“In-out” recursive probability modeling of branched step-growth polymerizations

This paper presents the derivation of mathematical formulae for molecular and network parameters of branched step-growth polymerizations. Weight-average molecular weight, gel point, and weight fractions of soluble, pendant and elastically-effective material in a gel are derived. The direct “in-out” recursive analysis of Macosko and Miller is applied to four general step-growth polymerization systems. The method is introduced using the simple case of A_f homopolymerization. Two new systems are then modeled; a homopolymerization of A_fB_g monomers with two types of reactive groups, and an A_f+B_g+C_h terpolymerization. The fourth system presented is a general A_f+B_g copolymerization of polydispersed reactants; we have partially analyzed this system before, but we give a new and complete presentation here to show the generality of the “in-out” analysis. We also survey some additional polymer systems that have been analyzed in the literature. Then, we discuss limitations of this modeling approach, the use of the models and their implementation in software. We give two numerical examples: a silicone rubber system and a segmented polyurethane network system. Appendices present the small amount of elementary probability theory and polymer distribution theory needed to support the analysis. This paper serves as an introduction to the “in-out” method; after reading this paper, the reader should be able to apply the “in-out” method to many step-growth polymer systems.     

Biobased step-growth polymers in powder coating applications

Co- and terpolyesters based on 1,4:3,6-dianhydro-d-glucitol (isosorbide), 1,4:3,6-dianhydro-l-iditol (isoidide) and succinic acid were evaluated for their applicability in solvent-cast and powder coatings. These biobased polyesters have functionalities and T_g values in the appropriate range for such applications and were cross-linked using conventional curing agents. Introduction of poly-functional monomers such as glycerol and citric acid led to coatings with enhanced performance with respect to mechanical and chemical resistance, compared to formulations based on linear polymers. The curing behavior of these systems was investigated with DSC and rheological experiments. Formulations containing citric acid-modified polyester resins showed rapid curing, probably facilitated by anhydride formation at the chain ends. Hydroxy- as well as carboxylic acid-functional 1,4:3,6-dianhydrohexitol-based polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance and hardness, with performance comparable to commercially available systems. Accelerated weathering experiments showed that functional groups such as hydroxyl groups, carboxylic acids, anhydrides and peroxides are formed during UV-exposure. The weathered coatings have reduced impact stability. On the other hand, the appearance of the coatings does not change significantly. Isosorbide-based coating systems appear to have similar weathering resistance as conventional terephthalic acid-based poly(ester urethane) coatings.     

Chemically-initiated solution polymerizations and radiation-initiated bulk polymerizations of isopropyl vinyl ether

The unusually high rates of polymerization of isopropyl vinyl ether initiated in bulk by high energy radiation, compared with other vinyl ethers, reported previously have been confirmed. The rates, molecular weights and heats of polymerization initiated by triphenylmethyl hexachlorantimonate have now been measured in methylene dichloride solution. Both methods of initiation are believed to involve essentially free ions. The chemically initiated polymerization rates however were similar to those found with the other vinyl ethers. The conflicting results are explained in terms of solvation effects rather than to differences in the methods of initiation. Qualitatively these results have been interpreted in terms of the Eyring theory of reaction rates between an unpaired ion and a neutral molecule.     

Living radical polymerizations in homogeneous solution by using organic sulfides as photoiniferters

Summary Some examples for living radical polymerization in homogeneous solution by four organic sulfides as photoiniferters have been proposed. In the photopolymerization of styrene (St) with diphenyl disulfide (DPD), tetraethyl thiuram disulfide (TD), benzyl diethyldithiocarbamate (BDC) and 2-phenylethyl diethyldithiocarbamate (PEDC), both the yields and the average-molecular weights of the polymers were found to increase as a function of the reaction time. The results obtained suggested that these polymerizations proceeded via a living radical mechanism. When these photoiniferters except DPD were used, the propagating polymer chain end was confirmed to be always the diethyldithiocarbamate [(C₂ H₅)₂NCSS] group, which can further photodissociate into a reactive propagating radical and a less reactive small radical[(C₂H₅)₂NCSS·] in order to result in successive insertion of monomer molecules into the dissociated bond.     

In-line evaluation of average particle size in styrene suspension polymerizations using near-infrared spectroscopy

The main objective of this article is evaluating the influence of average polystyrene particle size upon the near-infrared (NIR) spectra collected during suspension polymerization experiments and observing whether NIR spectroscopy may be used for in-line monitoring and control of average particle size. It is shown that NIR spectra are sensitive to changes of the average particle size, and that standard empirical models (PLS—partial least squares—and NN—neural networks) may be built to correlate average particle size and light absorbance at certain wavelengths fairly well. Finally, it is shown that these models allow the in-line evaluation of average particle size in styrene suspension polymerizations with NIR spectroscopy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1737–1745, 1998     

The effect of limited monomer solubility in heterogeneous step-growth polymerization

Limited monomer solubility imposes very intriguing features on poly(p-phenylenebenzobisoxazole) polymerization. Only one type of functional group is detected at oligomer chain ends, and a high-molecular-weight polymer is obtained even when an excess of the monomer with low solubility is used. These remarkable phenomena are interpreted as an unprecedented "spoon-feeding-of-monomer" mechanism. A novel apparatus for staged polymerization is described that was triggered by the uniqueness of the heterogeneous step-growth polymerization. Hyperbranched polyesters and a polyurethane/polyethylene blend, which represent two phases in the polymerization process, are also discussed.     

Syntheses and polymerizations of macromers

Summary Living poly(tetrahydrofuran) (PTHF) was coupled with sodium p-vinylbenzyloxide quantitatively to prepare a macromer of p-vinylbenzyloxyl poly(tetrahydrofuran) (VBO-PTHF). The radical polymerization of the macromer with AIBN was performed. From the GPC measurement the conversion of the macromer to poly-macromer was shown to be high percentage, but the degree of polymerization of poly-macromer was much lower than that expected in the case of regular monomers such as styrene.     

In situ polymerizations of thiophene on TiO2 films using the semiconductors as initiators

In this work, we prepare the TiO₂ nanoparticle film and anatase TiO₂ nanoarray film, and we achieve the polymerizations of thiophene using the photoexcited TiO₂ film as the initiators. It is measured that the in situ polymerizations of thiophene take place on the surfaces of the two films. The growth of polythiophene (PTh) on the TiO₂ nanoarray is monitored using Fourier‐transform Raman spectroscopy. The TiO₂ nanoarray is found to strongly interact with the PTh polymers. It is observed using scanning electron microscope that the microspores in the nanoarray are filled by the polymers after the reaction of 3 h, and the nanoarray is fully covered by the polymer layer when the polymerization lasts for 5 h. The PTh–TiO₂ nanoarray composite films are measured for the transient photocurrents and photocurrent‐voltage characteristics. The dependence of the photocurrents on the reaction time is revealed and discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40187.     

Experimental investigation of continuous conductivity measurements during emulsion polymerizations having unstable/high‐fouling reaction mixture

Conductimetry is one of the online monitoring techniques employed for emulsion polymerization reactions, which can give continuous information about nucleation and growth of particles. The most important factor affecting conductivity sensors performance especially contacting (resistance) types is fouling. To investigate the consequences of fouling, four monomers with different tendencies for fouling were selected: methyl methacrylate, butyl acrylate, styrene, and butadiene. Two types of conductivity sensors were also selected to continuously measure conductivity: a two‐electrode sensor and an inductive sensor, and the performance of these sensors were evaluated based on some criteria such as conductivity behavior, amount of fluctuation, change in cell constant, repeatability, and status of the minimum of conductivity. The results obtained from the contacting sensor showed that fouling significantly decreased the performance of this sensor in different ways even in reaction mixtures having moderate fouling rates. However, the inductive conductivity sensor provided the possibility of reliably measuring conductivity during very high‐fouling and highly unstable emulsion polymerizations with very good repeatability. The capabilities of this sensor also allowed an exact recognition of the important points in the conductivity curves particularly the minimum of conductivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44446.     

Effect of reactor type on polymer product: A backmix reactor for polymerizations and other viscous reaction media

A continuous-flow, backmix reactor, based upon the principle of drag flow and capable of handling viscous reactions, was designed and constructed. Its backmixing effectiveness was demonstrated via residence time distribution measurements, flow visualization experiments, and a stepwise polymerization reaction. The molecular weight distribution of the resulting polymer, which was measured and contrasted with that produced in a plug-flow type (extruder) reactor, was significantly altered by backmixing, as predicted computationally.     

Dynamic studies of molecular imprinting polymerizations

Mechanisms of interaction of a three-dimensional polymer with solutes are of interest in the development and function of synthetic biomimetic polymers. We have investigated the effects of template/monomer interactions and template concentration on conversion and polymerization rates of a molecularly imprinted polymer. Copolymers of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (PEG600DMA) were prepared in the presence of glucose. The polymerization reaction kinetics of non-imprinted networks as well as those imprinted with glucose at concentration ratios of [HEMA]/[Glucose] between 11 and 1 were monitored in situ by ATR-FTIR spectroscopy and differential photocalorimetry (DPC). The rates of polymerization for imprinted polymers showed an early lag period followed by a late autoacceleration, indicative of the complexation between monomer and template. Hydrogen-bonding was also observed using FTIR through the CO (carbonyl) bond of the monomers by FTIR. A significant effect of the template on conversion and polymerization rate of imprinted polymers was observed compared to non-imprinted ones. These values provide guidelines for kinetic models of interacting systems.     

Mechanical coagulation in emulsion polymerizations

Coagulum formation for different emulsion polymerizations was correlated to various agitation parameters. For low Reynolds numbers, rotational speed was shown to be important, whereas, for high Reynolds numbers, power consumption was the important parameter. These results were theoretically tied to first-order coagulation kinetics by incorporating shear rate relationships for flow in an agitated tank. For low Reynolds numbers, the average shear rate was assumed to be proportional to the rotational speed of the impeller. And for high Reynolds numbers, Kolmogorov's theory of locally isotropic flow was employed to relate the average shear rate to the power consumption.     

Optimization of batch solution polymerizations: Simulation studies using an inhibitor and a chain-transfer agent

Multiobjective constrained optimizations are carried out to compute optimal operation policies for batch solution polymerizations of styrene. It is shown by simulations how specified values for conversion, average molecular weight, and polydispersity may be achieved through the proper manipulation of the temperature profile and the initial amounts of the initiator, chain-transfer agent (modifier), and inhibitor. The optimizations show that the use of inhibitors and/or modifiers is seldomly required, unless the process economics is taken into consideration or the high-molecular weight chain fraction of the final polymer resin is to be minimized. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1137–1152, 1998     

Dynamics of continuous isobutylene cationic polymerizations

Polyisobutylene can be produced in either continuous cationic precipitation or solution polymerization reactors. It is known that the open-loop behavior of polymerization reactors may be very complex and may lead to oscillatory behavior, which is usually caused by thermal positive feedback (due to the large heats of reaction of polymerization reactions) and high viscosity effects (such as the gel effect in radical polymerization reactors and the decrease of heat transfer coefficients at high polymer concentrations). Oscillatory behavior may be observed in industrial isobutylene reactors, and it is intended to know whether these oscillations are inherent to the kinetic mechanism. Based on published experimental data, mathematical models are developed for both solution and precipitation processes. Steady-state solutions are calculated and steady-state stability is analyzed. Dynamic simulations and stability results reveal that only single stable steady-state solutions are possible for such reactors at usual operation conditions, which means that oscillatory behavior is not intrinsic to the reaction mechanism. © 1996 Wiley & Sons, Inc.     

反应釜高压水射流清洗设备研制

根据反应釜的结构特点设计出了合适的清洗设备.设备中三维旋转喷头伸缩机构和三维旋转喷头的合成运动保证了高压水射流可以覆盖反应釡内任何位置,完成对反应釜的清洗,并在应用中得到了较好的效果.     

Structurally controlled polymerizations of methacrylates and acrylates

Progress in the structure control of polymethacrylates and polyacrylates through stereospecific living polymerization are described. Three types of stereospecific living polymerizations have been developed for methacrylate polymerization: isotactic with t‐C₄H₉MgBr, syndiotactic with ­t‐C₄H₉Li/R₃Al, and heterotactic with t‐C₄H₉Li/bis(2,6‐di‐t‐butylphenoxy)methylaluminium [MeAl(ODBP)₂]. The last initiator system has been proved effective for monomer‐selective living copolymerization of methacrylates. The living nature of these polymerizations allows extensive use for the syntheses of stereoregular block polymers and copolymers, and end‐functionalized polymers such as macromonomers. Through stereospecific polymerizations and copolymerizations of macromonomers, comb polymers and graft copolymers with defined stereoregularities in the main chain and side chains could be obtained. Some properties of these stereoregular polymers are also described, including stereocomplex formation and solution viscosity. Stereospecific polymerizations of crotonates leading to diisotactic, diheterotactic and disyndiotactic polymers are also discussed. Supercritical fluid chromatography (SFC) has been proven to be useful for isolating uniform polymers from stereoregular poly(methyl methacrylate)s (PMMAs) with narrow molecular weight distribution. Uniform end‐functionalized polymers have been used to construct more elaborate uniform polymer architectures such as stereoblock, star, and comb polymers, and copolymers. The uniform polymers have been proven quite useful for the studies of the relationship between structures and properties such as glass transition temperature, melting temperature and solution viscosity. Particularly interesting is the use of isotactic and syndiotactic uniform PMMAs for the understanding of stereocomplex formation in certain solvents such as acetone. Furthermore, a uniform stereoblock PMMA was found to undergo intramolecular complexation in addition to intermolecular complexation in acetone. Uniform star and comb PMMAs were also prepared and found useful for discussing the effect of branching on the solution viscosity. © 2000 Society of Chemical Industry     

Carbocationic polymerizations in supercritical carbon dioxide

The first carbocationic polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) has been accomplished. It was demonstrated that in CO₂ at 32.5°C and 120 bar the 2-chloro-2,4,4-trimethyl-pentane (TMPCl)/SnCl₄ and TMPCl/TiCl₄ initiating systems lead to 30% IB conversion, and gave polyisobutylenes (PIB) with M_n2000 and M_w/M_n2.0. This is the highest temperature IB was ever polymerized to reasonably high molecular weight products. Polymerizations at 32.5 °C under similar but conventional (non-living) conditions in the absence of SC·CO₂ would yield only very low molecular weight oligomers (tetramers). The structure of the PIBs obtained in SC·CO₂ is virtually identical to those obtained at much lower temperatures in conventional liquid-phase systems indicating the presence of chain transfer to monomer in both systems. In contrast to TMPCl initiated polymerizations, the 1,3-bis-(2-hydroxy-2-propyl)-5-tert-butylbenzene (HPBB) initiator in conjunction with BCl₃ and SnCl₄ yields only oligomers (M_n500) in SC·CO₂.     

Ring-opening polymerizations of heterocycles with organometallic catalysts

Recent developments in the field of ring-opening polymerizations using organometallic initiators are discussed, particularly in the case of epoxides, episulfides, lactones and cyclosiloxanes. For classical anionic polymerizations, generally initiated by compounds of alkali metals, the complexity of the kinetics is linked to the presence of aggregates of active centres. But kinetics could be largely simplified by a suppression of these aggregates through the addition of complexing agents of the counter ions. This permits the measurements of absolute rate constants on various ionic species. This addition generally leads to large increases in the observed rates, and may modify the relative rate of formation of cyclic oligomers. When the monomer contains at least one chiral centre, stereospecific polymerizations may be realized both in homogeneous and heterogeneous phase, using derivatives of bivalent metals such as Zn or Cd. If asymmetric catalysts are used, the resolution of monomer racemic mixtures may be performed, giving optically active polymers and permitting in some cases the preparation of pure enantiomers.