Barrier membrane

Kit for preparing a cell-occlusive membrane, comprising

• a first precursor A comprising a core carrying n chains each having a conjugated unsaturated group or a conjugated unsaturated bond attached to any of the last 20 atoms of the chain and
• a second precursor B comprising a core carrying m chains each having a thiol group attached to any of the last 20 atoms of the chain,
• wherein
• m is greater than or equal to 2,
• n is greater than or equal to 2, and
• m+n is greater than or equal 5, and
• each core of the precursors forms a crosslinking-point if m and n are greater than 2, and
• if m is equal to 2 the corresponding crosslinking-point corresponds to the core of the adjacent first precursor A, and
• if n is equal to 2 the crosslinking-point corresponds to the core of the adjacent second precursor B, and
• the adjacent crosslinking-points are connected by a chain having less than 600 atoms,
• wherein the first precursor A and the second precursor B are separated from each other;
• and
• wherein the first precursor is selected from the group consisting of:
• where v=3 to 8.