Homogeneous Solution Polymerization Research Articles

Morphology and Surface Area of Emulsion-Derived (PolyHIPE) Solid Foams Prepared with Oil-Phase Soluble Porogenic Solvents: Span 80 as Surfactant

Poly(divinylbenzene) emulsion-derived (PolyHIPE) solid foams prepared with porogens (toluene, chlorobenzene, (2-chloroethyl)benzene, 1,2-dichlorobenzene, and 1-chloro-3-phenylpropane) in the oil phase have morphologies and surface areas that are strongly influenced by the nature of the porogen. For the case where the surfactant employed is Span 80, we show that the solid foam structure depends on (i) the ability of the solvent to swell the growing network, (ii) the solvent polarity, and (iii) the ability of the solvent to adsorb at the emulsion interface. In particular, relatively polar solvents that are able to transport water through the emulsion continuous phase (Ostwald ripening) are shown to produce much lower surface areas than analogous resins prepared by homogeneous solution polymerization of divinylbenzene in the presence of the solvent in question alone. The influence of Ostwald ripening is further suggested by the observation that surface area decreases with increasing emulsion aqueous phase content for relatively polar solvents whereas little variation in surface area with aqueous phase content is observed for more hydrophobic solvents. All PolyHIPEs prepared were characterized by SEM, TEM, N2 sorption analysis, and mercury intrusion porosimetry. The relative merits of TEM and mercury intrusion porosimetry as techniques for the reliable characterization of the solid foams are discussed.

Synthesis of Poly(sodium styrenesulfonate-block-vinylnaphthalene) by Nitroxide-Mediated Free Radical Polymerization

The new block amphiphilic copolymer, poly(sodium styrenesulfonate-block-vinylnaphthalene) (PSSS-block-VN), was synthesized by nitroxide-mediated “living” radical polymerization in homogeneous solution. The composition of the copolymer was determined by 1H NMR spectroscopy and elemental analysis. On the basis of GPC, viscometric, and spectroscopic measurements, we proposed that the copolymer adopts a highly compressed, pseudomicellar conformation in aqueous solution.

Microemulsion Polymerization of Methyl Methacrylate Photoinitiated by Symmetrical Azocompounds of Different Hydrophobicity

Symmetrical azo compounds of different charge were used as photoinitiators of methyl methacrylate (MMA) polymerization in homogeneous solution and in microemulsions supported by cationic and anionic surfactants. The measured constants for association of initiators to the aggregates are those expected from the micellar surface potential, which is reduced by the presence of monomer. Polymerization rates and photocleavage yields of azo compounds were measured in different media. The results are interpreted in terms of a fast interchange of the counterions between micelles that reduces the intra-Stern layer primary radical combination.

Polyelectrolytes of High Charge Density in Organic Solvents. Synthesis and Viscosimetric Behavior

An easy anion exchange between electrolyte monomers of the quaternary ammonium halide type such as [(2-methacryloyloxy)ethyl]trimethylammonium chloride or 1-vinyl-3-methylimidazolium iodide and various cyanocarbon salts such as 1,2,2-tricyanoethenolate, 1,1,2,3,3-pentacyanopropenide, α,α-dicyano-p-toluoylcyanide, or p-(tricyanovinyl)phenyldicyanomethide readily leads to a series of new hydrophobic electrolyte monomers with yields generally over 70%. [(2-Methacryloyloxy)ethyl]trimethylammonium 1,1,2,3,3-pentacyanopropenide is a most representative example. Its free radical polymerization in homogeneous solution (DMF, 60 °C) currently yields atactic chains (Bernoulli stereopropagation process, probability of meso placement Pm = 0.31) of fairly high degree of polymerization (DPw ∼ 1600) which show an unique spectrum of solubility in dipolar organic solvents (dipole moment μ > 2.6 D) covering a very broad range of dielectric constants (e ∼ 10−180). Viscosity measurements performed in 13 solvents allow us to a...

Aqueous solution properties of polyampholytes: effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.

Aqueous solution properties of polyampholytes: effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.

Homogeneous and heterogeneous free radical polymerizations in environmentally responsible supercritical carbon dioxide

AbstractFluoropolymers are used in many technologically demanding applications because of their balance of high‐performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids (SCFs). The homogeneous solution homo‐ and copolymerization of highly fluorinated acrylic, styrenic and olefinic monomers in supercritical carbon dioxide using free radical methods will be discussed [Science, 257, 945 (1992)]. Detailed decomposition rates and efficiency factors will be presented for azobisisobutyronitrile (AIBN) in supercritical carbon dioxide and will be compared to conventional liquid solvents [Macromolecules, 26, 2663 (1993)]. Additionally, viscosities of polymer solutions in supercritical CO2 have been measured using a high pressure, falling cylinder viscometer. The results show that the polymer solution viscosities in supercritical CO2 are an order of magnitude lower than with the same polymers in conventional organic solvents.The results from these homogeneous solution polymerization studies has allowed us to also consider heterogeneous polymerizations in a carbon dioxide continuous phase. Conventional emulsion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersion media with addition of surface active agents (surfactants) to stabilize the colloidal dispersion that forms. With free radical initiators that are preferentially soluble in the continuous phase, high rates of polymerization and high molar mass polymers can be obtained simultaneously. Herein we describe an environmentally responsible alternative to aqueous and organic dispersing media for emulsion polymerizations which utilizes supercritical carbon dioxide, in conjunction with molecularly engineered free radical initiators and amphiphilic molecules that are specifically designed to be interfacially active in CO2. Conventional lipophilic monomers, exemplified by methyl methacrylate and styrene, can be polymerized heterogeneously using a fluorinated azo‐initiator in supercritical CO2 in the presence of added surfactant to form stable emulsions that result in submicron size particles. Detailed surfactant and initiator syntheses and phase behavior will also be discussed.

Shear flow induced orientation development during homogeneous solution polymerization of rigid rodlike molecules

The dynamic variation of optical birefringence during solution polycondensation of rigid rodlike molecules (p-phenylenediamine and terephtaloyl chloride) in a simple shear flow is obtained. At relatively high shear rates (413 s -1 ) and late stages of the polymerization the orientation of the molecules is found to be significant. Molecular orientation is important in such reactions since it increases the polymerization rate and alters the molecular weight distribution. The birefringence at different shear rates γ over the course of the polymerization is found to depend only on γ/D r , where D r is the rotational diffusivity

Synthesis of Fluoropolymers in Supercritical Carbon Dioxide

Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids. The homogeneous solution polymerization of highly fluorinated acrylic monomers can be achieved in supercritical carbon dioxide by using free radical methods. In addition, detailed decomposition rates and efficiency factors were measured for azobisisobutyronitrile in supercritical carbon dioxide and were compared to those obtained with conventional liquid solvents.

Heterogeneous radical polymerization: Reactivity and morphology control

AbstractIn the first part of that review, some physical effects are studied, causing changes in the kinetics and mechanism of polymerization reaction when going from an homogeneous solution polymerization to heterogeneous polymerizations. Three main cases are considered: acrylonitrile polymerization in which the polymer is neither soluble nor swollen by its monomer, vinyl chloride polymerization in which the polymer is not soluble in its monomer but is swollen by it, and styrene‐divinylbenzene resin where the apparent reactivity of the second double bond is governed by the syneresis phenomenon. In addition to the Tromsdorff effect on the termination reactions, perturbation due to the heterogeneous character of the reaction may affect the termination reaction by isolating free radicals, propagation reaction by restricting the mobility of the monomer or that of the growing radical through a template effect, or even transfer reactions on the polymer. Via concentration of pendent double bonds are observed inside crosslinked nodules of styrene‐divinylbenzene copolymers.The second part is devoted to the study of morphology. Special emphasis is paid to the case of vinylchloride polymerization where the aggregation phenomena are governed by electrostatic interactions, and also to the case of styrene‐divinylbenzene resins where the formation of the morphology is discussed in terms of critical conversions for phenomena such as appearance of microgels, overlapping of nodules and phase separation. Similarities between porous morphology of PVC and styrene‐divinylbenzene resins are pointed out. Some discussions are also devoted to the supermolecular structures inside small particles in PVC, and also in multistep emulsion copolymerizations.

Effects of Pressure on Methyl Methacrylate Polymerization and Polymer Stereoregularity

In a modest pressure range of 1–250 kg cm−2, the conversion and rate in free radical aqueous heterogeneous and homogeneous solution polymerization of methyl methacrylate increase with applied pressure to a maximum value and subsequently fall to attain a limiting value with further increase of pressure. Possible effects of pressure on kinetically important steps are discussed. The molecular weights also show similar variation with applied pressure due to enhanced chain-transfer with monomer at higher pressure. The thermal stability of the polymer is not influenced in this pressure range. 13C NMR spectra analyses of the polymer obtained at three different applied pressures do not reveal any differences in the percentages of isotactic, heterotactic and syndiotactic configurations in the polymer.

Segmented organosiloxane copolymers. 1. Synthesis of siloxane—urea copolymers

Siloxane—urea linked segmented copolymers were synthesized from α,ω-bis(aminopropyl)poly dimethylsiloxane oligomers and various aromatic and cycloaliphatic diisocyanates such as MDI, TDI and H-MDI. Molecular weights of the siloxane oligomers were varied in the range of 1000–4000 g mole −1 and high molecular weight linear copolymers were obtained by employing homogeneous solution polymerization techniques. The solvent used during the reactions has a very critical role on the average molecular weight of the final product. Bis(2-ethoxy ethyl) ether (EEE) and THF were most useful. Chain extenders such as aliphatic or cycloaliphatic diamines were also used in some reactions and in this case polar cosolvents such as NMP were also required. The yields were usually very high and the amorphous products obtained from the simple stoichiometric linking reaction were soluble in various common organic solvents. Formation of urea linkages during the polymerization were followed by FTi.r. spectroscopy. The copolymers were characterized by g.p.c. and intrinsic viscosity measurements, FTi.r., n.m.r. and thermal analysis. All these results together with mechanical characterization described in the accompanying second paper of this series indicate the formation of novel, segmented elastomeric siloxane—urea copolymers.

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

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.

Particulate precipitation polymerization: A convenient procedure for the synthesis of crosslinked polymers useful as polymeric supports

Suitable choice of monomer/nonsolvent and monomer plus solvent/nonsolvent ratios affords a very simple and convenient laboratory scale method for the synthesis of functionalized crosslinked polymers suitable as polymeric supports in a wide variety of applications. The method involves an initially homogeneous solution polymerization which, because of the presence of nonsolvents ultimately produces insoluble, particulate (i.e., nonswollen) resin. Advantages over the usual suspension polymerization processes include the absence of stabilizers and suspension agents and complete freedom to utilize water soluble or water insoluble monomers, or mixtures of the two. Reaction conditions must be determined experimentally for individual systems and a number of representative examples are given.

The relation between the molecular weight and intrinsic viscosity of polyvinyl alcohol

A series of unfractionated and fractionated samples of polyvinyl acetate were prepared by homogeneous solution polymerization of vinyl acetate in N,N-dimethylformamide at 90 °C. in presence of γ, γ-azo-(γ-cyano-n-valeric acid) as initiator under a variety of conditions. A portion of each sample was hydrolysed to polyvinyl alcohol. The number average molecular weights have been determined by end-group titrations. The following molecular weight-intrinsic viscosity relationships for polyvinyl alcohol have been obtained. [η] = 33.88 X 10−5M0.716 — for unfractionated samples in water at 30 °C. [η] = 29.51 X 10−5M0.716 — for fractionated samples in water at 30 °C.

Estimation of the Characteristic Ratio kp(f/kt)½and Its Temperature Dependence in Bulk Polymerization of Vinyl Chloride

Abstract According to a reaction scheme which as its main features assumes that polymerization is predominantly in the interior of the monomer swollen polyvinyl chloride) particles and that all the decaying initiator finally contributes to the polymerization within the polymer particles, the ratio kp (f/kt)½ = K (where kp, kt are rate constants for chain propagation and chain termination, respectively, within the particles and f is initiator efficiency) has been calculated for bulk polymerization of vinyl chloride at three temperatures. K is found to be markedly larger than the corresponding quantity for homogeneous solution polymerization, e.g., at 50°C it is seven times this latter quantity. The characteristic ratio K shows a marked negative temperature dependence, which corresponds to approximately -4.5 kcal/mole for Ep - (Et/2), when f is assumed to be independent of temperature. This behavior is quite consistent with a strong gel effect being operative at the site of reaction, i.e., the swollen polym...

On the Mathematical Modeling of Emulsion Polymerization Reactors

I. INTRODUCTION Emulsion polymerization often has significant advantages over homogeneous bulk or solution polymerization. Aside from the obvious physical advantages when a polymer latex is the final product as in paints or other coatings, there are distinct processing advantages. For example, low viscosity and good temperature control can often be achieved in an emulsion polymerization when this is impossible in bulk. In addition, high molecular weight polymer can usually be produced at much higher reaction rates in an emulsion polymerization reactor than in a bulk polymerization. For these and other reasons, emulsion polymerization has become a multibillion dollar/year processing operation in terms of sales in the United States alone.

Suggested interpretation for the anomalous kinetics of acrylonitrile polymerization in homogeneous solution

AbstractThe polymerization in homogeneous solution of acrylonitrile shows an anomalous kinetic behavior. The reaction order in respect to the monomer appears higher than 1, and approaches the order of 2 at low acrylonitrile concentrations (< 2M). This behavior was given various interpretations. No completely satisfactory explanation is, however, available. By taking into account some secondary radical reactions recently discovered (polymerization through CN), a new interpretation of the kinetic anomalous behavior is suggested, and a kinetic model is given which also takes into account the propagation through the triple CN bond.The equations so fully derived justify the experimental results. A reaction order of 2 in respect to the monomer for (AN) tending to zero, and approaching 1 for (AN) > 2M, is deduced from the assumptions made. According to the proposed mechanism, the kinetic deviations from theory do not depend on the initiation rate, as confirmed by experimental results, but only on monomer concentration.

Radical polymerization of N‐vinylcaprolactam in homogeneous solution. II

AbstractThe polymerization of N‐vinylcaprolactam in toluene, dioxane, chlorobenzene, dimethylformamide, and ethylene carbonate with various peroxides, perbenzoates and azobisisobutyronitrile as initiators at 60–80°C, was studied. Under these conditions azobisisobutyronitrile and tert‐butyl perbenzoate have satisfactory activity as initiators. Under these conditions N‐vinylcaprolactam polymerization in homogeneous solution is first order towards the monomer and 0.5 order towards the initiators.

Acrylonitrile polymerization in homogeneous solution

AbstractPrevious kinetic studies of acrylonitrile polymerization in bulk disclosed unexpected features that were associated with the heterogeneous nature of the system. In the present work, polymerization was carried out in homogeneous solution, principally in dimethyl formamide. Polymerization rate in dimethylformamide was dependent on the square root of the azo initiator concentration and approximately on the three‐halves power of the monomer concentration. Over‐all activation energy was 21 kcal./mole. Rates were slow in this solvent and molecular weights were low. Chain transfer activity of several liquids was estimated by substituting them for part of the dimethylformamide. Contrast between results in the homogeneous and heterogeneous cases is explained as due to removal by solvent of any opportunity for radical burial or catalyst enrichment. Standard kinetic treatments do not explain quite adequately the details of rate and molecular weight dependence on monomer. It appears that sluggish radicals are formed by chain transfer to solvent. A kinetic scheme is proposed to account for these observations.