<?php
error_reporting(-1);

$test = <<<_END
intKey=6 , floatKey=12.34, simpleString=simple_value , booleanValue=true , 
quotedString="test\"value", singlQuoted='singlQuotedValue',nullValue=null,
willItWork="a=1,b=2,c=3"
_END;

function parseString($incomingString) {
	$result = [];
	$parts = preg_split('/,/u', $incomingString, 0, PREG_SPLIT_NO_EMPTY);
	
	foreach ($parts as $part) {
		$tempString = trim($part);
		$brokenString = preg_split('/=/u', $tempString, 0, PREG_SPLIT_NO_EMPTY);
		$result[$brokenString[0]] = $brokenString[1];
	}
	return $result;
}

$a = parseString($test);
print_r($a);