$re = '/^.*Optional Imprint[^.]*\./m';
$str = 'Front: 1 1/2" W x 1" H ... Back: 2 1/4" W x 1 1/4" H Standard Imprint Area is the front. Optional Imprint Area is the back. Imprint on Standard Location Unless Otherwise Specified on Order. For Printing on Both Positions, Add $40.00(G) Set Up Plus .25(G) Per Piece.';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php