Polyisobutylene-based polyurethanes with unprecedented properties and how they came about

Synthesis of High-Molecular-Weight and Strength Polyisobutylene-Based Polyurethane and Its Use for the Development of a Synthetic Heart Valve

Under optimized synthesis conditions, for the first time, polyisobutylene-based polyurethane (PIB-PU) is prepared with 70% PIB soft segment (i.e., a bioinert and calcification-resistant PU) with M_n > 100 000 Da, 32 MPa ultimate strength, and 630% elongation. The key parameters for this achievement are a) the precise stoichiometry of the polyurethane forming reaction, specifically the use of highly purified di-isocyanate (4,4'-methylene-bis (phenyl isocyanate), MDI), and b) the increased solid content of the synthesis solution to the limit beyond which increased viscosity prevents stirring. The shape of the stress-strain trace of PIB-PU indicates a two-step failure starting with a reversible elastic (Hookean) region up to ≈50% yield, followed by a slower linearly increasing high-modulus-deformation region suggesting the strengthening of PIB soft segments by entanglement/catenation, and the hard segments by progressively ordering urethane domains. This PIB-PU is a candidate for a fully synthetic bioprosthetic heart valve since preliminary studies show that PIB-PU has impressive fatigue life.

Synthesis of linear and star-shaped telechelic polyisobutylene by cationic polymerization

Hydroxyl-terminated linear and star-shaped telechelic polyisobutylene have been successfully synthesized by living cationic polymerization using propylene oxide (PO)/Titanium tetrachloride (TiCl₄) as the initiator system. A one-step method to prepare the terminal hydroxyl group was realized by selecting the cheap and beautiful epoxide as the functional initiator, which has the prospect of industrial application. The polymerization mechanism was proposed by the end structure analysis and Gaussian calculation results. At the same time, the living linear macromolecular chain was used as the starting point to react with divinyl compounds for synthesis of star-shaped hydroxyl-terminated polyisobutylene. The effects of initiator-crosslinking agent ratio, arm length, and reaction time on the coupling reaction were studied.

Hydroxyl-terminated linear and star-shaped telechelic polyisobutylene have been successfully synthesized by living cationic polymerization using propylene oxide (PO)/Titanium tetrachloride (TiCl₄) as the initiator system.

An Efficient Synthesis of Geminal-Dialkyl Dienes for Olefin Metathesis Polymerization

A robust synthesis of gem-dialkyl acyclic diene monomers has been developed. This route is scalable, flexible, and biorenewable, allowing for the production of a wide range of diene monomers of different lengths and different gem-dialkyl substitution starting from unsaturated esters derived from seed oils. The metathesis polymerization of these monomers and the hydrogenation of the resulting polyolefins leads to telechelic gem-dialkyl polyethylenes, which can be used as elastomers in the synthesis of polyurethanes and other block polymers.

Synthesis and characterization of hydroxyl-terminated butadiene-end-capped polyisobutylene and its use as a diol for polyurethane preparation

Hydroxyl-terminated telechelic polyisobutylene (PIB) was prepared through living cationic polymerization. A living PIB chain was formed using the t-Bu-m-DiCuOMe/TiCl₄ initiating system and then capped with 1,3-butadiene (BD) to prepare chlorine-terminated telechelic PIB. The chlorine-terminated telechelic PIB was then hydrolysed with tetrabutylammonium hydroxide to form hydroxyl-terminated PIB. Nuclear magnetic resonance spectroscopy confirmed hydrolysis completion. The hydroxyl-terminated PIB was subsequently used as a diol to react with 4,4-methylenebis(phenylisocyanate) (MDI) and produce a PIB-based polyurethane, which showed stronger acid resistance, hydrolysis stability and thermal oxidation stability than a commercial polyurethane.

Synthesis of random copolymer of isobutylene with p-methylstyrene by cationic polymerization in ionic liquids

Poly(isobutylene-co-p-methylstyrene) (IB/p-MeSt) random copolymer is a new generation of polyisobutylene-based elastomer. The cationic copolymerization of IB with p-MeSt was thoroughly examined by using various initiating systems in [Hmim][NTf2] at −30°C. The effects of initiating systems and monomer feed ratio on the monomer conversion, molecular weight and copolymer composition are discussed. The polymers were characterized by 1H-nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and matrix-assisted laser desorption/ionization-time-of-flight-mass spectroscopy (MALDI-TOF-MS) to determine their chemical composition and molecular structure. The results show that high polarity, high viscosity and ionic environment of ionic liquids (ILs) influenced the copolymerization. The corresponding mechanism of cationic copolymerization in ILs is also proposed.

Surface modification of polyisobutylene via grafting amino acid-based poly (acryloyl-6-aminocaproic acid) as multifunctional material

Amino acid-based P(acryloyl-6-aminocaproic acid) (PAACA) brushes were fabricated on polyisobutylene (PIB) surface combined with plasma pre-treatment and UV-induced grafting polymerization to construct an antifouling and functional material. The hydrophilicity and hemocompatibility of PIB were largely improved by surface modification of AACA, which were confirmed by water contact angle and platelet adhesion, respectively. PAACA brushes were precisely located onto the surface of PIB to create a patterned PIB-g-PAACA structure, and then the carboxyl groups on PAACA was activated to immobilize functional protein-Concanavalin A (Con A). The obtained Con A-coupled microdomains could further capture erythrocytes. This method developed a platform on commercial PIB surface via amino acid-based polymer brushes which had a promising application in drug delivery and disease diagnosis.

Oxidatively Stable Polyolefin Thermoplastics and Elastomers for Biomedical Applications

Statistical copolymers were prepared by the Ring Opening Metathesis coPolymerization (ROMP) of (Z)-5,5-dimethylcyclooct-1-ene and cis-cyclooctene. Subsequent hydrogenation yielded poly(ethylene-co-isobutylene) (PEIB) materials. The feed ratio of the comonomers controls the degree of branching and resulting thermal and mechanical properties of the PEIB samples. Oxidative degradation studies, conducted under accelerated in vitro conditions were used to assess and predict their long-term biostability. Relative to commercial poly(ether urethanes) and a structurally similar polyolefin, poly(ethylene-co-1-butylene), the PEIB samples showed much better oxidative resistance. The facile synthesis, improved stability, and excellent mechanical performance of these PEIB materials bode well for their use in biomedical applications that require long-term biostability.

Hydroxy-telechelic poly(ethylene-co-isobutylene) as a soft segment for thermoplastic polyurethanes

Facile preparation of linear amorphous hydroxy-telechelic poly(ethylene-co-isobutylene) (PEIB) was enabled by ROMP of a new monomer, (Z)-5,5-dimethylcyclooct-1-ene (Me₂COE).