Cyclic carbonates copolymerisation

Coordination polymerisation of heterocyclic monomers comprises polymerisation and copolymerisation processes of such monomers as oxacyclic monomers, especially epoxides [2,61-71], thiacyclic monomers like episulphides [72-76], azacyclic monomers [77,78] and phosphacyclic monomers [79]. Monomers with an exocyclic oxygen atom, such as cyclic esters like lactones [80-90] and lactide [90-92], cyclic acid anhydrides [93-98], cyclic carbonates [99,100] and related monomers, belong to oxacyclic monomers undergoing coordination polymerisation or copolymerisation. 

Since oxiranes are representative heterocyclic monomers containing an endo-cyclic heteroatom, and the most commonly polymerised of such monomers, they have been subjected to copolymerisations with heterocyclic monomers containing both an endocyclic and an exocyclic heteroatom. Coordination copolymerisations of heterocyclic monomers with different functions are focused on oxirane copolymerisation with cyclic dicarboxylic acid anhydride and cyclic carbonate. However, the statistical copolymerisation of heterocyclic monomers with an endocyclic heteroatom and monomers with both endocyclic and exocyclic heteroatoms have only a limited importance. Also, the block copolymerisation of oxirane with lactone or cyclic dicarboxylic acid anhydride is of interest both from the synthetic and from the mechanistic point of view. Block copolymerisation deserves special interest in terms of the exceptionally wide potential utility of block copolymers obtained from comonomers with various functions. It should be noted, however, that the variety of comonomers that might be subjected to a random, alternating and block polymerisation involving a nucleophilic attack on the coordinating monomer is rather small. 

It seems that the initiation step of the copolymerisation most likely involves the oxirane reaction [according to scheme (3)]. Zinc alcoholate species formed in this reaction can easily propagate the copolymer chain, coordinating and enchaining both the oxirane [scheme (3)] and the cyclic carbonate [scheme (15)] comonomers. However, in the case of the cyclic carbonate, its enchainment may also proceed according to scheme (14), leading to decarboxylation. Thus, the obtained poly(ether-carbonate)s are characterised by a lower content of carbonate units with respect to the ether units [82,146]. 

Fairly good confirmation of the postulated mechanism of cyclic carbonate enchainment according to scheme (15) may be the obtaining of poly(oxypro-pylene-co-oxycarbonyloxypropylene) of predominant head-to-tail regioregular-ity from bispropylene spiroorthocarbonate with a zinc-based coordination catalyst [146]. It must be emphasised that the copolymerisation of propylene... 

The formation of a cyclic carbonate, e.g. propylene carbonate, accompanying the copolymerisation has been explained in terms of the backbiting reaction involving zinc alcoholate species [206,207], This has been confirmed recently [147] by degrading polypropylene carbonate) by using catalysts with zinc phenolate species. The degraded copolymer thus obtained was terminated in its chains with zinc alcoholate species and phenylcarbonate groups. The course... 

It may be mentioned that the use of ionic nucleophilic initiators, instead of zinc-based coordination catalysts, in order to promote propylene oxide/carbon dioxide copolymerisation, did not result in the formation of any copolymer but led to the cyclic carbonate, propylene carbonate [194,236,237]. Also, zinc-based coordination catalysts with non-condensed zinc atoms in their molecules (formed by the reaction of diethylzinc with a monoprotic compound such as... 

Nozaki s zirconium(iv) BOXDIPY initiator was inactive for the copolymerisation of PO/carbon dioxide with the addition of 1 equivalent of [PPN]Cl (2.0 MPa carbon dioxide, 60 °C) forming the cyclic carbonate in 100% yield. ° Tbe complex was able to produce a polycarbonate with CHO, although the proportion of ether linkages was high. Titanium(iv) and germanium(iv) complexes were also screened, with more success than the zirconium(iv) analogue. In 2014 Ko prepared a series of zirconium(iv) amine-bis(benzo-triazole) phenolate complexes for the ROP of rac-LA and the production of... 

PTMC synthesis is realised either by copolymerisation of epoxides with carbon dioxide or by the ring-opening polymerisation (ROP) of cyclic carbonate monomers. It is also possible to obtain aliphatic carbonates via polycondensation of dialkyl or diphenyl carbonate or chlorophormates and aliphatic diols. However, polycondensation usually leads to polymers with rather low molar masses (Hyon et al., 1997). Besides, side reactions often occur during polycondensation (Jerome and Lecomte, 2008). 

The coordination polymerisation of heterounsaturated monomers, such as aldehydes [101-103] and ketones [104], isocyanates [105] and ketenes [106,107], in homopolymerisation systems has not been widely described in the literature. However, the coordination copolymerisation of heterounsaturated monomers not susceptible to homopropagation, such as carbon dioxide [71,108-113], with heterounsaturated monomers such as cyclic ethers has been successfully carried out and is of increasing interest. 

Heterocyclic monomers containing both endocyclic and exocyclic heteroatoms such as cyclic esters (lactones, lactide, carbonates) and cyclic anhydrides undergo coordination polymerisation or copolymerisation involving complex formation between the metal atom and the exocyclic heteroatom [100,124]. Polymerisation of /1-lactones is representative of such coordination polymerisations with catalysts containing an Mt-X active bond the initiation and propagation steps are as follows ... 

Although rather scant information concerning the structure of active sites in the above copolymerisation systems is available [183-189], cyclic acid anhydrides can be considered as coordinating to metal species via the carbonyl oxygen atom and reacting by nucleophilic attack of the metal substituent on the carbon atom of the coordinated carbonyl group [190,191], Thus, the oxi-rane/cyclic acid anhydride copolymerisation pathway may be presented schematically as follows [82] ... 

Copolymerisation of propylene oxide as well as other oxiranes with carbon dioxide in the presence of zinc-based coordination catalysts is generally accompanied with the formation of a cyclic five-membered carbonate, propylene carbonate or another alkylene carbonate [147,206,207,210,212,230]. The alky-lene carbonate, however, is not the precursor for poly(alkylene carbonate), since it hardly undergoes a polymerisation under the given conditions [142-146],... 

In order to clarify the mechanism, the reaction of carbon disulphide with mercury bis(n-butanethiolate) was studied. On the basis of results obtained, it was suggested that this reaction involved the formation of a coordination complex, followed by the formation of active species containing the Hg-SC(S) bond. Moreover, the cyclic trithiocarbonate, ethylene trithiocarbonate, found to be present in trace amounts in copolymerisation products, was excluded as a possible intermediate for the copolymer formation, since it did not undergo any polymerisation under the given conditions [249],... 

At the end of considerations concerning the coordination polymerisation of heteroatom-containing cyclic and acyclic monomers, it is obvious that future development (beyond carbon monoxide copolymerisations) is to be anticipated, especially concerning new catalytic processes, including both new... 

While homopolymerization of cyclopentene results in 1,3-enchainment of the monomer units in copolymerisation, blocks of cyclic monomer units are rarely observed due to the unfavorable copolymerization parameters. The isolated cyclopentene units may be incorporated in a cis-1,2 or ds-1,3 fashion, their ratio depending on the catalyst used [194-196], Thus ethene is able to compensate the steric hindrance at the a-carbon of the growing chain after the insertion of a cyclopentene. 

Chemical catalysts such as stannous octanoate, methylaluminoxane and aluminium isopropoxide have been used for the copolymerisation of TMC and 15-pentadecanolide (PDL), and the results showed that TMC had much greater reactivity than PDL. In contrast, for the Novozyme-435-catalysed copolymerisation, PDL had a greater reactivity than TMC. Cyclic dicarbonates, cyclo/ /s(hexamethylene carbonate) and cyclo/ 2s(diethylene glycol carbonate) have been copolymerised with e-CL and 12-dodecanolide (DDL) using CAL in toluene at 60 °C for 48 h (Scheme 12.12) [62]. 

---