$re = '/^\{(((?<url>\'\S+\') : ExpandedURL:\{(?<exp_url>\S+)}(?:, |\}))+)/m';
$str = '{\'https://www.google.com/search?q=red+cars\' : ExpandedURL:{https://www.google.com/search?q=red+cars&sca_esv=3c36029106bf5d13&source=hp&ei=QTuIaI_t...}, \'https://www.youtube.com/watch?v=dQw4w9WgXcQ\' : ExpandedURL:{https://www.youtube.com/watch?v=dQw4w9WgXcQ/diuwheiyfgbeioyrg/39486y7834....}, \'https://www.reddit.com/\' : ExpandedURL:{https://www.reddit.com/r/regex/...}}';
preg_match_all($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