PHP - split String in Key/Value pairs

if you change your string to use & instead of , as the delimiter, you can use parse_str()

<?php parse_str(str_replace(", ", "&", "key=value, key2=value2"), $array); ?>

If you don't mind using regex ...

$str = "key=value, key2=value2";
preg_match_all("/([^,= ]+)=([^,= ]+)/", $str, $r); 
$result = array_combine($r[1], $r[2]);
var_dump($result);

If you can change the format of the string to conform to a URL query string (using & instead of ,, among other things, you can use parse_str. Be sure to use the two parameter option.