Photoinduced thiol-ene crosslinking of globalide/ε-caprolactone copolymers: Curing performance and resulting thermoset properties

Bio-Based Thiol-ene Network Thermosets from Isosorbide and Terpenes

Thermoset networks are chemically cross-linked materials that exhibit high heat resistance and mechanical strength; however, the permanently cross-linked system makes end-of-life degradation difficult. Thermosets that are inherently degradable and made from renewably derived starting materials are an underexplored area in sustainable polymer chemistry. Here, we report the synthesis of novel sugar- and terpene-based monomers as the enes in thiol-ene network formation. The resulting networks showed varied mechanical properties depending on the thiol used during cross-linking, ranging from strain-at-breaks of 12 to 200%. Networks with carveol or an isosorbide-based thiol incorporated showed plastic deformation under tensile stress testing, while geraniol-containing networks demonstrated linear stress-strain behavior. The storage modulus at the rubbery plateau was highly dependent on the thiol cross-linker, showing an order of magnitude difference between commercial PETMP, DTT, and synthesized Iso2MC. Thermal degradation temperatures were low for the networks, primarily below 200 °C, and the Tg values ranged from -17 to 31 °C. Networks were rapidly degraded under basic conditions, showing complete degradation after 2 days for nearly all synthesized thermosets. This library demonstrates the range of thermal and mechanical properties that can be targeted using monomers from sugars and terpenes and expands the field of renewably derived and degradable thermoset network materials.

Collagen-decorated electrospun scaffolds of unsaturated copolyesters for bone tissue regeneration

Many efforts have been devoted to bone tissue to regenerate damaged tissues, and the development of new biocompatible materials that match the biological, mechanical, and chemical features required for this application is crucial. Herein, a collagen-decorated scaffold was prepared via electrospinning using a synthesized unsaturated copolyester (poly(globalide-co-pentadecalactone)), followed by two coupling reactions: thiol-ene functionalization with cysteine and further conjugation via EDC/NHS chemistry with collagen, aiming to design a bone tissue regeneration device with improved hydrophilicity and cell viability. Comonomer ratios were varied, affecting the copolymer's thermal and chemical properties and highlighting the tunable features of this copolyester. Functionalization with cysteine created new carboxyl and amine groups needed for bioconjugation with collagen, which is responsible for providing biological and structural integrity to the extra-cellular matrix. Bioconjugation with collagen turned the scaffold highly hydrophilic, decreasing its contact angle from 107 ± 2° to 0°, decreasing the copolymer crystallinity by 71%, and improving cell viability by 85% compared with the raw scaffold, thus promoting cell growth and proliferation. The highly efficient and biosafe strategy to conjugate polymers and proteins created a promising device for bone repair in tissue engineering.

Crosslinking of Electrospun Fibres from Unsaturated Polyesters by Bis-Triazolinediones (TAD)

Crosslinking of an unsaturated aliphatic polyester poly(globalide) (PGl) by bistriazolinediones (bisTADs) is reported. First, a monofunctional model compound, phenyl-TAD (PTAD), was tested for PGl functionalisation. 1H-NMR showed that PTAD-ene reaction was highly efficient with conversions up to 97%. Subsequently, hexamethylene bisTAD (HM-bisTAD) and methylene diphenyl bisTAD (MDP-bisTAD) were used to crosslink electrospun PGl fibres via one- and two-step approaches. In the one-step approach, PGl fibres were collected in a bisTAD solution for in situ crosslinking, which resulted in incomplete crosslinking. In the two-step approach, a light crosslinking of fibres was first achieved in a PGl non-solvent. Subsequent incubation in a fibre swelling bisTAD solution resulted in fully amorphous crosslinked fibres. SEM analysis revealed that the fibres' morphology was uncompromised by the crosslinking. A significant increase of tensile strength from 0.3 ± 0.08 MPa to 2.7 ± 0.8 MPa and 3.9 ± 0.5 MPa was observed when PGI fibres were crosslinked by HM-bisTAD and MDP-bisTAD, respectively. The reported methodology allows the design of electrospun fibres from biocompatible polyesters and the modulation of their mechanical and thermal properties. It also opens future opportunities for drug delivery applications by selected drug loading.

Lipase-Catalyzed Synthesis of Renewable Plant Oil-Based Polyamides

Enzyme catalyzed synthesis of renewable polyamides was investigated using Candida antarctica lipase B. A fatty acid-derived AB-type functional monomer, having one amine and one methyl ester functionality, was homopolymerized at 80 and 140 °C. Additionally, the organobase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was used as a catalyst. The results from the two catalysts were comparable. However, the amount of lipase added was 1.2 × 10³ times lower, showing that the lipase was a more efficient catalyst for this system as compared to TBD. Moreover, the AB-type monomer was copolymerized with 1,12-diaminododecane to synthesize oligoamides of two different lengths.

Functional biodegradable polymers via ring-opening polymerization of monomers without protective groups

Biodegradable polymers are of current interest and chemical functionality in such materials is often demanded in advanced biomedical applications. Functional groups often are not tolerated in the polymerization process of ring-opening polymerization (ROP) and therefore protective groups need to be applied. Advantageously, several orthogonally reactive functions are available, which do not demand protection during ROP. We give an insight into available, orthogonally reactive cyclic monomers and the corresponding functional synthetic and biodegradable polymers, obtained from ROP. Functionalities in the monomer are reviewed, which are tolerated by ROP without further protection and allow further post-modification of the corresponding chemically functional polymers after polymerization. Synthetic concepts to these monomers are summarized in detail, preferably using precursor molecules. Post-modification strategies for the reported functionalities are presented and selected applications highlighted.

Bio-derived polymers for coating applications: comparing poly(limonene carbonate) and poly(cyclohexadiene carbonate)

Two fully bio-based polycarbonates, poly(limonene carbonate) and poly(cylcohexadiene carbonate), were post-functionalized via thiol–ene reactions and tested as future coating materials.

Dependence of Copolymer Sequencing Based on Lactone Ring Size and ε-Substitution

The copolymerization of an ε-substituted ε-lactone, menthide (MI), and a range of nonsubstituted lactones (6-, 7-, 8-, and 9-membered rings) was investigated in order to determine the factors that affect the sequencing of the MI copolymers. Analysis by quantitative ¹³C NMR spectroscopy showed the copolymerization of MI with a nonsubstituted lactone of ring size 7 or less produced a randomly sequenced copolymer, as a consequence of the smaller lactone polymerizing first and undergoing rapid transesterification as MI was incorporated. Conversely, copolymerization with larger ring lactones (ring size 8 and above) produced block-like copolymers as a consequence of MI polymerizing initially, which does not undergo rapid transesterification side reactions during the incorporation of the second monomer. Terpolymerizations of a small ring lactone, macrolactone, and menthide demonstrated methods of producing lactone terpolymers with different final sequences, depending on when the small ring lactone was injected into the reaction mixture.

Crosslinkable polyesters based on monomers derived from renewable lignin

Crosslinked polyesters based on renewable resources have been successfully prepared, they have better tensile property and biodegradability.

UV-cured thiol–ene eugenol/ZnO composite materials with antibacterial properties

ZnO nanoparticles, i.e. efficient antimicrobial inorganic compounds, are combined to eugenol-based networks to design by “click chemistry” new promising eugenol/ZnO composite with enhanced antibacterial properties for biomedical applications.

Organocatalyzed Synthesis of Aliphatic Polyesters from Ethylene Brassylate: A Cheap and Renewable Macrolactone

The use of organocatalysts for the polymerization of ethylene brassylate, a commercially available, cheap, and renewable macro(di)lactone is reported for the first time. Ethylene brassylate was polymerized by ring-opening polymerization under bulk and solution conditions at 80 °C. Polymerizations were carried out in the presence of several organic catalysts, such as dodecylbenzenesulfonic acid (DBSA), diphenyl phosphate (DPP), p-toluenesulfonic acid (PTSA) and bases, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,2,3-tricyclohexylguanidine (TCHG), and 1,2,3-triisopropylguanidine (TIPG), using benzyl alcohol as initiator. Results agreed with a ring opening polymerization process in which the rate of polymerization was accelerated by the catalysts presence in the order of TBD > PTSA > DBSA > DPP > TIPG > TCHG. Complementary computational studies supported the experimental results. The obtained poly(ethylene brassylate) aliphatic polyesters were characterized by NMR, SEC, MALDI-TOF, DSC, and TGA. They showed molecular weights ranging from 2 to 13 kg mol^-1 and polydispersity index between 1.5 and 2. Poly(ethylene brassylate) is a semicrystalline polyester similar to poly(ε-caprolactone) with slightly higher melting and glass transition temperatures (T_m = 69 °C, T_g = -33 °C) and good thermal stability.

Functional films from unsaturated poly(macrolactones) by thiol–ene cross-linking and functionalisation

The synthesis of cross-linked surface-functional polyester films from natural macrolactones and their subsequent reaction with a fluorescent marker are presented.

Utilizing thiol–ene coupling kinetics in the design of renewable thermoset resins based on d-limonene and polyfunctional thiols

Off-stoichiometric manipulations on the initial thiol–terpene composition strongly favor the formation of di-addition product (a) over mono-additions (b + c) when the reaction system contains an equimolar or relative excess of thiol.

Thiol–ene “click” reactions and recent applications in polymer and materials synthesis: a first update

This contribution serves as an update to a previous review (Polym. Chem.2010,1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification.

Biodegradable networks for soft tissue engineering by thiol–yne photo cross-linking of multifunctional polyesters

Degradable and biocompatible networks have been prepared via thiol–yne photochemistry from novel alkyne multifunctional PCL. The mechanical properties of these cross-linked biomaterials could make them good candidates for soft tissues scaffolds.