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

[Display omitted] •Methyl cellulose was modified by introducing acylamino, carboxyl, and amino groups.•The macro−phase separation of MC solutions was eliminated after modification.•When above critical temperatures, modified products exhibited thermothickening.•The mechanism comes from the balance between hydrophilicity and hydrophobicity. 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 (Tass), MC solutions experienced obvious macro-phase separation and thermothinning phenomenon; on the contrary, HMMCs solutions exhibited thermo- and salt-thickening behaviors, and Tass 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.