Hatice Mutlu

Sustainable routes to polyurethane precursors

Environmentally friendly products and procedures are being developed both in industry and academia, mainly due to the depletion of fossil resources and the growing global awareness of the need to protect the environment. Thus, since polyurethanes represent a highly demanded class of polymers, straightforward, isocyanate and phosgene-free methods are required for the synthesis of their precursors (monomers) in order to achieve a sustainable production. To foster the discussion with the final goal to meet such a sustainable production, this review provides an overview of classic as well as modern and more sustainable routes towards polyurethanes and their precursors.

TBD catalysis with dimethyl carbonate: a fruitful and sustainable alliance

This work presents the synthesis of unsymmetric and symmetric organic carbonates as well as the synthesis of polycarbonates in an efficient and sustainable approach. All reactions were carried out at atmospheric pressure at 80 °C and the use of classic toxic and harmful chemicals, such as phosgene and carbon monoxide, was avoided. The key finding of this manuscript is that the use of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD, an organocatalyst, in combination with dimethyl carbonate (DMC), a non-toxic and renewable starting material, allows the synthesis of the mentioned unsymmetric carbonates in yields of up to 98% under optimized conditions. The structure of the alcohols used for this approach was found to influence the DMC–ROH ratio required to maximize the yield of the desired structure. Finally, the results obtained for the synthesis of low molecular weight building blocks could be transferred to the catalytic synthesis of high molecular weight polycarbonates.

Self-metathesis of fatty acid methyl esters: full conversion by choosing the appropriate plant oil

Herein, we report results on olefin self-metathesis in the presence of low catalyst loadings as an efficient approach for the synthesis of α,ω-difunctional monomers from plant oils containing a high ratio of polyunsaturated fatty acids. It was clearly observed that the driving force for the synthesis of the C18-diester was the formation of cyclohexa-1,4-diene and hex-3-ene, both of which, in contrast to self-metathesis of oleic acid methyl ester, can easily be removed from the reaction mixture by distillation and thus help to shift the metathesis equilibrium to full conversion. The resulting unsaturated C18-diester was hydrogenated and subsequently converted to the corresponding diol. Both monomers were used for the synthesis of a long-chain polyester in the presence of 1,5,7-triazobicyclodecane (TBD) as a catalyst. The molecular weight of the resulting polymer was determined by static light scattering. Moreover, DSC analysis was applied to determine the thermal properties of the final polymer.

Photo- and Metallo-responsive N-Alkyl α-Bisimines as Orthogonally Addressable Main-Chain Functional Groups in Metathesis Polymers

N-alkyl α-bisimines were employed as main-chain functional groups in acyclic diene metathesis (ADMET)-polymers, conferring dual responsiveness for the controlled switching of the polymeric particle shape with light and metal ions. Photochemical Z/E-isomerization leads to a significant and reversible change in hydrodynamic volume, thus introducing simple imines as novel photoswitches for light-responsive materials. Mild imine-directed CH activation by Pd(OAc)2 is demonstrated as a new single-chain nanoparticle (SCNP) folding process, enabling a controlled atom- and step-economic SCNP synthesis. The combination of light- and metallo-responsiveness in the same polymer provides the ability for orthogonal switching, a valuable tool for advanced functional material design.

About the activity and selectivity of less well-known metathesis catalysts during ADMET polymerizations

Summary We report on the catalytic activity of commercially available Ru-indenylidene and “boomerang” complexes C1, C2 and C3 in acyclic diene metathesis (ADMET) polymerization of a fully renewable α,ω-diene. A high activity of these catalysts was observed for the synthesis of the desired renewable polyesters with molecular weights of up to 17000 Da, which is considerably higher than molecular weights obtained using the same monomer with previously studied catalysts. Moreover, olefin isomerization side reactions that occur during the ADMET polymerizations were studied in detail. The isomerization reactions were investigated by degradation of the prepared polyesters via transesterification with methanol, yielding diesters. These diesters, representing the repeat units of the polyesters, were then quantified by GC-MS.

Dynamic covalent single chain nanoparticles based on hetero Diels–Alder chemistry

We introduce the fully reversible folding of single chain nanoparticles (SCNPs) based on covalent hetero Diels-Alder (HDA) chemistry. A cyclopentadiene (Cp)-protected cyanodithioester (CDTE) monomer is designed and copolymerized with methyl methacrylate (MMA) via RAFT polymerization. The polymer chains are folded and subsequently unfolded by exploiting the reversible nature of the HDA reaction.

The para-fluoro-thiol reaction as a powerful tool for precision network synthesis

We introduce the regioselective para-fluoro-thiol reaction (PFTR) as a novel strategy for network formation. Here, a novel fluorinated linker is designed and further reacted with several bifunctional thiols to demonstrate the versatility of the method. Critically, the formation of the networks is evidenced by XPS and ToF-SIMS.

Stepwise Light‐Induced Dual Compaction of Single‐Chain Nanoparticles

A photochemical strategy for the sequential dual compaction of single polymer chains is introduced. Two photoreactive methacrylates, with side chains bearing either a phenacyl sulfide (PS) or an α-methylbenzaldehyde (photoenol, PE) moiety, are selectively incorporated by one-pot iterative reversible-addition fragmentation chain transfer copolymerization into the outer blocks of a well-defined poly(methyl methacrylate) based ABC triblock copolymer possessing a nonfunctional spacer block (Mn = 23 400 g mol-1 , Đ = 1.2; ≈15 units of each photoreactive moieties of each type) as well as in model statistical copolymers bearing only one type of photoreactive unit. Upon UVA irradiation, PS and PE lead to highly reactive thioaldehydes and o-quinodimethanes, which rapidly react with dithiol and diacrylate linkers, respectively. The monomerfunctional copolymers are employed to establish the conditions for controlled intramolecular photo-crosslinking, which are subsequently applied to the bifunctional triblock copolymer. All compaction/folding experiments are monitored by size-exclusion chromatography and dynamic light scattering. The dual compaction consists of two events of dissimilar amplitude: the first folding step reveals a large reduction in hydrodynamic diameters, while the second compaction lead to a far less pronounced reduction of the single-chain nanoparticles size, consistent with the reduced degrees of freedom available after the first covalent compaction step.

Untapped potential for debonding on demand: the wonderful world of azo-compounds

We highlight and explore recent advances in the design of debonding on demand soft matter materials based on the azo-motif. While azo-motifs are most frequently exploited for their light induced cis/trans isomerization behavior, we herein focus on their arguably less-known function as a cleavable linker. We demonstrate that the use of azo-units as cleavable linkers provides access to a rich chemistry of materials, rapidly establishing their place in the field of adaptable soft matter materials design. Critically, we identify the outstanding challenges that will equip the degradable nature of the azo-unit with to-date inaccessible property profiles including light gated on/off switches, allowing soft matter materials to be cleaved depending on specific colors of light.

Two-in-One: λ-Orthogonal Photochemistry on a Radical Photoinitiating System

An alkyne functional radical photoinitiator, 2-(4-(2-hydroxy-2-methylpropanoyl)phenoxy)ethyl hex-5-ynoate, and evidence that both reactive moieties - the alkyne and the photoinitiator terminus - can be independently addressed with light of disparate wavelength (λ-orthogonality) are introduced. The alkyne functionality is subjected to a visible light (420 nm) induced copper-catalyzed Huisgen reaction, which is employed for the selective functionalization of the initiator with a poly(ethylene glycol) (PEG) chain. This reaction proceeds completely λ-orthogonal in the presence of the UV-reactive photoinitiating moiety. Conversely, it is demonstrated that the alkyne functionality of the photoinitiator is quantitatively orthogonal to UV irradiation emitted by the pulsing action of an excimer laser (351 nm, pulsed-laser polymerization, PLP) and the generated radical species. In turn, the PEGylated initiator can readily be employed as a macrophotoinitiator during PLP. The introduced λ-orthogonally addressable dual functional initiator can be used in a wide range of applications, including surface lithography and post-synthetic modification of photocured materials.