For a start, rinse your hair through clear water before you get in the pool. Dry hair tends to act as a large sponge when it comes into contact with water, absorbing it very quickly and deeply. And this equally applies to chlorine.
But if you wet your first then this will reduce chlorine absorption and the risk of any damage. And try having short breaks, such as every 30 minutes or so where you leave the pool and rinse your hair off under clear water. This will also help to minimise the risk of chlorine-related damage.