Langmuir 1992,8, 1931-1936
1931
Polymerization of Microstructured Aqueous Systems Formed Using Methyl Methacrylate and Potassium Undecenoate W. R. Palmi Raj, Mohan Sasthav, and H. Michael Cheung' Department of Chemical Engineering, The University of Akron, Akron, Ohio 44325-3906 Received December 20, 1991. I n Final Form: April 14,1992 The formation of microstructured systems of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA) in water using potassium 10-undecenoate(PUD) as the surface-active agent was investigated. Phase behavior studies for this system were conducted. Characterization of the thermodynamically stable single phase domain of the phase diagram indicated microstructural order similar to Winsor-IV microemulsions at certain compositions and lyotropic liquid crystalline behavior at higher PUD concentrations. Photoinitiated polymerizations of certain microemulsioncompositions from the single phase region were conducted. Investigation of the morphology of the polymerized samples by scanning electron microscopy revealed the existence of a microporous porous structure. The continuity of the pore structure in the polymer was shown to be dependent on the microstructure of the monomer system using thermogravimetricanalysis. BET adsorption studies of the dried polymer samples indicated the surface area of the porous samples to increase with water content of the precursor microemulsions. The incorporation of the polymerizable surfactant PUD in the polymer matrix was confirmed by X-ray fluorescence measurements and extraction studies. The extent of PUD incorporation in the polymer was found to be dependent on the content of MMA and EGDMA in the precursor microemulsion.
Introduction Recently there has been considerable interest in the formation of porous polymeric solids from microstructured monomer containing aqueous systems by preserving the microstructure during the process of The present study representa acontinuation of earlier work in using single phase Winsor-IV microemulsions (thermodynamically stable single phase microstructured systems of oil, water, and amphiphileg) containing acrylic acid (AA) and methyl methacrylate (MMA)to form porous polymeric solids.8 This study utilizes 10-undecenoic acid which is an acrylic acid homolog having a long hydrocarbon moiety in the formation and polymerization of microstructured aqueous systems containing MMA and the crosslinking agent ethylene glycol dimethacrylate (EGDMA). In order to achieve surface-active properties, the potassium salt of 10-undecenoic acid was used in forming the microstructured systems. The results obtained from this study have been compared with the results of the earlier study which used AA as the amphiphile. The objective of this study was to form single phase microstructured systems containing MMA, potassium 10undecenoate (PUD), and EGDMA with water and investigate the ability of these systems to form porous solids upon polymerization. Earlier studies on the homopolymerization of sodium 10-undecenoate in micellar solutions
* Author to whom correspondence should be addressed.
(1)Qutubuddin,S.;Haque,E.; Benton,W. J.; Fendler,E. J. In Polymer Association Structures: Microemulsions and Liquid Crystals;El-Nokaly, Magda A., Ed.; ACS Symposium Series No. 3&4; American Chemical Society Washington,DC, 1989; p 64. (2)Sasthav,M.;Cheung, H. M.hngmuir 1991,7,1378. (3)Anderson, D. M.; Strom, P. In Polymer Association Structures: Microemu&ions and Liquid Crystals; El-Nokaly, Magda A., Ed.; ACS Symposium Series; No. 3&4, American Chemical Society: Washington, DC,1989; p 204. (4)Friberg, S.E.; Fang, J. J. Colloid Interface Sci. 1987,118,2,543. (5)Ruckenstein, E.; Chen, H. H. J. Appl. Polym. Sei. 1991,42,2429. (6) Menger, F. M.; Teuno,T.; Hammond, G. S. J. Am. Chem. SOC. ISSO,112,1263. (7)Stoffer, J. 0.; Bone, T. J. Diaperaion Sci. Technol. 1980,1, 393. (8)Palmi Fkj, W. R.; Sasthav, M.; Cheung, H. M.Langmuir 1991,7, 2586. (9) Winsor, P. A. Trans. Faraday SOC.1948,44,376.
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had yielded low molecular weight oligomers which were soluble in water.lOJ1 The effect of the presence of the polymerizable species MMA and EGDMA on the incorporation of PUD into the polymeric solid was examined in the present study. The microstructure of the WinsorIV systems formed was also examined. The polymeric solids obtained were characterized, and the relation between the microstructure of the Winsor-IV system and porous structure of the polymeric solid was investigated.
Experimental Section Materials. MMA and EGDMA obtained from Aldrich were of purity greater than 99%. The water used in the study was doubly-distilled. 10-Undecenoic acid was obtained from Aldrich and its potassium salt was prepared by addition of the stoichiometricamount of potassium hydroxide. The photoinitiator used for the study,2,2-dmethoxy-2phenylacetophenone(DMPA) was obtained from Aldrich. Monomer samples for polymerization were prepared by vacuum distillationfollowed by treatment for the removal of polymerization inhibitor. PhaseBehavior Studies. Samplesfor phase behavior studies were prepared by adding the required amounts of the various components into clean glass tubes which were then sealed. The compositions used throughoutthis studywere on a weight percent basis. The pH of the samples used for phase behavior studies was maintained at 10 f 0.01 using potassium hydroxide in order to have a constant ionic strength in all regions of the phase behavior diagram. The EGDMA used was measured on an EGDMA free basis and was always 4 % by weight of MMA and PUD present. The sampleswere hand shaken and equilibrated in a constant temperature water bath for a period of 48 h at 25 f 0.1 O C before making measurements. The criterion for equilibrium was the reproducibilityof phases in shaking and standing cycles. The phase boundarieswere determined with an accuracy of 3% by weight. Microemulsion Characterization. The microstructure of the microemulsions was investigated using conductivity measurements, quasielastic light scattering (QELS),and measurement of scattered intensity at 90° to the incident beam. The (10)Larrabee, C. E.,Jr.; Sprague, E. D. J. Polym. Sci., Polym. Lett. Ed. 1979,17,749. (11)Pale-, C. M.;Stassinopoulou, C. I.; Malllaris, A. J. Phys. Chem. 1983, 87, 251.
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conductivity measurements of the microemulsions were made using a Omega PHH-80 conductivity meter. The QELS and scattered intensity measurement studies were carried out on filtered microemulsion samples using a 500-mW argon ion laser source. A unique receiving optics systems12 was used which eliminated flare from the walls of the sample cell, thus enabling cylindrical sample cells to be used for the study without the use of an index matching fluid bath. A Brookhaven Instruments BI-DS ECL photomultiplier tube and BI 2030 AT digital correlator were used for the QELS studies. The same basic light scattering apparatus was used for the SLS studies, but a RCA 941 photomultiplier tube was utilized. All experimental measurements of the microemulsion samples were conducted at 25 i 0.1 "C. The details pertaining to the microemulsion characterization procedures are described in our earlier study.8 Screening of samples for liquid crystalline structure was carried out by observing birefringence in stagnant samples placed between a cross polarizing screen and subjected to an incident beam of light. Polymerization Procedure. Photoinitiated polymerization of the microemulsion systems was carried out using DMPA as the photoinitiator. The amount of initiator used was 0.02 g for 10g of sample. The liquid sampleswere purged with dry nitrogen gas at a flow rate of 0.56 L/h at 1 atm for 15 min prior to polymerization. The polymerization was conducted in a reaction cell using a 450-W ultraviolet source at a temperature of 25 i 0.1 "C for a duration of 1h. The transparent nature of the microemulsions was utilized in initiating polymerization by the effect of ultraviolet radiation on DMPA to generate free radicals. Morphology Observation. The polymer morphology was examined using scanning electron microscopy (SEM). Samples for SEM studies were made by drying the polymer formed at 55 "C and using the freeze fracture technique.13 The polymer samples were coated using a Polaron E5400 coating machine and a IS1 SX 40 scanning electron microscope was used to study the polymer morphology. Pore Continuity Determination. The continuity in the pore structure of the polymer was determined by examining the shape of the drying rate curve obtained using thermogravimetric analysis. Solid materials containing water in interconnected pores exhibit a drying rate curve which has a linear falling rate period, whereas the drying rate for closed-cell materials has an exponentially decreasingfalling rate.I4-l6 A Dupont instruments TGA 2950 thermogravimetric analyzer was used for the study. The polymer obtained from the polymerization cell which contained water in its pores was dried in a stream of dry nitrogen gas at a temperature of 70 "C for 300 min. The isothermal drying rate curve for the polymer sample was constructed using the data on the loss in weight of sample which was recorded as a function of time by the thermogravimetric analyzer. SurfaceArea Measurement. BET adsorptionanalysis using the Quantasorb System (QSJR-1) was used to determine the surface area of the polymeric materials. The single point BET adsorption technique using a nitrogen-helium mixture having nitrogen relative pressure of 0.3 was utilized. The study was carried out by using dry powdered porous polymer sample (1620 mesh). The surface area results of the porous polymer were corrected for the increase in surface area caused by grinding by subtracting the surface area of an equal amount of powdered nonporous poly(methy1 methacrylate) sample (16-20 mesh). Determination of PUD Incorporation. The incorporation of PUD in the polymer matrix by copolymerization with MMA and EGDMA was evaluated by leaching the dried polymer samples in hot water at 60 "C for 24 hand determiningthe change in sampleweight. The 24-h duration for the leaching experiment was used as our studies had indicated the PUD removed after (12) Cheung, H. M.; Qutubuddin, S.; Edwards, R. V.; Mann, J. A., Jr. Langmuir 1987,3,744. (13) Sawyer, L. C.; Grubb, D. T. In Polymer Microscopy; Chapman and Hall: New York, 1987; p 146. (14) Corben, R. W.; Newitt, D. M. Trans. Inst. Chem. Eng. 1955,33, 52. (15) Coulson, J. M.; Richardson, J. F. In Chemical Engineering, 2nd ed.; Pergamon Press: New York, 1968; Vol. 11, p 620. (16) McCabe, W. L.; Smith, J. C.; Harriott, P. In Unit Operations of Chemical Engineering, 4th ed.; McGraw-Hill: New York, 1985; p 716.
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Figure 1. Ternary phase diagram for the system, methyl methacrylate (MMA), potassium 10-undecenoate(PUD), water (W), and ethylene glycol dimethacrylate (EGDMA) at 25 i 0.1 "Cand 1atm. Compositions are on weight percent basis and EGDMA content is 4 % of the combined weight of MMA and PUD: domain A, two-phase region; domain B, liquid crystalline region; domain C, w/o Winsor-IV region; domain D, bicontinuous Winsor-IV region; domain E, o/w Winsor-IV region.
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this period to be less than 2.0% of the sample weight. The homopolymer of PUD is water soluble and so the weight loss on leaching would correspond to the amount of PUD not incorporated in the polymer. The PUD left in the polymer after leaching could be in the form of a copolymer with MMA or EGDMA or physically bound in the polymer matrix. Qualitative analysis for the presence of PUD in the solid polymer after leaching employed a Philips PV9550 energy dispersive X-ray fluorescence spectrometry system (EDXRF). A pellet of the leached polymer was used for the study and the detection of the characteristic X-ray spectral line corresponding to potassium was taken as indicative of PUD presence. A measure of PUD incorporation was obtained gravimetrically using the weight of the polymer sample before and after leaching. The PUD incorporated in the polymer was calculated by mass balance. This study was conducted as a function of the MMA/EGDMA ratio of the microemulsion and also its water and EGDMA contents. The polymer samples for this study were made from single phase microemulsions by varying the EGDMA concentration from 5 % to 35% of MMA and PUD present on a EGDMA-free basis.
Results The results of the phase behavior study are shown in Figure 1. The unshaded portion (region A) of the phase behavior diagram represents samples which were not made up of a single phase. This region alsoincludescompositions which contained high PUD and were nonhomogeneous with the presence of undissolved PUD. The compositions pertaining to regions B-E are macroscopically monophasic systems. Samples from region B exhibited high viscosity, were birefringent in polarized light, and resembled lyotropic liquid crystals. Regions C, D, and E of the phase diagram represent samples resembling transparent, isotropic Winsor-IV microemulsion systems. The demarcation between regions C, D, and E is based on the microstructure of the Winsor-IV system in each region. Samples in region C exhibited characteristics similar to Winsor-IV systems with a water in oil (w/o) droplet microstructure, whereas samples in region E had an oil in water (o/w) droplet microstructure. In region D, a microstructure which is bicontinuous in oil and water was suggested by experimental observations. The conductivityof single phase sampleshaving a MMA: PUD ratio of 1.5:l was measured as a function of water
Microstructured Systems of MMA with EGDMA
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content, and the results are shown in Figure 2. A small increasein conductivity is observed on increasingthe water content of the system up to 20%. This is followed by a substantial increase in conductivity with water content in the 20-80% water content range. A decrease in conductivity is observed on increasing the water content beyond 80% The shape of the conductivity-water content curve obtained for the MMA/PUD/water system is similar to that for the MMA/AA/water system.8 QELS measurements of samples from the PUD-based system with water contents below 20 % yielded an intensity autocorrelation function which exhibited a single exponential decay. A similar nature of the intensity autocorrelation function was observed from QELS measurements of samples containing greater than 80% water content. The droplet equivalent diameter for these samples was determined using the method of cumulants and the results are shown in Figure 3. QELS studies on samples containing intermediate water contents (20-80% by weight) did not provide an intensity autocorrelation function exhibiting a single exponential decay. The intensity autocorrelation function for these compositions exhibited a long tail. This could result from fluctuations in the microstructureon a long time scale, indicative of the existence of large domain sizes, making the use of QELS inappropriate. Qualitatively similar results were obtained from QELS studies of the AA-based system.8 The droplet diameter obtained for the PUD-based system is smaller than the droplet diameter for the AA-based system.8 Figure 4 represents the results of total scattering intensity measured at a scattering angle of 90° plotted as a function of increasingwater content. The dimensionless scattered intensity plotted is the ratio of the scattered
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Figure 5. SEM micrograph of the morphology of the polymer obtained by polymerizing a microemulsion sample of composition MMA (30%),PUD (20%), water (50%), and EGDMA (4% of combined weight of MMA and PUD).
intensity for a microemulsion a t any water content to the scattered intensity at a water content of 99%. The plot indicates an increase in the total scattered intensity with increasing water content up to a water concentration of 80% by weight. The total scattered intensity shows a decrease for water contents above 80 % . The similarity in the variation of conductivity (Figure 3) and scattered intensity (Figure 4) with water content is striking. The trend in the variation of scattered intensity with water content for the PUD-based system is identical to that observed for the AA-based system.8 The oil in water microemulsions yielded stable latices on polymerization. However detailed characterization of the latices was not done, as the focus of this study was on porous polymeric solids. Rigid polymeric materials were obtained by polymerizing the single phase systems with a water content below 65%. Morphology of the materials obtained from precursor microemulsions containing a MMA:PUD ratio of 1.5:l was studied as a function of the water content of the system. The SEM micrographs for polymers obtained from precursor systems containing 50%, 35%, and 25% water content are shown in Figures 5,6, and 7,respectively. The typical pore size range of the polymeric materials in the micrographs is observed to be 1-3 pm. The micrographs indicate the existence of a microporous structure in the polymer which is related to the water content of the precursor system. The micrographs indicate the microporous structure of polymeric materials
1934 Langmuir, Vol. 8, No.8, 1992
Palani Raj et al.
400
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Figure 8. Drying rate curve for porous polymer formed from the precursor microemulsion of composition MMA (36%1, PUD (24%), water (40%), and EGDMA (4% of combined weight of MMA and PUD). Figure 6. SEM micrograph of the morphology of the polymer obtained by polymerizing a microemulsionsample of composition MMA (39%), PUD (26%), water (35%), and EGDMA (4% of combined weight of MMA and PUD).
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from precursor systems containing low water content (25%) to be more ordered compared to polymer from precursors having a high water content (50%). At water contents of 50-65%, the polymer obtained exhibited a more random microporous structure. The microporous structure of the polymer formed in the case of the AAbased system8 resembled that of the polymer obtained from the PUD-based system for water contents above 50% Examination of the continuity in pore structure using thermogravimetric analysis for polymer obtained from precursors containing a MMA:PUD ratio of 1.5:l indicates the existence of an open-cell porous structure at water contents above 20%. A representative drying rate curve for polymer from precursor of 40 % water content is shown in Figure 8. The existence of the linear falling rate period in Figure 8 is characteristic of open-cell porous materials. Polymer obtained from precursors containing less than 20% by weight of water exhibited a closed-cell porous structure. A representative drying rate curve for polymer obtained from a precursor microemulsion of 10% water content is illustrated in Figure 9. The exponential decay in the falling rate period is typical for closed-cell porous solids.
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The surface area of polymeric solids obtained from precursor systems containing a MMA:PUD ratio of 1.51 is shown as a function of the water content of the precursor in Figure 10. The surface area, which was determined using the BET adsorption technique, shows a steady increase with increasing water content of the precursor microemulsion. The XRF spectra obtained for leached polymer samples obtained from precursor systemscontaining a MMA.PUD ratio of 1.5:l and various water contents indicated a sharp peak corresponding to potassium. This is a qualitative indication of the presence of PUD in the leached sample.
Langmuir, Vol. 8, No. 8, 1992 1935
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single phase systems have been observed. The high viscosity and birefringence are characteristic of lyotropic liquid crystalline phases which have been observed in similar system^.^ This behavior was not observed in the MMA/water/AA system.8 PUD has a longer alkyl group and is more amphiphilic compared to AA17 and its molecules locate at the oil-water interface, resulting in a strongly surface active behavior. At high PUD concentrations the molecules are organized densely at the interface; this could explain the formation of lyotropic liquid crystals due to packing restrictions on the PUD molecules at high concentrations.16J8 The present study was confined to compositions from the microemulsion domain of the phase behavior diagram. Work is currently in progress in our laboratory to polymerize compositions from the liquid crystalline regions and investigate the microporous structure of the polymer obtained. Characterization studies of the microemulsion domain reveal the existence of droplet or bicontinuous microemulsions depending on the composition of the system. The low values of conductivity at water content below 20% (Figure 2) can be explained by the presence of a droplet structure of water in oil. With an increase in the water content of the microemulsion system, the water droplets become connected, yielding a structure which is bicontinuous in oil and water. Due to the establishment of conducting water channels, the conductivity increases sharply. Upon further dilution, at water contents above 80% the system changes to an oil in water droplet structure. The conductivity of the system shows a small decrease as the conducting aqueous phase is progressively diluted with water. The results for the MMAlwaterlPUD system are similar to that observed for other microemuleion system~.l99~~ The conductivity measurements indicate the existence of water in oil droplet structure at low water contents, oil in water droplet structure at high water contents, and a structure bicontinuous in oil and water at intermediate water contents. The trends observed from the total scattered intensity measurements (Figure 4) are similar to that observed from conductivitymeasurements. The total scattered intensity is directly related to the dimensions of the microstructure present in the system. The initial increase in scattered intensity up to 20% water content represents an increase in the diameter of water droplets dispersed in the continuous oil phase. The sharp increase in the intensity of scattered laser light for the 20-80 7% water content range represents an increase in the dimensions of the water domain, resulting in the formation of a bicontinuous structure. The scattered intensity increases on dilution with the formation of additional interconnected water channels. At water content beyond 80%, the scattered intensity decreases with increasing water content due to a reduction in droplet diameter of the dispersed oil phase. These results are in agreement with similar results observed with other microemulsion systems.21*22 QELS studies also indicate the existence of droplet microstructures at water content below 20% and above 80 % (17) Tsaw, S.L.Ph.D. Dissertation, University of Connecticut, 1983. (18) Winsor, P. A. Chem. Rev. 1968,68, 1. (19) Finkelmann, H.;Rehage, G. In Advances in Polymer Science: Liquid Crystal Polymers II/IZfi Gordon, M., Ed.;Springer-Verlag: New York, 1984, Vole. 60/61, p 99. (20)Chen, S. J.; Evans, D. F.; Ninham, B. W. J. Phys. Chem. 1984,88, 1631. (21) Auray, L.; Cotton, J. P.; Ober,R.; Taupin, C. In Microemulsion System; Rosano,H. L., Clauese, M., Eds., Marcel Dekker: New York, 1987; p 226. (22)Friberg, S.E.; Liang, Y. In &Ogress in Microemulsions; Martellucci, S., Chester, A. N., Eds.; Plenum Press: New York, 1989; p 73.
1936 Langmuir, Vol. 8, No. 8, 1992
as seen from the nature of the intensity autocorrelation function obtained. At intermediate water content, the intensity autocorrelation function does not show a single exponential decay but exhibits a long tail which could be indicative of fluctuations in the microstructure on a long time scale. This behavior can be interpreted as representing the formation of large domain sizes. The water content at which the nature of the intensity autocorrelation function changes also corresponds to the water content a t whichchanges in the conductivity and scattered intensity were observed. The results of QELS measurements in conjunction with the results of conductivity and scattered intensity measurements can be interpreted as suggesting a change in the microstructure from a droplet microstructure to a bicontinuous microstructure in the 20-8075 water content range. Similar results have been reported on QELS studies on other bicontinuous microemul~ions.23*~~ The droplet diameter obtained from QELS measurements on compositions possessing a droplet microstructure is comparable to the droplet diameter reported for other micro emulsion^.^^^^^ The droplet diameter for the PUD-based system (Figure 3) is smaller than the droplet diameter for the AA-based systems of comparable compositionby about 15 nm. The smaller droplet diameter in the case of the PUD-based system could result from the better surface-active properties of PUD compared to A A , I 7 leading to the effective placement of PUD molecules at the oil-water interface. The existence of open-cell porous structures in polymer formed from precursor microemulsions having water compositions greater than 20% is revealed by SEM and thermal gravimetric analysis (TGA) studies (Figures 58). With polymerized microemulsions containing less than 20 % water, the polymer obtained had a closed-cell porous structure as seen by TGA measurements (Figure 9). These results indicate the preservation of the microemulsion microstructure to a considerable degree on polymerization. The bicontinuous microemulsions yield open-cell porous polymers whereas microemulsions having a water in oil droplet structure provide closed-cellporous polymers. The typical dimensions of the pores in the open-cell polymeric materials are 1-3 pm. This is significantly larger than the typical width of the channels of bicontinuous microemulsions reported in literature (600-800 A) by using the technique of freeze fracture transmission electron mic r o ~ c o p y . ~ This ~ ~ 2 ~change can be attributed to the existence of phase separation effects during polymerization as well as the structural deformation effects during drying of the polymer. Similar observations have also been reported from earlier studies on the formation of polymeric solids from microemulsions.2*618 Examination of SEM micrographs (Figures 5-7) indicates the microporous structure of the polymer to be more ordered a t low water content of the precursor microemulsion. At water contents below 40 % the precursor mi~~~~
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(23) Odian,G. Principles ofPolymerization; 2nd ed.;Wiley: New York, 1981; p 250. (24) Bodet, J. F.; Bellare, J. R.; Davis, H. T.;Scriven, L. E.; Miller, W. G. J. Phys. Chem. 1988, 92, 1898. (25) Marion, G.; Graciaa, A.; Lachaise, J. J . Phys. Chem. 1988, 92, 1553. (26) Perez-Luna, V. H.; Puig, J. E.; Castano, V. M.; Rodriguez, B. E.; Murthy, A. K.; Kaler, E. W. Langmuir 1990,6, 1040. (27) Jahn, W.; Strey, R. J.Phys. Chem. 1988, 92, 2294.
Palani Raj et al.
croemulsions were closer to the liquid crystalline domain of the phase diagram and were more viscous. This could result in the microporous structure of polymer obtained from these compositions being more ordered, as the higher viscosity of the precursor systems would minimize phase separation effects and rearrangement of the structure on polymerization. The formation of ordered polymeric structures by polymerization of lyotropic liquid crystals has been reported by othem4 Surface area measurements of the porous polymer by BET adsorption studies indicate an increase in surface area with increasing water content of the microemulsion (Figure 10). This could be due to an increase in the number of bicontinuous oil and water channels with increasing water content. The preservation of the gross features of this microstructure on polymerization could yield a porous polymeric solid having a high surface area. The observed trends in the surface area of the porous polymer as a function of water content agree with the results of other studies.6 The XRF and gravimetric measurements provide conclusive support on the partial incorporation of PUD in the polymer matrix. The study indicates some of the PUD present in the polymer to be insoluble in hot water. Hence it can be inferred that a part of the PUD monomer reacts with MMA and EGDMA to form insoluble copolymer. Some of the PUD monomer could also form water-soluble homopolymer and also low molecular weight oligomers as a result of allylic i n h i b i t i ~ n . The ~ ~ extent of PUD incorporation by this process is observed to be directly related to the amount of MMA and EGDMA present in the microemulsion (Figures 11 and 12). A higher water content in the microemulsion results in enhanced water soluble homopolymer of PUD since a larger fraction of PUD monomer remains in the water phase and does not copolymerize with MMA or EGDMA.
Conclusions Studies using conductivity, scattering intensity, and QELS measurements on the MMA/water/PUD/EGDMA system indicate the existence of microstructures similar to microemulsions in certain areas of the phase behavior diagram. The microstructure of the system is dependent on its composition. At low water content, a w/o droplet structure exists, whereas a o/w droplet structure exists at high water content. At intermediate water content a microstructure which is bicontinuous in oil and water is observed. The use of PUD as the surfactant in the system results in the formation of viscous, birefringent systems for certain compositions on the phase behavior diagram. These systems exhibit characteristics similar to lyotropic liquid crystals. Work is currently in progress in our laboratory to polymerize these systems and characterize the polymeric materials obtained. Polymerization of the microemulsion compositions and analyses of the microcellular structure indicate the possibility of controlling the morphology and microcellular structure by the polymerization of microemulsions formulated with PUD. This study also indicates the incorporation of PUD in the polymer matrix in an insoluble form by using MMA and EGDMA as monomer and crosslinking agent, respectively.
