Study on the Synthesis and Application of Functional Polymers on Asymmetric Structure Induction and Actuator Fabrication

Abstract

Abstract Functional polymers are now being pushed through the short-term market for new functional materials which can be used in modern technology Development of functional materials for some specific purpose is getting important This dissertation investigates on synthesis and application of functional polymers on asymmetric structure induction and actuator fabrication This research work consist of following parts: Part I: One predesigned chiral steroid base compound cholesteryl 4-(carbonyloxy) 4-(hexyloxyl) benzoate (CCH?) and two achiral compounds with various alkyl chain length oxalyl acid N’ N’-di(4-(hexyloxy)benzoyl)-hydrazide (AG6) and oxalyl acid N’ N’-di(4-(undecyloxy)benzoyl)-hydrazide (AG11) have been successfully synthesized Formation of asymmetric self-assembled constructions via self-assembly of achiral molecules in chiral environment was investigated Due to steric hindrance CCH? could not form gel in any kind of organic solvents On the other hand AG6 and AG11 formed achiral gels in many kinds of solvent The results suggest that polarity side branch and intermolecular forces are the key factors for the gelation Temperature-dependent 1H-NMR analysis of the fabricated gels show that van der Waals forces and π-π interactions are key factors leading to self-assembly of molecules result in three-dimensional networks In addition CCH? was used as a chiral dopant added into achiral compounds forming asymmetric selfassembled constructions The results indicate that doping of CCH? into achiral gelators giving a chiral environment leads to the formation of helical constructions The fabricated asymmetric constructions were confirmed using circular dichroism (CD) spectroscopy and small angle X-ray scattering (SAXS) Part II: The intelligence complexity and diversification of nature is a continuous source of inspiration for humankind Imitating natural intelligence to devise bionic microrobots with self-regulated features remains an enormous challenge Herein we demonstrate a biomimetic soft material that uses light to trigger mechanical motion This light-sensitive mimosa mimetic film was designed based on liquid crystal elastomers (LCEs) and photoisomerizable azo compounds To control the bending direction a predesigned UV-induced gradient polymerization was used The energy-controlled polymerized film comprises one high-density and one low-density liquid crystal mesogen face Similar to mimosas the fabricated films achieved stimuli-responsive actuation exhibiting shape deformation upon light illumination The elastic network undergoes reversible shape changes via photochemical trans-cis isomerization of an azo compound in response to a stimulus In this study only a small amount of photoisomerizable 1-Hydroxy-n-(4-nitro-azobenzene-4′-oxy) hexane (AZO) was used; however the domino effect caused a significant reversible actuation The mesogen density of the top and bottom faces was found to be an important factor for the bending control This study explores a new way to fabricate films that can bend in controlled directions during light irradiation This phototunable film is expected to be used for applications in microrobotics and micromachinery Part III: A new series of symmetric bis-cholesteryl-appended isosorbide derivatives (BCIE BCIC2 and BCIC4) were designed as gelators to respond to changes to their environment and were synthesized successfully The results from the gelation ability in different solvents revealed that changing the linking group (ester/carbamate) attached to the cholesteryl units can produce a dramatic change in the gelation behavior of the compounds The morphology of the as-formed organogels can be regulated by changing the types of organic solvents The results from the electron microscopy studies revealed that the gelator molecule self-assembled into different aggregates from wrinkled fibers to dense fibers with the change of solvents The gels of BCIE in 1-hexanol and 1-octanol exhibited strong CD (circular dichroism) signals indicating that the gelation induced supramolecular chirality in these gel systems Secondary forces of van der Waals and π-π stacking (from both 1 2 3-triazole and aromatic units) played important roles in the aggregation of compounds in the solvents according to the FTIR and variable temperature 1H-NMR analysis and a mechanism for the gel formation was proposed The gel-tosol phase transition can be triggered by the addition of trifluoroacetic acid (TFA) and the gel state was obtained slowly (after 1 day) when neutralizing with triethyl amine (TEA) which indicated that the solgel phase transitions are tunable by pH which is further supported by the 1H-NMR and SEM analysis In addition the results showed that the gel-to-sol phase transition process could be selectively controlled by interaction with Pd2+ and Zn2+ because complexation with 1 2 3-triazoles destroyed the interactions between the triazoles collapsing the gel However the gel stability of BCIE was enhanced by the addition of Pd2+ and Zn2+ in presence of pyridine whereas the gel collapsed in other solvents which may be due to the chelating effect of the pyridine moiety Another interesting factor of this gel is that when using the gelator as a stabilizer stable water in oil (W/O) gel-emulsions were created in which styrene can be used as the continuous phase water as the dispersed phase with a stabilizer in the continuous phase of only 2% (w/v) Gel-emulsions were observed with any ratio of water to styrene Part IV: Two structurally isomeric azobenzene- and cholesteryl-based derivatives with varying alkyl chain lengths were developed as ALS-type gelators (N2 and N4) and synthesized and characterized spectroscopically Of the two N4 acted as a more efficient gelator than N2 since N4 could gel a larger number of solvents The critical gelation concentration (CGC) of N4 was found to be less than that of 15 N2 in the same solvent system The morphological analyses of both gelators using SEM and TEM revealed that N4 exhibited selfassembled fibrous structures whereas N2 exhibited spherical nanoparticles The van der Waals interactions between the cholesteryl units hydrogen bonding between the amide linkages and π-π stacking between the azobenzene units provided the driving force for the aggregation and gel formation These driving forces were evidenced by temperature dependent 1H-NMR FTIR and XRD analyses Increasing the temperature of the gels shifted (upfield and downfield) the protons in the 1H-NMR spectra as well as the absorption bands 20 in the FTIR spectra indicating that the intermolecular forces between the molecules became disrupted and caused gel→ sol transitions These transitions were reversible after cooling to room temperature Similarly the gel→ sol transitions could be triggered by UV light (due to trans/cis isomerization); however the transition was irreversible in the presence of visible light due to the formation of the more stable cis isomer Hence the gel state could be retained by heating and cooling the cis-conformation In addition the length of the molecule as determined by simulation software was found to match the values observed from the XRD analysis and the interlayer 25 distances were found to be 1 78 and 1 85 nm for N2 and N4 respectively Based on this evidence an aggregation mechanism was proposed The differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results revealed that both gelators exhibited grainy nematic mesophase textures during the heating and cooling cycles These gelators underwent phase-selective gelation in the solvent mixtures containing gelling and nongelling solvents which demonstrated the applicability of these gelators for the separation and purification of solvents

Date of Award	2021
Original language	English
Supervisor	Jui-Hsiang Liu (Supervisor)