Polyamide Pseudorotaxanes, Rotaxanes, and Catenanes Based on Bis(5-carboxy-1,3-phenylene)-(3x+2)-crown-x Ethers

Abstract

We previously reported that the polyamide 3a derived from bis(5-carboxy-1,3-phenylene)-32-crown-10 (BCP32C10, 1a) and 4,4‘-oxydianiline (ODA, 2) was completely insoluble and attributed this to the formation of mechanical cross-links via self-threading of the crown ether moieties by the amide backbone through hydrogen bonding. Moreover, polycondensation of 1a with bis[4-(m-aminophenoxy)phenyl]phenylphosphine oxide (m-BAPPO, 4) produced polyaramide 5a that, like its analogue 3a, was insoluble in all solvents examined, including H2SO4. In the present work bis(5-carboxy-1,3-phenylene)−(3x+2)-crown-x ethers [BCP(3x+2)Cx] with 26-membered (BCP32C10, 1b), 20-membered (BCP20C6, 1c) and 14-membered (BCP14C4, 1d) rings were utilized to investigate further the proposed topological branching via in situ threading during polymerization. Condensation of BCP26C8 (1b) with ODA (2) and m-BAPPO (4) gave two new poly(amide crown ether)s, 3b and 5b, which were soluble in dipolar aprotic solvents. However, the GPC traces of aramides 3b and 5b exhibited bimodal behavior indicative of two distinct molecular weight fractions, one very high, DPn > 800! Similarly the aramide 3c formed by condensation of BCP20C6 (1c) and ODA (2) displayed a bimodal GPC curve. As a reference system BCP14C4 (1d) was prepared and polymerized with ODA; the resultant aramide 3d displayed a monomodal GPC trace and relatively narrow molecular weight distribution. Mass spectrometric studies show that cyclic aramides (lactams) form in the larger crown ether-based systems 3b and 5b. Model aramide 6 from isophthalic acid and ODA also contains cyclic polymers, as expected from Kricheldorf's recent results, but has a “normal” molecular weight distribution. Mass spectrometric examination of aramides 3c and 3d does not indicate any cyclic polymer formation. Inasmuch as lactam formation by itself does not necessarily produce branching or cross-linking, e.g., 6, we conclude that threading of the crown ether moieties is the key step, leading to polypseudorotaxane, polyrotaxane and polycatenane structures to an extent dependent upon the their cavity size and the propensity for cyclization of the polymer backbone.

Synthesis and characterization of new aromatic polyamides bearing crown ethers and acyclic ethylene oxide units in the pendant structure. III. Benzo‐18‐crown‐6 systems and their open‐chain counterparts

“…On the basis of this, Gibson et al 22 indicated the possible formation of polyrotaxanes, catenanes, and polycatenanes due to cyclization in the polymerization reaction. The highmembered ring cycles can first form branched polyamides that can finally progress to networks because of crosslinked catenate species.…”

The Role of Self‐Dilution in Step‐Growth Polymerizations

“…(5) Threading of cycles on linear polymers (pseudorotaxanes) and the formation of catenanes may take place as suggested by the experiments of Gibson and coworkers. [42] In summary, it may be concluded that self-dilution (plus self-acceleration) more or less compensates or overcompensates the reduction of Ct resulting from increasing chain length. At this point it should be mentioned that this conclusion is also relevant for the proper understanding of Equation (2).…”

Crown Ether‐Based Polymeric Rotaxanes

“…Recently, a new class of polyaramides has been synthesized by Gibson et al that contain the crown ether motif in the repeat unit [16]. The class is synthesized using a step growth reaction with a given bis(5-carboxy-1,3-phenylene)crown ether (BCP) and a diamine.…”