Synthesis of fluorinated polymers via ROMP: a review

This review is concerned with the work conducted in the Durham group during the last twenty years. It is specifically concerned with ROMP of fluorinated monomers with classical and well-defined initiators, with the synthesis of stereoregular polymers, block and stereoblock copolymers.     

A convenient synthesis of high-loaded palladium(II) ROMP polymers

Bis[1-(5-norbornen-2-yl)butan-1,3-dionato]palladium(II) was conveniently prepared from 5-acetoacetyl-2-norbornene and sodium tetrachloropalladate. The former could be subjected to ROMP to give a highly-loaded palladium(II) ROMP polymer with a palladium loading of 23% by weight.     

Coil-helix and sheet-helix block copolymers via macroinitiation from telechelic ROMP polymers

Coil-helix and sheet-helix block copolymers are synthesized by combining the ring-opening metathesis polymerization (ROMP) of norbornene or paracyclophanediene with the anionic polymerization of phenyl isocyanide. Key to the design is the use of an μ-ethynyl palladium (II) functionalized chain-transfer agent (CTA) that can be exploited in a stepwise manner for the termination of ROMP and the initiation of the anionic polymerization. Both the coil- and sheet-macroinitiators, and the ensuing covalent block copolymers, are analyzed using ¹H NMR spectroscopy and gel-permeation chromatography. In all cases, the Pd-end group is maintained and all polymers demonstrate a monomodal distribution with dispersities (Đ) of 1.1–1.4. The resulting helix-coil and helix-sheet block copolymers formed by the macroinitiation route still demonstrate their intrinsic properties (fluorescence, preferential helix-sense). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2991–2998     

New photochromic polymers

New photochromic polymers were synthesized by quaternization of amino groups of N-methyldiethanolamine polyterephthalate with a mixture of bis(2,5-dimethyl-4-chloromethyl-3-thienyl)-1,3-dioxol-2-one and p-or m-xylylene dichloride. The spectral-kinetic studies of coatings based on the obtained polymers showed that these coatings have photochromic properties, the efficiency of which decreases with an increase in the sample thickness.     

Novel photochromic spiroheterocyclic molecules via oxidation of 1,8-diaminonaphthalene

[reaction: see text] Novel spiroheterocyclic molecules, namely, 2,3-dihydro-2-spiro-7'-[8'-imino-7',8'-dihydronaphthalen-1'-amine]perimidine, PNI, and 2,3-dihydro-2-spiro-4'-[8'-aminonaphthalen-1'(4H)-one]perimidine, PNO-p, were obtained by oxidation of 1,8-diaminonaphthalene using manganese dioxide. These molecules exhibit thermally reversible photochromism with good photofatigue resistance, and their photogenerated forms possess broad absorption in the visible region.     

Novel synthesis of photocrosslinkable polymers

A new preparative route to photocrosslinkable polymers in which the polymers are produced directly from the polymerization of vinyl monomers having photocrosslinkable groups has been investigated. The photosensitive resins thus produced have higher sensitivity and resolution than conventional photosensitive resins. The monomers were synthesized from the esterification of vinylphenols or vinyl β-chloroethyl ether with cinnamic acid, β-styrylacrylic acid, and their homologs, and from the etherification of vinyl β-chloroethyl ether with hydroxychalcones. Homopolymerizations of these monomers and their copolymerizations with other comonomers were investigated with the use of both radical and ionic initiators. It is shown that radical polymerization of the monomers gave soluble polymers only at low conversion. Anionic initiators did not initiate polymerization. Cationic polymerization imparted soluble polymers in high yield, except for the monomers bearing cyano groups, which generally gave insoluble polymers. Infrared and NMR spectroscopic investigation of the cationically obtained soluble polymers and comparative investigation by cationic polymerization of model compounds indicated that polymerization of the monomers proceeds through the vinyl double bond without affecting the photosensitive unsaturated bond. Thus, linear photocrosslinkable polymers with an intact photoreactive group may be produced by cationic polymerization. In general, these polymers have uniform structure and modifiable physical properties depending on the monomer used. The polymer thus obtained from β-vinyloxyethyl cinnamate has been shown to have excellent properties for use as a photo-resist.     

End-functionalized ROMP polymers for Biomedical Applications

We present two novel allyl-based terminating agents that can be used to end-functionalize living polymer chains obtained by ring-opening metathesis polymerization (ROMP) using Grubbs' third generation catalyst. Both terminating agents can be easily synthesized and yield ROMP polymers with stable, storable activated ester groups at the chain-end. These end-functionalized ROMP polymers are attractive building blocks for advanced polymeric materials, especially in the biomedical field. Dye-labeling and surface-coupling of antimicrobially active polymers using these end-groups were demonstrated.     

Drug-loaded, bivalent-bottle-brush polymers by graft-through ROMP

Graft-through ring-opening metathesis polymerization (ROMP) using ruthenium N-heterocyclic carbene catalysts has enabled the synthesis of bottle-brush polymers with unprecedented ease and control. Here we report the first bivalent-brush polymers; these materials were prepared by graft-through ROMP of drug-loaded polyethylene-glycol (PEG) based macromonomers (MMs). Anticancer drugs doxorubicin (DOX) and camptothecin (CT) were attached to a norbornene-alkyne-PEG MM via a photocleavable linker. ROMP of either or both drug-loaded MMs generated brush homo- and co-polymers with low polydispersities and defined molecular weights. Release of free DOX and CT from these materials was initiated by exposure to 365 nm light. All of the CT and DOX polymers were at least 10-fold more toxic to human cancer cells after photoinitiated drug release while a copolymer carrying both CT and DOX displayed 30-fold increased toxicity upon irradiation. Graft-through ROMP of drug-loaded macromonomers provides a general method for the systematic study of structure-function relationships for stimuli-responsive polymers in biological systems.     

Long‐chain branched ROMP polymers

This article describes the construction of branched ROMP‐polymer architectures via polycondensation of AB_n‐type macromonomers. For this convergent strategy, a polymer was synthesized that carries several hydroxyl‐groups along the polymer chain and one carboxylic acid group at the chain end. An esterification reaction between these functional groups yielded long‐chain branched polymers. The polymers were analyzed by NMR and SEC to monitor the condensation reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

New developments in photochromic polymers

New developments on photochromic polymers have been obtained with systems containing spirobenzopyran derivatives. The importance of the chemical incorporation of the photochrome within the polymer backbone is stressed, and the influence of matrix orientation on the rate of fading is shown. Well known fatigue phenomena are illustrated on the basis of the changes of photostationary optical density on repeating the irradiation–dark recovery cycle. The photomechanical properties and characteristics of rubbery polyethylacrylates crosslinked with the photochrome bismethacrylate are considered in detail. Another principle of photochromism based on photodissociation phenomena is also discussed in the case of the photodissociation and photorecombination of anthracene derivatives and benzacridizinium tosylate, as well as in the case of the photodissociation and thermal recombination of benzpinacol groups incorporated in the polymer main chain. In these experiments in the solid state, it can be shown that the recombination involves always two successive steps: a rapid step corresponding to cage recombination and a second slow step related to diffusion and segment mobility (T_g) of the polymer.     

Influence of topology on the gelation behavior of coordination polymers prepared via ROMP of macrocyclic olefins

This work reports on the consequences of concatenation of two twin macrocycles on the gelation behavior of coordination polymers obtained via ring‐opening metathesis polymerization (ROMP) initiated by 2^nd generation Grubbs' catalyst. The influence of concatenation is evaluated by comparison with the behavior of a non‐interlocked model complex under the same reaction conditions. The suitability of the choice of the non‐interlocked model complex is discussed in terms of molecular structure and effective molarity (EM). It is found that concatenation has a primary role in the gelation process, resulting in lower critical gelation concentrations for the endotopic, interlocked complex compared with the exotopic, non‐interlocked one. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1237–1242     

Branched Polymers via ROMP of Termimers

Today's olefin metathesis catalysts show high reactivity, selectivity, and functional group tolerance and allow the design of new syntheses of precisely functionalized polymers. Here the synthesis of a new end‐capping reagent is investigated allowing the introduction of a highly reactive activated ester end‐group at the polymer chain end as well as its prefunctionalization to directly introduce functional moieties. The versatility of this new end‐capping reagent is demonstrated by utilizing it to synthesize a so‐called termimer (a monomer with termination capabilities). Copolymerization of a norbornene derivative with the termimer leads to hyperbranched ring‐opening metathesis polymerization polymers as proven by gel permeation chromatography and MALDI‐ToF‐(matrix‐assisted laser desorption/ionization time of flight) mass spectrometry.

     

Amino acid-bearing ROMP polymers with a stereoregular backbone

The ruthenium-catalyzed ring-opening polymerization (ROMP) of 1-cyclobutenecarbonyl glycine methyl ester provides translationally invariant, head-to-tail ordered polymers. This polybutadiene backbone contains (within the limits of detection) only E-trisubstituted olefins, and it has no stereocenters that would serve as a source of structural ambiguities. Characterization of the polymer products indicates that they have polydispersities ranging from 1.2 to 1.6 and suggests that they are the products of a "living" polymerization. 1-Cyclobutenecarboxamide-derived ROMP polymers are excellent prospects for applications that require stereoregular chains functionalized with polar ligands.     

Novel photochromic dithienylperfluorocyclopentenes with rhodanine fragments: synthesis and spectroscopic properties

Novel photochromic dithienylperfluorocyclopentenes with rhodanine fragments 1a-c were obtained and their spectrokinetic characteristics were examined. The open-chain and cyclic forms of these compounds absorb at longer wavelengths compared to known symmetrical dithienylperfluorocyclopentenes. The influence of the substituent nature on the photochromism of these compounds was studied.     

Novel photochromic macrocycles composed of thiophene and ethylene building blocks: synthesis, structure, and photochromic property

Two novel photochromic macrocycles composed of thiophene and ethylene building blocks have been synthesized, and their crystal structure and photochromic properties are described. Macrocycle 2 shows good photochromic properties.     

Novel Initiators for Thermally and UV-Triggered ROMP

Novel ruthenium-based photoactive transition metal catalysts, i.e. [Ru(CF₃CO₂)₂(p-cymene)(IMes)] ( 2 ), [Ru(CF₃CO₂)₂(PhNC)₃(IMes)] ( 3 ), [Ru(CF₃CO₂)₂(p-cymene) (IMesH₂)] ( 4 ), [Ru(CF₃CO₂)₂(PhNC))₃(IMesH₂)] ( 5 ), have been prepared and investigated for their use as initiators for the thermally and photo-initiated ring-opening metathesis polymerization (photo-ROMP). The polymerization behavior of the novel systems for both norborn-2-ene and functional monomers, such as norborn-5-ene- 2-ylmethanol, has been investigated.     

Synthesis of cis,syndiotactic ROMP polymers containing alternating enantiomers

Ring-opening metathesis polymerization (ROMP) of rac-endo,exo-5,6-dicarbomethoxynorbornene (inter alia) yields a cis,syndio,alt-polymer, one in which the sequential units in the cis,syndiotactic polymer consist of alternating enantiomers. Cis selectivity arises through addition of the monomer to produce an all-cis-metallacyclobutane intermediate, while syndioselectivity and alternating enantiomer structures arise as a consequence of inversion of configuration at the metal center with each metathesis step.     

Solid-phase synthesis of photochromic spiropyrans

[reaction: see text] A convenient solid-phase synthesis of spiropyrans is described. A succinate linker was employed, which allows base-catalyzed cleavage of the desired photochromophore derivatized with a succinimide. Excellent yields and purities were obtained for the compounds that comprise a library of 23 spiropyrans. Opening of the succinimide ring in spiropyran could be realized under mild conditions.     

Microwave-assisted synthesis of photochromic fulgimides

A series of photochromic fulgimides have been successfully synthesized from their respective fulgides using microwave methodology. The yields of the fulgimides synthesized through this method, were an improvement over the thermal methods usually employed.