Hydrophilic modification of methylcellulose to obtain thermoviscosifying polymers without macro-phase separation

Methylcellulose (MC) has received considerable attention because of its thermogelation behavior in aqueous solutions upon heating; however, the accompanied macro-phase separation results in demixing and detriment of thickening power. To alleviate this drawback, a novel family of hydrophilically modified methylcelluloses (HMMCs) was prepared by introducing acylamino, carboxyl, and amino groups onto MC side chains. Above association temperature (T_ass), MC solutions experienced obvious macro-phase separation and thermothinning phenomenon; on the contrary, HMMCs solutions exhibited thermo- and salt-thickening behaviors, and T_ass could be adjusted from 44 °C to 87 °C by altering the nature of HMMCs or salt content in solutions. The mechanism to eliminate the macro-phase separation of HMMC stems from the balance between hydrophilicity and hydrophobicity. This work opens a new avenue for cellulose derivatives to sustain their thermoviscosifying ability and widen their applications in hostile environments.