Separate [Advanced Custom Field] values by commas

Try to grab the output and echo together.

<?php $post_objects = get_field('field');
   if($post_objects!='') :
   $value = array(); ?>
   <?php foreach( $post_objects as $post): ?>
       <?php setup_postdata($post); ?>
       <?php $values[] = '<a href="'. get_permalink() .'">'. the_title('','',false) .'</a>'; ?>
   <?php endforeach; ?>
   <?php endif; ?>
<?php wp_reset_postdata(); ?>

<?php echo join( ', ', $values); ?>