Title

Synthesis and characterization of novel, well-defined, polyisobutylene-based polymers

Date of Award

1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Robson F. Storey

Advisor Department

Polymers and High Performance Materials

Abstract

A study was performed of the mechanism, kinetics, and applications of the living carbocationic polymerization of isobutylene (IB) initiated by a system consisting of a cumyl chloride-type multifunctional initiator, TiCl$\sb4$, and pyridine, in mixed hexane/methyl chloride cosolvents. The kinetic investigation revealed that at $-$80$\sp\circ$C the rate of polymerization was first order in monomer (IB) concentration, first order in the concentration of the initiator 1,4-bis(1-chloro-1-methylethyl)benzene (DCC), second order in coinitiator (TiCl$\sb4$) concentration, and was proportional to the $-$0.28 power of the pyridine concentration. A study of the application of the DCC/TiCl$\sb4$/pyridine initiating system to the synthesis of poly(styrene-b-isobutylene-b-styrene) (S-IB-S) block copolymers was conducted. It was found that the most important aspect of the synthesis was the time of styrene addition to PIB dications. The effect of molecular geometry on the physical properties of S-IB-S block copolymers was investigated by synthesizing linear and three-arm star block copolymers possessing equivalent arm compositions, i.e. block molecular weights were equivalent for each polymer on a per arm basis. The results of this investigation indicated that the three-arm star polymer possessed much higher tensile strength and rubbery plateau modulus than the linear block copolymer while exhibiting essentially the same morphology. The effect of copolymer composition on the physical properties of S-IB-S block copolymers was investigated by synthesizing linear and three-arm star-block copolymers possessing various block lengths and polystyrene/polyisobutylene ratios. Results of this investigation indicated that physical properties varied dramatically with the wt% of polystyrene in the copolymer. S-IB-S block copolymer ionomers were produced by partially sulfonating the phenyl rings of the polystyrene blocks with acetyl sulfate. The presence of the sulfonate groups in these polymers was found to greatly affect the physical properties of the material. For instance, tensile strength increased while elongation at break decreased for S-IB-S block copolymer ionomers as compared to their parent block copolymers. The feasibility of the synthesis of multi-arm polyisobutylene-based star polymers, derived by formation of a microgel core, was investigated. Results of this study indicated that dIPB does in fact tie polyisobutylene chains together, however the functionality of polymers produced has not yet been determined. (Abstract shortened by UMI.)