A study of chain addition polymerizations with temperature variations: III. Thermal runaway and instability in styrene polymerization—an experimental study

Thermal runaway arid parametric sensitivity were experimentally demonstrated in styrene polymerizations. Ignition boundaries were established for several initiator concentrations and a dimensionless boundary plotted. Runaway sensitivity was shown to disappear under specific conditions.     

A study of chain-addition polymerizations with temperature variations. IV. Copolymerizations—Experiments with styrene-acrylonitrile

Free-radical copolymerizations were studied under nonisothermal conditions with emphasis on their thermal runaway and ignition behavior. Computational models are presented in generalized form and compared with experiments on the system styrene-acrylonitrile. A new, useful method is proposed for the evaluation of runaway parameters from scant kinetic data.     

Effect of temperature variations on molecular weight distributions: batch,chain addition polymerizations

The Maximum Principle was applied to determine the types of temperature variations that minimize and maximize the breadth of the molecular weight distribution (MWD) for chain addition polymerizations in batch reactors. It was found that the variations which minimize the breadth of the MWD keep the instantaneous number average chain length constant. The variations which maximize the breadth of the MWD are step changes in temperature resulting in bimodal distributions. Numerical and experimental examples of such variations are presented. MWD's with minimum and maximum breadths are compared to those that might be formed by temperature variations in real reactors. Under most conditions, temperature variations appear to have a much greater effect on MWD than residence time distributions and micromixing.     

A study of chain addition polymerization with temperature variations: I. Thermal drift and its effect on polymer properties

Models of chain addition polymerizations have been analyzed for effects of reaction parameters on thermal behavior during reaction and, consequently, on properties of the polymer formed. Emphasis was placed on the investigation of thermal drift phenomena in particular. Several dimensionless parameters were identified and their role in predicting thermal behavior was established.     

Palladium(II)-catalyzed addition polymerizations of nadimides with linear alkyl and alicyclic pendant groups

Two series of polynadimides with pendant linear alkyl and alicyclic groups have been prepared by addition polymerization of N-alkyl-exo-norbornene dicarboximides (nadimides; alkyl = propyl, butyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl) in the presence of palladium(II) catalyst. The catalytic reactivity of the nadimides strongly depends on the nature and the steric bulk of the pendant groups. Nadimides with alicyclic groups (except for N-cyclopropyl nadimides) exhibit higher reactivity than the nadimides with linear alkyl groups and substituents with the same number of carbons. The polynadimides with alicyclic groups present lower dielectric constants than those with linear alkyl groups. All resulting polynadimides exhibit better thermal stability than the unsubsitituted polynorbornenes.     

Method for quantitative evaluation of kinetic constants in olefin polymerizations. II. Kinetic study of a high‐activity Ziegler–Natta catalyst used for bulk propylene polymerizations

A method for quantitative evaluation of kinetic constants in Ziegler–Natta and metallocene olefin polymerizations presented previously (Matos, V.; Mattos Neto, A. G.; Pinto, J. C. J Appl Polym Sci 2001, 79, 2076) is adapted to allow the estimation of kinetic constants for bulk propylene polymerizations by using a conventional fourth‐generation high‐activity Ziegler–Natta catalyst (HAC). In this particular case, reaction rate profiles are not available, so that estimation of kinetic data must rely on average polymer yields. The method comprises some fundamental steps, including the initial design of a statistical experimental plan, the execution of the designed experiments, the development of simple mathematical models to describe the polymerization, and the estimation of kinetic parameters from available yields, gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) data. It is shown that the proposed method allows the successful interpretation of experimental olefin polymerization data and the quantitative evaluation of kinetic parameters, which can be inserted into a process simulator to provide an accurate picture of actual industrial plant behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3226–3245, 2002     

Thermal degradation of EVA and EBA—A comparison. II. Changes in unsaturation and side group structure

This is the second in a series of papers in which the thermal degradation of ethylene-vinyl acetate (EVA) and ethylene-butyl acrylate (EBA) copolymers are compared. The EBA samples contain 0.8, 1.6, and 5.4 mol % butyl acrylate (BA), respectively, and the EVA samples 1.2 and 6.7 mol % vinyl acetate (VA). The samples were heated in nitrogen in a tubular oven at 285, 333, 350, 370 and 390°C for 6–120 min. The samples were analyzed with IR, NMR, gravimetry, and titration of carboxylic groups. The EVA samples were rapidly degraded by deacetylation, which was complete after about 30 min at 333°C. A linear relation between the loss of acetate groups and the formation of trans double bonds was found. A small amount of keto groups and traces of lactones were also observed. The data confirm the previously proposed mechanisms for deacetylation and the formation of acetaldehyde. A mechanism for lactone formation is suggested. The deacetylation rate is increasing with the VA content, presumably because of an increased amount of block sequences and an enhanced acid catalytic effect. The acrylate sidegroups are much more stable than the acetate groups, and are similar in stability to the main hydrocarbon chain. The BA decomposition results in carboxylic and anhydride groups. Decarboxylation also occur and increases with the thermal treatment. In LDPE and EBA the increase in unsaturation is small and mainly due to vinyl end groups formed via β-cleavage or disproportionation. In EVA the formation of vinyl end groups is suppressed.     

Melamine - formaldehyde resins II.—Thermal degradation of model compounds and resins

The thermal degradation of a series of cured melamine-formaldehyde resins and of two relevant model compounds has been investigated using thermogravimetry accompanied by the analysis of volatile products. Low temperature degradation reactions which occur up to ～350°C involve the loss of water and formaldehyde, the latter arising from reversible demethylolation reactions. It is proposed that ether linkages, which model compound studies indicate would yield formaldehyde in the low temperature region, are not present to any significant degree in cured resins. Deep-seated rupture of the polycondensate system takes place at temperatures above ～375°C when a number of independent reactions involving both side-chain and ring degradation give rise to products among which ammonia, hydrogen cyanide, carbon monoxide and melamine have been examined.     

Propylene polymerization — a computer efficient algorithm with orthogonal collocation

This paper presents a new approach to the modelling of solid catalyzed Ziegler-Natta polymerization of propylene, using orthogonal collocation technique. It is shown that this model can predict the width of the molar mass distribution (MWD) of the product polymer. Its computation time is much shorter compared to other models. An interesting feature of the model is that it considers the discrete nature of the microcatalyst particles and takes advantage of solving a smaller number of stiff differential equations by choosing the number of internal collocation points judiciously. In addition, pseudo-steady state approximation (QSSA) is applied to some of the moment generating equations.     

Thermal degradation of biomedical polyurethanes—A kinetic study using high‐resolution thermogravimetry

The kinetics of thermal degradation of polyurethanes (PUR) has been studied by means of high‐resolution and constant heating rate thermogravimetry (TG), under nitrogen and synthetic air atmospheres. The high‐resolution TG provided a way to increase resolution with decreasing the time of data acquisition. In this mode, the heating rate is dynamically varied to maximize resolution. A method to calculate the kinetic parameters from this technique was used. The TG curves showed two or three decomposition steps, depending on the atmosphere employed. The parameters calculated for the PUR decomposition were the activation energy, reaction order, and preexponential factor. A method to estimate the polymer lifetime was also used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 910–919, 2001     

Thermal degradation of EVA and EBA—A comparison. I. Volatile decomposition products

This is the first in a series of papers in which structural changes during thermal degradation of ethylene-vinyl acetate (EVA) and ethylene-butyl acrylate (EBA) copolymers are compared. EVA, containing 11.4 mol% vinyl acetate (VA) and EBA, containing 5.4 mol% butyl acrylate (BA), were pyrolyzed at 280°C in nitrogen for 30 min. In another series of pyrolysis, EVA containing 1.2, 2.2, and 11.4 mol% VA were treated at 150–190°C for 3 h. The volatile decomposition products were collected in cooled traps respectively gas bags and then analysed with GC-MS and ion-chromatography. EVA is rather labile. The main volatile decomposition product is acetic acid. A linear decomposition rate was found already at the lowest investigated pyrolysis temperature, 150°C. After 30 min at 280°C every 15th of the acetate side groups had been eliminated. EBA is much more stable to pyrolysis. Thirty minutes at 280°C resulted in a decomposition of one out of 1500 BA groups. Butene is the main volatile decomposition product. Ester pyrolysis is supposed to account for the degradation of both types of polymers. The big difference in reactivity is presumably due to conformational differences. The ester pyrolysis mechanism will result in random unsaturations in EVA and carboxylic groups in EBA. To a minor extent acetaldehyde is formed when EVA is degraded. According to the mechanisms suggested, carbonyl groups remain in the main chain. Contrary to what is reported for poly(butyl acrylate), no alcohol was formed when pyrolysing EBA. This indicates that adjacent acrylate groups are needed for alcohol formation. For both types of polymer, scissions of the main chain results in hydrocarbon fragments mainly. In addition, acrylate containing fragments are observed when EBA is degraded. EVA, however, does not give any acetate-containing fragments.     

Thermal degradation of EVA and EBA—A comparison. III. Molecular weight changes

This is the third in a series of papers in which the thermal degradation of ethylene-vinyl acetate (EVA) and ethylene-butyl acrylate (EBA) copolymers are compared. The EBA samples contained 0.8, 1.6, and 5.4 mol % butyl acrylate (BA), respectively, and the EVA samples 1.2 and 6.7 mol % vinyl acetate (VA). The samples were heated in nitrogen in a tubular oven at 285–390°C, for 6–120 min. The molecular weight distribution (MWD), long chain branching, and gel content were analyzed with size exclusion chromatography (SEC). The columns were connected to refractive index, viscometric, and light scattering detectors. EVA gave a pronounced molecular enlargement at all degradation temperatures. In EVA-6.7, gel was formed at all degradation levels, whereas the low content sample, EVA-1.2, did not form any visible amount of gel. The strong tendency to molecular enlargement is due to allyl radicals formed after thermal deacetylation and the formation of internal double bonds. These macroradicals will combine or, less frequently, add to double bonds. The EBA copolymers show a more polyethylenelike degradation behavior. At 285°C molecular enlargement dominates, but already at 333°C a net reduction in molecular size is observed. At high temperatures, ester pyrolysis of the BA groups give carboxylic groups and anhydrides. Alkaline treatment will not give any appreciable change in MWD, showing that the anhydride formation is mainly intramolecular. The chain scission increases with the BA content. This is probably due to β-cleavage of tertiary macroradicals formed in the chain at the acrylate or carboxylic side groups.     

Optimization of batch polymerization processes—narrowing the MWD. II. Experimental study

Programmed solvent injection was previously proposed and analyzed in the first part of this two-paper series as a viable alternative for controlling the average molecular weight and narrowing the polydispersity of products from a free-radical polymerization process with an inherent tendency to exhibit strong gel and glass effects. Here, methyl methacrylate is chosen for experimental verification of this idea. The product molecular weight distribution is indeed narrowed.     

Characterization,properties, and processing of LaRC PETI‐5 as a high‐temperature sizing material. II. Thermal characterization

In this publication the glass transition, melting behavior, cure behavior, and thermal stability of LaRC PETI‐5 have been extensively studied utilizing differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The material used here was subjected to different thermal history (cumulative cure and individual cure) including an isothermal cure. The extent of cure for the partially cured resin was evaluated taking into account the residual solvent in the resin with the aid of a correction factor. The data show that the thermal history for the imidization reaction may influence the extent of cure for the partially cured LaRC PETI‐5. The reaction of the CC bonds in the phenylethynyl groups located in the imide polymer chain ends is completed to produce a fully cured LaRC PETI‐5 within 1 h at 350°C in air. The result is very consistent with the result obtained using Fourier Transform infrared (FT‐IR) spectroscopy in the previous work. This study also demonstrates that no reaction takes place above 350°C prior to degradation. LaRC PETI‐5 with a molecular weight of 2500 g/mol has excellent thermal stability up to 550°C as long as it is fully imidized. The result of the isothermal stability suggests that this material may be used without significant loss of its integrity for extended periods of time below 450°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1278–1287, 2000     

Method for quantitative evaluation of kinetic constants in olefin polymerizations. I. Kinetic study of a conventional Ziegler–Natta catalyst used for propylene polymerizations

A method for quantitative evaluation of kinetic constants in Ziegler–Natta and metallocene olefin polymerizations is presented. The method comprises some fundamental steps, which include the initial design of a statistical experimental plan, the execution of the designed experiments, the development of simple mathematical models to describe the polymerization, and the estimation of kinetic parameters from available rate, gel permeation chromatography, and NMR data. The method is applied to the slurry propylene polymerization, using a conventional first generation Ziegler–Natta catalyst, in a lab‐scale polymerization reactor. It is shown that the proposed method allows the successful interpretation of experimental olefin polymerization data and the quantitative evaluation of kinetic constants, which can be inserted into a process simulator to provide an accurate picture of actual industrial plant behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2076–2108, 2001     

‘Monte carlo’ computer simulation of chain molecules: II. The limiting distribution of end-to-end distance for two-dimensional excluded-volume chains

A computer technique for simulating configurational behaviour of chains, developed previously, was used to study the nature of the distribution of the magnitude of end-to-end vectors of excluded-volume chains constrained to two dimensions. The study revealed that the above distribution in the limit of infinite chain length deviates greatly from Gaussian behaviour and that the deviation is much greater than for three-dimensional chains. The probability distribution function A exp (—αR^5.8) was derived.     

A computer approach toward automation of a chemical services laboratory: II. Management information

A Real Time Information Management System is described which is based on several interacting data bases. Fifteen dynamic files are accessed by 70 chemists and microbiologists through the use of computer terminals and more than 25 programs. The System provides for real time work scheduling for a chemical laboratory and the generation of all reports. The System also handles accounting, billing, summarization, analysis and distribution of all laboratory functions. The system is open ended, and therefore, expandable. There is no dependency to a particular computer but rather only the need for a computer that can handle terminals and dynamic files. One of seven papers being published from the Symposium, “Computer Systems and Applications in the Oil and Fat Industry” presented at the ISF-AOCS World Congress, Chicago, September 1970.     

Condensation polymerization of multifunctional monomers and properties of related polyester resins. II. Thermal properties of polyester—imide varnishes

Polyester—imide prepolymers containing synthesized N,N′-bis(hydroxyethyl)pyromellitic diimide (PMDI) or N,N′-bis(hydroxyethyl)-3,3′-4,4′-benzophenone tetracarboxylic diimide (BTDI) were synthesized under conditions previously reported. One-component varnishes were obtained by mixing the synthesized prepolymers with commercial Desmodur CT-stable. Thermal behavior of these varnishes was investigated using thermogravimetric analysis. Activation energy of cured film, which was a polyester—imide varnish, was determined by using a multiple heating rate method. Polyester—imides coated copper wires were characterized, and were found to be acceptable, according to the specification of Japanese Industrial Standard (JIS-C-3214).     

Hydrodynamics of disturbed flow and erosion–corrosion. Part II — Two-phase flow study

Erosion–Corrosion in turbulent, two-phase liquid/particle flow with recirculation, after a sudden pipe expansion is studied by the application of a numerical flow model along with two different erosion models. The flow model, which is based on a two-phase flow version of a standard two-equation model of turbulence and a stochastic simulation of particle-fluid turbulence interactions, is capable of successfully predicting local values of time averaged fluid velocities and turbulent fluctuations, as well as predicting particle dispersion and particle-wall interaction. The erosion models used are that of Finnie (1960) and a modified version suggested by Bergevin (1984). The agreement of the predicted and measured hydrodynamic parameters, for flow through a sudden expansion, was satisfactory. Predictions of erosion rates using Bergevin's modified model were in good agreement with the stainless steel erosion measurements for a 2% water/sand slurry flow. The erosion–corrosion model was successful in predicting the overall pattern and rates of metal loss for carbon steel.