Synthesis of Well-Defined Unsaturated Polyesters by Transition-Metal-Catalyzed Polycondensation of Bis(diazoacetate)s

A variety of aliphatic- and aromatic-type unsaturated polyesters (UPs) were prepared by transition-metal-catalyzed single-component polycondensation of bis­(diazoacetate)­s under a mild condition. With the second-generation Grubbs catalyst, the polycondensation proceeded exclusively through an intermolecular highly <i>cis</i>-selective CC forming coupling of diazo-bearing carbons with N₂ release, giving well-defined UPs. The <i>cis</i>-CCs of the resulting polymers could be isomerized quantitatively into <i>trans</i>-CCs with a catalytic amount of diethylamine. Additionally, other metal complexes, the first-generation Grubbs catalyst, rhodium­(II) acetate, and copper­(II) acetylacetonate, also produced UPs from the bis­(diazoacetate)­s, with lower stereoselectivities, although an unexpected carbene oligomerization of the monomers partially occurred along with the CC bond-forming coupling

Fluorinated Poly(substituted methylene)s Prepared by Pd-Initiated Polymerization of Fluorine-Containing Alkyl and Phenyl Diazoacetates: Their Unique Solubility and Postpolymerization Modification

Pd-initiated polymerization of fluorine (F)-containing alkyl and phenyl diazoacetates is described. Polymerization of 2,2,2-trifluoroethyl diazoacetate [Et­(CF₃)­DA] with π-allylPdCl afforded a C–C main chain polymer bearing a 2,2,2-trifluoro­ethoxycarbonyl group on each main chain carbon atom. The polymer showed upper critical solution temperature (UCST)-type phase separation in multiple common organic solvents with differing polarities. Although homopolymerization of 3,3,4,4,5,5,6,6,6-nonafluorohexyl diazoacetate [Hex­(C₄F₉)­DA] with a higher fluorine content yielded an insoluble product, copolymerization of Hex­(C₄F₉)­DA with non-fluorinated ethyl diazoacetate (EDA) proceeded homogeneously to give a soluble F-containing copolymer. Polymerization of a series of F-containing phenyl diazoacetates was also conducted with the same initiator, giving poly­[(F-containing aryloxy­carbonyl)­methylene]­s, which showed significant solubility differences depending on the substitution pattern of F atoms on the phenyl ring. Efficient postpolymerization modification of poly­[(F-containing aryloxycarbonyl)­methylene]­s was achieved with a primary amine, affording a polymer with both a five-membered cyclic imide structure and an <i>N</i>-alkylcarbamoyl group in its side chains

Ru-Catalyzed Polycondensation of Dialkyl 1,4-Phenylenebis(diazoacetate) with Dianiline: Synthesis of Well-Defined Aromatic Polyamines Bearing an Alkoxycarbonyl Group at the Adjacent Carbon of Each Nitrogen in the Main Chain Framework

Transition-metal-catalyzed N–H insertion of a diazocarbonyl compound is applied for polycondensation for the first time to give a new type of aromatic polyamine. The well-defined polyamines were obtained by [RuCl₂(<i>p</i>-cymene)]₂-catalyzed reaction of diethyl 1,4-phenylenebis­(diazoacetate) with dianilines bearing a variety of linkers between two aniline units. The polycondensation proceeded at 30 °C in CH₂Cl₂ with 5.0 mol % of the Ru metal to [NH₂ or N₂C] to afford the products with <i>M</i>_n = 6400–28 300 in moderate to high yield. Ethoxycarbonyl groups located at an adjacent position to NH imparted solubility to the polyamines, and their glass transition temperatures can be varied depending on the linker structure in a range of 88–173 °C

Polymerization of Hydroxy-Containing Diazoacetates: Synthesis of Hydroxy-Containing “Poly(substituted methylene)s” by Palladium-Mediated Polymerization and Poly(ester–ether)s by Polycondensation through O–H Insertion Reaction

Two types of polymerization of hydroxy-containing diazoacetates are described. The polymerization of hydroxy-containing diazoacetates using palladium complexes proceeded successfully under chain-growth mechanism even without a protecting group to give C–C main chain polymers bearing a hydroxy-containing ester substituent on each carbon of the backbone. The resulting polymers had a slightly branched structure due to chain transfer reaction with the hydroxy groups, while the polymers obtained by polymerization of silyl-protected diazoacetates and subsequent deprotection had a completely linear structure. The hydroxy-containing polymers with an appropriate hydrophilic/hydrophobic balance showed a lower critical solution temperature-type phase separation in an aqueous medium. On the other hand, the polymerization of hydroxy-containing diazoacetates using InCl₃ as a catalyst proceeded under step-growth mechanism to give oligomers having a distinct repeating unit (ester–ether), where a new ether bond was generated through O–H insertion reaction of diazocarbonyl groups into hydroxy groups

Self-Assembly of Hierarchical Structures Using Cyclotriphosphazene-Containing Poly(substituted methylene) Block Copolymers

The cyclotriphosphazene-substituted diazoacetate homopolymer (polyPNDA′) (PNDA′ = hexaphenoxy-substituted phosphazene-containing methylene) and a novel poly­(substituted methylene) block copolymer, polyPNDA′-<i>block</i>-poly­(hexyloxycarbonylmethylene) (polyPNDA’-<i>b</i>-polyHDA′), were synthesized, and the self-assembly behavior of these polymers was studied in detail. A hexagonally packed aggregated structure was observed in the self-assembled structure of polyPNDA′, whereas a lamellar structure was observed in the microphase-separated nanoassembly of polyPNDA′-<i>b</i>-polyHDA′. These results indicate that a hierarchical structure composed of highly regular polyPNDA′ nanoaggregates and the long-range microphase-separated polyPNDA′ and polyHDA′ domains had formed

π‑AllylPdCl-Based Initiating Systems for Polymerization of Alkyl Diazoacetates: Initiation and Termination Mechanism Based on Analysis of Polymer Chain End Structures

Polymerization of ethyl and benzyl diazoacetates (EDA and BDA) initiated with π-allylPdCl-based systems [π-allylPdCl/NaBPh₄, π-allylPdCl/NaBAr^F₄ (Ar^F = 3,5-{CF₃}₂C₆H₃), and π-allylPdCl] is described. Initiation efficiencies of the π-allylPdCl-based systems are much higher than those of the previously reported (NHC)­Pd/borate (NHC = <i>N</i>-heterocyclic carbene) systems, and the new systems are capable of polymerizing the alkyl diazoacetates at low temperatures (0 ∼ −20 °C), where the (NHC)­Pd/borate systems cannot initiate the polymerization. MALDI–TOF–MS analyses of the polymers obtained from EDA provide information for the chain-end structures of the polymers, based on which initiation and termination mechanisms are proposed. Interestingly, EDA polymerization by the π-allylPdCl-based systems in the presence of alcohols (EtOH, nPrOH, and nBuOH) or water was found to afford RO- or HO-initiated polymers as major products, as confirmed by MALDI–TOF–MS analyses

Excited-State Dynamics of Pyrene Incorporated into Poly(substituted methylene)s: Effects of Dense Packing of Pyrenes on Excimer Formation

The excited-state dynamics of pyrene incorporated into poly­(substituted methylene)­s is investigated by picosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved near-IR absorption spectroscopy in the 900–1400 nm region. The pyrene rings in poly­(substituted methylene)­s are photoexcited to the monomer excited state immediately after UV irradiation, followed by prompt excimer formation with time constants of a few picoseconds to a few hundred picoseconds. The excimer formation in poly­(substituted methylene)­s proceeds with much shorter time constants than that in pyrene-incorporated polyacrylates, vinyl polymer counterparts with the same side-chain structures, indicating the presence of stronger electronic interaction between the pyrene rings in poly­(substituted methylene)­s. The effects of every methylene substitution hold when each pyrene ring is connected to the polymer backbone with a monomethylene linker, while the effects are observed only weakly when a tetramethylene linker is employed. The results demonstrate the effectiveness of every methylene substitution in the prompt excimer formation of pyrene connected to the polymer backbone either directly or with the monomethylene linker