Functional Group Polymerization

Polymer Number of Weight fraction Tm(°C) Water absorption 

Polymerization by a ring-opening reaction is confined to cyclic monomers which contain at least one heteroatom. The mechanism is very often a polyaddi-tion-type with a product which has a polycondensation-type character. For example, ethylene oxide and other cyclic esters can be polymerized into linear chains by this type of reaction. An even more complicated example of this type of polymerization reaction is the polymerization of e-caprolactam into Nylon 6 (PA 6). 

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Although a considerable effort has been undertaken to understand proton conduction in PEMs, much remains to be understood in terms of how molecular chemistry and hydrated morphology dictate fuel cell performance. Molecular modeling of acidic functional groups, polymeric fragments, proton diffusion, and dielectric properties of the confined water in several different PEMs has suggested that the critical ingredients of proton conduction include complexity ... 

We define the problem by assuming the polymerization involves AA and BB monomers and that the B groups are present in excess. We define and to be the numbers of A and B functional groups, respectively. The number of either of these quantities in the initial reaction mixture is indicated by a superscript 0 the numbers at various stages of reaction have no superscript. The stoichiometric imbalance is defined by the ratio r, where... 

For a fixed extent of reaction, the presence of multifunctional monomers in an equimolar mixture of reactive groups increases the degree of polymerization. Conversely, for the same mixture a lesser extent of reaction is needed to reach a specified with multifunctional reactants than without them. Remember that this entire approach is developed for the case of stoichiometric balance. If the numbers of functional groups are unequal, this effect works in opposition to the multifunctional groups. 

In Chap. 5, p was defined as the fraction (or probability) of functional groups that had reacted at a certain point in the polymerization. According to the current definition provided by Eq. (6.66), p is the fraction (or probability) of propagation steps among the combined total of propagation and termination steps. The quantity 1 - p is therefore the fraction (or... 

Fig. 25. Schematic representation of imprinting (a) cross-linking polymerization ia the presence of a template (T) to obtain cavities of specific shape and a defined spatial arrangement of functional groups (binding sites. A—C) (b) cross-linked polymer prepared from the template monomer and ethylene...

Carboxylic Acid Functional Group Reactions. Polymerization is avoided by conducting the desired reaction under mild conditions and in the presence of polymeriza tion inhibitors. AcryUc acid undergoes the reactions of carboxyUc acids and can be easily converted to salts, acryhc anhydride, acryloyl chloride, and esters (16—17). 

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

Other Organolithium Compounds. Organoddithium compounds have utiHty in anionic polymerization of butadiene and styrene. The lithium chain ends can then be converted to useflil functional groups, eg, carboxyl, hydroxyl, etc (139). Lewis bases are requHed for solubdity in hydrocarbon solvents. 

A low temperature catalytic process has been reported (64). The process involves the divalent nickel- or zero-valent palladium-catalyzed self-condensation of halothiophenols in an alcohol solvent. The preferred halothiophenol is -bromothiophenol. The relatively poor solubiHty of PPS under the mild reaction conditions results in the synthesis of only low molecular weight PPS. An advantage afforded by the mild reaction conditions is that of making telecheHc PPS with functional groups that may not survive typical PPS polymerization conditions. 

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