Methyl methacrylate copolymer with stability

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)... 

Tatsuzawa et aq 36,37,45,59 separat.ed cold drugs and neuroleptics by using a styrene-divinyl benzene-methyl methacrylate copolymer as stationary phase. The best results were obtained with methanol - ammonia (99 1) as mobile phase. The effect of the pH and of the composition of the mobile phase on the separation were discussed. Aramaki et al.70 analyzed a series of alkaloids on a macroporous styrene-divinylbenzene copolymer with alkaline acetonitrile - water mixtures as mobile phase (Fig. 7.10). The columns showed excellent stability, and also under the strong basic conditions used for the analysis of the alkaloids. 

Styrene and methyl methacrylate copolymers onto UV stabilizer moieties that were fixed were characterized by UV spectroscopy and size exclusion chromatography. The stability of intramolecular hydrogen bonds is important for the performance of UV stabiUzers. The highest stability of the intramolecular hydrogen bonds is obtained for polymers with phen-ylbenzotriazole unit attached to the backbone. It was shown that the UV stabilizer units were statistically distributed along the polymer backbone. " A number of polymerizable ultraviolet stabilizers of the 2-(2-hy-drox5 henyl)-2H-benzotriazole t) es have been synthesized. E.g., 5-vinyl and 5-isopropenyl derivatives of 2-(2-hydroxyphenyl)-2H-benzotriazole and 4-acrylates or 4-methacrylates of 2-(2,4-dihydroxyphenyl)-2H-benzo-triazole or 2-(2,4-dihydrox5 henyl)-1,3-2H-dibenzotriazole have been prepared and copolymerized with various monomers. ... 

Styrene and methyl methacrylate copolymers onto UV stabilizer moieties that were fixed were characterized by UV spectroscopy and size-exclusion chromatography. The stability of intramolecular hydrogen bonds is important for the performance of UV stabilizers. The highest stability of the intramolecular hydrogen bonds is obtained for polymers with phenyl-benzotriazole unit attached to the backbone. It was shown that the UV stabilizer units were statistically distributed along the polymer backbone [58]. 

With regard to the behavior of polar polymers in microemulsions, it has been reported that polymerization in methyl methacrylate microemulsions with non-polymerizable surfactants and cosurfactants [28] leads to phase separation of the system in spite of the fact that the poly(methyl methacrylate) is soluble in its monomer. On the other hand, polar polymers such as amphiphilic block copolymers, e.g., poly(2-vinyl p5nidine-fc-ethylene oxide), have been used as cosurfactants to stabilize microemulsions [65, 66] and a specific mechanism has been proposed for polar polymers as stabilizers for emulsions and microemulsions [67]. 

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

Poly(methyl methacrylate) provides a level of stabilization even though the solution in CCl is below the 0-temperature. All the copolymers, both random and block, are better stabilizers than PMM, the methacrylate units acting as anchors, with stabilizing sequences of styrene loops, of block copolymers, or mixed loops and tails, of random copolymers, at better than 0-conditions. Higher M.W. polystyrenes give silica dispersions too unstable to measure by our optical method the sediment volumes are between those of poly(methyl methacrylate) solutions and pure solvent. 

Non-ionic polymers have also been blended with ionic block copolymers. Poly(vinyl phosphanate)-l7-polystyrene and PS-l -SPS have been blended with PPO. In both cases, improvements were seen in MeOH permeability over that of fhe unmodified block copolymers and conductivity values dropped as a function of increasing PPO confenf. PVDF has been blended wifh SEES in order fo improve its mechanical and chemical stability, but aggregation was found fo be a problem due fo incompafibility between components. However, it was found that a small amount (2 wt%) of a methyl methacrylate-butyl acrylate-methyl methacrylate block copolymer as com-patibilizer not only led to greater homogeneity but also improved mechanical resistance, water management, and conductivity. ... 

Another interesting positive-tone polyacrylate DUV resist has been reported by Ohno and coworkers (82). This material is a copolymer of methyl methacrylate and glycidyl methacrylate. Such materials are negative e-beam resists, yet in the DUV they function as positive resists. Thermal crosslinking of the images after development provides relief structures with exceptional thermal stability. The reported sensitivity of these copolymers is surprising, since there are no obvious scission mechanisms available to the system other than those operative in PMMA homopolymer, and the glylcidy side-chain does not increase the optical density of the system. 

Ethylene copolymers with methyl methacrylate and ethyl, butyl, and methyl acrylates are similar to EVA products but have improved thermal stability during extrusion and increased low-temperature flexibility. The commercial products generally contain 15-30% of the acrylate or methacrylate comonomer. Applications include medical packaging, disposable gloves, hose, tubing, gaskets, cable insulation, and squeeze toys. 

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). 

The emulsion was stabilized with 0.25% block copolymer of starch and methyl methacrylate synthesized by mastication. 

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. 

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