miniemulsion photo-copolymerization of styrene/butyl acrylate in a continuous tubular reactor

Miniemulsion Photo-Copolymerization of Styrene/Butyl Acrylate in aContinuous Tubular ReactorRadmila Tomovska,†,‡ Jose C. de la Cal,† and Jose M. Asua*,†

†POLYMAT and Departamento de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country UPV/EHU,Joxe Mari Korta zentroa, Tolosa Etorbidea 72, Donostia-San Sebastian 20018, Spain‡IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

*S Supporting Information

ABSTRACT: The 40 wt % solids content styrene/butyl acrylate miniemulsion photopolymerization was successfully carried outin a continuous tubular reactor. The effect of the type and concentration of photoinitiator (PI), the incident light irradiance(ILI), and the residence time on polymerization kinetics and polymer microstructure was investigated. An optimal value for theILI that maximizes monomer conversion was found. The shape of the molecular weight distribution (monomodal versusbimodal) can be varied by modifying the particle size and the type of photoinitiator.

1. INTRODUCTIONThe use of photoinitiators in free radical polymerization isappealing because it allows better control of the initiatingprocess. The reported photopolymerizations in dispersed mediainclude works in emulsion,1−6 miniemulsion,7−13 and micro-emulsion.14−17 However, most of these works were carried outin batch reactors, where the irradiation is not efficiently usedbecause of the limited penetration depth of the light in thedispersed media.Tubular reactors overcome this limitation and in addition

offer the advantage of an easy removal of the polymerizationheat. Tubular reactors have been used to synthesize hybridpolyurethane/acrylics pressure sensitive adhesives by mini-emulsion polymerization12 and ultrahigh molecular weightpolystyrene by emulsion polymerization.6 However, theseworks were performed at solids content (20 wt %), which aretoo low for commercial use. Higher solids contents are prone tosuffer coagulation caused by the preferential interaction of theorganic phase with the reactor wall.13 A way to overcome thislimitation is to modify the reactor wall for the first part of thereactor (until reaching about 45% monomer conversion).13 Inspite of these advances, further investigation is needed to fullyexploit the possibilities of this technique.In this work, the photoinitiated miniemulsion copolymeriza-

tion of styrene and butylacrylate carried out in a tubular reactoris studied. A relatively high solids content (40 wt %) was usedand the effects of the photoinitiator type and concentration,incident light irradiance (ILI), and residence time (τ) on thepolymerization kinetics and polymer microstructure wereinvestigated.

2. EXPERIMENTAL SECTION2.1. Materials. Technical grade monomers, styrene (S,

Quimidroga), and butyl acrylate (BA, Quimidroga) were usedas received. To prepare the miniemulsions, Dowfax 2A1 (alkyldiphenyloxide disulfonate, Dow Chemicals), was used as asurfactant, n-octadecyl acrylate (SA, Aldrich) as a reactivecostabilizer, and sodium bicarbonate (NaHCO3, Aldrich) as a

buffer. All of them were used as received. As SA is notcompletely insoluble in water, it may diffuse from small to largedroplets, reducing its efficiency as a costabilizer. Therefore,polystyrene (PS, Mw = 280.000 g/mol, Aldrich) was added toincrease the miniemulsion stability. The role of PS was tominimize the diffusion of SA, which in turn minimizes dropletdegradation by monomer diffusion.18 Nonbleaching (2,2-dimethoxy-2-phenyl acetophenone (DMPA), ε ∼ 35 L/molcm, Aldrich) and photobleaching (bis acyl phosphine oxide(BAPO), ε ∼ 300 L/mol cm, BASF; 2,4,6,-trimethylbenzoyldi-phenylphosphine oxide (MBPO), ε ∼ 520 L/mol cm, BASF)oil-soluble photoinitiators were used as received. Oxygen-freegrade nitrogen was used for purging the feed. Double deionizedwater (DDI) was used throughout this study.

2.2. Formulation. The formulation of the 40 wt % solids S/BA miniemulsion used in the study is given in Table 1. Allpolymerizations were carried out at 60 °C.

Special Issue: John Congalidis Memorial

Received: August 23, 2013Revised: November 12, 2013Accepted: December 12, 2013Published: December 12, 2013

Table 1. Formulation of the St/BA Miniemulsion

40 wt % solids content St/BA miniemulsion

component amount (g) weight %

organic phase S 35 50a

BA 35 50a

SA 2.8 4a

PS 1.4 2a

PI 0.35−1.05 0.5−1a

aqueous phase DDI-water 105Dowfax 2A1 3.206 2(45 wt % active)a

NaHCO3 0.23 0.05 Mb

aWeight based on monomer weight (wbm). bBased on water weight.

Article

pubs.acs.org/IECR

© 2013 American Chemical Society 7313 dx.doi.org/10.1021/ie402779y | Ind. Eng. Chem. Res. 2014, 53, 7313−7320

pubs.acs.org/IECR

2.3. Miniemulsion Preparation. 40 wt % solids contentminiemulsions were prepared by mixing the organic andaqueous phases (Table 1) under magnetic stirring (15 min at1000 rpm) and subjecting the resulting coarse emulsion tosonication (15 min, at 9 output control and 80% duty cycle)with a Branson 450 instrument (Danbury, CT). The diameterof the miniemulsion droplets as measured by dynamic lightscattering was around 140 nm.2.4. Reactor Setup. A continuous tubular reactor

composed of 11 quartz tubes connected with each other with10 semicircular silicone bends with 2 mm inner diameter wasused throughout this study. Each quartz tube had 400 mmlength, 1 mm inner diameter, and 3 mm outer diameter. Thetotal length of the reactor was 4.67 m. The reactor was placedin a water bath that was inside an UV chamber (Dr. GrobelUV-Elektronik GmbH, model BS 03), equipped with 20 UVlamps (wavelength range from 315 to 400 nm with a maximumintensity at 368 nm). A radiometer UV sensor was used tomeasure the incident light irradiance (ILI), which was varied inthe range 2.5−7 mW/cm2. A gear pump (Gilson, model 305)was utilized to control the miniemulsion flow rate (0.14−0.43mL/min). All runs were carried out under laminar conditions(Re ≤ 61). The feeding tank of the miniemulsion was purgedwith nitrogen, under magnetic stirring at 450 rpm for 30 minprior to starting the reaction. The reaction samples werecollected after reaching the steady-state conditions (>4residence times). In preliminary experiments, it was determinedthat (i) the irradiation of the miniemulsion without PI did notlead to any monomer conversion and (ii) no polymerization ofthe monomers took place in the presence of initiator at roomtemperature without UV irradiation.2.5. Characterization. Stability of the miniemulsion at 25

and 60 °C was measured by recording the backscattering signalof the dispersion (TurbiscanLAB equipment) every 15 min for5 h. The evolution of the backscattering signal over time givesan indication of the miniemulsion stability: no change in thebackscattering signal over time is the fingerprint of a stableminiemulsion.It has been recently demonstrated that reactor clogging

occurs when the interfacial tension monomer/wall (γms) islower than that of the aqueous phase/wall (γws).

13 Under theseconditions, monomer diffuses to the reactor wall where it ispolymerized. Accumulation of polymer at the reactor wallresults in plugging. Therefore, the ratio γws/γms provides a faciletest to check if a given miniemulsion will lead to plugging in thequartz tubular reactor. This is assessed by measuring thecontact angle of a droplet of an aqueous solution of surfactantsurrounded by the monomer mixture on a quartz cuvette. If thecontact angle is less than 90°, then γws/γms < 1 and no reactorclogging is expected.13

To measure the miniemulsion droplet and polymer particleaverage diameters, dynamic light scattering was used. Measure-ments were carried out in a Zetasizer Nano Z (MalvernInstruments) by diluting one drop of latex or miniemulsion indeionized water. The z-average diameters reported are anaverage of two measurements, and each of them was analyzedin 11 runs of 30 s.The monomer conversion was followed gravimetrically. In

order to determine the polymer microstructure, the gel contentand sol molecular weight distribution were measured. The gelcontent was determined by Soxhlet extraction. 10−15 latexdrops were deposited on glass fiber square pads (weight W1)and dried 12 h at 60 °C (weight W2), followed by 24 h of

Soxhlet extraction under THF reflux. After the extraction, thepads were dried overnight (weight W3). The gel content wascalculated as the ratio of the dry polymer remaining after theextraction and the initial amount of dry polymer

= −−

·W WW W

gel content (wt %)3 12 1

100(1)

Size exclusion chromatography (SEC) was utilized formeasuring the MWD of the sol part obtained in the Soxhletextraction. The system consisted of a pump (Waters 2410), UV(Waters 2487) and RI (Waters 2410) detectors, and threecolumns in series (Styragel HR2, HR4, and HR6; with a poresize of 102−106 Å). The analyses were performed at 35 °C withTHF as the carrier at a flow rate of 1 mL/min. The equipmentwas calibrated using polystyrene standards (fifth order universalcalibration), and therefore, the molecular weights presented inthis study were referred to polystyrene.

2.6. Particle Separation Procedure. A 20 mL portion oflatex was centrifuged in 38.5 mL polyallomer tubes (Beckman),in a TFT 70.38 fixed-angle rotor using a Centrikon T-2190centrifuge (both Kontron Instruments, Milano, Italy) at 4 °Cfor 2 h at 15 000 rpm. Four color distinctive fractions wereobtained. The samples for MWD determination were collectedfrom the top and bottom fractions, namely, from the fractionswith the highest differences in particle diameter.

3. RESULTS AND DISCUSSION3.1. Miniemulsion Stability and Clogging Test. Figure 1

shows the evolution of the light backscattered by the

miniemulsion at 60 °C. It can be seen that almost no variationwas observed in 5 h, showing that the miniemulsion was stableat least for this period of time.Figure 2 shows that the contact angle of the aqueous solution

of surfactant surrounded by the monomers on quartz was lessthan 90°; therefore, γws/γms < 1 and no reactor clogging wasexpected.

3.2. Reaction Kinetics. The kinetics of the S/BAminiemulsion photopolymerization in the quartz tubularreactor was investigated varying the PI type and concentration,ILI, and residence time. The photolysis of DMPA, BAPO, andMBPO is presented in Scheme 1. DMPA is oil soluble, is notphotobleaching, and has an extinction coefficient of 32 L mol−1

cm−1 at 365 nm. After light absorption, benzoyl and methylradicals are generated (see Scheme 1a).19 BAPO and MBPOare oil soluble photobleaching PIs with high extinctioncoefficients (ε ∼ 300 and 520 L mol−1 cm−1, respectively, at

Figure 1. Time evolution of light backscattered by the S/BAminiemulsion.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie402779y | Ind. Eng. Chem. Res. 2014, 53, 7313−73207314

365 nm), which after cleavage of the C−P bond producebenzoyl and phosphinoyl radicals (Scheme 1b and c). Theseradicals are efficient in initiating the polymerization; thephosphinoyl radicals have a higher rate coefficient than thebenzoyl radicals for addition to carbon−carbon double bonds.20The phosphinoyl radical formed from BAPO can suffer a

second photolysis (Scheme 1b). The double radical formed hasbeen used to synthesize ultrahigh molecular weight polymers ina tubular reactor.6

The kinetics of the S/BA miniemulsion photopolymerizationinitiated with DMPA is presented in Figure 3. For most of thecases (Figure 3c and d), a decrease of the particle size with theresidence time was observed. This decrease cannot be onlyexplained by the shrinkage due to the higher density of thepolymer, and it is likely due to secondary homogeneousnucleation occurring mainly at higher residence times.On the other hand, monomer conversion increased with

initiator concentration and residence time. However, intensify-

ing the irradiation from 3.5 to 7 mW cm−2 had a very modesteffect on polymerization rate at low values of residence timeand led to lower conversions at higher residence times.Actually, for the three different concentrations of DMPA used,the monomer conversion achieved at τ = 30 min showed amaximum for intermediate values of ILI (Figure 4).The occurrence of a maximum in the conversion versus ILI

curves was explained as follows. An increase of ILI acceleratesthe photolysis of the initiator and consequently the formationof radicals. The result is that plenty of radicals are formed in thefirst part of the reactor, which accelerates the polymerization,but the PI is exhausted sooner and the polymerization stops.While the rate of decomposition of PI is such that it does notdisappear for the residence time considered (30 min in Figure4), monomer conversion increases with ILI, but for ILIs thatlead to the complete consumption of the PI at residence timeslower than 30 min, monomer conversion decreases with ILI.An increase in the concentration of DMPA results in a less

pronounced maximum. Also, as the DMPA concentrationincreases, the relative differences in monomer conversion arelower, because the penetration depth of UV light decreases withPI concentration and at high conversions there is less room forconversion increase.In order to check if the maximum in the conversion versus

ILI curve is particular for DMPA or it is a characteristic featureof photopolymerization, the other two PIs with much higherextinction coefficient were selected (MBPA and BAPO) andthe influence of ILI on conversion was investigated. Figure 4shows that the maxima were even more pronounced, indicatingthat the occurrence of the maximum is a characteristic ofphotopolymerization in tubular reactors.

3.3. Polymer Microstructure. None of the latex obtainedcontained gel. The reason was the relatively high S/BA ratioused in the experiments. In acrylic containing latexes, gel isformed by intermolecular chain transfer to polymer followed bytermination by combination.21 Styrene is not prone to sufferchain transfer to polymer because it does not have labile

Figure 2. Drop of aqueous solution of surfactant in the monomermixture on quartz substrate.

Scheme 1. Photolysis of (a) DMPA, (b) BAPO, and (c) MBPO Photoinitiators



hydrogen. In addition, styrene radicals are not particularlyactive to abstract the tertiary hydrogen of the BA units in thepolymer.22

Figure 5 shows the effect of the residence time on the MWDfor different ILIs. It can be seen that a bimodal MWD wasobtained at low residence times and that the relative intensity ofthe low molecular weight peak decreased as the residence timeincreased. In addition, the bimodality was more marked at highILI.The presence of the two peaks indicates the existence of two

mechanisms or two polymerization environments. Differencesin the mechanisms may be caused by monomer compositiondrift due to the differences in the reactivity ratios (rS = 0.88:rBA= 0.223). As styrene is more reactive, one may speculate that thelow molecular weight peak, which is more evident for lowresidence times, is richer in styrene. The lower kp of styrene

24,25

Figure 3. Effect of residence time and ILI on monomer conversion and particle size for different concentrations of DMPA (a, c) 0.23 mol % and (b,d) 0.5 mol %.

Figure 4. Effect of ILI on monomer conversion for different types andconcentrations of PI at a residence time of 30 min.

Figure 5. Effect of the residence time on the MWD with 0.23 mol % DMPA for (a) ILI = 7 mW/cm2 and (b) ILI = 3.5 mW/cm2.



and the absence of chain transfer to polymer would justify thesmaller molecular weight.In order to check this point, the MWDs determined with

refractive index (signal proportional to the total mass) and UV(able to detect only S units) detectors were compared (Figure6). In polymers with unimodal or slightly bimodal MWD(Figure 6a), no differences were observed, indicating that thestyrene units were homogeneously distributed in the wholesample. However, in samples with bimodal distributions(Figure 6b), although the MWDs determined by both detectorswere still bimodal, the relative contributions of both peakschanged. Figure 6b clearly shows that the polymers with lowmolecular mass contain a fraction of styrene units larger thanthe polymers with higher molecular weights. The inhomoge-neous distribution of styrene units indicates that thecomposition drift may contribute to the bimodal MWD, butthis effect was not sufficient to explain the clear separationbetween the two peaks of the bimodal MWDs. Therefore,attention was turned toward the number of radicals. Becauseparticle size (dp) plays a major role in determining the numberof radicals per particle, the effect of dp on the MWD wasstudied by separating the particles by centrifugation. Figure 7shows that indeed the MWD depended on the particle size.Figure 7a shows that the MWD evolved from bimodal for the

large particles (180 nm) to monomodal for the small particles(88 nm). The MWDs obtained for the intermediate sizespresented in Figure 7b give additional proof for the evolutionfrom monomodal to bimodal MWD as particle size increases.

In this process, as oil soluble initiators are used, radicals areformed in pairs within the polymer particles. Thus, benzoyl andmethyl radicals are created by photolysis of DMPA (Scheme1a). In the small particles, these radicals will undergo fasttermination, unless one of them desorbs from the particle.26

Rapid termination will lead to a small amount of low molecularweight polymer, difficult to detect in SEC. On the other hand,radical desorption will strongly increase the molecular weight.Considering that styryl radicals have a non-negligible rate ofdesorption,27 the less hydrophobic and more mobile methylradicals are expected to desorb more rapidly. Even benzoylradicals may contribute to radical desorption. Radicaldesorption is largely controlled by the competition betweenthe diffusion and propagation. The rate of addition of the firstBA unit to the benzoyl radical has been determinedexperimentally to be 1.8 × 105 L mol−1 s−1 at 25 °C.28 For aBA concentration of 3.4 mol L−1, this gives a pseudo-first-orderpropagation rate coefficient of 6 × 105 s−1. Comparison of thisvalue with the rate of desorption of benzoyl radicals fromsodium dodecyl sulfate micelles (1.7 × 106 s−1)29 shows thatdesorption of benzoyl radical may be significant even thoughlower desorption rates are expected for polymer particles (dueto the size effect on radical desorption26). Therefore, one of theinitiator radicals may desorb from the small polymer particlesand the remaining one may grow to give high molecular weightpolymer chains. In large particles, the radical desorption is lesslikely, and hence, the amount of high molecular weightpolymers is less. On the other hand, bimolecular radical

Figure 6. Comparison of MWD curves obtained by UV and RI detectors: (a) DMPA = 0.23 mol %, ILI = 3.5 mW cm−2, 20 min residence time; (b)DMPA = 0.7 mol %, ILI = 3.5 mW cm−2, 30 min residence time.

Figure 7. MWD in the particles with different size: (a) 3.5 mW cm−2, DMPA = 0.23 mol %, 10 min residence time; (b) 7 mW cm−2, DMPA = 0.5mol %, 30 min residence time.



termination is also less likely than in small particles, and theradicals may grow to a significant length before terminating,leading to molecular weights smaller than those produced byradicals that grow alone. The result is that a bimodal MWD isproduced in large particles.The bimodality becomes less defined as polymerization

advances, and for the final sample, it is reduced to a shoulder. Apossible reason for this behavior is that, as the reactionadvanced, the termination rate decreased, increasing thelifetime of the radicals, and hence the polymer resulting frombimolecular termination had a molecular weight intermediatebetween the small and large peaks of the initial MWD.Figure 8a shows that MBPO presented an evolution of the

MWD similar to that of DMPA (Figure 5), likely due to thesimilar decomposition mechanism, which seems to counteractthe differences in the extinction coefficient and the fact thatMBPO is photobleaching, whereas DMPA is not. The effect ofthe decomposition mechanism is highlighted in Figure 8b,where the effect of ILI on the MWD in the polymerizationinitiated with BAPO is presented. It can be seen that, even at τ= 30 min, this photoinitiator led to a much more pronouncedbimodal distribution for the whole range of ILI used. Evenmore, two peaks can be distinguished in the high molecularweight mode. The effect of the particle size on the MWD whenBAPO was used is presented in Figure 9.It can be seen that, for both small (113 nm) and large

particles (178 nm), a bimodal distribution was obtained,although the relative area of the modes varied with the particlesize. For large particles, the low molecular weight peak was thehigher one, whereas the opposite occurred for the smallerparticles. Comparison with the case of DMPA (Figure 7a)shows that, for similar particle sizes, BAPO yielded a moreprominent small molecular weight peak and higher molecularweights for the second mode. The more prominent smallmolecular weight peak indicates that bimolecular termination ismore frequent in the case of BAPO likely due to lowerdesorption rates of the radicals generated by photolysis of theinitiator. The presence of a high molecular weight peak showsthat some radical desorption occurred. On the other hand, thepeak of high molecular weight comprises two distributions, thelarge one likely formed from the double phosphynoil radical.

4. CONCLUSIONSIn this work study, the high solids S/BA miniemulsionphotopolymerization carried out in a continuous tubularreactor was investigated. The effect of the PI type andconcentration, ILI, and residence time on reaction kinetics andpolymer microstructure was investigated. It was found thatmonomer conversion increased with PI concentration andresidence time, but the effect of ILI was more complex, showingan optimum value that maximizes monomer conversion. At lowILIs, monomer conversion at τ = 30 min increased with ILI, butat higher ILIs, it decreased with ILI because the PI wasexhausted in the first part of the reactor of the monomers. Theeffect is less pronounced at higher PI concentrations.Photopolymerization led to bimodal MWDs. The bimodality

was mainly caused by the effect of particle size, with a smallcontribution of the monomer composition drift due to thedifferent reactivities of the monomers. It was found that, for

Figure 8. Molecular weight distribution (a) evolution with residence time, for 1% of MBPO and ILI 2.5 mW/cm2; (b) effect of ILI for 1% BAPOand τ = 30 min.

Figure 9. Effect of particle size on the MWD of the latex synthesizedwith BAPO and following conditions (3.5 mW cm−2, PI = 0.23 mol %,τ = 10 min).



initiators that yield two radicals upon photolysis, the MWDshifted from monomodal for small particles to bimodal for largeparticles. The peak of small molecular weights was attributed tochains formed by bimolecular termination of the active chainscreated from the radicals formed from the same photoinitiatormolecule, whereas the high molecular weight peak wasattributed to the polymer formed from initiator radicalswhose pair had desorbed from the polymer particle. Thebimodality was more pronounced in the case of a photoinitiator(BAPO) able to yield four radicals (two of them on the samemolecule) upon suffering two photolysis.

■ ASSOCIATED CONTENT*S Supporting InformationFigures showing particle size distributions of different latexfractions, separated by centrifugation. This material is availablefree of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: [email protected].

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSDiputacion Foral de Gipuzkoa, University of Basque Country(UFI 11/56), Basque Government (GVIT373-10 and EtortekNanoiker IE11-304), and Ministerio de Economia y Com-petitividad (CTQ2011-25572) are gratefully acknowledged fortheir financial support.

■ REFERENCES(1) Shim, S. E.; Shin, Y.; Jun, J. W.; Lee, K.; Jung, H.; Choe, S. Living-free-radical emulsion photopolymerization of methyl methacrylate by asurface active iniferter (Suriniferter). Macromolecules 2003, 36, 7994.(2) Hu, X.; Zhang, J.; Yang, W. Preparation of transparentpolystyrene nanolatexes by an UV-induced routine emulsion polymer-ization. Polymer 2009, 50, 141.(3) Fisher, O. Z.; Peppas, N. A. Polybasic nanomatrices prepared byUV-initiated photopolymerization. Macromolecules 2009, 42, 3391.(4) Zang, L.; Guo, J.; Luo, J.; Zhang, H. Synthesis andcharacterization of fluorine-containing polyacrylate latex with core−shell structure by UV-initiated seeded emulsion polymerization. Polym.Adv. Technol. 2012, 23, 15.(5) Zhang, H.; Li, C.; Zang, L.; Luo, J.; Guo, J. Preparation of Bead−String Shaped Attapulgite/Poly(methyl methacrylate) Particles bySoapless Emulsion Polymerization Based on UV Irradiation in thePresence of Iron(III). J. Macromol. Sci., Part A: Pure Appl. Chem. 2012,49, 154.(6) Laurino, P.; Hernandez, H. F.; Bra uer, J.; Kruger, K.;Grutzmacher, H.; Tauer, K.; Seeberger, P. H. Snowballing RadicalGeneration Leads to Ultrahigh Molecular Weight Polymers. Macromol.Rapid Commun. 2012, 33, 1770.(7) Taniguchi, T.; Takeuchi, N.; Kobaru, S.; Nakahira, T. Preparationof highly monodisperse fluorescent polymer particles by miniemulsionpolymerization of styrene with a polymerizable surfactant. J. ColloidInterface Sci. 2008, 327, 58.(8) Tonnar, J.; Pouget, E.; Lacroix-Desmazes, P.; Boutevin, B.Synthesis of poly(vinyl acetate) − block - poly(dimethyl siloxane) −block - poly(vinyl acetate) copolymers by iodine transfer photo-polymerization in miniemulsion. Macromol. Symp. 2009, 281, 20.(9) Chemtob, A.; Kunstler, B.; Croutxe-Barghorn, C.; Fouchard, S.Photoinduced miniemulsion polymerization. Colloid Polym. Sci. 2010,288, 579.

(10) Hoijemberg, P. A.; Chemtob, A.; Croutxe-Barghorn, C.; Poly, J.;Braun, A. M. Radical photopolymerization in miniemulsions.Fundamental investigations and technical development. Macro-molecules 2011, 44, 8727.(11) Hoijemberg, P. A.; Chemtob, A.; Croutxe-Barghorn, C. Tworoutes towards photoinitiator-free photopolymerization in miniemul-sion: acrylate self initiation and photoactive surfactant. Macromol.Chem. Phys. 2011, 212, 2417.(12) Daniloska, V.; Tomovska, R.; Asua, J. M. Hybrid miniemulsionphoto polymerization in a continuous tubular reactor A way toexpand the characteristics of polyurethane/acrylics. Chem. Eng. J. 2012,184, 308.(13) Daniloska, V.; Tomovska, R.; Asua, J. M. Designing tubularreactors to avoid clogging in high solids miniemulsion photo-polymerization. Chem. Eng. J. 2013, 222, 136.(14) Jain, K.; Klier, J.; Scranton, A. B. Photopolymerization of butylacrylate-in-water microemulsions: polymer molecular weight and end-groups. Polymer 2005, 46, 11273.(15) Peinado, C.; Bosch, P.; Martin, V.; Corrales, T. Photoinitiatedpolymerization in bicontinuous microemulsions: fluorescence mon-itoring. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 5291.(16) Wan, T.; Hu, Z. W.; Ma, X. L.; Yao, J.; Lu, K. Synthesis of silanemonomer-modified styrene−acrylate microemulsion coatings byphotopolymerization. Prog. Org. Coat. 2008, 62, 219.(17) Zhang, L.; Zang, L.; Zhang, H.; Guo, J. Synthesis of fluorine-containing latexes with core−shell structure by UV-initiated micro-emulsion polymerization. Iran. Polym. J. 2013, 22, 93.(18) Asua, J. M. Miniemulsion Polymerization. Prog. Polym. Sci. 2002,27, 1283.(19) Groenenboom, C. J.; Hageman, H. J.; Overeem, T.; Weber, A. J.M. ″Photoinitiators and photoinitiation. 3. Comparison of thephotodecompositions of alpha-methoxy-and alpha, alpha-dimethox-ydeoxybenzoin in 1,1-diphenylethylene as model substrate. Macromol.Chem. Phys. 1982, 183, 281.(20) Rutsch, W.; Dietliker, K.; Leppard, D.; Kohler, M.; Misev, L.;Kolczak, U.; Rist, G. Recent developments in photoinitiators. Prog.Org. Coat. 1996, 27, 227.(21) Plessis, C.; Arzamendi, G.; Leiza, J. R.; Schoonbrood, H. A. S.;Charmot, D.; Asua, J. M. Seeded Semibatch Emulsion Polymerizationof n-Butyl Acrylate. Kinetics and Structural Properties. Macromolecules2000, 33, 5041.(22) Plessis, C.; Arzamendi, G.; Leiza, J. R.; Schoonbrood, H. A. S.;Charmot, D.; Asua, J. M. Kinetics and polymer microstructure of theseeded semibatch emuslion copolymerization of n-butylacrylate andstyrene. Macromolecules 2001, 34, 5147.(23) Chambard, G.; Klumperman, B.; German, A. L. Dependence ofchemical composition of styrene/butyl acrylate copolymers ontemperature and molecular weight. Polymer 1999, 40, 4459.(24) Buback, M.; Gilbert, R. G.; Hutchinson, R. A.; Klumperman, B.;Kuchta, F. D.; Manders, B. G.; O’Driscoll, K. F.; Russell, G. T.;Schweer, J. Critically evaluated rate coefficients for free-radicalpolymerization, 1. Propagation rate coefficient for styrene. Macromol.Chem. Phys. 1995, 196, 3267.(25) Asua, J. M.; Beuermann, S.; Buback, M.; Castignolles, P.;Charleux, B.; Gilbert, R. G.; Hutchinson, R. A.; Leiza, J. R.; Nikitin, A.N.; Vairon, J. P.; van Herk, A. M. Critically Evaluated Rate Coefficientsfor Free-Radical Polymerization, 5a,b. Propagation Rate Coefficient forButyl Acrylate. Macromol. Chem. Phys. 2004, 205, 2151.(26) Autran, C.; de la Cal, J. C.; Asua, J. M. (Mini)emulsionPolymerization Kinetics Using Oil-Soluble Initiators. Macromolecules2007, 40, 6233.(27) Asua, J. M.; de La Cal, J. C. Entry and Exit Rate Coefficients inEmulsion polymerization of Styrene. J. Appl. Polym. Sci. 1991, 42,1869.(28) Colley, C. S.; Grills, D. C.; Besley, N. A.; Jockusch, S.;Matousek, P.; Parker, A. W.; Towrie, M.; Turro, N. J.; Gill, P. M. W.;George, M. W. Probing the Reactivity of Photoinitiators for FreeRadical Polymerization: Time-Resolved Infrared Spectroscopic Studyof Benzoyl Radicals. J. Am. Chem. Soc. 2002, 124, 14952.



http://pubs.acs.org

mailto:[email protected]

(29) Turro, N. J.; Wu, C.-H. Laser Flash Spectroscopic Investigationof Micellized Radical. J. Am. Chem. Soc. 1995, 11, 11031.



miniemulsion photo-copolymerization of styrene/butyl acrylate in a continuous tubular reactor

Documents