<my:DataGridTextColumn
                Visibility="{Binding Path=DataColumns[21].IsVisible, Source={StaticResource viewmodel}, Converter={StaticResource vc}}"
                Binding="{Binding SdDevDuration}"
                />

var newCol = new DataGridTextColumn();
newCol.Binding = new Binding("SdDevDuration");

var visiblityBinding = new Binding("IsVisible");
visiblityBinding.Source = col;
visiblityBinding.Converter = new VisibilityConverter();
BindingOperations.SetBinding(newCol, DataGridTextColumn.VisibilityProperty, visiblityBinding);