Solvent composition effect polymerization

A reliable chromatographic method has been developed for the quantitative aneilysis of hydrophobic impurities in water-soluble polymeric dyes. The method utilizes both the molecular sieve effect of normal gel permeation chromatography and solute-column packing interaction, modified by solvent composition. This method eliminates the need to extract the impurities from the polymeric dye with 100 extraction efficiency, as would be required for an ordinary liquid chromatographic analysis. 

A linear relationship between (AHf — Aff5 ) and (ASf — ASj ) is obeyed for all but one system checked so far. The compensation effect holds for different solvents and different initial monomer/solvent compositions, as Figure 1 shows for the s/i and i/s additions of the free radical polymerization of methyl methacrylate. 

In the alkyllithium initiated polymerizations of vinyl monomers, Lewis bases such as ethers and amines alter the kinetics, stereochemistry, and monomer reactivity ratios for copolymerization. In general, the magnitude of these effects has been directly or indirectly attributed to the extent or nature of the interaction of the Lewis base with the organolithium initiator or with the organolithium chain end of the growing polymer. Unfortunately, all of these observed effects are kinetic in nature, and therefore the observed effects of solvent represent a composite effect on the transition-state versus the ground state as shown below in Eq. (6), where 5 represents the differential... 

The initiation step could also be positively affected by the above-mentioned transport properties, as the efficiency factor f assumes higher values with respect to conventional liquid solvents due to the diminished solvent cage effect One further advantage is constituted by the tunability of the compressibility-dependent properties such as density, dielectric constant, heat capacity, and viscosity, all of which offer additional possibilities to modify the performances of the polymerization process. This aspect could be particularly relevant in the case of copolymerization reactions, where the reactivity ratios of the two monomers, and ultimately the final composition of the copolymer, could be controlled by modifying the pressure of the reaction system. 

Because of its heterophase nature, emulsion polymerization is generally more complicated than simple solution polymerization in which monomers and polymers are soluble in a suitably chosen solvent. In emulsion polymerization the different relative solubilities of monomers in water and in the polymer particles lead to different reaction locales and to different particle structures. Another complicating factor is the need to achieve and maintain colloidal stability throughout the polymerization and subsequent handling of the dispersions. Emulsion polymers can properly be called products by process since the process details exert such a powerful effect on the properties of the particles and resultant films. Consequently, an emulsion polymer is far more than a product defined by a simple polymer composition. 

Table V. Effect of Solvent Composition on Polymer Yield, Tacticity and Molecular Weight in the Polymerization of p-Chloro-a-methylstyrene with SnCl ...

Intensive studies with UV-VIS and MALDI-TOF analysis opened new insights into the effect of the solvent composition on the polymerization of... 

The polymerization of m-cresol was also carried out successfully in ethanol/buffer mixtures [79]. The molecular weight was controllable by changing the solvent composition. Enzyme kinetics revealed the effect of the solvent on the enzyme activity and substrate portioning between bulk solvent and the enzyme. While the polymer solubiUty increased with increasing ethanol content in the solvent mixture, the enzyme activity went through a maximum (around 20v/v% ethanol content) with increasing amoimt of ethanol. This was similar to the results found previously for aqueous 1,4-dioxane/buffer mixtures. The enzyme showed no activity at 100% ethanol content, but it was found to be not irreversibly deactivated. Hence, gradual addition of buffer led to nearly complete restoration of the enzyme activity. 

Up to this point, the discussion has concerned systems with one or more polymer species dissolved in a pure solvent. However, thermodynamic behavior in the more general case of systems with multiple solvents involves additional effects that are of considerable interest. Here, for simplicity, only a three-component system of a polymer (component 2) in two low molecular weight solvents (components 1 and 3) is considered but an exhaustive analysis of the general multicomponent case is available. The classification of solvents and solute is of course arbitrary, but it has utility with respect to specific experimental measurements. For instance, the operative principle in an osmotic measurement is that solvents pass through the membrane that confines a polymeric solute. The obvious effect of the additional thermodynamic degree of freedom in the three-component system is the possibility of selective interaction (preferential solvation or binding ) of the solute with a solvent component. In an osmotic experiment this will be manifested by equilibrium solvent compositions that are different in the solute and solvent compartments of the osmometer. It is possible, though not always very useful, to formally redefine a solute component so as to include in it any excess (or deficiency) of a solvent component required to make the free solvent mixture appear... 

Acrylamide copolymerizes with many vinyl comonomers readily. The copolymerization parameters ia the Alfrey-Price scheme are Q = 0.23 and e = 0.54 (74). The effect of temperature on reactivity ratios is small (75). Solvents can produce apparent reactivity ratio differences ia copolymerizations of acrylamide with polar monomers (76). Copolymers obtained from acrylamide and weak acids such as acryUc acid have compositions that are sensitive to polymerization pH. Reactivity ratios for acrylamide and many comonomers can be found ia reference 77. Reactivity ratios of acrylamide with commercially important cationic monomers are given ia Table 3. 

An excellent review of composite RO and nanofiltration (NE) membranes is available (8). These thin-fHm, composite membranes consist of a thin polymer barrier layer formed on one or more porous support layers, which is almost always a different polymer from the surface layer. The surface layer determines the flux and separation characteristics of the membrane. The porous backing serves only as a support for the barrier layer and so has almost no effect on membrane transport properties. The barrier layer is extremely thin, thus allowing high water fluxes. The most important thin-fHm composite membranes are made by interfacial polymerization, a process in which a highly porous membrane, usually polysulfone, is coated with an aqueous solution of a polymer or monomer and then reacts with a cross-linking agent in a water-kniniscible solvent. 

Any understanding of the kinetics of copolymerization and the structure of copolymers requires a knowledge of the dependence of the initiation, propagation and termination reactions on the chain composition, the nature of the monomers and radicals, and the polymerization medium. This section is principally concerned with propagation and the effects of monomer reactivity on composition and monomer sequence distribution. The influence of solvent and complcxing agents on copolymerization is dealt with in more detail in Section 8.3.1. 

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