Acrylic polymer radicals solvent effects

Structure and mechanism in photochemical reactions. The reactions of geminal radical pairs created in bulk polymers are presented by Chesta and Weiss in Chapter 13. Of the many possible chemical reactions for such pairs, they are organized here by polymer and reaction type, and the authors provide solid rationalizations for the observed product yields in terms of cage versus escape processes. Chapter 14 contains a summary of the editor s own work on acrylic polymer degradation in solution. Forbes and Lebedeva show TREPR spectra and simulations for many main-chain acrylic polymer radicals that cannot be observed by steady-state EPR methods. A discussion of conformational dynamics and solvent effects is also included. 

The TREPR experiments and simulations described here have provided an enormous amount of structural and dynamic information about a class of free radicals that were not reported in the hterature prior to our first paper on this topic in 2000. Magnetic parameters for many main-chain acrylic radicals have been established, and interesting solvent effects have been observed such as spin relaxation rates and the novel pH dependence of the polyacid radical spectra. It is fair to conclude from these studies that the photodegradation mechanism of acrylic polymers is general, proceeding through Norrish 1 a-cleavage of the ester (or acid) side chain. Recently, model systems have... 

In the homogeneous MMA polymerization with 1-32 (Y = CH3)/CuBr/L-9 (R = n-Pen), the rate increased in the order xylene < DMB < DPE,179 probably due to the differences in the dielectric constant and coordination ability of the solvents. With the homogeneous Ru-1 catalyst, the polymerization of MMA was faster in a polar solvent such as CPI2C12 than in toluene.159 A more detailed analysis on solvent effects was carried out by end-capping a polymer radical with hydroxyl-TEMPO, where the radical intermediate was generated from bromide macroinitiators via CuBr/L-4 catalyst.242 A polar solvent such as butyl acetate increases the radical-generation rate from poly(acrylate)s but not from polystyrene. On the other hand, no rate increase was found for both macroinitiators in DMF, which is... 

New types of metal-containing polymers can be effectively produced 1 construction of polymer supports in the form of gels which, in use, are capable of swelling, insoluble in the reaction medium, but permeable to the molecules, substrate and solvent (23-25). they are based on ethylene-prcpylene rubbers and also ternary copolymers of ethylene, propylene and nonconjugated diene, siloxane rubbers with the radically grafted vinylpyridine, acrylic acid (AAc), methylmethacrylate (MMA), etc. Fu2 her cross-linking of the rubber base allows the syntheses of three-dimensional networks to avoid the dispersion of these particles in the reaction media. MX is bound within these networks. Such polymers were termed mosaic their structure is shown in Fig. 2. It is evident... 

A different form of retardation occurs when a radical species formed from transfer (S in Scheme 4.3) reinitiates at a slow rate. In addition to the slower reaction rate with monomer to form a polymer radical, the termination of S with other radicals in the system may also need to be considered (Scheme 4.8). Explicit balances must be written for S, and the extra mechanisms must be included when deriving expressions for [Ptot], Rpoi, and DP . As solvent/transfer agent is generally not completely consumed, the retardation effect will last the duration of the polymerization (curve b in Figure 4.2). The degree of retardation depends on the value of which can vary with monomer type many carbon-centered radicals show much lower reactivity toward vinyl esters (for example, vinyl acetate) than (meth)acrylates [3]. 

In the 2P process (4), a thin photopolymerizable liquid layer is cured in situ between a smooth substrate (cut from a polymer sheet or molded) and a master and stripped off to effect pattern transfer. The liquid layer ensures accurate, defect-free replication. Examples of solvent-free formulations include multifunctional acrylates with adhesion, wetting, and release agents. Free radical and cationic polymerization processes have been described (9). At the present disk volume levels, this method is claimed to be cost competitive with injection molding. 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

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