Molecular weight gegenion

A spontaneous deactivation can also occur when a growing macroion and low-molecular-weight gegenion isomerize into an inactive compound (see Chapter 18). 

It is important to note that regardless of how termination occurs, the molecular weight is independent of the concentration of the initiator. However, the rate of ionic chain polymerization is dependent on the dielectric constant of the solvent, the resonance stability of the carbonium ion, the stability of the gegenion, and the electropositivity of the initiator. 

We have found that the size of the gegenion is more important than the fact that it is nonmetallic. Potassium dimethyl malonate/18-crown-6 polymerizes MMA at 25-60 °C to give quantitative yields of PMMA, MWD 1.5-1.9. Excess malonate or methanol lowered the molecular weight of the PMMA but did not shut down the polymerization [67]. It is tempting to postulate that a hydrogen-bonded version of the Quirk intermediate (Scheme 13) is stabilizing enolate ends (Scheme 30). 

Time Effect of Gegenion on Molecular Weight Distribution. The... 

Time Effect of Gegenion on GPC Results. Figure 4 shows some typical normalized gel permeation chromatography results for the PFG polymers before equilibrium conversion is reached. The curves shown are for PF6 polymers after 0.5, 1.5, and 8 hours of polymerization. In agreement with the viscosity results the increase of molecular weight with time is evident. As expected, the distribution starts off quite narrowly. Then it quickly becomes broader. 

Electrically neutral substituents in macromolecular chains exhibit no peculiarities with respect to low-molecular-weight compounds in terms of constitution, nomenclature, or, in general, modes of reaction. Polymers with substituents having ionizable bonds are called polyelectrolytes. Polyelectrolytes can dissociate to form a polyion and an oppositely charged gegenion. They can be polyacids, such as poly(acrylic acid)... 

When low-molecular-weight aldehydes such as methanal (formaldehyde, CH2=0) (Chapter 9) or ethanal (acetaldehyde, CH3CH=0) (Chapter 9) are treated with catalytic quantities of acids with non-nucleophilic gegenions (e.g., HBF4), cyclization to trimers (e.g., (CH20)3) (Thble 8.8) and tetramers (e.g., (CH3CFtO)4) (Table 8.8)... 

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