A Simple and Facile Approach to Aliphatic N-Substituted Functional Eight-Membered Cyclic Carbonates and Their Organocatalytic Polymerization

Abstract

Aliphatic N-substituted functional eight-membered cyclic carbonates were synthesized from N-substituted diethanolamines by intramolecular cyclization. On the basis of the N-substituent, three major subclasses of carbonate monomers were synthesized (N-aryl, N-alkyl and N-carbamate). Organocatalytic ring opening polymerization (ROP) of eight-membered cyclic carbonates was explored as a route to access narrowly dispersed polymers of predictable molecular weights. Polymerization kinetics was highly dependent on the substituent on the nitrogen atom and the catalyst used for the reaction. The use of triazabicyclodecene (TBD), instead of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), as the catalyst for the N-alkyl substituted monomers significantly enhanced the rate of polymerizations. Computational studies were performed to rationalize the observed trends for TBD catalyzed polymerizations. With the optimal organocatalyst all monomers could be polymerized generating well-defined polymers within a timespan of ≤2 h with relatively high monomer conversion (≥80%) and low molar-mass dispersity (Đ(M) ≤ 1.3). Both the glass transition temperatures (T(g)) and onset of degradation temperatures (T(onset)) of these polymers were found to be N-substituent dependent and were in the range of about -45 to 35 °C and 230 to 333 °C, respectively. The copolymerization of the eight membered monomers with 6-membered cyclic comonomers including commercially available l-lactide and trimethylene carbonate produced novel copolymers. The combination of inexpensive starting materials, ease of ring-closure and subsequent polymerization makes this an attractive route to functional polycarbontes.

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“…The former can be achieved utilizing cyclic carbonates, which can provide pendant side‐chain functionality (such as tert‐butyloxycarbonyl (BOC)‐protected amines), and the latter includes the use of (meth)acrylates to provide an end‐chain reactive double bond . Ideally, a combination of the two approaches can result in the flexibility to synthesize a wide range of possible polymeric functionalities and structures which can undergo further reactions post‐polymerization …”

Broad Spectrum Macromolecular Antimicrobials with Biofilm Disruption Capability and In Vivo Efficacy

“…Recently, we used N ‐methyldiethanolamine as an inexpensive and readily available initial material to synthesize eight‐membered heterocyclic carbonate monomer . Subsequent organocatalytic polymerization of the monomer affords a polycarbonate with a heteroatom in the backbone capable of subsequent quaternization with methyl iodide ( Scheme ).…”

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“…1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU) has been studied as an efficient organocatalyst for the ROP of both six‐membered and eight‐membered cyclic carbonates with the carbamate group . In our previous work, well‐controlled ROP of six‐membered cyclic monomers C1 and C2 (Scheme ) was explored using DBU as a catalyst and 4‐methoxybenzyl alcohol (4‐MeOBnOH) as an initiator in CH 2 Cl 2 at 25 °C.…”

“…Recently, a series of aliphatic N ‐substituted eight‐membered cyclic carbonates were synthesized from diethanolamine (DEA) with moderate yields. These monomers could be polymerized under organic base catalysis, and the ROP rates were dependent on the structure of the N ‐substitutes as well as the catalysts . The inexpensive and readily available starting material, ease of functionalization of the secondary amine, and the regulated ROP rate enable this type of eight‐membered cyclic carbonates promising monomers for the development of varied versatile functional PCs …”