Hydrophobically associating polymer thermal stability

This conclusion has been reached in the copolymerization of acrylic acid (AA) and methacrylic acid (MAA) with N-vinylpyrrolidone (34, 35) (a monomer noted for its thermal stability (36) and discussed in Chapter 9) and with acrylamide (37). The incorporation of the acid monomer in the copolymer decreases with increasing solution pH. The r values with MAA are particularly low at pH <5 because of hydrophobic associations of the methyl groups. Laser-Raman studies (38) have also indicated intramolecular association among the methyl groups of syndiotactic poly(methacrylic acid) (PMAA) in aqueous solution. The addition of NaCl, at a moderate pH, increases the amount of neutralized, weak acid monomer incorporated (Table III). A more gradual change is observed with pH in the MAA-AM combination than in the AA-AM pair because of the hydrophobic interactions cited. The relationships are nearly quantitative with the ionization of the acids as reflected by the pK of the monomer and polymer acid sequences. 

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