polymerization of styrene in miniemulsion: model studies of alkoxyamine-initiated systems

A mathematical model has been developed to describe the behavior of the nitroxide-mediated miniemulsion polymerization (NMMP) of styrene initiated by alkoxyamine initiators. The model includes mechanisms describing reactions in the aqueous and organic phases, particle nucleation, the entry and exit of oligomeric radicals, and the partitioning of nitroxide and styrene between the aqueous and organic phases. The influence of nitroxide partitioning on the polymerization kinetics was examined by modeling systems initiated by the alkoxyamines BST and hydroxyl-BST; BST and hydroxyl-BST are benzoylstyryl radicals terminated by the nitroxides TEMPO and 4-hydroxyl-TEMPO, respectively. Predicted monomer conversions, number average molecular weights and polydispersities were in agreement with experimentally measured values. Simulations and mathematical analysis showed that the rate of styrene NMMP is not strongly influenced by the partitioning properties of TEMPO and 4-hydroxyl-TEMPO because of the complex interaction between reaction equilibrium, phase equilibrium, termination and thermal initiation. However, in the absence of styrene thermal initiation, nitroxide partitioning was found to have a significant influence on the polymerization kinetics. The model was also used to make quantitative estimates of: the population of active and dormant polymer radicals derived from both alkoxyamine initiators and thermal initiation; the population of dead polymer chains; and the number molecular weight distributions of living and dead polymer chains.

Model Studies of Nitroxide‐Mediated Styrene Miniemulsion Polymerization – Opportunities for Process Improvement

AbstractModeling studies were performed to investigate how persulfate‐initiated nitroxide‐mediated styrene miniemulsion polymerizations are influenced by changes to the polymerization recipe. By manipulating the initial concentrations of potassium persulfate and nitroxide, and the aqueous phase volume, trends in the predicted polymerization time, number average molecular weight, polydispersity and degree of polymer livingness were identified that indicate operating conditions for improved process performance. Specifically, our model predicts the existence of experimental conditions that simultaneously minimize polymer polydispersity and maximize the livingness of the polymer. The mechanisms responsible for the predicted trends were identified from the predicted molecular weight distributions of the living and dead polymer chains.Predicted number MWDs at 20% monomer conversion for styrene NMMP systems employing various levels of [KPS]aq,0. Dormant KPS‐initiated polymer radicals.imagePredicted number MWDs at 20% monomer conversion for styrene NMMP systems employing various levels of [KPS]aq,0. Dormant KPS‐initiated polymer radicals.

Monte Carlo simulation of tri-functional branching and tetra-functional crosslinking in emulsion polymerization of butadiene

A direct Monte Carlo method is used to simulate the effect of tri-functional long chain branching and tetra-functional crosslinking on molecular weight distribution in emulsion polymerization of butadiene. Butadiene polymerization, due to high extent of reaction with internal or pendant double bonds of polymer chains, can be used as a model to study the effect of tetra-functional crosslinking on polymer microstructure. In this simulation, elementary reactions included propagation, chain transfer to monomer, termination by disproportionation, transfer to C–H bond (BN3) and reaction with internal or pendant CC bond (CL4) of growing and dead polymer chains. The initial polymerization volume of the simulation was 105nm3. The ratio of monomer to initiator concentration and initiator to polymer particles were 500 and 2.5, respectively, and the number of simulated polymer particles were 400. For simulated conversions in the range of 20–75% a bimodal molecular weight distribution was observed. The maximum of the second peak of the bimodal distribution moved to higher molecular weights as the conversion was increased. As the conversion was increased from 20 to 75%, the increase in the number average molecular weight of the polymer was linear but a slight increase in the slope of the weight average molecular weight was observed. More importantly, as the conversion was increased, a relatively sharp change in the slope of the weight fraction of the second peak of the molecular weight distribution curve was observed at approximately 20% conversion. According to the results, in polymerization systems with high extent of tetra-functional crosslinking, the development of the molecular weight distribution in emulsion polymerization is different from bulk systems.

Modelling of infectious spreading in heterogeneous polymer oxidation I. Development of a stochastic model

The heterogeneous features of the oxidation of polypropylene in the amorphous region are consistent with infectious spreading from a small number of sites, such as catalyst residues. A stochastic model was developed for demonstrating the spatial and temporal development of oxidation from these sites. In this model, the probability of passing the infection from one site to an adjacent site could be used in place of conventional rate constants. The probability of spreading was assumed to be temperature dependent, and modelled with Arrhenius behaviour. Each site was given a predefined lifetime such that the maximum probability of spreading coincided with the maximum rate of oxidation at a particular site. This has enabled visualisation of the spatial development of oxidation within the amorphous region. The epidemiological fractions corresponding to the remaining (unoxidised) polymer, the dead (oxidised) polymer and the infectious (oxidising) polymer, were calculated and used to test the limitations of the simple epidemiological model.

Crosslinking during radical polymerization of dodecyl methacrylate

A much more efficient formation of crosslinks was observed in the free-radical polymerization of dodecyl methacrylate with respect to the amount of decomposed peroxide than it would correspond to the additional peroxide crosslinking of formed poly(dodecyl methacrylate). Polymer crosslinking also proceeds after using 2,2´-azoisobutyronitrile as initiator of the polymerization of dodecyl methacrylate, although with a substantially lower efficiency compared to the initiation by peroxide under comparable conditions. The efficient formation of crosslinked structures can be explained by branching and copolymerization of monomer with multifunctional dead polymer. Multifunctionality of the formed macromolecules is a result of transfer and addition reactions of the present free radicals with the formed polymer. The difference in the influence of the initiator follows from the higher reactivity of oxy radicals in transfer reactions with monomer dodecyl methacrylate which results in a greater number of polymerizable double bonds built in the polymer chain.

Crosslinking during radical polymerization of dodecyl methacrylate

A much more efficient formation of crosslinks was observed in the free-radical polymerization of dodecyl methacrylate with respect to the amount of decomposed peroxide than it would correspond to the additional peroxide crosslinking of formed poly(dodecyl methacrylate). Polymer crosslinking also proceeds after using 2,2´-azoisobutyronitrile as initiator of the polymerization of dodecyl methacrylate, although with a substantially lower efficiency compared to the initiation by peroxide under comparable conditions. The efficient formation of crosslinked structures can be explained by branching and copolymerization of monomer with multifunctional dead polymer. Multifunctionality of the formed macromolecules is a result of transfer and addition reactions of the present free radicals with the formed polymer. The difference in the influence of the initiator follows from the higher reactivity of oxy radicals in transfer reactions with monomer dodecyl methacrylate which results in a greater number of polymerizable double bonds built in the polymer chain.

Termination mechanism of polymethyl methacrylate and polystyrene studied by ultrasonic degradation technique

A new method for determining the dominant termination mechanism in radical polymerization based on ultrasonic scission of long chains is used to study the termination of polystyrene and polymethyl methacrylate. The method is extended to obtain the disproportionation/combination ratio. Long dead polymer chains in solution were broken by ultrasound. The chain radicals thus formed were then allowed to terminate in the presence and absence of a chain terminating agent (radical trap). The resulting molecular weights are compared to find the dominant termination mechanism. It is found that the dominant mechanism in polystyrene is combination and that in polymethyl methacrylate is disproportionation. These results are in accordance with those quoted in the literature and obtained by other methods.The effectiveness of the radical trap used (2-chloroethyl benzene) was tested by NMR and it was found that when the trapping agent is present it terminates 100% of the polymethyl methacrylate chains. The time evolution of the degree of polymerization was compared to simulations based on Schmid's model. The disproportionation/combination ratios were found for polymethyl methacrylate as 2 and for polystyrene as 1/7 respectively through simulation studies.

Pulsed laser polymerization: Analytical solutions of the chain length distribution revisited

A new solution for chain-length distributions of dead polymer and their moments (obtained by solving the coupled system of non-linear differential equations in full generality) is presented and compared to existing theoretical and numerical approaches. The new solution for chain-length distributions (cld) (at least numerically) coincides with our earlier results (analytical solution as well as data computed by use of numerical models) which were obtained by starting with strict coupling of time and degree of polymerization followed by an a posteriori Poisson broadening. (As a consequence the new solution also coincides with a numerical treatment based on fluctuating propagation probabilities by introducing an a priori Poisson broadening.) In turn, for termination exclusively by disproportionation this earlier solution is fully equivalent to Aleksandrov's approach (after some modification of the latter expression). This holds true also for termination exclusively by combination if one corrects for errors in Aleksandrov's derivation. The new solution of the moments of the cld agrees with our former results, while Aleksandrov's expressions are shown to be worthless under the usual experimental conditions.

Decomposition of Stable Free Radicals as “Self-Regulation” in Controlled Radical Polymerization

A new concept for controlled radical polymerization in the presence of stable free radicals is presented. Due to irreversible side reactions of free polymer radicals, the amount of dead polymer cha...

Living polymers in random media: a 2D Monte-Carlo investigation on a square lattice

The evolution of the mean chain length $$\langle L\rangle $$ and mean end to end square radius $$\langle R_e^2\rangle $$ of a two dimensional system of living polymers at constant monomer concentration is studied as a function of the obstacle density $$\rho $$ . The fact that the system adapts the mean chain length $$\langle L\rangle $$ in order to reduce the entropic constraint does not lead to a different asymptotic dependence of $$\langle R_e^2\rangle $$ on $$\rho $$ than what is observed for dead polymers. The change of the molecular weight distribution form in the presence of obstacles suggests that a Levy flight could appear in system of wormlike micelles in a porous medium.

Modeling and control of continuous stirred tank reactor for thermal copolymerization

A mathematical model is developed for solution copolymerization in a continuous stirred tank reactor. For the thermal copolymerization of styrene and acrylonitrile (SAN), the kinetic rate expression for thermal initiation is derived by applying the pseudo-steady-state hypothesis to the intermediates, and the kinetic parameters are estimated by experimental investigation. The moment equations of living and dead polymer concentrations are derived by applying the pseudokinetic rate constantmethod. The model is used to calculate the conversion, the copolymer composition, the weight-average molecular weight, and the polydispersity. It is demonstrated that this model can predict the industrial data very well under various operating conditions. The dynamic analysis of the reaction system enables us to determine the polymer properties against the changes in the operation parameters. It is noticed that the monomer conversion is controlled to some extent by the reaction temperature and the feed monomer fraction. The monomer conversion control of a solution copolymerization reactor is treated with different control algorithms. The fuzzy/proportional–integral–derivative controller shows satisfactory performances for both setpoint tracking and disturbance rejection and can be easily applied to continuous polymerization processes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:921–931, 1998

Synthesis of a Well-Defined Glycopolymer by Nitroxide-Controlled Free Radical Polymerization

This is the first report of the synthesis of a well-defined glycopolymer by free radical polymerization. N-(p-vinylbenzyl)-[O-β-d-galactopyranosyl-(1→4)]-d-gluconamide (VLA), a styrene derivative with an oligosaccharide moiety, was polymerized in N,N-dimethylformamide solution at 90 °C by the nitroxide-mediated free radical polymerization technique. Acetylated VLA gave polymers with a molecular weight from about 2000 to 40 000, an Mw/Mn ratio of about 1.1 in all cases, and a conversion of up to about 90%, where Mw and Mn are the weight- and number-average molecular weights. Indispensable for this success were (1) the use of di-tert-butyl nitroxide (DBN) rather than other nitroxides such as TEMPO, (2) the acetylation of VLA, and (3) the use of a radical initiator DCP (dicumyl peroxide) as an accelerator. DBN provided a well-controlled polymerization of VLA at 90 °C (VLA becomes unstable at higher temperatures, e.g., >120 °C). The acetylation effectively prevented the chain transfer that leads to dead polymers and broad polydispersities. DCP remarkably accelerated the rate of polymerization (the rate of chain extension), which otherwise was impractically slow, without causing any appreciable broadening of polydispersity.