Carboxylic Acid-Functionalized Butyl Rubber: Synthesis, Characterization, and Physical Properties

Abstract

Polyisobutylene (PIB) and other PIB-based materials are of significant interest for a vast array of applications, but chemical modification is often required to obtain the desired properties. Described here are two new approaches for the preparation of carboxylic acid-functionalized PIB. The ring opening of cyclic anhydrides from an allylic alcohol derivative of butyl rubber and the atom transfer radical polymerization of tert-butyl methacrylate from a rubber derivative both ultimately afford carboxylated materials. These materials displayed significantly enhanced adhesion to stainless steel, as well as increased ultimate tensile strength and Young's modulus in comparison to unmodified rubbers. Rheological studies suggested that they exhibit a greater degree of cross-linking-type behavior than the parent butyl rubber. Combined, these studies suggest that the properties of PIB can be readily tuned through synthetic modifications of the backbone, even at low mole percent, and that carboxylic acid moieties can impart desirable properties for various applications.

Polyisobutylene‐paclitaxel conjugates with pendant carboxylic acids and polystyrene chains: Towards multifunctional stent coatings with slow drug release

“…Both PIB-PTX-COOH and PIB-PS-PTX-COOH have ultimate tensile strengths of 2 MPa, approximately 10-fold higher than that of butyl rubber. This was expected as in previous work carboxylic acids, 34 PTX, 57,58 and PS 40 were each independently found to increase the tensile strength of butyl rubber. Despite the increase in tensile strength, the elongation at break was similar for butyl rubber and the functionalized derivatives, ranging from 770 to 900%.…”

“…This is consistent with previous results for PIB with similar percentages of pendant carboxylic acids, whereas higher amounts of carboxylic acids tended to increase the modulus. 34 The incorporation of PS in PIB-PS-PTX-COOH also did not increase the modulus (1.2 MPa). Polystyrene itself has a modulus of approximately 3300 MPa, 73 and the copolymer could be expected to have a higher modulus than butyl rubber; however, it appears this is not a sufficient amount of polystyrene to influence the modulus significantly.…”

“…The properties of the starting butyl rubber as previously reported are also included for comparison. 34 Representative stress-stain curves are shown in Figure 2 and the results are summarized in Table 2. The modulus of PIB-PTX-COOH (0.8 MPa) was not significantly different from that of butyl rubber.…”

“…74 However, they might be enhanced by the incorporation of larger factions of the moieties by starting with butyl rubber with higher isoprene content. 34,40 A primary reason for incorporating carboxylic acid groups was to enhance the adhesion of the materials to the surface of the metal stent in order to prevent coating delamination. It was previously shown that the introduction of carboxylic acids or other ionomeric functionalities improved the adhesion of materials to stainless steel.…”

“…31 These alcohol groups were activated and functionalized to prepare graft copolymers [31][32][33] and have also been further derivatized to afford carboxylic acid groups. 34 The carboxylic acid groups imparted increased tensile strength, which was proposed to result from crosslinking through hydrogen bonding, 24,35,36 as well as enhanced adhesion to stainless steel as a result of binding between the carboxylic acid groups and the metal surface.…”