*Article* **pH Behavior of Polymer Complexes between Poly(carboxylic acids) and Poly(acrylamide derivatives) Using a Fluorescence Label Technique**

#### **Yuriko Matsumura 1,\* and Kaoru Iwai 2,\***


Received: 19 June 2019; Accepted: 11 July 2019; Published: 17 July 2019

**Abstract:** In order to clarify the local environment during interpolymer complex formation between poly(carboxylic acids) and poly(acrylamide derivatives) with di fferent *N*-substitutions, a fluorescence label technique was used. 3-(2-propenyl)-9-(4- *<sup>N</sup>*,*<sup>N</sup>*-dimethylaminophenyl) phenanthrene (VDP) was used as an intramolecular fluorescence probe. All polymers were synthesized by free radical polymerization. Interpolymer complexation was monitored by charge transfer emission from the VDP unit. Both of the poly(carboxylic acids) formed interpolymer complexes with poly( *<sup>N</sup>*,*<sup>N</sup>*-dimethylacrylamide) (polyDMAM). The micro-environments around the VDP unit in the acidic pH region for the poly(methacrylic acid) (polyMAAc) and polyDMAM mixed systems were more hydrophobic than those of the poly(acrylic acid) (polyAAc) and polyDMAM mixed systems, as the α-methyl group of the MAAc unit contributed to hydrophobicity around the polymer chain during hydrogen bond formation. This suggests that, when the poly(carboxylic acids) and poly(acrylamide derivatives) were mixed, with a subsequent decrease in the solution pH, a hydrogen bond was partially formed, following which the hydrophobicity of the micro-environment around the polymer chains was changed, resulting in the formation of interpolymer complexes. Moreover, the electron-donating ability of the carbonyl group in the poly(acrylamide derivatives) had an e ffect on complexation with poly(carboxylic acids).

**Keywords:** poly(acrylic acid); poly(methacrylic acid); poly(acrylamide derivatives); complexation; fluorescence label technique
