L-Methionine sulfoxide and L-alanine copolymers for ice control

Abstract

Amphiphilic copolymers are reported to show excellent ice control activity for their special interaction with ice and water. In this work, amphiphilic L-methionine sulfoxide and L-alanine copolymers (MSACPs) with different block ratio (PMeto48-b-PAlay), different molecular weight and random (P(Meto48-co-Ala20)) structures are prepared respectively to study the structure and ice control activity relationship. The ice control activity is well studied by ice nucleation, dynamic ice shaping (DIS) and ice recrystallization inhibition (IRI). The MSACPs are self-assembled into micelles from 11 to 78 nm in aqueous solution, which promotes the heterogeneous ice nucleation. For block copolymers with different block ratio (PMeto48-b-PAlay) and molecular weight, PMeto48-b-PAla20 with proper block ratio and molecular weight shows the highest nucleation temperature (-18.2 °C), excellent DIS and best IRI (the mean largest grain size is 34%) activities. And, for the block copolymers with similar block ratio to PMeto48-b-PAla20, the DIS and IRI is closely related to the molecular weight as the ice control property is enhanced at high molecular weight. Compared with PMeto48-b-PAla20, the corresponding random copolymer, P(Meto48-co-Ala20), shows weaker ice control activity. Meanwhile, low-field nuclear magnetic resonance results show that the polymer-water interaction is increasing with hydrophobic block ratio, but has less effect on the molecular weight. The ice control activity is probably related to the balance between polymer-water interaction and polymer-ice interaction, which is optimized at both strong interactions.