MPTMA • AMPS

Preparation of Poly(3-methacrylamidopropyltrimethylammo-nium-2-acrylamido-2-methylpropanesulfonate. Ten mL of an aque-ous solution composed of 1.96g (ca. 5 mmol) of MPTMA AMPS (mp 146.0-147.2°C) and 2.8 mg (0.2 mol % ) of ACVA were prepared. The solution was degassed, sealed, and placed in a thermostated bath at 55°C. After 10 hr the cloudy gel was dissolved in 200 mL of distilled water. 

The preparation of cationic-anionic monomer pairs (MPDMA AMPS and MPTMA AMPS) is best considered as the neutralization of a strong acid and a strong base, that is, AMPS and MPDMA, respectively (see Reaction 1). 

In the preparation of MPTMA AMPS, the ionic moieties seemed to be stable in dilute solution at room temperature. Thus, the lyophilization of a 5% solution yielded the cationic-anionic monomer pair directly. The NMR spectrum of MPTMA AMPS showed the same chemical shifts as those shown by MPDMA AMPS except for the methyl groups on the quatemized nitrogen. The quatemized ammonium group (of MPTMA) showed a slightly more deshielded effect on its methyl groups (83.12)... 

An alternative method of preparation for MPTMA AMPS involved the use of a cation-exchange resin, IRA-120 (Na+ form). The resin was saturated with methacrylamidopropyltrimethylammonium chloride, washed thoroughly with deionized water, and then washed with a dilute solution of AMPS. Lyophilization of the neutral eluent yielded the crude product. Some contamination of this product with sodium 2-acrylamido 2-methylpropanesulfonate was expected this species was removed with methylene chloride using soxhlet extraction, followed by recrystallization from chloroform to yield pure MPTMA AMPS. 

In the polymerization of the ion monomer pairs (which is carried out in aqueous solution) the cationic moieties (MPTMA+ or MPDMA+) and the anionic moiety (AMPS ) could have similar Q and e values, since they are the derivatives of acrylamide, resulting in a random incorporation of these units into the chain. Under these circumstances, a resulting network of ionically cross-linked chains seemed possible. Indeed, initially, hydrogels were formed in the polymerization of the monomer pairs of MPTMA AMPS and MPDMA AMPS. 

Preliminary viscosity studies in KC1 solution have been conducted for poly(MPTMA AMPS) and poly(MPDMA AMPS). The results are reported in Table I. The results shown came from treating the data in two ways using the Huggins equation (Equation 1) and plotting... 

For the preparation of poly(MPTMA/AMPS) and poly(METMA/MES), the monomers (12,13) and the initiator were mixed in two polymerization ampules as follows ampule 1 1.60 g (4.1 mmol) of ion-pair comonomer, MPTMA/AMPS, 10.7 mg (ca. 0.93 mol%) of 4,4 -azobis-4-cyanovaleric acid, ACVA, and deionized water to make the final volume to 50 ml of solution ampule 2 5.50 g (15.0 mmol) of ion-pair comonomer, METMA/MES, 17.0 mg (ca. 0.40 mol%) of ACVA and deionized water to make the final volume to 50 ml of solution. Both ampules were degassed by the freeze-thaw technique, evacuated and sealed. Ampule 1 was placed in a water bath at 50 C for 24 h and ampule 2 was placed in a water bath at 60°C for 9 h. The polymer solutions were then dialyzed exhaustively... 

Comparative plots of usual(+) and modified(a) Huggins Equation for A)poly(4VMP/pSS), B)poly(MPTMA/AMPS), and C)poly(METMA/MES) in 1.5 M aqueous NaCl solution. 

The third polyampholyte, poly(METMA/MES), followed the usual Huggins equation and showed typical polyampholyte behavior. This polymer should be a random copolymer of the two methacryl monomers and therefore should have a lower degree of disparity of the charges between different chains compared to poly(MPTMA/AMPS). 

Figure 3 represents the effect of added electrolyte concentration on the [nl obtained from the modified Huggins plot for poly(4VMP/pSS) and poly(MPTMA/AMPS), and the usual Huggins plot for poly(METMA/MES). The intrinsic viscosity increases with increasing salt concentration for all three ampholytic systems. Similar results are also reported for other polyampholyte-salt systems (6,13,27,28). This behavior may be rationalized on the basis of chain expansion which results in increased solute-solvent interaction. The [ri] is related to the hydrodynamic volume of macromolecules in solution (29). An expansion of the chain results in the viscosity increase due to an increase in effective hydrodynamic volume of the solute in the given solvent. It is expected that the added electrolyte would disrupt the intramolecular and intermolecular interactions and allow the polymers to behave more freely. Thus, the increase in [n] may be related to extended chain conformations resulting from the increased polymer-solvent interactions. 

Figure 2. Reduced viscosity as a function of polymer concentration for poly(MPTMA/AMPS) in 1)deionized water, 2)0.5 M aq. NaCl,...

Figure 3. Intrinsic viscosity as a function of salt concentration for 1)poly(4VMP/pSS), 2)poly(MPTMA/AMPS), 3)poly(METMA/MES).

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