Butyl Rubber-Aliphatic Polyester Graft Copolymers for Biomedical Applications: Synthesis and Analysis of Chemical, Physical and Biological Properties

Biomaterials can be used in a wide variety of medical applications owing to their breadth of characteristics that can be imparted by varying their chemical structures. Butyl rubber (IIR), which is a copolymer of isobutylene (IB) and small percentages of isoprene (IP), is particularly attractive as a biomaterial because of its elastomeric mechanical properties, biocompatibility, impermeability and high damping characteristics. IIR is typically vulcanized through chemical-based crosslinking mechanisms. However, these methods are not acceptable for biological applications. This thesis focuses on the synthesis of IIR-polyester graft copolymers by grafting biodegradable and biocompatible polyesters including poly(caprolactone) (PCL) and poly(d,l-lactide) (PDLLA) to the IIR backbone, and on the study of their properties

Synthesis, properties, and degradation of polyisobutylene-polyester graft copolymers

The development of copolymers is a promising approach for combining the favorable properties of two polymers and obtaining new properties of the combination. In this work, graft copolymers of polyisobutylene (PIB) and polycaprolactone (PCL) or poly(D,L-lactide) (PDLLA) were synthesized and studied. Amine terminated polyesters were synthesized and were grafted onto an activated PIB backbone synthesized from butyl rubber, a copolymer of isobutylene and 2 mol % isoprene. The polyester content was tuned from 15 to 44 wt % by varying the molar mass of the polyester blocks and the number of molar equivalents used in the grafting reaction. The graft copolymers with higher polyester content underwent nanoscale phase separation, as demonstrated by differential scanning calorimetry and atomic force microscopy imaging. This was found to provide enhanced mechanical properties such as increased tensile strength and Young’s modulus relative to the starting rubber or physical blends. Despite the significant polyester content of the graft copolymers and the susceptibility of the polyesters to degradation, the graft copolymers underwent negligible mass loss in 5 M NaOH over a period of 8 weeks. These results suggest that polyesters can be incorporated into PIB to tune and enhance its properties, while maintaining high chemical stability

Covalent Polyisobutylene-Paclitaxel Conjugates for Controlled Release from Potential Vascular Stent Coatings

© 2015 American Chemical Society. The development of covalent polyisobutylene (PIB)-paclitaxel (PTX) conjugates as a potential approach to controlling drug release from vascular stent coatings is described. PIB-PTX materials containing ∼24 and ∼48 wt % PTX, conjugated via ester linkages, were prepared. The PTX release profiles were compared with those of physical mixtures of PTX with carboxylic acid-functionalized PIB and with the triblock copolymer polystyrene-b-PIB-b-polystyrene (SIBS). Covalent conjugation led to significantly slower drug release. Atomic force microscopy imaging of coatings of the materials suggested that the physical mixtures exhibited multiple domains corresponding to phase separation, whereas the materials in which PTX was covalently conjugated appeared homogeneous. Coatings of the conjugated materials on stainless steel surfaces suffered less surface erosion than the physically mixed materials, remained intact, and adhered well to the surface throughout the thirty-five day study. Tensile testing and rheological studies suggested that the incorporation of PTX into the polymer introduces similar physical changes to the PIB as the incorporation of a glassy polystyrene block does in SIBS. Cytotoxicity assays showed that the coatings did not release toxic levels of PTX or other species into a cell culture medium over a 24 h period, yet the levels of PTX in the materials were sufficient to prevent C2C12 cells from adhering to and proliferating on them. Overall, these results indicate that covalent PIB-PTX conjugates have promise as coatings for vascular stents