Phase separation polymerization

Microdialysis was achieved in a fused silica chip with in situ photopattemed porous membrane, as shown in Figure 5.13. Phase-separation polymerization of the membrane (7-50 pm thick) was formed between posts. The posts maximize the mechanical strength of the membrane so that it can withstand a pressure drop of 1 bar. Low MW cutoff (MWCO) membrane, which can be formed by using less organic solvent, 2-methoxyethanol, appears to be more transparent (see Figure 5.13). This low MWCO membrane can be used to dialyze away low MW molecules, such as rhodamine 560, but not fluorescently labeled proteins (insulin, BSA, anti-biotin, and lactalbumin). Fligh MWCO membrane, which was formed by more organic solvent, allows diffusion of lactalbumin [347]. 

FIGURE 5.13 Left low MWCO membrane (deionized water 2-methoxyethanol = 3.7 1). Right high MWCO membrane (deionized water 2-methoxyethanol = 0.34 1). The post diameter is 50 pm. For phase-separation polymerization, the monomer is 2-(N-3-sulfo-propyl-N,N-dimethylammonium) ethyl methacrylate, the cross-tinker is methylene bisacry-lamide, and the plotoinitiator is 2,2 -azobis(2-methylpropanimidamide dihydrochloride). To prevent unwanted polymerization that may occur by heat and molecular diffusion outside the UV-irradiated region, a polymerization inhibitor, hydroquinone, is also added. To facilitate covalent attachment of the porous membrane to the silica surface, it is first coated with 3-(trimethoxysilyl)propylacrylate [347]. Reprinted with permission from the American Chemical Society. 

When the appropriate precautions are taken the method appears particularly suited for measuring very low tensions 10 mN m sometimes even as low as 10 mN m ). Such ultralow tensions are for example encountered in micro-emulsion systems and in just phase-separated polymeric or micellar solutions. For phase-separated colloid-polymer systems de Hoog and Lekkerkerker ) even reported values down to a few pN m , reproducibly being obtained after implementing a number of methodical improvements. (Alternatives for low tensions are the sessile and pending (micro-) drop but these do not usually go below 10 mN m ) Commercial apparatus are nowadays available. A variant proposed by Than et al. J employs a thin rod in the axis of the cylinder, to reduce spin-up time and suppress drift. Another variant, proposed by Kokov, analyses the centrifugal field required to squeeze liquid out of an orifice" ). 

Chemically bonded silica gels with cyanopropyl, aminopropyl, and diol functional groups are also available and each has been used for normal-phase as well as reversed-phase separations. Polymeric-based packings are available and can be used for ion-exchange or reversed-phase applications. Cross-linked polymeric based packings have been combined with ion-exchange materials to create a more pH-stable stationary phase. Graphitized carbon... 

A major application of solid state NMR is the study of polymer morphology. Information potentially available includes the amount and orientation of crystalline phases in semi-crystalline polymers and the domain sizes in phase-separated polymeric systems. For the determination of crystallinity, a common method is to measure Ti relaxation in NMR (or NMR for deuterated polymers). The relaxation data can often be resolved into two (or more) components, which may correspond to magnetization arising from crystalline and amorphous phases (11-15,130-134). The development of the maximum entropy regularization method has permitted more facile and less subjective analysis of the data (143). In optimal cases, multiple components can be identified. 

Microdialysis, Fig. 4 (a) Microdialysis membrane sandwiched between two etched sets of silicon microchannels with interdigitated sensing electrodes (Image taken from Pan et al. [10]) (b) Schematic of optical setup for phase separation polymerization to define the... 

Okay O (2010) Production of macroporous polymeric materials by phase separation polymerization. In Mattiasson B, Kumar A, Galaev I (eds) Macroporous polymers production, properties and biological/biomedical applications. CRC, Boca Raton, p 3... 

A process in which melted plastic is injected into a mold cavity, where it cools and takes the shape of the cavity. Bosses, screw threads, ribs, and other details can be integrated, which allows the molding operation to be accomplished in one step. The finished part usually does not require additional work before assembling. Any IPN in which the individual polymers are thermoplastic. The polymers may contain physical cross-links as in ionomers where ionic clusters join two or more chains together. Nowadays, phase-separated polymeric systems, e.g., block and graft copolymers or thermoplastic polyurethanes, are frequently considered thermoplastic IPNs. 

Consequently, structurally uniform, transparent hydrogels (NC gels) are obtained without syneresis or phase separation. Polymerization yields are almost 100%, regardless of the NC gel composition. By strictly controlling the polymerization conditions, it is possible to decrease the residual monomer content to less... 

Mitov Z, Kumacheva E. Convection-induced patterns in phase-separating polymeric fluids. Phys Rev Lett 1998 81 3427-30. 

Keywords Nanoparticles Phase separation Polymeric architecture Reversible-deactivation radical polymerization Self-assembly... 

It is thought that by improving the compatibility of the resinous ester-amide based polymeric dyes with PP, the domain sizes of the phase separated polymeric dye should decrease, thus reducing the observed residual haze. Waxes are often used to improve pigment dispersion in polypropylene, and more recently to improve... 

By combining Eqs. (8.60) and (8.115), the following relationship is obtained between the critical temperature for phase separation and the degree of polymerization ... 

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

After epoxidation, propylene oxide, excess propylene, and propane are distilled overhead. Propane is purged from the process propylene is recycled to the epoxidation reactor. The bottoms Hquid is treated with a base, such as sodium hydroxide, to neutralize the acids. Acids in this stream cause dehydration of the 1-phenylethanol to styrene. The styrene readily polymerizes under these conditions (177—179). Neutralization, along with water washing, allows phase separation such that the salts and molybdenum catalyst remain in the aqueous phase (179). Dissolved organics in the aqueous phase ate further recovered by treatment with sulfuric acid and phase separation. The organic phase is then distilled to recover 1-phenylethanol overhead. The heavy bottoms are burned for fuel (180,181). 

In contrast to ionic chain polymerizations, free radical polymerizations offer a facile route to copolymers ([9] p. 459). The ability of monomers to undergo copolymerization is described by the reactivity ratios, which have been tabulated for many monomer systems for a tabulation of reactivity ratios, see Section 11/154 in Brandrup and Immergut [14]. These tabulations must be used with care, however, as reactivity ratios are not always calculated in an optimum manner [15]. Systems in which one reactivity ratio is much greater than one (1) and the other is much less than one indicate poor copolymerization. Such systems form a mixture of homopolymers rather than a copolymer. Uncontrolled phase separation may take place, and mechanical properties can suffer. An important ramification of the ease of forming copolymers will be discussed in Section 3.1. 

The effects of increasing the concentration of initiator (i.e., increased conversion, decreased M , and broader PDi) and of reducing the reaction temperature (i.e., decreased conversion, increased M , and narrower PDi) for the polymerizations in ambient-temperature ionic liquids are the same as observed in conventional solvents. May et al. have reported similar results and in addition used NMR to investigate the stereochemistry of the PMMA produced in [BMIM][PFgj. They found that the stereochemistry was almost identical to that for PMMA produced by free radical polymerization in conventional solvents [43]. The homopolymerization and copolymerization of several other monomers were also reported. Similarly to the findings of Noda and Watanabe, the polymer was in many cases not soluble in the ionic liquid and thus phase-separated [43, 44]. 

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