Improving the Sustainability of Enzymatic Synthesis of Poly(butylene adipate)-Based Copolyesters: Polycondensation Reaction in Bulk vs Diphenyl Ether

In response to mounting global concerns such as CO2 emissions, environmental pollution, and the depletion of fossil resources, the field of polymer science is shifting its focus toward sustainability. This research investigates the synthesis of poly(butylene adipate)-co-(dilinoleic adipate) (PBA-DLA) copolymers using two distinct methods: bulk polycondensation and polycondensation in diphenyl ether. The objective is to assess the environmental impact, chemical structure, composition, and key properties of the resulting copolymers, with a particular emphasis on determining the viability of bulk synthesis as a more sustainable approach. Various analytical methods, including nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and size exclusion chromatography, were employed to confirm successful copolymerization and highlight differences in molecular weight and microstructure. Additionally, thermal and dynamic mechanical analyses were conducted to thoroughly characterize the copolymers’ properties. This research provides significant findings into the sustainable production of PBA-DLA copolymers, offering a more environmentally friendly approach without compromising product quality or performance.


Molecular mass calculation from
H is the ratio between hard and soft segments, I 1.70 is the integral of the signal at 1.70 ppm and I 0.85 is the integral of signal at 0.85 ppm.The weight percentage of hard segments (%W h ) of PBA-DLA copolyester was computed from H using equation ( 2): (2) where %W H is the weight percentage of PBA hard segments, M h is the molecular weight of the hard segment (200 g/mol) and M s is the molecular weight soft segment (652 g/mol).Likewise, using the signals of BDO and DLD, we can also compute the mole percent of each block using equations (3-4): (3) where %Mol h and %Mol s are mol percentage of hard and soft segments, respectively.n 1,70 and n 0,88 are number of protons in BDO and DLA units.
Following the equations (5-6) we can also calculate the number of hard and soft segments (Num h and Num s ) by comparing the BDO and DLD signals to that of the end groups, which are signals arising from hydroxyl end-groups of BDO at 3.68 ppm (-CH 2 OH) and the macromolecules can be expected to be capped by a BDO on either end, so there will be two such end-groups (n end ). (5) Finally, by multiplying the number of each block times the molecular weight of each block and summing, we are able to calculate molecular weight of copolymer using equation ( 7):

Degree of polymerization calculation from SEC
In order to calculate the degree of polymerization (DP) for copolymers, which contain two different repeating units (hard and soft segments), consideration of the composition of the copolymer was required.The degree of polymerization was calculated for each repeating unit separately, and then a weighted average was calculated based on the composition of the copolymer assessed via 1 H NMR analysis.
General approach to calculate the DP for a copolymer with two different repeating units: For calculations, weight fractions of each monomer unit were denoted as f 1 and f 2 , where f 1 + f 2 = 1.Degree of polymerization for hard and soft segments were further calculated using equations ( 8), and (9), respectively.
Where DP H and DP S is the degree of polymerization of hard and soft segment, respectively.M n is the number averaged molecular weight of copolymer acquired from SEC measurement (14 400 g/mol), and M H and M S is the molecular weight of PBA hard (200 g/mol), and DLA soft segment (652 g/mol), respectively.
Furthermore, averaged degree of polymerization (DP) was calculated based on equation ( 10): This calculation provides an average degree of polymerization for the copolymer, taking into account the different repeating units and their respective proportions in the polymer chain.