Segmented copolymers are important polymers with attractive properties and wide applications. In this dissertation, segmented polyurethanes containing triptycene units and multiblock copolymers containing poly(arylene ether sulfone) (PAES) and poly(1,4-cyclohexyldimethylene terephthalate) (PCT) segments were synthesized and systematically studied.
Investigation of the influence of the bulky triptycene structure on the morphologies and properties of segmented polyurethanes was carried out by using triptycene-1,4-hydroquinone bis(2-hydroxyethyl)ether (TD) as the chain extender. Segmented polyurethanes based on poly(tetramethylene glycol) (PTMG) of 1000 g/mol were synthesized using a two-step polymerization procedure. Hydroquinone bis(2-hydroxyethyl)ether (HQEE) was used for the purpose of comparison. Hard segments with different bulkiness and flexibility were prepared with hexamethylene diisocyanate (HDI) and 4,4'-methylenebis(phenyl isocyanate) (MDI), and HQEE or TD as chain extenders. The incorporation of bulky TD and less flexible MDI significantly inhibited hydrogen bonding based on the Fourier transform infrared (FTIR) results. In addition, the microphase separation was also disturbed by the bulky and less flexible hard segments with confirmation from tapping mode atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). The flexible HDI can be used to overcome the bulkiness of triptycene, promote microphase separation, and enhance mechanical properties.
Novel PTMG based soft segments containing triptycene units were also prepared with number average molecular weight (Mn) around 2500 g/mol. Then this soft segment was reacted with MDI and HQEE to prepare segmented polyurethanes. Soft segments such as hydroquinone (HQ) containing PTMG (Mn = 2100 g/mol), and pure PTMGs (Mn = 1000 and 2000 g/mol) were used for comparison. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrated that triptycene units led to an increased glass transition temperature (Tg) and an elimination of the crystallization of the soft segments. The absence of strain hardening for the triptycene-containing sample suggested a suppressed strain induced crystallization of soft segments, which was also confirmed by the analysis of wide-angle X-ray diffraction (WAXD) on the films strained to 370 %.
Crystallizable PCT segments were copolymerized with PAESs to enhance solvent resistance and mechanical properties. PAES oligomers (Mn = 2000 g/mol) were first synthesized, and then reacted with dimethyl terephthalate (DMT) and 1,4-cyclohexanedimethanol (CHDM). Weight percentages of PCT segments were gradually changed from 20 wt% to 80 wt%. With PCT content greater than 50 wt%, crystallinity was observed by DSC, DMA, and WAXD. The extent of crystallinity of the copolymers was dependent on the wt% of PCT. Furthermore, crystallization behavior of copolymers based on two CHDMs with different isomer ratios (cis/trans 30/70 and all trans) were studied. Due to their more symmetric structure, copolymers based on all trans CHDM exhibited a higher extent of crystallization. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/73294 |
| Date | 27 April 2015 |
| Creators | Chang, Zhengmian |
| Contributors | Chemistry, Turner, S. Richard, Moore, Robert Bowen, Frazier, Charles E., Gibson, Harry W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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