Multiblock [-A-B-]<sub>n</sub> copolymers of bisphenol-A polycarbonate (I) and several poly(arylether sulfones) (II) have been investigated. The copolymers
[see document for a diagram of copolymers (I) and (II)]
were prepared from hydroxyl terminated oligomers (4,000 < M̅<sub>n</sub> < 30,000) by an interfacial technique which utilized phosgene as the coupling agent. Characterization of the oligomers and copolymers included end group analysis, membrane osmometry, and gel permeation chromatography.
One of the most interesting aspects of block copolymers is their ability to undergo microphase separation above a critical block length. Either one or two phase block copolymers can be prepared by controlling the molecular weights of the parent oligomers. In the bisphenol-A polycarbonate/bisphenol-A polysulfone system, for example, strictly one phase materials, with only one intermediate glass transition temperature, were obtained at block lengths of less than 10,000 g/mole. Two-phase copolymers resulted when blocks exceeding 20,000 g/mole were coupled. Copolymers comprised of intermediately sized blocks (M̅<sub>n</sub> ≃16,000) could be obtained as either single or multiphase systems depending upon their previous thermal history. Homogeneous films, with a single intermediate Tg, were obtained via solution casting, whereas compression molding provided films exhibiting two Tg's. Subsequent DSC studies pointed out that microphase separation could be thermally, and irreversibly, induced by annealing above the Tg of the polysulfone blocks (190°C).
Since polycarbonate and polysulfone are leading examples of tough, amorphous thermoplastics, the effects of microphase separation on the tensile, impact, and melt flow properties of the copolymers were investigated. A novel falling weight impact tester was designed and constructed to meet the needs of this study. The device was fully instrumented to provide a deceleration-time plot of the impact process by means of an accelerometer mounted in the projectile. Fracture energies for commercial homopolymers and graphite reinforced composites, in addition to polysulfone-polycarbonate block copolymers, were calculated from the impact curves.
Both the tensile and impact properties of the copolymers improved with increasing polycarbonate content. Both single and multiphase materials were ductile and transparent as opposed to physical blends of the two. oligomers which were opaque and possessed poor mechanical properties. No differences due to microphase separation were observed in either the tensile or impact studies.
The homogeneous copolymers displayed melt viscosities and activation energies nearly equal to those of the homopolymers. Much greater viscosities and activation energies were exhibited by the phase separated materials indicating that the heterogeneity was retained in the melt. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/72101 |
| Date | January 1979 |
| Creators | Wnuk, Andrew J. |
| Contributors | Materials Engineering Science |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xii, 211, [3] leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 5712194 |
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