Date of Award

Fall 12-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

Committee Chair

Dr. Robson Storey

Committee Chair Department

Polymers and High Performance Materials

Committee Member 2

Dr. Kenneth Mauritz

Committee Member 2 Department

Polymers and High Performance Materials

Committee Member 3

Dr. Robert Moore III

Committee Member 3 Department

Polymers and High Performance Materials

Committee Member 4

Dr. William Jarrett Jr.

Committee Member 4 Department

Polymers and High Performance Materials

Committee Member 5

Dr. Charles L. McCormick

Committee Member 5 Department

Polymers and High Performance Materials

Abstract

There exist two main focus areas of academic research within the area of quasiliving polymerization of isobutylene (IB): (1) the in-depth study and understanding of mechanistic features of the polymerization, and (2) the utilization and manipulation of the unique aspects of these quasiliving polymerizations in order to produce practically useful polymeric materials. Both are quite important for advancing the knowledge base in the area and for attracting new research efforts in the area. The research included in this dissertation falls mainly in the latter focus area. In the process of finding new and unique materials based on polyisobutylene, we have also developed more of an understanding regarding its polymerization and copolymerization. This work details four main areas of research: (1) the copolymerization of IB and styrenic monomers to form gradient block copolymers, (2) the discovery and exploration of a new quencher that yields exo-olefin PIB in situ, (3) a small molecule model study to verify by-products formed during the in situ quenching process, and (4) the post-polymerization conversion of exo-olefin PIB to carboxylic acid functional polymer.

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 permselective 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 polisobutylene 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 P-proton elimination as with the previously reported hindered bases; however, a major difference with these quenchers is that the complex of the alkoxysilane with TiCU 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 (TiClaOEt). Features unique to alkoxysilane quenching include a low TiCU 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 lH 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. Therefore we carried out the synthesis of a model compound which mimics the exo-olefin coupled product, and through variations in the synthetic method were able to produce a range of exo- and endo- olefin coupled product mixtures. The model compounds have been fully characterized using NMR techniques, and we herein conclusively report the proton shift (for 500 MHz *H NMR in CDC13) of 4.82 ppm for the exo-coupled product and that of 5.11 ppm for the ew/o-coupled product.

Finally, tert-chloride-terminated polyisobutylenes (PIB) (1,020 < M„ < 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 haloform reaction. Titration revealed near-quantitative functionalization, but the haloform reaction was judged to be too slow.

Tetrahalomethane oxidation was identified as a preferred alternative method, and was conducted using either CCI4 as the reaction solvent, THF as the solvent with CCI4 in reagent amounts, or hexane as the solvent with CCI4 in reagent amounts. The system using hexane, with tefra-butylammonium chloride as phase transfer catalyst showed complete conversion in approximately 4 h. PIB carboxylic acid was recovered by acidification and isolation.

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