Using Square Polypropylene container for no chill brewing

Regular Polypropylene will release mild to moderate toxins at high temperatures.

While Polypropylene (PP) is food-grade safe at room temperatures, and commonly used for containers (arguably safe for chilled wort according to comments in the previous link), the Energy Working Group gives it a "low" rating for overall hazard. My recommendation, don't use it for homebrewing when you have safer alternatives for the same price.

I can't comment on the safety of the material, but I can say that No Chilling does not really work if you try to drop the wort temps down before adding the liquid.

When the wort goes into the tank, it is the fact that the wort is very close to 100C/212F that guarantees against infection while its sealed. The super-hot wort does a wet pasteurization of all the surface area inside the vessel, and this is NOT the same as "sanitizing" via StarSan or iodine, as it is WAAAY more effective.

If you drop the temps of your wort down past 85C/185F or so, then the wort might not stay hot enough for long enough to do a true pasteurization of the tank. If that happens, you are guaranteeing an infection, ranging from immediate tank-swelling to more subtle off-flavors.

The temperature risk, combined with the less well known material (as it related to No Chilling), would lead me to recommend that you do not use these vessels. The "standard" No Chilling HDPE vessels run less than $20, so I can't see a reason to risk it with something else.