Click polymerisation

EIS Eissa, A.M. and Khosravi, E., Synthesis of a new smart temperature responsive glycopolymervia click-polymerisation, Eur. Polym. J., 47,61, 2011. 

There are many reports on azide-alkyne click polymerisation (a subject not discussed in the present chapter) but research on thiol-yne click polymerisation is in its early stages. New reaction types, novel catalyst systems other than those existing (i.e., photon, heat, organic base, transition-metal complexes) and new functionalities of the ensuing polymers are waiting to be developed [51]. 

Only a few studies on oleochemistry have been reported until now. Similar to the effects seen with the thiol-ene reaction, one can take advantage of this interesting tool for the synthesis of novel monomers to be polymerised further by classical methods. Also, the possibility of two thiol groups reacting with one ethynyl group via two-step addition makes thiol-yne click polymerisation an interesting method for the preparation of hyperbranched polymers. 

Nurmi L, Lindqvist J, Randev R, Syrett J, Haddleton DM (2009) Glycopolymers via catalytic chain transfer polymerisation (CCTP), Huisgens cycloaddition and thiol-ene double click reactions. Chem Commun 2727... 

Gandini and co-workers described a unique double click strategy related to the preparation of monomers based on vegetable-oil derivatives bearing furan heterocycles appended through thiol-ene click chemistry, and their subsequent polymerisation via the Diels-Alder (DA) polycondensation between furan and maleimide complementary moieties (i.e., a second type of click chemistry). Details about the DA reaction, its mechanism, applications and the reason why it is classified as a click reaction can be found in Chapter 7. 

Application of the thiol-ene click reaction as a direct polymerisation tool consists of the synthesis of monomers in the form of a,(0-dienes that are photo-polymerised with dithiol componnds (Scheme 6.10a). That is, the coupling, via thiol-ene reactions, of an AA (with ene-ene end groups) and a BB (with thiol-thiol end groups) structure or, alternatively, in the synthesis of AB monomers (with ene and thiol functions as end-groups. Scheme 6.10b). Studies reporting on the latter approach are scarce. 

In the first example, the research team of Meier described a ronte to the development of a,(0-dienes with ester and anhydride linkages (Scheme 6.11). These were polymerised further via acyclic diene metathesis (ADMET) polymerisation and thiol-ene click chemistry to compare the two processes for polyester/polyanhydride syntheses [33]. 

PA can also be obtained via the thiol-ene click reaction from a,ro-diene monomers bearing amide groups in the main backbone or as side moieties via the Ugi four-component reaction [36, 37]. In one such study [38], the authors used 10-undecenoic acid as carboxylic acid, 10-undecen-l-al as an aldehyde, and different primary amines and isonitriles to synthesise a,C0-diene monomers, and then applied them to polymerisation reactions. The main focus of this specific work was the ADMET mechanism, though thiol-ene photopolymerisation was also implemented to prepare linear aliphatic PA with Mn values of 3-9 kDa and Tg values of 1-10 °C. 

The research team of Cramail also carried out a pol) hioether synthesis but used a different approach. They undertook the synthesis of AB-type monomers and then polymerised them via the thiol-ene click reaction [41, 42]. The work consisted of the synthesis of 10-undecene-l-thiol from 10-undecenoic acid. Photochemical or thermal initiations were tested for self-polymerisation of this AB monomer, and also by varying the reaction time. Polymers with Mn = 15-40 kDa were obtained and oxidised further, leading to materials with an increased T [21]. 

There are four different chemical reactions that have been used to crosslink polymers with peptide sequences (Fig. 6.8) (i) amide bond formation (ii) Michael-type addition (iii) Huisgen cycloaddition (click reaction) and (iv) radical polymerisation. The amide bond formation follows typical solid phase peptide synthesis (SPPS) protocols and does not require functionalisation of the termini of the peptide sequence. Fluorenyhnethoxycarbonyl (Fmoc) protection of the N-terminus allows attachment of the peptide sequence to an amine-bearing polymer. After removal of the Fmoc group, the amine-terminated peptide-polymer conjugate can be reacted with a second polymer bearing carboxylic acid functionalities using the same coupling chemistry (Maier et al, 2011). For Michael-type additions the peptide... 

Hanson et al. have developed a synthesis of triazoles (91) and utilisation of oligomeric triazole phosphates (OTP) (89) for direct triazolation of N-, O- and -nucleophilic species (90) in a click -capture ring-opening metathesis polymerisation (ROMP)-derived protocol (Scheme 22). ... 

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