| Popis: |
This thesis contains five chapters. The first three chapters are allocated to linear chain extension via associative termini. Chapter 4 describes the effect of soft segment structure on crystalline domains in block copolymers. Chapter 5 presents the synthesis and characterization of amine-terminated PEEK's. Oligomers described in Chapter 2 comprise conformationally-flexible mid-blocks of poly(butadiene) or poly(ethylene-co-1-butene) capped with bis-aromatic esters which carry benzyl ester or carboxylic acid termini. Hydrogen-bonded chain termini resemble rigid rod-like hard segments. These hydrogen bond-linked hard segments are able to microphase separate and crystallize, locking the hydrogen bonds within the crystal lattice and preventing hydrogen bond dissociation. Dissociation is not possible below the melting temperature of the crystalline domains. Non hydrogen bonding ester-terminated oligomers are used as controls to highlight the effects of hydrogen bonding. Two important structural variable effects on oligomer mechanical properties are examined. These are: the use of an hydrocarbon soft segment to increase the degree of microphase separation and the effect of soft segment topology to promote network formation. Oligomers were studied by DSC, POM, and rheology. Rheological data demonstrated that chain end aggregation increased the moduli of the carboxylic acid terminated oligomers as compared to non-associative benzyl blocked oligomers. Soft segment topology played an important role in oligomer properties. Chapter 3 presents a new approach to improving the mechanical properties of the carboxylic acid-terminated oligoethylene-co-1-butenes. One ester linkage at each terminus of the oligomers described in Chapter 2 was replaced with an amide linkage. DSC data suggested that amide-containing oligomers might have more stable crystalline domains based on the fusion enthalpies. In chapter 4, we tested a hypothesis about how soft segment substituents proximate to hard segments affect microphase separation and crystallization behavior of segmented block copolymers. We synthesized copolymers with aryl ester hard segments and Reverse Pluronic$\sp\circler$ soft segments. DSC and POM data were suggestive that the substituents proximate to the hard segment dramatically affected polymer thermal properties. The last chapter, chapter 5, describes our effort to simplify the large scale synthesis of amine-terminated t-butylhydroquinone based PEEK's. High solubility of the oligomers in common organic solvents made it possible to characterize them by VPO and GPC in addition to elemental analysis. GPC analysis demonstrated that oligomers had a broad molecular weight distribution in all cases. Amine-termination step showed no dramatic molecular weight changes by GPC analysis. We could not force extensive Schiff base formation even under forcing conditions. |
