Synthesis and Characterization of Novel Polyisobutylene-Based Materials: Gradient Block Copolymers, Exo-Olefins Via In Situ Quenching, and Carboxylic Acid-Functional Telechelics
Date of Award
Doctor of Philosophy (PhD)
Polymers and High Performance Materials
Robson F. Storey
Polymers and High Performance Materials
In the past, quasiliving cationic polymerization (QCP) has been utilized to make ideal block copolymers (IBCP) comprised of polystyrene (PS) outer blocks and polyisobutylene (PIB) inner blocks for use as thermoplastic elastomeric membranes. In this work we report the successful synthesis and characterization of gradient block copolymers (GBCP) containing a gradient, or tapered, segment between the PS and PIB blocks. The technique for producing the gradient segments for the desired triblock copolymers involves a slow delivery of monomer; this technique was evaluated using model diblock copolymers. The model diblock gradients were evaluated against ideal, statistical, microblock, and multiblock model controls. The gradient triblock materials are desired for evaluation as improved perrnselective membranes with increased elongation to break and broadened damping response due to an increased interphase size. Secondly, this work reports the discovery of ether compounds that are able to quench quasiliving polyisobutylene reactions in situ to high yields of exo- olefin chain ends. Specifically, alkoxysilanes are able to yield nearly 100% exo- olefin PIB under extremely high concentration, in situ quenching conditions (≥0.1 CE). This makes this system quite valuable for industrial use to produce exo- olefin PIB that can later be modified through a host of post-polymerization procedures to create a variety of functional PIBs. While the exact mechanism of quenching has not been confirmed, it is proposed that these quenchers operate by β-proton elimination as with the previously reported hindered bases; however, a major difference with these quenchers is that the complex of the alkoxysilane with TiCl 4 is the proposed active quenching agent, and it is believed that there is an ongoing balance of Lewis acidity of the reaction medium with conversion to exo- olefin by the in situ by-product generation of the less active titanium trichloroethoxide (TiCl3 OEt). Features unique to alkoxysilane quenching include a low TiCl4 demand during quench and the lack of precipitate formation, even at very high CE concentration. These systems will continue to be explored to better understand the true mechanism by which they convert polyisobutylene chain ends to exo- olefin and the kinetics of quenching. To confirm the NMR spectral shifts of a by-product seen in unsuccessful quenching reactions, we examined the synthesis and characterization of a model compound representing exo- olefin coupled polyisobutylene (PIB). We have observed the generation of exo- olefin coupled PIB as a side-product of the in situ quenching of living PIB through the coupling reaction of exo- olefin PIB chains with ionized PIB chains. Characterization of the signals that arise in 1 H NMR from the presence of coupled product has not yet been properly performed; the accurate chemical shifts of these products, specifically the exo- olefin product, have been in debate recently. Finally, tert- chloride-terminated polyisobutylenes (PIB) (1,020 ≤ Mn ≤ 6,700 g/mol) were dehydrochlorinated non-regiospecifically using basic alumina or regiospecifically either via potassium tert- butoxide or in situ quenching of living PIB. Olefin-terminated PIBs were quantitatively ozonized at -78°C using hexanes/methylene chloride/methanol, 62/31/7 (v/v/v) cosolvents and an ozone generator employing pure oxygen as source gas. The primary ozonides were reduced using trimethyl phosphite to yield pure PIB methyl ketone from exo- olefin PIB and a mixture of PIB methyl ketone and PIB aldehyde from mixed olefin-PIB. PIB methyl ketone was oxidized to carboxylate via the haloforrn reaction. Titration revealed near-quantitative functionalization, but the haloform reaction was judged to be too slow. (Abstract shortened by UMI.)
Kemp, Lisa Kay, "Synthesis and Characterization of Novel Polyisobutylene-Based Materials: Gradient Block Copolymers, Exo-Olefins Via In Situ Quenching, and Carboxylic Acid-Functional Telechelics" (2007). Dissertation Archive. 423.