Solvent-free polyurethane liquid membrane

A composition composed of:

• a first component comprising:
• at least one polymer polyol which is a dispersion of a polymer that is solid at room temperature in a polyether polyol that is liquid at room temperature,
• at least one diol chain extender
• and optionally other polyols;
• and
• a second component comprising:
• monomeric diphenylmethane diisocyanate;
• where at least one of the first component and the second component additionally comprises at least one aldimine of the formula (I),
• where
• A is an (m+n)-valent hydrocarbon moiety which optionally comprises ether units and which has from 2 to 20 C atoms,
• X is O or N—R5,
• R1 and R2 are mutually independently respectively a monovalent hydrocarbon moiety having from 1 to 12 C atoms, or together are a divalent hydrocarbon moiety which has from 4 to 12 C atoms and which is part of an optionally substituted carbocyclic ring having from 5 to 8;
• R3 is a hydrogen atom or is an alkyl or arylalkyl or alkoxycarbonyl moiety having from 1 to 12 C atoms;
• R4 is a monovalent hydrocarbon moiety which has from 6 to 20 C atoms and which optionally comprises ether units or aldehyde units;
• R5 is a monovalent hydrocarbon moiety which has from 1 to 30 C atoms and which optionally comprises at least one carboxylic ester group, nitrile group, nitro group, phosphonic ester group, sulfonic group or sulfonic ester group, or a group of the formula
• and
• m is 0 or 1, and n is 1 or 2 or 3, with the proviso that m+n is 2 or 3.