First Investigation of the Kinetic Hydrate Inhibition of a Series of Poly(β-peptoid)s on Structure II Gas Hydrate, Including the Comparison of Block and Random Copolymers

A series of poly(β-peptoid)s, specifically poly(N-alkyl-β-alanine) homopolymers and copolymers with various N-alkyl substituents, have been synthesized. The activity of poly(β-peptoid)s as kinetic hydrate inhibitors (KHIs) was studied for the first time. Gas hydrate inhibition was studied in high-pressure rocking cells using a synthetic natural gas blend to promote the formation of gas hydrate structure II. The best gas hydrate kinetic inhibition was observed with poly(N-ethyl-β-alanine)-co-N-propyl-β-alanine) with a molecular weight of 4075 Da. The structure–activity relationship (SAR) observed in this investigation confirms the notion that, for water-soluble polymers, the presence of larger aliphatic side chains leads to improved kinetic inhibition. Two isomeric forms of poly(N-ethyl-β-alanine)-co-N-propyl-β-alanine) were studied, a random copolymer and a block copolymer. The random isomeric form performed better than the block analogue. This fact suggests that the correct molecular spacing of the monomeric units is required for best kinetic hydrate inhibition. To our knowledge, this is the first report comparing the KHI performance of random and block copolymers of the same molecular weight and empirical formula