Polyamide pseudorotaxanes, rotaxanes, and catenanes based on bis(5-carboxy-1,3-phenylene)-(3x+2)-crown-x ethers

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 Kricheldorfs 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.