Technology Spotlight: Episode 5
1,3-Phenylene-bis-oxazoline: Welcome to the best kept secret for formulating hybrid thermoset resins
Overwhelmed by the versatility of Pyromellitic dianhydride, featured in Technology Spotlight: Episode 4? Well here comes another one, perhaps more of a sleeper, but no less important to your formulating success!
1,3-Phenylene-bis-oxazoline, (1,3-PBO or just plain PBO*), CAS# 34052-90-9, is a multi-purpose crosslinker that finds commercial use as a chain extender and compatibilizer for various types of thermoplastics. PBO solves many processing/ property challenges behind the scenes for both prime and recycled feedstocks. PBO is also a novel crosslinker for thermoplastic vulcanizates.
Oxazolines undergo a variety of ring opening reactions under suitable thermal and/or catalytic conditions, so let’s go in another direction and explore how PBO can add value to hybrid thermoset resin applications. Literature references include the following uses:
Crosslinker for polyaryletheramine (PEAR) resins, first developed by Ashland, scaled by SWRI, and advanced with catalyst technology by Evonik. PBO provides additional thermal stability and improved FST response.
Polybenzimidazole (PBI) modification with PBO for improved thermal and mechanical properties
Bisoxazoline (BOXP) resin synthesis via homopolymerization of PBO for improved Tg, FST, ILSS performance
Unsaturated polyester (UP) resin modification with PBO for chain extension, more rapid MW build
These examples illustrate PBO’s role as a building block to join various chemistries together into hybrid resins, mostly for the high-temperature aerospace and electronics sectors. But how is this realized?
Affinity for -OH and -COOH groups (acid scavenging)
Reactive and/or thermal ring opening for free-radical polymerization
Homo- and co-polymerization
So now there is a single compound that can potentially unite
Epoxy
Phenolic
Polyimide
Bismaleimide
Cyanate
Vinyl
chemistries and create new classes of hybrid resins with tailored processing/property characteristics for composites, adhesives, and coatings. Have all of these variations been proven? No, but they divert attention from traditional crosslinkers and open the door to fresh thinking.
What about supply, do you ask? While PBO may be familiar to some, sourcing has been a challenge. Manufacturers have come and gone, and in the present “China+1” supply chain landscape, a reliable producer of PBO is needed. Enter Nexam Chemical with NEXAMITE A99, a commercial-scale, made-in-USA, REACH-registered alternative.
Curious about trying this novel crosslinker for your next resin formulating project? Reach out for a free initial consultation today.
*PBO as an acronym may also refer to Polybenzoxazole (ex. Zylon), or Lead Oxide (PbO), outside the scope of this blog.