Neat Monomer Research Articles

Functionalization of Surfaces by Water-Accelerated Atom-Transfer Radical Polymerization of Hydroxyethyl Methacrylate and Subsequent Derivatization

We report the synthesis of unusually thick poly(2-hydroxyethyl methacrylate) (PHEMA) films on gold surfaces by surface-initiated atom transfer radical polymerization (ATRP). Polymerization from the surface occurs rapidly at room temperature in aqueous media, resulting in the formation of 700 nm thick polymer films in just 12 h. Control experiments using neat monomer and catalyst (no water) yield films with thicknesses of only 6 nm, demonstrating the accelerating effect of water on surface-initiated ATRP. Kinetic studies reveal a nearly linear increase in thickness with reaction time, indicating that chain growth from the surface is a controlled process with some “living” character. A second block can be grown from dormant initiators at the end of PHEMA chains, providing further evidence of “living” chain ends. Derivatization of the hydroxyl groups of grafted PHEMA with a variety of molecules allows dense functionalization of these films. Reflectance FTIR spectroscopy shows a virtually quantitative yield i...

Fast pH- and Ionic Strength-Responsive Hydrogels in Microchannels

A simple method for the preparation of pH- and ionic strength-sensitive hydrogels that exhibit fast response times is described. Patterned hydrogel objects were prepared inside microchannels by photopolymerization of monomer mixtures containing water and surfactant. The swelling process, initiated by an abrupt change in pH, exhibited second-order kinetics. Compared to conventional hydrogels synthesized from a neat monomer mixture alone, the new hydrogels swell and shrink faster by approximately one order of magnitude. Fully swollen hydrogels prepared from mixtures containing water and surfactant were observed to be sensitive to ionic strength changes. The effects of cross-linking density and acrylic acid composition on the response rate were investigated and were found to have little effect on response times. The fast response was thus attributed to the porous structure generated from the surfactant phase template during the polymerization.

Highly Reactive 2,5-Disubstituted Styrene-Based Monomer Polymerized via Stable Free Radical Polymerization: Effect of Substitution and Liquid Crystallinity on Polymerization

The stable free radical polymerization (SFRP) of a liquid crystalline monomer 2,5-bis[(4-butylbenzoyl)oxy]styrene, BBOS, was investigated. BBOS is a substituted styrenic monomer, which polymerizes an order of magnitude faster than styrene under identical bulk polymerization conditions. A comparative study of the polymerization behavior in bulk and solution for BBOS and a model compound was undertaken to elucidate the effect of both electron-withdrawing substituents and liquid crystallinity of the monomer on the polymerization kinetics. Molecular simulation was used to identify a non-LC model monomer, 2,5-diacetoxystyrene (DAS). DAS was polymerized by stable free radical polymerization both in bulk and in solution. In all cases narrow molecular weight distribution (<1.4) was obtained. In bulk, DAS polymerized significantly slower than BBOS, whereas in a dilute solution, the rate of polymerization was quite similar. In-situ X-ray studies carried out during polymerization of BBOS in the neat monomer indicate the presence of a nematic phase which could lead to localized ordering of the monomers during polymerization. In comparison, DAS was found to be more reactive than styrene, because of the electronic effect of the acetoxy groups. However, p-acetoxystyrene (PAS) was found to have almost the same observed rate of polymerization as DAS, indicating that steric factors also play an important role in O-substituted compounds.

Agitation effects in the semicontinuous emulsion polymerization of styrene and butyl acrylate

The effect of agitation on the semicontinuous emulsion copolymerization of styrene and butyl acrylate was investigated. Both neat monomer addition and preemulsified feed were used. Experiments with and without a chain-transfer agent were carried out. For neat monomer addition, a mild degree of agitation (≥ 0.1 kW/m3) was required to avoid monomer mass-transfer limitations, but even a moderate degree of agitation (0.3 kW/m3) was not enough to overcome the CTA mass-transfer limitations. Agitation was much less critical when preemulsified feeds were used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 841–851, 2001

Study of different types of monomer emulsion feedings to semibatch emulsion polymerization reactors

Semibatch emulsion polymerization processes with a monomer emulsion feed are of great importance in both academia and industry. Monomer emulsion feeds can be applied to semibatch reactors using either a stream of an emulsified monomer or two streams of a neat monomer feed and an aqueous solution of an emulsifier. The effect of the feeding policy on the rate of polymerization and on the secondary particle formation was studied for a seeded semibatch emulsion polymerization of styrene. When a single-stream monomer emulsion feed is applied to a semibatch process, the monomer-swollen micelles formed in the feed might become the locus of initiation upon entering the reaction vessel. Under the conditions of this study, the application of monomer emulsion feed in either one stream or two streams did not result in secondary particle formation. The incoming monomer-swollen micelles were disintegrated to supply emulsifier molecules for the stability of growing particles, before they can capture radicals and become polymer particles. The rate of polymerization was found to be independent of the way that the monomer emulsion feed is added. In the absence of nitrogen, the rate of polymerization decreased more appreciably for the monomer emulsion feed, due to the oxygen dissolved in the emulsified monomer. The number of particles, however, was not affected by the purging policy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2472–2477, 2001

Semibatch emulsion polymerisation reactors: polybutyl acrylate case study

Semibatch emulsion polymerisation of butyl acrylate with neat monomer feed in the presence of sodium lauryl sulphate as emulsifier and potassium persulphate as initiator was investigated. The effects of monomer feed rate, emulsifier concentration, initiator concentration, temperature, and pre-period time on the kinetic features were studied. It was shown that a steady state is established which can be best described by the correlation suggested by Wessling as 1/ R p =1/ K+1/ R a . An expression was derived for instantaneous monomer conversion which can predict the effects of important variables such as feed rates, seed composition, and seed contents on the evolution of steady state. Those predictions were compatible with the experimental results. For all practical purposes, it was shown that the time it takes to reach the near steady-state increases with monomer feed rate for non-swollen particles, and decreases with monomer feed rate for monomer-swollen particles. However, the time required to reach the real steady state is always minimum at the lowest monomer feed rate for all seed compositions. Pre-period time was shown to have considerable effects on the time required to reach a steady state, but had no appreciable effects on the final number of particles formed or on the steady-state rate of reaction at the conditions studied. However, the particle nucleation process was influenced by the size of the initial monomer charge and by the duration of the pre-period. The average number of radicals per particle reached a steady-state value early in the polymerisation. Polymerisation rate and particle number both increased with temperature.

Unseeded semibatch emulsion polymerization of butyl acrylate: Bimodal particle size distribution

Unseeded semibatch emulsion polymerization of butyl acrylate (BA) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator was carried out at the conditions where secondary nucleation was probable. This was achieved by using no emulsifier in the initial reactor charge. The effects of changes in monomer emulsion feed rate, initiator concentration and distribution, emulsifier concentration in the feed, and temperature on the evolution of particle size averages and distribution were investigated. Bimodal particle size distributions (PSD) were obtained for most of the latexes. Inhibition effects were found to be important in the development of PSD. Primary particle formation occurred through micellar nucleation, whereas secondary nucleation probably occurred through homogenous nucleation. The polydispersity index (PDI) of the latexes increased with the decreasing monomer emulsion feed rate. The application of a larger amount of initiator to the reactor charge or using a higher temperature, reduced the formation of secondary particles and resulted in a formation of an unimodal PSD. The overall steady-state rate of polymerization was found to approach the rate of monomer addition (Rp ≈ Ra ), if the emulsifier concentration in the aqueous phase was appreciable. This is different from the correlation 1/Rp = 1/K + 1/Ra obtained for the BA semibatch process with neat monomer feed. This suggests that different rate expressions can be used for BA semibatch emulsion polymerization at different conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 528–545, 2000

Controlled Cationic Polymerization of p-Methoxystyrene in Aqueous Media with Yb(OTf)3

This study shows that ytterbium triflate [Yb(OTf)3; OTf = OSO2CF3] induces cationic polymerizations of isobutyl vinyl ether (IBVE) and p-methoxystyrene (pMOS) in aqueous media in conjunction with the hydrogen chloride−vinyl monomer adduct [CH3−CHR−Cl; R = OiBu, C6H4−OCH3] as the initiator at room temperature. These “suspension” polymerizations are carried out by adding neat monomer and then a solution of the initiator into an aqueous solution of Yb(OTf)3 under vigorous stirring, and the polymerizations occur smoothly without being inhibited by water. Under these conditions, IBVE polymerization was uncontrolled, but pMOS can be polymerized in a controlled fashion where the molecular weight distributions (MWDs) are relatively narrow (M̄w/M̄n ∼ 1.4) and the molecular weights increase in proportion to monomer conversion. The reactions proved to be cationic, being quenched by NaOH and EtOH but not by 1,4-benzoquinone. The aqueous hydrochloric acid/Yb(OTf)3 initiating system also generates similar long-lived pMOS polymer in water. The success in such controlled cationic polymerizations in aqueous media is due to the stability of Yb(OTf)3 as well as the dormant C−Cl poly(pMOS) terminal in water.

Catalytic Synthesis of Poly(arylmethylgermanes) by Demethanative Coupling: A Mild Route to σ-Conjugated Polymers

A variety of poly(arylmethylgermanes) have been synthesized from aryldimethylgermanes in high yield via mild catalytic demethanative coupling using tetrakis(trimethylphosphine)dimethylruthenium as a convenient catalyst precursor. Polymerizations of germanes Me2GeArH (Ar = phenyl, p-tolyl, p-fluoro, p-trifluorotolyl, p-anisyl, and m-xylyl) proceed in neat monomer at room temperature. Catalyst removal can be effected by treatment of the reaction mixture with air, which gives polymer yields between 70% and 100%. Alternatively, separation of the catalyst by precipitation of the polymers from THF solution with methanol gives lower yields, but of somewhat higher molecular weight material. The new polygermanes are characterized by 1H NMR and by gel permeation chromatography (GPC) using both polystyrene standards and light scattering methods. Molecular weights calculated by polystyrene analysis fall in the ranges of Mw = 3 × 103 to 7 × 103 and Mn = 2 × 103 to 6 × 103. Values obtained from light scattering are app...

On-line monitoring, modeling, and model validation of semibatch emulsion polymerization in an automated reactor control facility

The modeling of the semibatch emulsion polymerization of styrene and its validation against data obtained from a reactor facility is presented. The model, which describes the growth of a monodisperse polystyrene seed as neat monomer is fed to the reactor, incorporates recent findings in radical diffusion and kinetics. The current controversy surrounding radical absorption into particles is handled by considering absorption via propagation, diffusion, and collision in the model. Simulation results including weight fraction polymer inside the particles and particle diameter are compared to data obtained from a custom-designed and built automated reactor control facility capable of on-line density and on-line particle diameter measurements. Good agreement between simulation results and experimental data are obtained for any of the three absorption mechanisms considered by varying only one adjustable parameter located in the absorption rate coefficient relation. A sensitivity analysis of the model to this adjustable parameter, using the program ODESSA, is also presented and shown to be an important tool in the validation procedure. Lastly, an analysis of the dynamics of the process shows the variety of phenomena that can be obtained in a semibatch reactor including regions that exhibit pseudosteady states, autoacceleration of the rate, and limiting conversion. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1553–1571, 1998

Surface modification of polyolefins by photografting of acrylic monomers

AbstractHigh‐speed surface modification of polypropylene (PP) and polyethylene (PE) films has been achieved by liquid phase photograft polymerisation of acrylic acid (AA) and hydroxypropyl acrylate (HPA). Benzophenone was used as photoinitiator to generate polymer radicals at the surface of the polyolefin film. The grafting reaction was carried out in aqueous solution or with the neat monomer, which was laminated between two PP films, in the presence of air. Under the intense illumination of a UV‐curing line, acrylic acid was grafted within seconds to polypropylene films or fabrics, which were thus made hydrophilic. Direct evidence of surface grafting was obtained through infrared spectroscopy analysis and surface energy measurements. This continuous photografting process proved to be very efficient to improve the adhesion of UV‐cured acrylate coatings on polyolefin‐made materials.

Cationic photopolymerization under visible laser light: polymerization of oxiranes with coumarin/onium salt initiator systems

The cationic bulk polymerization of oxiranes such as cyclohexene oxide and 4-vinyl cyclohexene dioxide can be induced by light in the visible wavelength range with the aid of an initiator system consisting of an onium salt and a coumarin (appropriate for applications of lasers emitting light between 400 and 500 nm). This was demonstrated by irradiating neat monomers containing either coumarin 153 (C-153) or coumarin 7 (C-7) and isoquinolinium hexafluorophosphate, diphenyliodonium hexafluorophosphate or triphenylsulfonium hexafluorophosphate with a continuous laser beam (λ inc = 488nm). The monomer conversion was limited to ca. 60% due to consumption of the coumarin and insolubility of the onium salt in the polymerizing medium at lower monomer content levels. Initiator fragments were not incorporated into the polymer. In the presence of onium salts, the photolysis of coumarins in the absence of O 2 results in proton formation: /gf(H +) = 1.3 × 10 −2 (C-7) and /gf(H +) = 2.3 × 10 −2 (C-153) and it is concluded that protons play a major role in the initiation of the polymerization.

The synthesis of a homochiral methacrylate macromonomer by polymerisation of (R)- or (S)-methyl ?-hydroxyisobutyrate

Polymerisations of either enantiomer of commercially available methyl β-hydroxyisobutyrates 1a and 1b were carried out. Ti(OBun)4 catalysed transesterification of the neat monomer generated either polymer 3 at lower temperatures (∼100°C) or homochiral macromonomer 2 at higher temperatures. Under optimal conditions for the preparation of the macromonomer 2, a soluble material (Mn 3600, Mw 7000) was produced which displayed high crystallinity as judged by X-ray powder diffraction analysis.

Free-radical frontal polymerization: self-propagating thermal reaction waves

Frontal polymerization is a mode of converting monomer into polymer via a localized reaction zone that propagates. Such fronts can exist with free-radical polymerization or epoxy curing. The necessary conditions for the existence of the free-radical frontal polymerization regime are considered. The physicochemical properties of monomers are classified in connection with complications arising in the experiments, including low conversion, convection and bubbles. The density gradient in the reaction zone leading to front decay is the most insidious problem. The analysis of forces that can withstand the Taylor instability allowed us to overcome experimental difficulties and develop approaches to polymerize low-viscosity monomers in the frontal mode. The factors affecting front shape, velocity, conversion, and molecular weight are considered.Historically, frontal polymerization has been performed in neat monomer but we have been able to obtain fronts of very reactive monomers in high-boiling-point solvents including water, DMSO and DMF. Periodic frontal polymerization modes have been observed, including single and multi-point spin modes in which ‘hot spots’(local high-temperature regions) migrate around the front as it propagates. We investigated experimentally the occurrence of the different modes as a function of the initial temperature and the intensity of heat losses and made a qualitative comparison to the results of theoretical analyses based on infinitely narrow reaction zone models.The future directions of research with frontal polymerization are considered, especially with regard to applications to materials synthesis.

Degradable Cyclooctadiene/Acetal Copolymers: Versatile Precursors to 1,4-Hydroxytelechelic Polybutadiene and Hydroxytelechelic Polyethylene

In addition to environmental issues associated with polymers possessing easily cleavable links, the selective degradation of copolymers at one of the monomer units is a convenient route to telechelic polymers. Ring-opening metathesis polymerization (ROMP) initiated by (Cy 3 P) 2 Cl 2 Ru=CHR (Cy = cyclohexyl ; Ph = phenyl ; R = CHCPh 2 or Ph) was used for the synthesis of cyclooctadiene (COD)/4,7-dihydro-1,3-dioxepin copolymers. 1,4-Hydroxytelechelic polybutadiene (HTPBD) is obtained upon fragmentation of a copolymer of COD and 4,7-dihydro-2-phenyl-1,3-dioxepin at the benzylidene acetal functionalities by stirring with acids (aqueous HCl/MeOH, aqueous H 2 SO 4 , or trifluoroacetic acid (TFAA)/MeOH in CH 2 Cl 2 ). For the benzylidene acetal the copolymerization reaction may be run in neat monomer with no additional solvent. Reaction quenching, and polymer cleavage, precipitation, and purification may be effected in one step by stirring the viscous reaction product in MeOH containing 10% HCl. A two-step procedure using trifluoroacetic anhydride (TFAA)/acetic acid (AcOH) in CH 2 Cl 2 followed by NaOMe/MeOH in THF was employed for the degradation of a COD/4,7-dihydro-1,3-dioxepin copolymer. Acetal incorporation and thus the molecular weights of the resulting telechelics are dependent upon the feed ratios. The percent methylene acetal incorporated into the COD/acetal copolymer is ∼60% of the amount of acetal in the feed (e.g., for COD/acetal feed = 2 :1, COD/acetal incorporation =∼4 :1). For the less reactive benzylidene acetal, incorporation is 40% of the amount of acetal in the feed. Polydispersities for 1,4-HTPBD prepared from the COD/benzylidene acetal copolymer are typically narrow (∼1.1-1.3). It was also demonstrated that the COD/benzylidene acetal copolymer may be simultaneously hydrogenated and degraded in one step using p-toluenesulfonohydrazide to produce hydroxytelechelic polyethylene (HTPE).

Syntheses, polymerization, and characterization of novel semifluorinated methacrylates, including novel liquid-crystalline materials

Ethyl α-(chloromethyl)acrylate was converted to a variety of new ether derivatives using triethylamine-catalyzed reaction with commercially available fluoroalkyl alcohols. Rapid, high-conversion polymerization of neat monomers occurred with AIBN at 50-70°C. Molecular weights M w ranged from 3.02x10 5 to 7.59x10 5 .

Hydrolytic stabilities of some polyurethane hydrogels

AbstractThe hydrolytic stability of some polyurethane hydrogels derived from UV‐curable urethane prepolymers and hydrophilic monomers was addressed. It was found that polyurethane hydrogels derived from prepolymers with hydrophilic polypropylene glycol soft segments were not stable when the films were cast from nonpolar solvent, whereas they are stable if the films were cast from neat monomer mix. The causes for this instability were analyzed. Spectroscopic and gel permeation chromatographic studies of the water extractables suggested that improper curing of hydrophilic monomers with the urethane prepolymers in nonpolar solvent was mainly responsible for the instability phenomenon.

Photochemical synthesis of nitroxyl free radicals in the presence of vinyl monomers

AbstractThe photochemical formation of an inhibitor in the presence of monomers and a photoinitiator offers the possibility of producing positive two‐step photoresists. As inhibitor precursor sterically hindred amines have been used in the presence of air oxygen and Rose Bengal as oxidation photosensitizer. On irradiation with visible light (546 nm). stable nitroxyle radicals are formed, which act as strong inhibitors of free radical polymerization. Hexanediol diacrylate and 2‐acryloxy‐2′‐propionyl oxydiethylether were used as monomers. The photoinitiator required for the second step polymerization is benzoin isopropyl ether, which photolyzes on irradiation at 340 n,. The quantum yield of nitroxyl radical formation has been determined in solution and in polymeric films. Polymerization inhibition experiments were carried out with methyl methacrylate in solution and with neat monomers. Though the quantum yield ΦNO° is low, especially in the last case, the experiments confirm the possibilities of this two‐step procedure.

Semicontinuous seeded emulsion copolymerization of vinyl acetate and methyl acrylate

AbstractThe semicontinuous seeded emulsion copolymerization of vinyl acetate and methyl acrylate was investigated. The effect of type of process (starved process versus semi‐starved process), type of feed (neat monomer addition versus monomer emulsion addition), amount of seed initially charged in the reactor, and feed rate on the time evolution of the overall conversion, copolymer composition, and polymer particle size was analyzed. It was found that, in the case of the starved process, both monomers, but mainly vinyl acetate, accumulated in the reactor. The preferential accumulation of vinyle acetate resulted in a drift of the copolymer composition. Both monomers accumulation and copolymer composition drift were reduced by increasing the amount of seed initially charged in the reactor and by decreasing the feed rate. For the semi‐starved process, it was found that a vinyl aceatate rich copolymer was formed when a low methyl acrylate feed was used, whereas a methyl acrylate rich copolymer was obtained at high methyl acrylate feed rates. For both starved process and semi‐starved process, the total number of polymer particles, after an initial increase, reached a plateau value which was the same in all of the experiments carried out. These results were analyzed by means of a mathematical model developed for this system.

Heat of polymerization of nine mono-, di-, and trimethacrylate esters tested neat and with low levels of peroxide by dynamic differential scanning calorimetry.

The heats of polymerization of nine methacrylate esters were measured using a differential scanning calorimeter in the dynamic mode. The esters were: allyl, 2-hydroxy ethyl, glycidyl, and tetra hydro furfuryl mono methacrylate; diethylene glycol, triethylene glycol, and poly ethylene glycol dimethacrylate; as well as trimethylol propane trimethacrylate and bis (methacrylato-2-hydroxy propoxy-4-phenyl) propane (Bis-Gma). Values ranged from 13–18 kcal per methacrylate gram equivalent weight for neat monomers, and slightly higher for monomers heated in the presence of benzoyl peroxide