New Synthetic Route To Polyacetylenes And Functionality Adjustment

The design and synthesis of functional polyacetylenes has been a hot topic in the field of polyacetylenes. Polyacetylene, with the simplest structure, is famous for its outstanding electrical conductivity. Generally, functional side groups can endow the whole polymer with corresponding functionality, such as liquid crystallinity. light emission, optical nonlinearity, optical activity, solvatochromism, hydrophilicity, and biological activity. Even versatile functionalities can be achieved by adjusting the interaction between polymer backbone and functional side groups, i. e. electronic interaction, steric effect, charge transfer, or energy transfer. However, functional groups are usually not easy to be attached to the desired position in the side chain. On one hand, the controlled polymerization of acetylenic monomers has not successfully been achieved with nomal catalysts; On the other hand, the polymerization catalysts, especially the metathesis catalysts, are intolerant of polar functional groups in the monomers. Therefore, it is necessary to develop new platform-like synthetic route toward various functional polyacetylenes, besides catalyst development and direct polymerization implementation, in order to systematically study the structure-property relationship.Four azobenzene-bearing polyphenylacetylenes, P1(6), P2(6), P1(12), and P2(12) were synthesized by using organorhodium complexes [Rh(diene)Cl]2as catalysts. Their photoinduced isomerization behavior, thermal stability, and liquid crystalline property were carefully studied. Results show that longer alky] spacer contributes to quicker isomerization rate and is essential to the formation of anisotropic liquid crystal phase. In addition. the mesophase was assigned to SmA phase when the azobenzene is attached with trifluoromethyl. Combind XRD results and theoretical calculation, we believe that a single polymer chain takes a fishbone configuration with a mesogen at the end of each side chain. The mesogens on the adjacent polymer side chains take an interdigital arrangement. In summary, this work demonstrated the interdependent properties between three key structural parameters of rigid polymer backbone, flexible alkyl spacer, and photoisomerization-capable mesogen. thus provides helpful information to the designation and preparation of conjugated polymers with desirable opto-electronic properties.We further explored the role of reactive pendants in the functionalization of monosubstituted polyacetylenes. Pentafluorophenyl (PFP) ester-functionalized poly(phenylacetylene)s (PPAs, P1, P2and P3) were designed and synthesized in desirable yields and molecular weight by using organorhodium complexes as catalysts. These PFP-containing PPAs were further used as precursors to prepare a series of18mono-and dual-functionalized PPAs by the substitution of the activated ester moieties with functional amines. The experimental details and the IR and NMR characterization data demonstrate that activated ester synthetic route to functional PPAs is facile (just stirring the precursor polymer with proper amine(s) at room temperature for hours), efficient (complete transition from ester to amide has been confirmed), and quantitative (the relative content of a specific functionality can be precisely preset by controlling the feed ratio of the functional amines). CD measurements indicated that the incorporation of chiral amine into polymer side chains induced helicity formation of P1backbone. P1-C*Ph(L) and P1-C*Ph(D) backbones adopt predominantly right-handed and left-handed helical conformation. respectively. While the flexible spacer between the chiral center and the rigid PPA backbone blocked the induction of main-chain helicity by chiral pendants, thus no CD signals were recorded for P2-C*Ph(L) and P3-C*Ph(L). Substitution of PFP ester with amine-functionalized PEGs transited the hydrophobic PPAs to hydrophilic. All of the PEG-contain ing PPAs can be dissolved in water and form clear solutions. Meanwhile, all of the aqueous solutions exhibit LCST behavior and the hydrophilic PEG chains and hydrophobic alkyl spacers have positive and negative impact on the cloud point, respectively. Contact angles measurements showed that the length and content of the PEG chains contribute greatly to the hydrophilic property, and the length of the alkyl spacers and the content of the alkyl amine component played a contrary role. By controlling the ratio of the PEGylated and alkyl amines, the amphiphilic property of the PPAs can be well tailored.Activated ester strategy was further utilized to synthesize functional disubstituted polyacetylenes. which contains highly polar groups on their side chain and can not be obtained through direct polymerization with metathesis catalysts. A pentafluorophenyl (PFP) ester-containing diphenylacetylene was designed and polymerized to obtain PFP activated ester-functionalized disubstituted polyacetylene (P4). P4was used as a parent polymer to further react separately with diverse amines, giving rise to a series of functional disubstituted polyacetylenes (P5-P10) with chiral moiety, and/or hydroxyl. carboxyl groups in high yields under mild condition. Spectral characterization data indicated that the polymers" structures were well consistent with the expected results. The helicity and emission property of polymers were also studied. Results show that different chiral structure has different ability to induce backbone helicity, and postfunctionalization cause different conjugation length and different emission property.Pyrene was incorporated into the side chain of four polyacetylenes through activated ester strategy, obtaing two monosubstituted (P12and P13) and two disubstituted (P14and P15) pyrene-containing polyacetylenes. Excited at343nm, P12and P13emit around400and480nm, which is ascribed to the pyrene "monomer" and "excimer" respectively. However, the emission property of P14and P15is rather complicated, because fluorescence resonance energy transfer (FRET) is occurred from pyrene to polymer backbone. When excited at380nm, only the polymer backbone emits around510nm. When excited at343nm, there are three kind of potential emissive species, i. e. pyrene "monomer", pyrene "excimer". and polymer backbone. However, the PL spectra only show two emission peaks around400and510nm which can be ascribed to pyrene "monomer" and polymer backbone respectively. The pyrene "excimer" emission is completely disappeared and the "monomer" emission is weaker, but the backbone emission intensity is2-3times stronger than excited at380nm.