STUDY OF RELAXATION TRANSITIONS IN SOME AROMATIC POLYESTERS

Методом спинового зонда проведено систематическое изучение основных релаксационных переходов жесткоцепных стеклообразных полимеров в широком интервале температур с применением спиновых зондов разного размера на примере полисульфона. В главной области релаксации ароматических полиэфиров с помощью метода спинового зонда обнаружены два перегиба. Два перегиба, обнаруженные на температурной зависимости времени корреляции вращения, являются следствием размораживания сегментальной подвижности в областях с различной упаковкой сегментов. Показано, что высокотемпературный перегиб соответствует размораживанию сегментальной подвижности кооперативного типа (а -переходу), а перегиб при более низкой температуре р -размораживанию сегментальной подвижности локального типа (а'-процессу). Для объяснения природы данного перехода была использована теоретическая модель полимера, где предполагается, что в аморфных полимерах возможны разные уровни надмолекулярной организации, т.е. существование более упорядоченных и более плотно упакованных областей, которые чередуются с более «рыхлыми» и менее упорядоченными областями. Исследовано влияние различных факторов на положение а’-перехода на температурной шкале. Выбор объема зонда на основе строго обоснованной модели его движения позволил выявить взаимосвязь между вращательным движением зонда и движением отдельных сегментов аморфного полимера ниже температуры стеклования. The spin probe method was used to systematically study the main relaxation transitions of rigid-chain glassy polymers in a wide temperature range using spin probes of different sizes using polysulfone as an example. In the main relaxation region of aromatic polyesters, two inflections were found using the spin probe method. The two inflections found in the temperature dependence of the rotation correlation time are the result of unfreezing of segmental mobility in regions with different packing of segments. It was shown that the high-temperature inflection corresponds to the defrosting of the cooperative-type segmental mobility (a -transition), and the inflection at a lower temperature corresponds to the / -defrosting of the segmental mobility of the local type (the a' -process). To explain the nature of this transition, a theoretical model of the polymer was used, where it is assumed that different levels of supramolecular organization are possible in amorphous polymers, i.e. the existence of more ordered and more densely packed regions, which alternate with looser and less ordered regions. The influence of various factors on the position of the a' -transition on the temperature scale is investigated. The choice of the probe volume on the basis of a strictly substantiated model of its motion made it possible to reveal the relationship between the rotational motion of the probe and the motion of individual segments of the amorphous polymer below the glass transition temperature.

Biocatalytic Formation of Novel Polyesters with para-Hydroxyphenyl groups in the Backbone - Engineering Cupriavidus necator for production of high-performance materials from CO2 and electricity

Synthetic materials are integral components of consumables and durable goods and indispensable in our modern world. Polyesters are the most versatile bulk- and specialty-polymers, but their production is not sustainable, and their fate at end-of-life of great concern. Bioplastics are highly regarded alternatives but have shortcomings in material properties and commercial competitiveness with conventional synthetic plastics. These constraints have limited the success in global markets. Enabling bio-production of advanced bioplastics with superior properties from waste-derived feedstocks could change this. We have created microbial cell factories that can produce a range of aliphatic and aromatic polyesters. A DphaC1 mutant of Cupriavidus necator H16 was complemented with hydroxyacyl-CoA transferases from either Clostridium propionicum (pct540) or Clostridium difficile (hadA), respectively. These were combined with a mutant PHA synthase (phaC1437) from Pseudomonas sp. MBEL 6 19, which rescued the PHA- phenotype of the knock-out mutant and allowed polymerization of various hydroxy carboxylates, including phloretic acid. This is the first-time, incorporation of an aromatic ring in the backbone of a biological polyester was achieved. Polymers contain para-hydroxyphenyl subunits are structurally analogous to synthetic aromatic polyesters like PET and high-strength polyarylates. In a further advance, the transgenic strain was cultivated in a bio-electrochemical system under autotrophic conditions, enabling synthesis of aromatic bio-polyesters from H2 and O2 generated in situ, while assimilating CO2. Follow-up elementary flux-mode analysis established the feasibility of de novo production of twenty different polyesters from five different carbon- and energy-sources. This comprehensive study opens the door to sustainable bio-production of high-performance thermoplastics and thermosets.

Ferulic Acid as Building Block for the Lipase-Catalyzed Synthesis of Biobased Aromatic Polyesters

Enzymatic synthesis of aromatic biobased polyesters is a recent and rapidly expanding research field. However, the direct lipase-catalyzed synthesis of polyesters from ferulic acid has not yet been reported. In this work, various ferulic-based monomers were considered for their capability to undergo CALB-catalyzed polymerization. After conversion into diesters of different lengths, the CALB-catalyzed polymerization of these monomers with 1,4-butanediol resulted in short oligomers with a DPn up to 5. Hydrogenation of the double bond resulted in monomers allowing obtaining polyesters of higher molar masses with DPn up to 58 and Mw up to 33,100 g·mol−1. These polyesters presented good thermal resistance up to 350 °C and Tg up to 7 °C. Reduction of the ferulic-based diesters into diols allowed preserving the double bond and synthesizing polyesters with a DPn up to 19 and Mw up to 15,500 g·mol−1 and higher Tg (up to 21 °C). Thus, this study has shown that the monomer hydrogenation strategy proved to be the most promising route to achieve ferulic-based polyester chains of high DPn. This study also demonstrates for the first time that ferulic-based diols allow the synthesis of high Tg polyesters. Therefore, this is an important first step toward the synthesis of competitive biobased aromatic polyesters by enzymatic catalysis.

The Catalytic Synthesis of Wholly Aromatic Polyesters Based on 4-hydroxybenzoic Acid via Direct Esterification

The synthesis and properties of wholly aromatic polyesters are of considerable practical importance to create functional and high-performance materials. In the present study, by means of catalytic polyesterification using titanium (IV) butoxide, we’ve synthesized wholly aromatic oligomers derived from 4-hydroxybenzoic acid (HBA), aromatic diacids and dibasic phenols. As revealed by FTIR measurements, the average molecular weight of oligomers has varied from 500 to 1400. The results of DSC have shown endotherm peaks attributed to a phase transition of low-molecular oligomers from crystalline state to mesophase and further isotropization. The synthesized oligomers were resistant to high temperatures up to about 300-320 °C.