Methyl dispersion polymerization

The same PVP series were also tried for the dispersion polymerization of styrene in the ethanol medium by using AIBN as the initiator and aerosol OT as the costabilizer [84]. PVP K-15 usually yielded polymeric particles with a certain size distribution and some coagu-lum. The uniform products were obtained with PVP K-30 and PVP K-90 in the presence of the costabilizer. The tendencies for the variation of the final particle size with the stabilizer concentration and with the molecular weight of the stabilizer were consistent with those obtained for the dispersion polymerization of methyl methacrylate [84],... 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

Morphology of the enzymatically synthesized phenolic polymers was controlled under the selected reaction conditions. Monodisperse polymer particles in the sub-micron range were produced by HRP-catalyzed dispersion polymerization of phenol in 1,4-dioxane-phosphate buffer (3 2 v/v) using poly(vinyl methyl ether) as stabihzer. °° ° The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. The particles could be obtained from various phenol monomers such as m-cresol and p-phenylphenol. 

For (c), a macromonomer that has a pendant group accustomed to the solvent is used as a comonomer in the dispersion polymerization of a monomer that composes the particle. The surface of resulting particles is covered with the pendant group and consequently stabilized by a steric stabilization effect (14,15). In this sense the macromonomer is a kind of stabilizer that shows its effect through polymerization, and it could be called as a stabilizer formed in situ. A copolymer of macromonomer and particle-composing monomer, which joins the polymer particle, is much more effective for dispersion than a soluble stabilizer. With the dispersion polymerization of methyl methacrylate, which uses a macromonomer composed of an oligo-oxazoline pendant group, it is possible to cut the amount of stabilizer used to one-tenth or less compared to the oxazoline homopolymer stabilizer (16). 

Of course, it is possible to first copolymerize the macromonomer and vinyl monomer and then use this as a stabilizer in dispersion polymerization. As mentioned earlier, HSM is a stabilizer copolymerized from a methyl methacrylate and a macromonomer that is a maleic ester of 12 hydroxystearic acid pentamer (17). 

In a mixed solvent system, it is possible to control the particle size by changing the composition ratio. In a dispersion polymerization of methyl methacrylate in a mixed solvent of trimethylpentane and carbon tetrachloride, the size of the particle increases as the fraction of carbon tetrachloride, which has affinity to methyl methacrylate, increases. 

Dispersion polymerizations of methyl methacrylate ntUizing poly(l,l,-dihydroper-fluorooctyl acrylate) as a steric stabilizer in snpercritical CO2 were carried out in the presence of helium. Particle size and particle size distribution were found to be dependent on the amonnt of inert helium present. Particle sizes ranging from 1.64 to 2.66 pm were obtained with varions amounts of helium. Solvatochromic investigations using 9-(a-perflnoroheptyl-p,p-dicyanovinyl)julolidine indicated that the solvent strength of CO2 decreases with increasing helium concentration. This effect was confirmed by calcnlations of Hildebrand solubility parameters (Hsiao and DeSimone, 1997). 

Several methodologies for preparation of monodisperse polymer particles are known [1]. Among them, dispersion polymerization in polar media has often been used because of the versatility and simplicity of the process. So far, the dispersion polymerizations and copolymerizations of hydrophobic classical monomers such as styrene (St), methyl methacrylate (MMA), etc., have been extensively investigated, in which the kinetic, molecular weight and colloidal parameters could be controlled by reaction conditions [6]. The preparation of monodisperse polymer particles in the range 1-20 pm is particularly challenging because it is just between the limits of particle size of conventional emulsion polymerization (100-700 nm) and suspension polymerization (20-1000 pm). 

The mechanism of polystyrene and poly(methyl methacrylate) particle formation in the presence of PEO-MA macromonomer in the presence of conventional stabilizer (PVPo) and the graft copolymers (PSt-gra/f-PEO), respectively, was discussed [77]. At the beginning of dispersion polymerization (in methanol) of MMA (0-250 s) using PVPo, very small particles were formed (12-35 nm in diameter). The population of bigger particles was roughly stabilized at ca. 345 nm in diameter. In the dispersion polymerization of styrene, small particles... 

Most dispersion polymerizations in C02, including the monomers methyl methacrylate, styrene, and vinyl acetate, have been summarized elsewhere (Canelas and DeSimone, 1997b Kendall et al., 1999) and will not be covered in this chapter. In a dispersion polymerization, the insoluble polymer is sterically stabilized as colloidal polymer particles by the surfactant that is adsorbed or chemically grafted to the particles. Effective surfactants in the dispersion polymerizations include C02-soluble homopolymers, block and random copolymers, and reactive macromonomers. Polymeric surfactants for C02 have been designed by combining C02-soluble (C02-philic) polymers, such as polydimethylsiloxane (PDMS) or PFOA, with C02-insoluble (C02-phobic) polymers, such as hydrophilic or lipophilic polymers (Betts et al., 1996, 1998 Guan and DeSimone, 1994). Several advances in C02-based dispersion polymerizations will be reviewed in the following section. 

It was previously reported that the homopolymer surfactant PFOA successfully stabilized poly(methyl methacrylate) (PMMA) dispersion polymerizations (DeSimone et al., 1994 Hsiao et ah, 1995), but was not successful for styrene dispersion polymerizations (Canelas et al., 1996). In these styrene polymerizations, the C02 pressure used was 204 bar. However, later studies showed that both PFOA and poly(l,l-dihydroper-fluorooctyl methacrylate) (PFOMA) could stabilize polystyrene (PS) particles (Shiho and DeSimone, 1999) when a higher pressure was used. These polymerizations were conducted at 370 bar, 65 °C, and the particle size could be varied from 3 to 10 pm by varying the concentration of stabilizer. These homopolymer surfactants are less expensive and easier to synthesize than block copolymer surfactants and provide access to a large range of particle sizes. 

Hsiao, Y.-L. Maury, E. E. DeSimone, J. M. Mawson, S. M. Johnston, K. P. Dispersion Polymerization of Methyl Methacrylate Stabilized with Poly(l, 1-dihydroperfluorooctyl acrylate) in Supercritical Carbon Dioxide. Macromolecules 1995, 28, 8159-8166. 

For the stabilization of various insoluble hydrocarbon polymers in carbon dioxide, it has been found that no one surfactant works well for all systems. Therefore it has become necessary to tailor the surfactants to the specific polymerization reaction. Through variation of not only the composition of the surfactants, but also their architectures, surfactants have been molecularly-engineered to be surface active—partitioning at the interface between the growing polymer particle and the CO2 continuous phase. The surfactants utilized to date include poly(FOA) homopolymer, poly(dimethylsiloxane) homopolymer with a polymerizable endgroup, poly(styrene-b-FOA), and poly(styrene-b-dimethylsiloxane). Through the utilization of these surfactants, the successful dispersion polymerization of methyl methacrylate (MMA), styrene, and 2,6-dimethylphenol in CO2 has been demonstrated. 

A similar principle is applied in dispersion polymerization in ionic liquids produced particles are in sub-micron range (41,42). The monomer, initiator and colloidal stabilizer are soluble in the liquid medium, but the obtained polymer is not. Different kinds of ionic liquids may be used, such as for styrene l-butyl-3-methylimidazolium tetrafluoroborate or N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide. In general, radical polymerization in ionic liquids provides higher polymerization rate and higher molecular weights than the process in bulk or organic solvents (homogenous system). 

Pich A, Lu Y, Adler HJP, Schmidt T, Arndt KF (2002) Dispersion polymerization of pyrrole in the presence of poly(vinyl methyl ether) microgels. Polymer 43(21) 5723-5729... 

Most research into the study of dispersion polymerization involves common vinyl monomers such as styrene, (meth)acrylates, and their copolymers with stabilizers like polyvinylpyrrolidone (PVP) [33-40], poly(acrylic acid) (PAA) [18,41],poly(methacrylicacid) [42],or hydroxypropylcellulose (HPC) [43,44] in polar media (usually alcohols). However, dispersion polymerization is also used widely to prepare functional microspheres in different media [45, 46]. Some recent examples of these preparations include the (co-)polymerization of 2-hydroxyethyl methacrylate (HEMA) [47,48],4-vinylpyridine (4VP) [49], glycidyl methacrylate (GMA) [50-53], acrylamide (AAm) [54, 55], chloro-methylstyrene (CMS) [56, 57], vinylpyrrolidone (VPy) [58], Boc-p-amino-styrene (Boc-AMST) [59],andAT-vinylcarbazole (NVC) [60] (Table 1). Dispersion polymerization is usually carried out in organic liquids such as alcohols and cyclohexane, or mixed solvent-nonsolvents such as 2-butanol-toluene, alcohol-toluene, DMF-toluene, DMF-methanol, and ethanol-DMSO. In addition to conventional PVP, PAA, and PHC as dispersant, poly(vinyl methyl ether) (PVME) [54], partially hydrolyzed poly(vinyl alcohol) (hydrolysis=35%) [61], and poly(2-(dimethylamino)ethyl methacrylate-fo-butyl methacrylate)... 

Poly(HEMA-co-MMA-g-PMMA) graft copolymer was also prepared with a commercially available poly(methyl methacrylate) (PMMA) macromonomer, HEMA, and MMA, and used as an efficient dispersant for the dispersion polymerization of styrene in ethanol [152]. 

The minimum requirements for a dispersion polymerization are monomer, solvent/nonsolvent, initiator, and steric stabilizer. The monomer must be soluble in the reaction mixture and its polymer, insoluble. The monomers used in systems of commercial interest are methyl methacrylate, vinyl chloride, vinyli-dene chloride, vinyl esters, hydroxyl alkyl acrylates. A typical recipe for dispersion polymerization is shown in Table 9. 

Poly(methyl methacrylate) (PMMA) nanofibers containing Ag nanoparticles were synthesized by radical-mediated dispersion polymerization. UV-visible spectroscopic analysis indicated that the Ag nanoparticles were continually released from the polymer nanofiber in aqueous solution [47]. In another study, the electrospinning conditions for PMMA were studied [48]. In this work, conductivity of the polymer solution containing Ag nanoparticles and its effect on fiber diameter were also studied. As the results showed, the maximum concentration for the electrospinning of PMMA was found to be 18 wt%, and the ratio of DMF to THF was 7 3 (v/v). The diameter of nanolibers obtained was found to be 100-400 nm when the PMMA solution contained 1,000 ppm of Ag nanoparticles [48]. 

Hsiao YL, Maury EE, DeSimone JM, Mawson S, Johnston KP. Dispersion polymerization of methyl methacrylate stabilized with poly(l,l-dihydroper-fluorooctyl acrylate) in supercritical carbon dioxide. Macromolecules 1995 28 ... 

Lepilleur C, Beckman EJ. Dispersion polymerization of methyl methacrylate in supercritical CO2. Macromolecules 1997 30 745-756. 

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