Poly(p-phenylene-2,6-benzobisoxazole) - Zylon

[M_K301]

I am researching polymers used in making Ballistic Vests and Zylon, Poly(p-phenylene-2,6-benzobisoxazole), is one of the polymers chosen.

Basic Information/ Structure:
http://www.matweb.com/search/datasheet.aspx?matguid=140045b4f06c4aea89f8900f4c7bb4fc&ckck=1"
http://www.toyobo.co.jp/e/seihin/kc/pbo/gif/structure.jpg

PBO is a thermosetting polymers however I cannot figure out how it can form cross-links or hydrogen bonds which make polymers thermosetting.

So I was wondering how it forms crosslinks to make it a thermosetting polymer.

And I also was wondering why it has such good flame retardancy, high limiting oxygen index and high decomposition temperature (650 C).

I know that the oxygen and nitrogen in the oxazoline are partially negative which can act as hydrogen bonds acceptor but there are no positive hydrogen from what I can tell. I thought maybe the compound structure could change to form crosslinks or hydrogen bonds when heat treated but couldn't find information.Thank you.

 

[Nino MMP]

Thermosetting polymers form crosslinks through the use of curing agents. These curing agents can be either in the form of a catalyst or an additive. The curing agent helps to break apart the polymer chains and form covalent bonds between them, forming a stronger network of molecules. This strong network makes it more difficult for the polymer chains to move, resulting in a thermoset material that is not easily deformed by heat or pressure. The good flame retardancy, high limiting oxygen index, and high decomposition temperature of Zylon, Poly(p-phenylene-2,6-benzobisoxazole), is due to its chemical structure. The oxazoline ring in the structure contains both oxygen and nitrogen atoms which gives it good flame retardancy. The oxygen atoms also act as both hydrogen bond donors and acceptors, allowing for strong intermolecular interactions that result in a higher decomposition temperature. In addition, the aromatic rings in the structure are highly resistant to oxidation, leading to the high limiting oxygen index.