Poly(2-imino-4-oxazolidinone)s via the Condensation of Diamidocarbenes with Bis(isocyanate)s

Abstract

S Supporting Information ■ INTRODUCTIONPolycyclic polymers continue to attract interest as high performance materials on account of their high degrees of chemical and thermal stabilities. 1,2 In particular, spiro-and other ladder-like polymers comprised of bicyclic repeat units wherein the rings connect through a common atom have received increasing attention due to their restricted rotational freedom and utility in forming thermally robust materials. 3,4 In some cases (e.g., the poly(spirobifluorene)s), the polycycles have been shown to adopt twisted helical structures that effectively prevented aggregation and enhanced their optical properties. 5−12 Unfortunately, the synthesis of spiro-polycycles is challenging due to the need for an efficient polymerization reaction that forms cyclic linkages between the repeating units. 12 Toward this end, we recently demonstrated that readily available N,N′-diamidocarbenes (DACs) 13−15 rapidly and selectively afford 2-imino-4-oxazolidinones 16 upon exposure to 2 equiv of an isocyanate. The reactivity was remarkable as most NHCs catalyze the cyclotrimerization of isocyanates to isocyanurates rather than undergoing cycloaddition chemistry. 17 We envisioned condensing DACs with bifunctional isocyanates to access new classes of polycycles with functionally rich heterocyclic cores. Herein we report the synthesis and study of novel polyspiro(iminooxazolidinone)s via the formal [2 + 2 + 1] cycloaddition of a stable DAC with various diisocyanates. The chemistry presented herein overcomes many of the challenges associated with the synthesis of stable spirocenters in polymeric materials and provides a unique approach to rapidly access a new structural class of polyheterocycles. ■ RESULTS AND DISCUSSIONPreviously, we demonstrated that an oxazolidinone forms upon treatment of DAC 1 with two equivalents of 3-nitrophenylisocyanate. In order to use this chemistry to form high molecular weight polymers, we anticipated that less polarized and more solubilizing diisocyanates, such as methylene diphenyl diisocyanate (MDI), would be advantageous. Thus, initial experiments focused on probing the reactivity and product selectivity of 1 with phenylisocyanate, a nonpolymerizable model. As summarized in Scheme 1, adding two equivalents of phenylisocyanate to a solution of 1 in benzene resulted in the initial formation of a purple solution that became colorless after stirring for an additional 1 h at room temperature. The product of this reaction (2) was subsequently isolated in high yield (98%) as a white solid by recrystallization from benzene/pentane. Characterization using 1 H and 13 C NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis supported the formation of a 2:1 isocyanate/DAC adduct. The structure of this product was unambiguously elucidated using single crystal X-ray diffraction (XRD) analysis (Figure 1, left), which confirmed the formation of the oxazolidinone heterocycle 2, rather than the isomeric hydantoin 3. 16 We postulated that the formation of 2 originate...

Multicomponent Spiropolymerization of Diisocyanides, Activated Alkynes, and Bis-Anhydrides

“…The introduction of spirorings in main polymer chains can not only improve the thermal and chemical stability of polymers , but also endow polymers with special properties, such as spiroconjugation, spiro-superconjugation, or heterohead effects. − Moreover, they are often applied in light-emitting devices, drug carriers, gas storage, and in the products of other fields. − The traditional strategies for the synthesis of spiropolymers mainly use presynthesized spiroring monomers to directly connect into the polymer main chain through metal-catalyzed condensation polymerization. However, this polymerization method usually has some disadvantages, such as cumbersome reaction processes, harsh polymerization conditions, difficulty in introducing multiple substituents, and a lack of suitable monomers. − At present, only a few non-spiroring monomers have been polymerized to obtain spiropolymers. − In 2019, Tang’s group developed a new polymerization method for preparing a series of new polysubstituted spiropolymers based on a palladium-catalyzed C–H activation reaction between naphthol and internal diacetylene . Therefore, the construction of spiropolymers based on non-spiroring monomers is a challenge in polymer synthesis chemistry.…”

Multicomponent Spiropolymerization of Diisocyanides, Diethyl Acetylenedicarboxylate, and Halogenated Quinones

“…[14][15][16] Bielawski's group developed a novel method to prepare spiro polymers using N,N'-diamidocarbenes and diisocyanates. [17] Jannasch et al synthesized N-spirocyclic polyelectrolytes with high alkaline stability and good conductivity from cyclopolycondensations of dipiperidines and tetrakis(bromomethyl) benzene. [18] Therefore, the construction of spiropolymers from easily synthesized monomers is a challenge in the synthetic chemistry of polymers.…”

“…[ 14–16 ] Bielawski's group developed a novel method to prepare spiro polymers using N , N' ‐diamidocarbenes and diisocyanates. [ 17 ] Jannasch et al. synthesized N ‐spirocyclic polyelectrolytes with high alkaline stability and good conductivity from cyclopolycondensations of dipiperidines and tetrakis(bromomethyl)benzene.…”

Diblock Copolymers with Similar Glass Transition Temperatures in Both Blocks for Comparing Shear Orientation Processes with DPD Computer Simulations

“…[14,15] With a deeper understanding of these dynamics, the formation of macroscopically oriented domains could be optimized to form macroscopically anisotropic mate rials for nanoscale patterning and other technical applica tions. [16][17][18][19][20][21][22][23][24][25] Often different properties of the polymers in BCPs are desired to tune the materials for different applications and further create new properties which are unique for BCPs, e.g., multiblock copolymers with different glass transition tempera tures in the different polymer blocks as thermoplastic elasto mers. [26,27] There are relatively few experimental investigations on BCPs with similar dynamic characteristics in each block and parameters for these systems are hard to find.…”