NMR analysis and triad sequence distributions of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Authors: Cheng, Huai; Biswas, Atanu; Vermillion, Karl; MELENDEZ-RODRIGUEZ, BEATRIZ - Consejo Superior De Investigaciones Cientificas (CSIC); LAGARON, JOSE - Consejo Superior De Investigaciones Cientificas (CSIC)

Submitted to: Polymer Testing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2020
Publication Date: 7/20/2020
Citation: Cheng, H.N., Biswas, A., Vermillion, K., Melendez-Rodriguez, B., Lagaron, J.M. 2020. NMR analysis and triad sequence distributions of poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Polymer Testing. 90:106754. https://doi.org/10.1016/j.polymertesting.2020.106754.
DOI: https://doi.org/10.1016/j.polymertesting.2020.106754

Interpretive Summary: Poly(hydroxybutyrate) (PHB) is a natural biodegradable polyester that is synthesized by microorganisms. It has similar properties as polypropylene with good moisture and aroma barrier properties but is relatively brittle and stiff. Its copolymer with hydroxyvalerate (called PHBV) is less stiff and tougher and may be used as a packaging material. Its end-use properties depend on copolymer composition and comonomer sequence distribution, both requiring NMR analysis. In this work, an improved NMR methodology was devised for PHBV. With this methodology, a more accurate structural information can be obtained from PHBV, thereby facilitating a better understanding of the nature of the polymerization and the structure-property relationships for this copolymer.

Technical Abstract: Polyhydroxyalkanoates (PHAs) are considered promising “green” alternatives to synthetic polymers because they are bio-derived, biodegradable and biocompatible. The properties of bacterial PHA copolymers depend on their microstructures, which can be modified with the use of different fermentation processes and feed materials. Thus, it is desirable to have an improved method for the determination of PHA microstructures. In this work, a detailed NMR analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microstructure was made. Previously only two of the hydroxyvalerate 13C NMR peaks have been assigned at the triad level. In this work, three of the 13C hydroxyvalerate peaks and two of the hydroxybutyrate peaks were found to be split into four peaks each due to comonomer sequence effects. Using eight copolymer samples with a wide compositional range, we were able to assign all these peaks to B-centered and V-centered triad sequences. Through curve deconvolution, the triad intensities were determined. These triad sequence intensities can then be analyzed via both the first-order Markovian and two-component Bernoullian models to obtain more in-depth information on copolymer composition and comonomer reactivities.