and textiles to transportation, construction, and electronics. As a cornerstone of
modern society, plastics and related organic compounds are continually evolving,
under the umbrella of fundamental research, into materials with ever more diverse
and tailorable physical properties. The fact that solution-processable organic materials are continually growing in their scope and reach provides ample motivation to
explore the properties of new classes organic polymers with well-defined (super)
structures in solution.
3.1 Folding in D–A Polyrotaxanes
Around the time that the copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition
(CuAAC) click reaction was emerging as a powerful tool for the construction [110,
111] of MIMs, we became interested in using this reaction to prepare
polyrotaxanes. Our first attempt turned up compelling evidence that the folded
solid-state structures described in Sect. 2 also persist to a large extent in solution.
We used CuAAC in the step-growth copolymerization of the azide-terminated
DNP monomer BN 3 EEN and the propargyl-terminated DNP monomer BPEEN to
prepare polymeric DNP threads. Applying different feed ratios (N BPEEN /N BN3EEEN )
of 0.905, 0.975, and 1.000 gives polyDNP dumbbells 81NPE(N 3 ) 2 (MW 32 kD;
polydispersity index, PDI 1.90), 133NPE(N 3 ) 2 (53 kDa, PDI 1.78), and 453NPE
(N 3 ) 2 (181 kDa, PDI 1.71) as products in the click reaction (Table 1) with a number
average n of approximately 81, 133, and 453 DNP units per chain, respectively.
Finishing the reaction with a slight excess of BN 3 EEN ensured that the dumbbells
were terminated with azide functionalities so that their corresponding
pseudorotaxanes could be subsequently stoppered with CuAAC using a bulky
propargyl-functionalized stopper. The threading reaction took 24 h to reach equilibrium after the addition of 0.6 equivalents of CBPQT
4+ with respect to the DNP
units. The slow equilibration was expected because threading can occur only at the
ends of the polymer, requiring each ring to migrate further toward the interior sites
of the polymer before new rings can thread. The final click reaction to stopper the
polypseudorotaxanes was initiated when the charge transfer absorption band near
λ ¼ 500 nm (characteristic of DNP & CBPQT
4+ complexes) reached its maximum
intensity. The pure polyrotaxane products 81NPR
4m+
, 133NPR
4m+
, and 453NPR
4m+
were obtained by precipitation into an aqueous EDTA solution to remove copper,
filtration through a DNP-functionalized membrane in DMF to eliminate unbound
CBPQT
4+
, and precipitation into CHCl 3 to remove uncharged monomers and low
molecular weight (LMW) oligomers.
1
H NMR spectroscopic analysis was used to
estimate DNP site coverage to be 90, 74, and 58%, respectively, corresponding to the
average values for m (number of threaded CBPQT
4+ rings) given in Table 1.
The polyDNP threads and corresponding rotaxanated polyelectrolytes were
characterized by gel permeation chromatography (GPC) in DMF. All three
polyrotaxanes exhibited smaller hydrodynamic radii than their parent threads, as
indicated by their increased retention volumes (Table 1, Fig. 6). The apparently
Mechanically Interlaced and Interlocked Donor–Acceptor Foldamers
279
modern society, plastics and related organic compounds are continually evolving,
under the umbrella of fundamental research, into materials with ever more diverse
and tailorable physical properties. The fact that solution-processable organic materials are continually growing in their scope and reach provides ample motivation to
explore the properties of new classes organic polymers with well-defined (super)
structures in solution.
3.1 Folding in D–A Polyrotaxanes
Around the time that the copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition
(CuAAC) click reaction was emerging as a powerful tool for the construction [110,
111] of MIMs, we became interested in using this reaction to prepare
polyrotaxanes. Our first attempt turned up compelling evidence that the folded
solid-state structures described in Sect. 2 also persist to a large extent in solution.
We used CuAAC in the step-growth copolymerization of the azide-terminated
DNP monomer BN 3 EEN and the propargyl-terminated DNP monomer BPEEN to
prepare polymeric DNP threads. Applying different feed ratios (N BPEEN /N BN3EEEN )
of 0.905, 0.975, and 1.000 gives polyDNP dumbbells 81NPE(N 3 ) 2 (MW 32 kD;
polydispersity index, PDI 1.90), 133NPE(N 3 ) 2 (53 kDa, PDI 1.78), and 453NPE
(N 3 ) 2 (181 kDa, PDI 1.71) as products in the click reaction (Table 1) with a number
average n of approximately 81, 133, and 453 DNP units per chain, respectively.
Finishing the reaction with a slight excess of BN 3 EEN ensured that the dumbbells
were terminated with azide functionalities so that their corresponding
pseudorotaxanes could be subsequently stoppered with CuAAC using a bulky
propargyl-functionalized stopper. The threading reaction took 24 h to reach equilibrium after the addition of 0.6 equivalents of CBPQT
4+ with respect to the DNP
units. The slow equilibration was expected because threading can occur only at the
ends of the polymer, requiring each ring to migrate further toward the interior sites
of the polymer before new rings can thread. The final click reaction to stopper the
polypseudorotaxanes was initiated when the charge transfer absorption band near
λ ¼ 500 nm (characteristic of DNP & CBPQT
4+ complexes) reached its maximum
intensity. The pure polyrotaxane products 81NPR
4m+
, 133NPR
4m+
, and 453NPR
4m+
were obtained by precipitation into an aqueous EDTA solution to remove copper,
filtration through a DNP-functionalized membrane in DMF to eliminate unbound
CBPQT
4+
, and precipitation into CHCl 3 to remove uncharged monomers and low
molecular weight (LMW) oligomers.
1
H NMR spectroscopic analysis was used to
estimate DNP site coverage to be 90, 74, and 58%, respectively, corresponding to the
average values for m (number of threaded CBPQT
4+ rings) given in Table 1.
The polyDNP threads and corresponding rotaxanated polyelectrolytes were
characterized by gel permeation chromatography (GPC) in DMF. All three
polyrotaxanes exhibited smaller hydrodynamic radii than their parent threads, as
indicated by their increased retention volumes (Table 1, Fig. 6). The apparently
Mechanically Interlaced and Interlocked Donor–Acceptor Foldamers
279