The inherent differences in reactivity between activated and non‐activated alkenes prevents copolymerization using established polymer synthesis techniques. Research over the past 20 years has greatly advanced the copolymerization of polar vinyl monomers and olefins. This Review highlights the challenges associated with conventional polymerization systems and evaluates the most relevant methods which have been developed to “bridge the gap” between polar vinyl monomers and olefins. We discuss advancements in heteroatom tolerant coordination–insertion polymerizations, methods of controlling radical polymerizations to incorporate olefinic monomers, as well as combined approaches employing sequential polymerizations. Finally, we discuss state‐of‐the‐art stimuli‐responsive systems capable of facile switching between catalytic pathways and provide an outlook towards applications in which tailored copolymers are ideally suited.
We
detail a polymer synthetic methodology that merges the techniques
of insertion and radical polymerization methods into a single organometallic
catalyst. This metal–organic insertion/light initiated radical
(MILRad) polymerization technique proves successful at polymerizing
methyl acrylate (MA) and hexene, using light as a critical stimulus
to activate the dormant photoresponsive nature of the insertion catalyst.
In this study, we describe a novel approach that uses visible light
(460 nm) to switch the catalytic activity of a cationic palladium
catalyst from an insertion route to a radical process when desired.
We discovered that in a mixture of MA and hexene one monomer can be
selectively polymerized using light and dark cycles, respectively.
As a result, this polymerization process enables the copolymerization
of MA and hexene to create homo- and block copolymer architectures
facilitated solely by visible light. In this work, we show the synthesis
of MA homopolymers in molecular weight ranges (M
n 50–400 kDa) with dispersities of ∼1.7. Synthesis
of MA (A) and hexene (B) block copolymers were accomplished with a
single catalyst in both a sequential and novel one-pot approach, relying
solely upon visible light irradiation. A series of BA block copolymers
were prepared with tunable monomer compositions, molecular weight
ranges of (M
n 11–36 kDa), and well-controlled
polydispersities (∼1.3–1.6) in a robust rapid synthesis.
MILRad polymerization circumvents the need for quantitative conversions
during block formation afforded by the orthogonal monomer reactivity
dependent upon a light stimulus to acquire distinct polymer architectures
with variable block compositions. The use of a photocontrollable “switch”
affecting a single organometallic catalyst allows access to block
polymers from nonpolar and polar olefins in a novel and facile approach.
The photoinitiated radical polymerization pathway of MILRad polymerization towards its ability to polymerize a variety of vinyl polar functional monomers is investigated.
2-Acyl-3-arylisoxazol-5(2H)-ones give
2-alkyl(aryl)-4-aryloxazoles in good yields at 540°C under flash vacuum
pyrolysis conditions, but at higher temperatures the expected oxazoles are
accompanied by increasing amounts of isomeric 2,5-disubstituted oxazoles, as
well as anilides and decomposition products of the 2,4-disubstituted oxazole.
The rearrangement mechanisms have been studied by the use of
13C labelled substrates and
p-substituted 3-arylisoxazolones. The 2,5-disubstituted
oxazoles are considered to arise from 1H-azirines, and
the anilides from the nitrone ketene isomer of the acylisoxazolone.
The heating of a levulinic acid and pentaerythritol 4:3 mixture with Sb2O3 catalyst at 23–210 °C gives poly(levulinic acid–pentaerythritol). This all renewable carbon based moldable white thermoplastic is shown to contain a structure with ester and ketal links.
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