Progress in Catalytic Ring-Opening Polymerization of Biobased Lactones

Stereo-electronic contributions in yttrium-mediated stereoselective ring-opening polymerization of functionalracemicβ-lactones: ROP of 4-alkoxymethylene-β-propiolactones with bulky exocyclic chains

“…This is what is expected from a ‘regular’ chain-end stereocontrol mechanism, in which minimization of steric repulsions in the transition state favors the enchainment of monomer units alternately with opposite absolute configurations (and hence the formation of syndiotactic/heterotactic polymers). 1 Only the specific combination of a BPL FG monomer containing two methylene hydrogens apart from the central oxygen on the methylene alkoxy side-functionality ( i.e. , FG = CH 2 OMe, CH 2 OAllyl, and CH 2 OBn) with a catalyst bearing chloro-substituents ( 2a ) produced isotactic PHAs; this is assumed to arise from attractive interactions between the ligand chloro substituents and the hydrogen atoms on the alkoxy (methoxy, allyloxy, and benzyloxy) side chain of the ring-opened monomer/growing polymer chain.…”

“…, tacticities), and hence polymer materials with differentiated and controlled properties. 1 One of the most ubiquitous examples in this area is probably the ROP of racemic lactide ( rac -LA) which has opened large avenues, in particular toward the formation of isotactic PLA stereocomplexes with significantly enhanced thermal characteristics. 1 a – e The formation of isotactic polyesters from the ROP of racemic lactones is clearly much less common than that of their syndiotactic (heterotactic) counterparts; indeed, the latter syndio/hetero tacticities are often the result of a chain-end stereocontrol 1 a , b where the minimization of steric tilting in the transition state induces the regular, alternated enchainment of consecutive monomer units with the opposite configuration.…”

“…On the other hand, the formation of isotactic polyesters from racemic cyclic esters usually requires the use of chiral catalysts, most often metal-based ones, 2 to proceed via a so-called enantiomorphic site control; isoselective ROP of racemic lactones with achiral catalysts is even less frequent and largely focused on rac -LA. 1,3 A recent, remarkable addition is the stereoselective ROP of eight-membered racemic cyclic diolides mediated by discrete rare earth-based catalysts developed by the group of Chen, which affords a variety of perfectly isotactic ( P m up to 0.99)‡‡ P m is the probability of meso linkages, that is, the enchainment of two monomer units with the same configuration. P m = 1 − P r , where P r is the probability of racemo linkage, that is, the enchainment of two monomer units with the opposite configuration. polyhydroxyalkanoates (PHAs).…”

Polyester synthesis based on 3-carene as renewable feedstock

“…[1][2][3] While a plethora of different feedstocks for the synthesis of monomers is available in nature, exploiting this kind of sources remains difficult to some extent. [3][4][5][6][7][8][9][10][11] Not only do we have certain demands regarding material properties, we also are looking for abundant and easy to transform resources which offer sustainability in both generation of the polymers as well as their degradation. 8,12,13 In general, bio-based polymers can be produced from various sources such as acids, sugars or different terpenes and terpenoids.…”

“…8,12,13 In general, bio-based polymers can be produced from various sources such as acids, sugars or different terpenes and terpenoids. [3][4][5][6][7]11,[14][15][16] However, pricing of those products usually remains a main hinderance for such materials to become substitutes for commodity polymers. 3,10,17 Another evident disadvantage one has to consider when looking for bio-based monomer sources is the use of crop space for culti-vation of biomass being transformed to materials rather than food.…”