Side-chain intercrossing of poly(alkyl glutamate): LB and CP-MAS studies

The side-chain intercrossing of the substituted polyglutamate has been suspected as the main reason for the inhomogeneous monolayer at the air/water interface as well as the multi-domains in bulk. Before the side-chain melting at 60°C, the substituted chain intercrossing was confused by several experimental approaches. Here, we investigated the side-chain intercrossing of ethyl, hexyl, and stearyl substituted polyglutamate by surface pressure–surface area (π–A) isotherms and CP-MAS (cross-polarization magic angle spinning) NMR. We verify that the solvent drying process may be the main cause of the intercrossing of the side-chains in the glutamate polymers and provide the quantitative information about the intercrossing ratios for the side-chain polyglutamates. At room temperature, 60–90% of the total length of the side-chain intercrossed and the intercrossing ratios decreased at higher temperatures.