Polymerisable compounds and the use thereof in liquid-crystal displays

A compound of formula I

• wherein the individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings
• A1, A2 an alicyclic, heterocyclic, aromatic or heteroaromatic group with 4 to 30 ring atoms, which may also contain fused rings, and is optionally substituted by one or more groups L, R or P-Sp-,
• Z1, Z2 —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —OCH2—, —CH2O—, —SCH2—, —CH2S—, —CF2O—, —OCF2—, —CF2S—, —SCF2—, —(CH2)n1—, —CF2CH2—, —CH2CF2—, —(CF2)n1—, —CH═CH—, —CF═CF—, —CH═CF—, —CF═CH—, —C≡C—, —CH═CH—CO—O—, —O—CO—CH═CH—, —CH2—CH2—CO—O—, —O—CO—CH2—CH2—, —CR0R00—, or a single bond,
• R0, R00H or alkyl having 1 to 12 C atoms,
• Ra, Rb P-Sp-, R or H, wherein at least one of Ra and Rb denotes P-Sp-,
• Rc, Rd H, C1-12-straight-chain or C3-12-branched alkyl or C2-12-straight-chain or C3-12-branched alkenyl, wherein one or more H atoms are each optionally replaced by F or Cl,
• R H, F, Cl, —CN, or C1-25-straight chain, C3-25-branched or C3-25-cyclic alkyl, wherein one or more non-adjacent CH2-groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —N(R0)—, —Si(R0R00)—, —CH═CH— or —C≡C— in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl,
• P a polymerizable group,
• Sp a spacer group that is optionally substituted by one or more groups P, or a single bond,
• L F, Cl, —CN, P, P-Sp-, or C1-25-straight chain, C3-25-branched or C3-25-cyclic alkyl, wherein one or more non-adjacent CH2-groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —N(R0)—, —Si(R0R00)—, —CH═CH— or —C≡C— in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by P, P-Sp-, F or Cl,
• a, b 0, 1 or 2,
• r1, r2 0, 1, 2 or 3,
• n1 1, 2, 3 or 4.