Conjugated Polymers with Self-Immolative Sidechain Linkers for Carbon Nanotube Dispersion.

Single-walled carbon nanotubes (SWNTs) are promising materials for generating high-performance electronic devices. However, these applications are greatly restricted by their lack of purity and solubility. Commercially available SWNTs are a mixture of semi-conducting (sc-) and metallic (m-) SWNTs and are insoluble in common solvents. Conjugated polymers can selectively disperse either sc- or m-SWNTs and increase their solubility; however, the conductivity of conjugated polymer-wrapped SWNTs is largely affected by the polymer side chains. Here, a poly(fluorene-co-phenylene) polymer that contains a self-immolative linker as part of its sidechains is reported. The self-immolative linker is stabilized with a tert-butyldimethylsilyl ether group that, upon treatment with tetra-n-butylammonium fluoride (TBAF), undergoes a 1,6-elimination reaction to release the sidechain. Sonication of this polymer with SWNTs in tetrahydrofuran (THF) results in concentrated dispersions that are used to prepare polymer-SWNT thin films. Treatment with TBAF caused side-chain cleavage into carbon dioxide and the corresponding diol, which can be easily removed by washing with solvent. This process is characterized by a combination of absorption and Raman spectroscopy, as well as four-point probe measurements. The conductance of the SWNT thin films increased ≈60-fold upon simple TBAF treatment, opening new possibilities for producing high-conductivity SWNT materials for numerous applications.

Incorporation of Loratadine-Cyclodextrin Complexes in Oral Thin Films for Rapid Drug Delivery.

Rapidly dissolving polymer thin films, or oral thin films (OTFs), have recently emerged as an improved oral drug delivery vehicle with its ability to bypass liver first pass metabolism, longer shelf-life, and simpler transport and distribution requirements, compared to traditional tablets and liquid formulations. Loratadine (LOR), an antihistamine commonly used to treat allergic rhinitis, undergoes liver first pass metabolism and is a prime candidate for incorporation within an OTF. However, loratadine is a BCS II drug with low aqueous solubility. Herein, the solubility of loratadine was improved by complexation with methyl ß-cyclodextrin (MBCD) by co-evaporation of 2:1, 1:1, and 1:2 LOR:MBCD ratios and incorporation into a pullulan-based OTF at 4 wt% by solvent casting at 50 °C for 30 - 35 min. A therapeutically relevant 10 mg LOR dose could be prepared in a 3 cm by 3 cm OTF. The feasibility of complexation was observed with a Bs-type phase solubility diagram, and complexation itself was confirmed via differential scanning calorimetry (DSC) by disappearance of the LOR melting peak, Fourier-transform infrared spectroscopy (FTIR) by shifting of the C=O peak, via 1H NMR spectroscopy by downfield shifting and change in peak multiplicity of the LOR aromatic protons, and via diffusion-ordered spectroscopy by a decrease in the diffusion coefficient of LOR:MBCD complex. LOR:MBCD could be incorporated homogeneously throughout an OTF, and LOR:MBCD OTFs exhibited reasonable mechanical strength and endured 12 ± 3 folds before breaking. LOR:MBCD OTFs disintegrated within 38 ± 10 s. The cumulative in vitro release of LOR:MBCD OTFs peaked at 80 % within 3-4 min of dissolution, and LOR in LOR:MBCD OTFs exhibited permeability across a 0.22 µm nitrocellulose membrane, demonstrating its applicability as a rapid drug delivery vehicle.

Intramacromolecular Conformational Changes in Low Generation PAMAM Dendrimers Probed by Pyrene Excimer Formation.

Pyrene excimer formation (PEF) was used to probe the intramacromolecular conformational change experienced by low generation pyrene-labeled PAMAM dendrimers referred to as PyCX-PAMAM-GY, where X (=4, 8, or 12) and Y (=0, 1, or 2) represent the number of atoms in the pyrenyl linker and the dendrimer generation, respectively. Each sample was studied in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) with and without 5 mM HCl. Global analysis of the monomer and excimer time-resolved fluorescence decays using the model free analysis (MFA) yielded the average rate constant of excimer formation, ⟨k⟩, which was compared with the local pyrene concentration ([Py]loc) of the PyCX-PAMAM-GY samples calculated by assuming that the oligomeric segments constituting the dendrimer's interior obeyed Gaussian statistics. A notable decrease in ⟨k⟩ was observed upon the addition of 5 mM HCl to the PyCX-PAMAM-GY solutions and was attributed to swelling of the dendrimers resulting from the protonation of the internal tertiary amines. The reversibility of this conformational change could also be monitored via PEF. Solvent differences between DMF and DMSO were accounted for by dividing ⟨k⟩ by kdiff, the bimolecular rate constant for diffusive PEF of a n-hexyl-1-pyrenebutyramide model compound, to yield the ⟨k⟩/kdiff ratio. Comparison between the ⟨k⟩/kdiff ratios obtained for all the PyCX-PAMAM-GY samples with and without 5 mM HCl revealed a 13% increase in the radius of the PAMAM-GY dendrimers upon protonation of their internal tertiary amines in agreement with earlier reports. These experiments illustrate that PEF represents a powerful experimental means to quantitatively probe the intramacromolecular conformational changes of complex macromolecules in solution, in a manner that complements scattering techniques.

Molecular Sieving with PEGylated Dendron-Protein Conjugates.

A series of generation 3-5 dendrons based on a bis(2,2-hydroxymethylpropionic acid) (bis-MPA) scaffold bearing three respective lengths of linear poly(ethylene glycol) at their periphery and a dibenzocyclooctyne unit at their core was prepared. These dendrons were appended to the surface of azide-decorated α-chymotrypsin (α-CT) via strain-promoted azide-alkyne cycloaddition to yield a library of dendron-protein conjugates. These conjugates were characterized by FT-IR and NMR spectroscopy and were imaged using cryo-electron microscopy. The activity of the PEGylated α-CT-dendron conjugates was investigated using a small molecule (benzoyl-l-tyrosine p-nitroanilide) as well as different proteins of different sizes and crystallinities (casein and bovine serum albumin) as substrates. It was found that the activity of the conjugates toward the small molecule was largely retained, while the activity toward the proteins was significantly diminished. Furthermore, the results indicate that for most of the conjugates the PEG length had a more pronounced impact on enzyme activity than the dendron generation. Overall, the highest sieving ratios were found for α-CT-dendron conjugates decorated with G3-PEG2000, G4-PEG2000, and G5-PEG1000, with the latter two structures offering the best combination of sieving ratio and small molecule activity.

Decoration of Polyfluorene-Wrapped Carbon Nanotubes with Photocleavable Side-Chains.

Functionalizing polyfluorene-wrapped carbon nanotubes without damaging their properties is effective via Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC). However, the length and nature of polymer side-chains can impact the conductivity of polyfluorene-SWNT films by preventing close contact between the nanotubes. Here, we investigate the functionalization of a polyfluorene-SWNT complex using photocleavable side-chains that can be removed post-processing. The cleavage of the side-chains containing an ortho-nitrobenzyl ether derivative is efficient when exposed to a UV lamp at 365 nm. The photoisomerization of the o-nitrobenzyl ether linker into the corresponding o-nitrosobenzaldehyde was first monitored via UV-Vis absorption spectroscopy and 1H-NMR spectroscopy on the polymer, which showed efficient cleavage after 2 h. We next investigated the cleavage on the polyfluorene-SWNT complex via UV-Vis-NIR absorption spectroscopy. The precipitation of the nanotube dispersion and the broad absorption peaks after overnight irradiation also indicated effective cleavage. In addition, Raman spectroscopy post-irradiation showed that the nanotubes were not damaged upon irradiation. This paper reports a proof of concept that may find applications for SWNT-based materials in which side-chain removal could lead to higher device performance.

Excess Polymer in Single-Walled Carbon Nanotube Thin-Film Transistors: Its Removal Prior to Fabrication Is Unnecessary.

Ultrapure semiconducting single-walled carbon nanotube (sc-SWNT) dispersions produced through conjugated polymer sorting are ideal candidates for the fabrication of solution-processed organic electronic devices on a commercial scale. Protocols for sorting and dispersing ultrapure sc-SWNTs with conjugated polymers for thin-film transistor (TFT) applications have been well refined. Conventional wisdom dictates that removal of excess unbound polymer through filtration or centrifugation is necessary to produce high-performance TFTs. However, this is time-consuming, wasteful, and resource-intensive. In this report, we challenge this paradigm and demonstrate that excess unbound polymer during semiconductor film fabrication is not necessarily detrimental to device performance. Over 1200 TFT devices were fabricated from 30 unique polymer-sorted SWNT dispersions, prepared using two different alternating copolymers. Detailed Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) studies of the random-network semiconductor films demonstrated that a simple solvent rinse during TFT fabrication was sufficient to remove unbound polymer from the sc-SWNT films, thus eliminating laborious polymer removal before TFT fabrication. Furthermore, below a threshold polymer concentration, the presence of excess polymer during fabrication did not significantly impede TFT performance. Preeminent performance was achieved for devices prepared from native polymer-sorted SWNT dispersions containing the "original" amount of excess unbound polymer (immediately following enrichment). Lastly, we developed an open-source Machine Learning algorithm to quantitatively analyze AFM images of SWNT films for surface coverage, number of tubes, and tube alignment.

Postsynthetic Modification of a Covalent Organic Framework Achieved via Strain-Promoted Cycloaddition.

Two-dimensional covalent organic frameworks (2D COFs) are layered, structurally regular, and permanently porous macromolecules. When reactive groups are embedded into a COF structure, subsequent chemical reactions can be performed following polymerization. As such, a postsynthetic modification (PSM) strategy provides diverse materials from a single set of COF monomers and polymerization protocols. Here, we report the synthesis of an asymmetric dibenzocyclooctyne-containing imine-linked 2D COF, which readily undergoes strain-promoted azide-alkyne cycloaddition (SPAAC) reactions without catalyst under mild and dilute conditions. This approach was used to quantitatively decorate the COF lattice with alkyl chains and amines, all without the need for exogenous species. Functionalization may result in spontaneous delamination of bulk COF materials into solution-stable sheets, demonstrating the utility of this technique. As such, this platform is useful for postsynthetic functionalization with sensitive chemical functionalities that are not amenable to direct polymerization or existing PSM strategies.

Click-Functionalization of a Poly(Tetrazine-co-Fluorene)-Conjugated Polymer with a Series of trans-Cyclooctene Derivatives.

A soluble poly(tetrazine) polymer was prepared via Suzuki polycondensation of 3,6-bis(5-bromofuran-2-yl)-1,2,4,5-tetrazine and a fluorene diboronate derivative. It can undergo efficient and quantitative post-polymerization inverse-electron-demand Diels-Alder click reactions with a variety of trans-cyclooctene (TCO) derivatives. The resulting polymers were oxidized to convert dihydropyridazine rings into pyridazines. The absorption spectra of the product polymers, both before and after oxidation, showed hypsochromic shifts that correlated with steric hindrance of the appended side chains. They also exhibited a significantly enhanced fluorescence intensity relative to the original poly(tetrazine). While gel-permeation chromatography indicated that the product polymers exhibited longer retention times, NMR end-group analysis showed that the polymers retained relatively constant degrees of polymerization. Graft copolymers were easily prepared via reaction with TCO-functionalized poly(ethylene glycol) chains and a cross-linked foam was produced by reacting the poly(tetrazine) with a bis-TCO crosslinker.

A Survey of Strain-Promoted Azide-Alkyne Cycloaddition in Polymer Chemistry.

Highly efficient reactions that enable the assembly of molecules into complex structures have driven extensive progress in synthetic chemistry. In particular, reactions that occur under mild conditions and in benign solvents, while producing no by-products and rapidly reach completion are attracting significant attention. Amongst these, the strain-promoted azide-alkyne cycloaddition, involving various cyclooctyne derivatives reacting with azide-bearing molecules, has gained extensive popularity in organic synthesis and bioorthogonal chemistry. This reaction has also recently gained momentum in polymer chemistry, where it has been used to decorate, link, crosslink, and even prepare polymer chains. This survey highlights key achievements in the use of this reaction to produce a variety of polymeric constructs for disparate applications.

Direct Measure of the Local Concentration of Pyrenyl Groups in Pyrene-Labeled Dendrons Derived from the Rate of Fluorescence Collisional Quenching.

The model-free analysis (MFA) was applied to measure the average rate constant () for pyrene excimer formation (PEF) in a series of pyrene-labeled dendrons referred to as Pyx-G(N), where x (= 2N) is the number of pyrenyl labels born by a dendron of generation N ranging from 1 to 6. was measured in four different solvents, namely tetrahydrofuran (THF), toluene, N,N-dimethylformamide (DMF), and dimethylsulfoxide (DMSO). was found to increase linearly with increasing local pyrene concentration ([Py]loc), where [Py]loc had been determined mathematically for the Pyx-G(N) dendrons. The slope of each straight line changed with the nature of the solvent and represented kdiff, the bimolecular rate constant for PEF. kdiff depended on the solvent viscosity (η) and the probability (p) for PEF upon encounter between an excited and a ground-state pyrene. In a same solvent, kdiff for the Pyx-G(N) dendrons was about 360 ± 30 times smaller than kdiff obtained for ethyl 4-(1-pyrene)butyrate (PyBE), a pyrene model compound similar to the pyrene derivative used to label the dendrons. The massive decrease in kdiff observed for the Pyx-G(N) samples reflected the massive loss in mobility experienced by the pyrenyl labels after being covalently attached onto a macromolecule compared to freely diffusing PyBE. Interestingly, the kdiff values obtained for the Pyx-G(N) dendrons and the PyBE model compound followed similar trends as a function of solvent, indicating that the difference in behavior between the kdiff values obtained in different solvents were merely due to the changes in the η and p values between the solvents. Normalizing the values obtained with the Pyx-G(N) dendrons by the kdiff values obtained for PyBE in the same solvents accounted for changes in η and p, resulting in a master curve upon plotting /(fdiff × kdiff) as a function of [Py]loc, where fdiff was introduced to account for some pyrene aggregation in the higher generation dendron (Py64-G(6)). This result demonstrates that represents a direct measure of [Py]loc in pyrene-labeled macromolecules.

Globular Polymer Grafts Require a Critical Size for Efficient Molecular Sieving of Enzyme Substrates.

A series of 2,2-bis(hydroxymethyl)propionic acid dendrons of generation 2 through 8 having a strained cyclooctyne at the core and hydroxy groups at the periphery were prepared by a divergent method and used to functionalize azide-decorated α-chymotrypsin. The ability of the appended dendrons to selectively block enzyme activity (through a molecular sieving effect) was investigated using a small molecule substrate (benzoyl-l-tyrosine p-nitroanilide), as well as two proteins of different size (casein and bovine serum albumin). Additionally, the ability of dendrons to block complexation with a chymotrypsin antagonist, α-antichymotrypsin, was investigated, and it was found that the dendron coating effectively prevented inhibition by this antagonist. We found that a critical generation is required to achieve efficient sieving with bis-MPA dendrons, which illustrates the importance of macromolecular architecture and size in the shielding of proteins.

Effect of Single-walled Carbon Nanotube (SWCNT) Composition on Polyfluorene-Based SWCNT Dispersion Selectivity.

Applications of single-walled carbon nanotubes (SWCNTs) are hampered by the mixtures of metallic and semiconducting SWCNTs that are present in commercial samples. Separation of SWCNTs according to electronic type is therefore extremely important. Recently, the selective interaction between the conjugated polymer, poly(9,9-di-n-dodecyl-fluorenyl-2,7-diyl) and semiconducting SWCNTs has been reported. However, the mechanism responsible for this selectivity is poorly understood. To determine whether this polymer is only selective for semiconducting SWCNTs, we exposed it to mixtures of metallic and semiconducting SWCNTs in different ratios. We found that the polymer is indeed selective for semiconducting SWCNTs in toluene, but only when the starting ratio is below 67:33 metallic:semiconducting. When the starting ratio is increased to 67:33 or higher, the amount of metallic SWCNTs dispersed dramatically increases. If the solvent is changed to THF, the threshold ratio at which metallic SWCNTs begin to be dispersed is much lower. This indicates that the polymer exhibits a preference for interaction with semiconducting SWCNTs, but is not precluded from interaction with metallic SWCNTs if exposed to a high enough concentration.

Pillar[5]arene-Decorated Single-Walled Carbon Nanotubes.

Control of single-walled carbon nanotube dispersion properties is of substantial interest to the scientific community. In this work, we sought to investigate the effect of a macrocycle, pillar[5]arene, on the dispersion properties of a polymer-nanotube complex. Pillar[5]arenes are a class of electron-rich macrocyclic hosts capable of forming inclusion complexes with electron-poor guests, such as alkyl nitriles. A hydroxyl-functionalized pillar[5]arene derivative was coupled to the alkyl bromide side chains of a polyfluorene, which was then used to coat the surface of single-walled carbon nanotubes. Noncovalent functionalization of carbon nanotubes with the macrocycle-containing conjugated polymer significantly enhanced nanotube solubility, resulting in dark and concentrated nanotube dispersions (600 µg mL-1), as evidenced by UV-vis-NIR spectroscopy and thermogravimetric analysis. Differentiation of semiconducting and metallic single-walled carbon nanotube species was analyzed by a combination of UV-vis-NIR, Raman, and fluorescence spectroscopy. Raman spectroscopy confirmed that the concentrated nanotube dispersion produced by the macrocycle-containing polymer was due to well-exfoliated nanotubes, rather than bundle formation. The polymer-nanotube dispersion was investigated using 1H NMR spectroscopy, and it was found that host-guest chemistry between pillar[5]arene and 1,6-dicyanohexane occurred in the presence of the polymer-nanotube complex. Utilizing the host-guest capability of pillar[5]arene, the polymer-nanotube complex was incorporated into a supramolecular organogel.

Enrichment of Metallic Carbon Nanotubes Using a Two-Polymer Extraction Method.

The large-scale enrichment of metallic carbon nanotubes is a challenging goal that has proven elusive. Selective dispersion of carbon nanotubes by specifically designed conjugated polymers is effective for isolating semiconducting species, but a comparable system does not exist for isolating metallic species. Here, we report a two-polymer system where semiconducting species are extracted from the raw HiPCO or plasma-torch nanotube starting material using an electron-rich poly(fluorene-co-carbazole) derivative, followed by isolation of the metallic species remaining in the residue using an electron-poor methylated poly(fluorene-co-pyridine) polymer. Characterization of the electronic nature of extracted samples was carried out via a combination of absorption, Raman, and fluorescence spectroscopy, as well as electrical conductivity measurements. Using this methodology, the metallic species in the sample were enriched 2-fold in comparison to the raw starting material. These results indicate that the use of electron-poor polymers is an effective strategy for the enrichment of metallic species.

Recent developments in the selective dispersion of single-walled carbon nanotubes using conjugated polymers.

A significant barrier that impedes the commercialization of single-walled carbon nanotube-related applications is that all known synthetic methods produce a complicated mixture of semiconducting and metallic species. For device applications, pure semiconducting or pure metallic samples are desirable. Thus far, the purification methods that have been identified are capable of separating individual carbon nanotube species on a microgram scale, but purification on a large scale has remained elusive. The use of conjugated polymers to selectively disperse specific nanotube species is a promising approach to resolve the scalability issue, but a comprehensive understanding of the selectivity mechanism has not yet been achieved. Here, several of the trends reported in the literature are outlined to further the rational design of conjugated polymers for nanotube sorting. Numerous variables influence dispersion selectivity, including polymer structure and molecular weight, nanotube type used, sonication temperature, amount of polymer relative to nanotube, and solvent. We have organized these seemingly disparate parameters into two simple categories: conjugated polymer structure, and dispersion preparation conditions. Most importantly, we consider the mechanistic arguments that have been proposed, and provide additional insights based on the observations in the literature.

Reproducible Dendronized PEG Hydrogels via SPAAC Cross-Linking.

A common issue with hydrogel formulations is batch-to-batch irreproducibility originating from poorly defined polymer precursors. Here, we report the use of dendritic polymer end-groups to address this issue and maintain reproducibility between batches of poly(ethylene glycol) (PEG) hydrogels. Specifically, we synthesized two end-functionalized PEG chains: one with azide-terminated first- and second-generation dendrons and the other with strained cyclooctynes. The two complementary azide and alkyne polymers react via strain-promoted alkyne-azide cycloaddition (SPAAC) to produce hydrogels quickly in the absence of additional reagents or catalyst at low polymer concentrations. Hydrogels made with first-generation dendrons gelled in minutes and exhibited a small degree of swelling when incubated in PBS buffer at 37 °C, whereas hydrogels made from second-generation dendrons gelled in seconds with almost no swelling upon incubation at 37 °C. In both cases, the hydrogels proved reproducible, resulting in identical Young's modulus values from different batches. The hydrogels prepared with second-generation dendrons were seeded with human mesenchymal stem cells and showed high cell viability as well as cell spreading over a two-week time frame. These studies show that the SPAAC hydrogels are noncytotoxic and are capable of supporting cell growth.

Influence of Polymer Electronics on Selective Dispersion of Single-Walled Carbon Nanotubes.

The separation and isolation of semiconducting and metallic single-walled carbon nanotubes (SWNTs) on a large scale remains a barrier to many commercial applications. Selective extraction of semiconducting SWNTs by wrapping and dispersion with conjugated polymers has been demonstrated to be effective, but the structural parameters of conjugated polymers that dictate selectivity are poorly understood. Here, we report nanotube dispersions with a poly(fluorene-co-pyridine) copolymer and its cationic methylated derivative, and show that electron-deficient conjugated π-systems bias the dispersion selectivity toward metallic SWNTs. Differentiation of semiconducting and metallic SWNT populations was carried out by a combination of UV/Vis-NIR absorption spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and electrical conductivity measurements. These results provide new insight into the rational design of conjugated polymers for the selective dispersion of metallic SWNTs.

Synthesis of Polyester Dendritic Scaffolds for Biomedical Applications.

Using a well-defined poly(2,2-bis(hydroxymethyl)propanoic acid) dendrimer scaffold, a series of G1 to G3 dendrons is functionalized at the periphery with alkynes to enable "Click" functionalization via the copper-catalyzed alkyne-azide cycloaddition (CuAAC). The resulting dendrons are further functionalized at the core with a dipicolylamine (DPA) moiety to enable radiolabeling with 99m Tc for molecular imaging applications. Efficient CuAAC coupling is achieved using an azide-functionalized triethylene glycol monomethyl ether (TEG-N3 ). Removal of copper from the DPA ligand is successfully performed on G1 and G2 dendrimers prior to radiolabeling with 99m Tc. Radiolabeling of the G3 dendrimer is accomplished via transmetallation of the [CuDPA]2+ ligand with 99m Tc, further demonstrating the feasibility of the synthetic strategies in the preparation of dendritic imaging agents. Subsequent attachment of an acyloxymethyl ketone (AOMK) derivative for targeting of cathepsin B is also explored. Despite demonstrating the ability to ligate multiple AOMK ligands, the AOMK-dendrimer conjugates are not able to bind to cathepsin B, which may be attributed to steric hindrance at the dendrimer periphery.

Properties of Poly(ethylene glycol) Hydrogels Cross-Linked via Strain-Promoted Alkyne-Azide Cycloaddition (SPAAC).

A series of poly(ethylene glycol) (PEG) hydrogels was synthesized using strain-promoted alkyne-azide cycloaddition (SPAAC) between PEG chains terminated with either aza-dibenzocyclooctynes or azide functionalities. The gelation process was found to occur rapidly upon mixing the two components in aqueous solution without the need for external stimuli or catalysts, making the system a candidate for use as an injectable hydrogel. The mechanical and rheological properties of these hydrogels were found to be tunable by varying the polymer molecular weight and the number of cross-linking groups per chain. The gelation times of these hydrogels ranged from 10 to 60 s at room temperature. The mass-based swelling ratios varied from 45 to 76 at maximum swelling (relative to the dry state), while the weight percent of polymer in these hydrogels ranged from 1.31 to 2.05%, demonstrating the variations in amount of polymer required to maintain the structural integrity of the gel. Each hydrogel degraded at a different rate in PBS at pH = 7.4, with degradation times ranging from 1 to 35 days. By changing the composition of the two starting components, it was found that the Young's modulus of each hydrogel could be varied from 1 to 18 kPa. Hydrogel incubation with bovine serum albumin showed minimal protein adsorption. Finally, a cell cytotoxicity study of the precursor polymers with 3T3 fibroblasts demonstrated that the azide- and strained alkyne-functionalized PEGs are noncytotoxic.

Click Functionalization of a Dibenzocyclooctyne-Containing Conjugated Polyimine.

A conjugated poly(phenyl-co-dibenzocyclooctyne) Schiff-base polymer, prepared through polycondensation of dibenzocyclooctyne bisamine (DIBO-(NH2)2) with bis(hexadecyloxy)phenyldialdehyde, is reported. The resulting polymer, which has a high molecular weight (M(n)>30 kDa, M(w)>60 kDa), undergoes efficient strain-promoted alkyne-azide cycloaddition reactions with a series of azides. This enables quantitative modification of each repeat unit within the polymer backbone and the rapid synthesis of a conjugated polymer library with widely different substituents but a consistent degree of polymerization (DP). Kinetic studies show a second-order reaction rate constant that is consistent with monomeric dibenzocyclooctynes. Grafting with azide-terminated polystyrene and polyethylene glycol monomethyl ether chains of varying molecular weight resulted in the efficient syntheses of a series of graft copolymers with a conjugated backbone and maximal graft density.