The classical route for the synthesis of this family of macromolecules is via nucleophilic aromatic substitution using dimethylsulfoxide (DMSO) as a dipolar aprotic solvent and aqueous sodium hydroxide as a base. High molecular weight homopolymers can be synthesized in a short time (1 hour). However, hydrolytic side reactions can limit its scope for the synthesis of block copolymers. An alternate route using potassium carbonate/dimethyl acetamide as base and solvent respectively has been cited in the patent literature. We have used this method for the synthesis of several homopolymers and copolymers derived from various bisphenols. Our investigation into the kinetics and mechanism of this process has demonstrated that this route deviates from simple second order kinetics. This deviation has been rationalized to be due to the heterogeneous nature of the reaction.
The utility of these polymers is a direct function of their excellent stability (hydrolytic, thermal and dimensional) wide use range and good mechanical properties. However, their poor solvent resistance can be considered and "Achilles heel". We reasoned that the introduction of a second ordered or crystalline component would vastly improve its solvent resistance. Hydroquinone polysulfone, homopolymer was reported to be semi-crystalline "as made". We thus synthesized and studied "random" copolymers obtained by reacting various mole ratio combinations of bisphenol-A and hydroquinone with dichlorodiphenyl sulfone. The molecular weight (M<sub>n</sub>) of these copolymers ranged from 20,000-40,000. Their glass transition temperature (T<sub>g</sub>) increased monotonically from 185°C for pure bis-A homopolymer to 210°C for hydroquinone homopolymer. Two different types of mechanical tests together with DSC and SEM measurements showed that improved solvent resistance (especially to liquids of interest to NASA for aerospace functions) could be achieved via a novel liquid induced crystallization process. ¹³C and proton NMR spectral assignments were successfully made using model compounds. The composition of the copolymers by NMR accurage to ±3%. Multiblock (-A-B-) copolymer of bisphenolA polycarbonate and several poly(arylether sulfones) were synthesized from well characterized oligomers. It was possible to prepare one or two phase block copolymers by controlling the molecular weights and/or interaction parameters of the parent oligomers. Surface characterization showed surface segregation even for the single phase material.
Triad distribution of monomers in non-equilibrium copolycondensation was investigated by Monte' Carlo simulation. In the one step process, where the intermonomer and/or comonomers had independent functional group reactivities, the resulting copolymer was always random irrespective of the reactivity ratio of the comonomers. A non random distribution was obtained when the reactivity ratio of the funtional groups in the intermonomer and those of the comonomer were much greater than unit. Monomers that resulted in a random copolymer in a one step process could be made with a non random distribution by a multi-step process. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106311 |
| Date | January 1981 |
| Creators | Viswanathan, Ravi |
| Contributors | Chemistry |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | viii, 308 pages, 3 unnumbered leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 08010344 |
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