Preparation of cast elastomers using 2-methyl-1,3-propanediol as chain extender

A process for preparing transparent polyurethane elastomers having tensile strengths ranging from 9 MPa to 42 MPa comprising reacting in a open mold at an isocyanate index of 90 to 110

• (a) an isocyanate prepolymer having an isocyanate content of 2 to 15% by weight and having a molecular weight of from 800 to 5000, wherein said prepolymer is a reaction product of
• (i) at least one organic polyisocyanate with
• (ii) at least one isocyanate-reactive compound having at least two isocyanate-reactive groups and having a molecular weight of from 250 to 4000 selected from the group consisting of (1) polyethers, (2) polyesters prepared by reaction of polyhydric alcohols with polybasic carboxylic acids, polybasic carboxylic acid anhydrides, or polybasic carboxylic acid esters, and (3) mixtures thereof;
• with
• (b) 2-methyl-1,3-propanediol as chain extender, optionally in admixture with up to 10 percent by weight of a different chain extender having two isocyanate-reactive hydrogen atoms and having a molecular weight of from 32 to 250;
• optionally in the presence of
• (c) one or more catalysis and/or additives, thereby giving a transparent polyurethane elastomer having a tensile strength of 9 MPa to 42 MPa.