Monomer mixture and curable composition containing same

A monomer mixture containing at least:

• a compound represented by Formulas (a-1) and/or (a-2):
• a compound (2B′), represented by Formula (2b-1):
• where X represents a single bond or a linking group;
• a compound (3B′) represented by Formula (3b-1):
• where each R′ represents an aliphatic hydrocarbon group, and s represents an integer of 3 to 6, and
• a compound represented by Formula (c-1):
• wherein a total content of the compound represented by Formula (a-1) and the compound represented by Formula (a-2) is from 1 to 20 wt. % of a total amount of the monomer mixture;
• a content of the compound represented by Formula (c-1) is from 5 to 95 wt. % of the total amount of the monomer mixture, and
• the monomer mixture meets one of conditions [1] and [2] as follows:
• [1] a weight ratio of contents of the compound (2B′)/the compound (3B′) is from 0.1 to 0.8;
• and
• [2] a weight ratio of contents of the compound (2B′)/the compound (3B′) is from greater than 0.8 to 1.8, and a content of a compound or compounds containing two or more oxetanyl groups per molecule, including the compound represented by Formula (c-1), is from 45 to 95 wt. % of the total amount of the monomer mixture.