Search for: All records

Convenient strategies for the deconstruction and reprocessing of thermosets could improve the circularity of these materials, but most approaches developed to date do not involve established, high-performance engineering materials. Here, we show that bifunctional silyl ether, i.e., R′O–SiR2–OR′′, (BSE)-based comonomers generate covalent adaptable network analogues of the industrial thermoset polydicyclopentadiene (pDCPD) through a novel BSE exchange process facilitated by the low-cost food-safe catalyst octanoic acid. Experimental studies and density functional theory calculations suggest an exchange mechanism involving silyl ester intermediates with formation rates that strongly depend on the Si–R2 substituents. As a result, pDCPD thermosets manufactured with BSE comonomers display temperature- and time-dependent stress relaxation as a function of their substituents. Moreover, bulk remolding of pDCPD thermosets is enabled for the first time. Altogether, this work presents a new approach toward the installation of exchangeable bonds into commercial thermosets and establishes acid-catalyzed BSE exchange as a versatile addition to the toolbox of dynamic covalent chemistry. 

Covering: 2010–Aug. 2016 In an effort towards enhancing function and sustainability, natural products have become of interest in the field of polymer chemistry. This review details the blending of chemistries developed through synthetic organic chemistry and polymer chemistry. Through synthetic organic chemical transformations, such as functional group interconversion, a protection/deprotection series, or installation of a functional group, various designs towards novel, synthetic, bio-based polymer systems are described. This review covers several classifications of natural products – oils and fatty acids, terpenes, lignin, and sugar derivatives – focusing on exploring monomers prepared by one or more synthetic steps. 

Honokiol, a highly functional phenolic- and alkenyl-containing neolignan natural product isolated from several Magnolia plant species, is an interesting bio-based resource, which is shown to be useful directly as a monomer for the rapid and scalable synthesis of poly(honokiol carbonate) (PHC). PHC was synthesized in one step from the natural product using condensation polymerization methods. Polymers of number average molecular weight ( M n ) ranging from 10–55 kDa were obtained on gram scales in yields up to 80%. Thermal analysis demonstrated high thermal stability, with degradation temperatures in excess of ca. 450 °C. Mechanical testing of several PHC polymers indicated a generally increasing storage modulus with increasing M n and a similar trend with T g . With an interest toward cardiovascular applications, initial cytotoxicity and fluorescence cell imaging studies were conducted and showed no cytotoxicity toward coronary venular endothelial cells (CVECs), which proliferated on PHC thin films up to a month. Bulk PHC is a robust material, as it underwent slow hydrolytic degradation under basic conditions ( ca. 0.1% per day under 1 M NaOH (aq) ), and no observable degradation under acidic and neutral conditions, each at 37 °C over 130 days. These polycarbonates serve as potential specialty engineering- or bio-materials derived from a commercially-available natural product monomer. 

The rapid synthesis of an optically-transparent, flexible elastomer was performed utilizing the naturally-derived source, isosorbide. A novel monomer based on isosorbide (isosorbide dialloc, IDA) was prepared by installing carbonate functionalities along with external olefins for use in thiol–ene click chemistry. Cross-linked networks were created using the commercially-available cross-linker, trimethylolpropane tris(3-mercaptopropionate) (TMPTMP) and resulted in IDA- co -TMPTMP, an optically-transparent elastomer. Systematically, IDA- co -TMPTMP networks were synthesized using a photoinitiator, a UV cure time of one minute and varied post cure times (0–24 h, 125 mm Hg) at 100 °C to observe effects on mechanical, thermal and surface alterations. The mechanical properties also had limited changes with post cure time, including a modulus at 25 °C of 1.9–2.8 MPa and an elongation of 220–344%. The thermal decomposition temperatures of the networks were consistent, ca. 320 °C, while the glass transition temperature remained below room temperature for all samples. A cell viability assay and fluorescence imaging with adherent cells are also reported in this study to show the potential of the material as a biomedical substrate. A degradation study for 60 days resulted in 8.3 ± 3.5% and 97.7 ± 0.3% mass remaining under accelerated (1 M NaOH, 60 °C) and biological conditions (pH 7.4 PBS at 37 °C), respectively. This quickly-synthesized material has the potential to hydrolytically degrade into biologically-benign and environmentally-friendly by-products and may be utilized in renewable plastics and/or bioelastomer applications.