Synthesis and Thermal Curing of Benzoxazine Functionalized Polyurethanes

Abstract

Benzoxazine (BOX) functionalized polyurethanes (PU) are introduced to provide a conceptually new thermal curing mechanism for polyurethanes. 3,4-Dihydro-3-methyl-2H-1,3-benzoxazine (P-m) was carefully oligomerized through thermal treatment. In a straightforward synthesis the newly formed hydroxyl groups are used for end-capping reactions with isocyanate-terminated polyurethane prepolymers. The isocyanate reactive hydroxyl content (IRH) of the benzoxazine oligomer was investigated in detail via 1 H NMR spectroscopy, HPLC-MS, indirect potentiometric titration in various solvents, and comparison with model substances and found to be strongly influenced by hydrogen bonding. The corresponding polyurethane/benzoxazine hybrid materials (PU/BOX) can cross-link at elevated temperatures and do not suffer from shelf-life issues or outgassing of blocked isocyanates. The thermally activated curing reaction was investigated via rheology and DSC. Significant improvements over state-of-the-art systems based on phenol-capped PU prepolymers are shorter curing times, increased moduli, and drastically increased glass transition temperatures.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

“…The H-bonding between the hydroxyl groups of polybenzoxazine influences physical crosslinks due to extension of intermolecular H-bonding with the polar functionalities (carbonyl, ether, amine, hydroxyl) present in other polymers such as poly(ɛ-caprolactone) (PCL) [ 354 , 355 , 356 ], poly(ethylene oxide), [ 357 , 358 ] chitosan (CS) [ 359 , 360 , 361 , 362 ], amino-cellulose [ 363 ] and polyurethane [ 364 , 365 , 366 , 367 ]. Although, the effect of OH groups on the polymerization of –OH or –NH 2 containing benzoxazine monomers, non-benzoxazine monomers and polymers is not explicitly stated.…”

A Nanocapsule‐Based Approach Toward Physical Thermolatent Catalysis

“…For thermosetting polymers, standard catalysts accelerate the curing kinetics, but on the downside reduce the timeframe of processability . Established solutions include the use of blocked isocyanates, surface deactivated micronized isocyanate powders or UV‐curable hybrid systems . However, they suffer from drawbacks like high temperature requirements or restriction to transparent films of low UV‐absorption .…”

Poly(benzoxazine-co-urea): A Solventless Approach Towards The Introduction of Alternating Urea Linkages In Polybenzoxazine

“…Self polymerizable monomers can be integrated in the polymeric network by functionalizing the benzoxazine with the co‐monomer, followed by thermal treatment (Figure , Approach 1) . Blending/reaction of benzoxazine with co‐monomer is usually performed, where the monomer mandates a curing agent (Figure , Approach 2) . Baqar et al .…”