title: Poly(limonene carbonate): Composites and Copolymers
Creators: name: Neumann, Simon
Publisher: name: University of Bayreuth
Year: 2021
Subjects: subject: Polymer
subject: Poly(limonene carbonate)
subject: Composites
subject: Copolymer
subject: Blend
subject: 540

description: Sustainability and climate protection are keywords for upcoming decades. Bio-based polymers can contribute to these ambitious goals and so research is focusing more on these types of polymers (Chapter 6).1–4 This thesis shall contribute to the further development and understanding of bio-based polymers. The main focus of this thesis is the terpene-based polymer poly(limonene carbonate) (PLimC) with its high glass transition temperature (Tg = 130 °C). PLimC was first discovered by COATES et al.5, who investigated the alternating copolymerization of limonene oxide (LO) and CO2. Both monomers are non-food-based and non-crop-based, so competition for resources with the food industry is not present with these monomers. This makes PLimC an excellent candidate as an alternative to bisphenol-A polycarbonate (PC). By masking impurities within the monomer LO, the molecular weight of PLimC could be increased drastically (&lt;100.000 Da).6 PLimC has excellent properties and tuning possibilities for practical applications, so the interest in further development of PLimC is given.6–8 Key factor for practical applications is processing via injection molding or hot-pressing, but neat PLimC is hard to process due to its high viscosity in the melt (η0 = 0.89 MPa‧s), the high onset of the viscous flow (~ T = 167 °C) and its low degradation temperature (~ T = 180 °C). The main objective of this thesis is to show ways to process PLimC despite the aforementioned processing obstacles for PLimC. Additives, blending, or copolymerization can be used as effective tools to achieve the processability of PLimC. Additives The first investigated way involves a bio-based plasticizer, which allows the processing of PLimC without the loss of optically and mechanical properties (Publication 1, Chapter 9.1). Ethyl oleate (EtOL) was chosen as a bio-based plasticizer for PLimC due to its nontoxicity. EtOL is a fatty acid ester, which displays good plasticizing properties due to its long alkyl chains. A loading of 7.5 wt% EtOL reduces the viscosity of PlimC in the melt (η0 = 0.12 MPa‧s) and decreases the onset of the viscous flow (T = 136 °C). At the same time, the glass transition temperature of PLimC is reduced to 90 °C. By applying EtOL, the narrow process window of PLimC can be extended and it can be processed at lower temperatures (~ T = 160 °C). This enables PLimC processing without decomposition and with improved mechanical properties. The E-modulus (E = 2.1 ± 0.19 GPa) and the elongation at break (εbr = 28 ± 9.3%) are increased significantly by the addition of 7.5 wt% EtOL. Higher amounts of EtOL (&gt; 7.5 wt%) do not result in improved mechanical properties. The optical properties of PLimC/EtOL compounds are comparable to the neat PLimC. The recyclability of PLimC/EtOL compounds was also investigated. It is shown that PLimC/EtOL compounds can at least be recycled once by melt reprocessing. Blending To explore the processing of PLimC even further, blends of PLimC as minority component and commodity polymers (e.g., polyamide (PA), polystyrene (PS), or poly(methyl methacrylate) (PMMA)) were produced. Blending should showcase the potential of bio-based polymers for sustainable applications (Publication 2, Chapter 9.2). The blend morphology was investigated by scanning electron microscopy (SEM) and Raman imaging. The difference in viscosity and incompatibility are usually leading to phase-separated blends with a bimodal PLimC domain distribution. Phase-separation also influences the thermal properties of the blends. Using differential scanning calorimetry (DSC), an increased crystallization temperature for PLimC could be observed. That is due to the nucleation effects of PLimC domains. Thermogravimetric analysis (TGA) of the different blends reveals higher thermal stability for matrix embedded PLimC. In terms of mechanical properties, blends of PLimC with polylactide (PLA), poly(butylene adipate-co-terephthalate) (PBAT), or copoly(ether ester) (COPE) show the most promising properties for applications. The most pronounced effect of PLimC in blends (e.g., PBAT or COPE blends) is, that it leads to a strong increased E-modulus, which can be interesting for applications. Copolymerization To improve the performances of phase-separated PLimC/PLA blends, block copolymers of PLimC and PLA were synthesized (Publication 3, Chapter 9.3). The produced block copolymers can be used as compatibilizers in blends to influence the morphology and mechanical properties. In this chapter, the copolymerization of LO, CO2, and lactide (LA) is discussed in detail. One-pot ring-opening copolymerization (ROCOP) of (D, L)-lactide and LO is performed to investigate the actual polymer architecture in one-pot reactions. Based on TEM measurements and 1H-1H-NOESY NMR experiments, a block copolymer structure could be identified. To show an active PLimC chain ending, sequential ring-opening copolymerization of (L)-lactide was performed to synthesize PLimC/PLLA block copolymers. Additionally, ROCOP was used as an efficient tool for tailoring the mechanical properties of PLimC. In a sequential approach, dihexyl-substituted lactides (diHLA) were used as monomers for ROCOP with LO and CO2. These block copolymers of PLimC and Poly(diHLA) (PdiHLA) showed an interesting elasticity and transparency for potential applications.