7 research outputs found
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
CC forming coupling of diazo-bearing carbons with N<sub>2</sub> release, giving well-defined UPs. The <i>cis</i>-CCs
of the resulting polymers could be isomerized quantitatively into <i>trans</i>-CCs 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 CC 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(CF<sub>3</sub>)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(C<sub>4</sub>F<sub>9</sub>)DA] with a higher fluorine content yielded an insoluble
product, copolymerization of Hex(C<sub>4</sub>F<sub>9</sub>)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 [RuCl<sub>2</sub>(<i>p</i>-cymene)]<sub>2</sub>-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 CH<sub>2</sub>Cl<sub>2</sub> with 5.0 mol % of the Ru metal to [NH<sub>2</sub> or N<sub>2</sub>C] to afford the products with <i>M</i><sub>n</sub> = 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 InCl<sub>3</sub> 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/NaBPh<sub>4</sub>, π-allylPdCl/NaBAr<sup>F</sup><sub>4</sub> (Ar<sup>F</sup> = 3,5-{CF<sub>3</sub>}<sub>2</sub>C<sub>6</sub>H<sub>3</sub>), 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