Synthesis and degradation of biomedical materials based on linear and star shaped polyglycidols

Selective ring-opening polymerization of glycidyl ester: a versatile synthetic platform for glycerol-based (co)polyethers

Linear polyglycerol is highly valued for its excellent hydrophilicity and biocompatibility as well as its multihydroxy nature. We report here a convenient route for controlled synthesis of polyglycerol through ring-opening...

Chemoselective Polymerization of Epoxides from Carboxylic Acids: Direct Access to Esterified Polyethers and Biodegradable Polyurethanes

Carboxylic-acid-initiated ring-opening polymerization (ROP) of epoxides is a fast approach to esterified polyethers which are cleavable at the termini or centers. A major challenge lies in conventional ROP methods because of the lability of ester groups formed in the initiation step. Here, we describe chemoselective ROP of epoxides from aliphatic, aromatic, and methacrylic carboxylic acids using two-component metal-free catalysts. Transesterification is clearly absent so that well-defined α-(carboxylic ester)-ω-hydroxy polyethers are generated in one step from monocarboxylic acids. The livingness of the ROP is verified despite the slow initiation mode. The ester end group can be readily cleaved from the polyether hydrolytically. An α,ω-dihydroxy poly(propylene oxide) with two central ester groups is generated from a diacid initiator and transformed in situ by the same catalyst to polyurethane which shows distinct enzymatic degradability. This study provides convenient access to α,ω-heterobifunctional polyethers with cleavable, releasable, or modifiable end groups and to biodegradable polyether-based materials.

Self-assembled dual-drug loaded core-shell nanoparticles based on metal-free fully alternating polyester for cancer theranostics

Recent research has been directed to the use of biocompatible and biodegradable metal-free fully alternating polyester nanomaterial in drug delivery application. The practice of triethyl borane (Et₃B)/Bis(triphenylphosphoranylidene)ammonium chloride (PPNCl) Lewis pair as non-metallic catalyst was carried out to synthesize alternating copolymer of commercially available tert-butyl glycidyl ether (tBGE) and phthalic anhydride (PA) (poly(tBGE-alt-PA) copolymer) of low M_nvia nearly controlled ring-opening copolymerization (ROCOP) reaction. This biocompatible, hemocompatible, and biodegradable copolymer was used in the fabrication of different nanodrug formulations (NDFs) loaded with doxorubicin (DOX), curcumin (CUR) and their combination. Transmission electron microscope (TEM) imaging showed the spherical shape and core-shell internal structure for all NDFs with an average particle diameter ranging between 200 and 250 nm. X-ray diffraction (XRD) analysis displayed the amorphous nature of both DOX and CUR after their entrapment into the copolymer matrix. Differential scanning colorimetry (DSC) analysis presented no potential chemical interactions between the drug and copolymer. The cellular drug uptake study showed the increased uptake for all NDFs compared to free drug and exhibited higher DOX and CUR accumulation in dual-drug loaded nanoparticles treated pancreatic cancer (MIA PaCa-2) cells. The in vitro drug release kinetic study displayed the slow sustained drug release behavior with anomalous transport for both DOX and CUR in a defined physiological environment. Further, the anti-tumor efficacy of all NDFs was examined on several different cancer cell lines and maximum cytotoxicity was observed in MIA PaCa-2 cells with low inhibitory concentration (IC₅₀) values. These NDFs inhibited the proliferation of MIA PaCa-2 cells due to cell cycle arrest in G2/M phase. In result, MIA PaCa-2 cells underwent apoptosis with significant changes in mitochondrial membrane potential and increased reactive oxygen species (ROS) level. In future, this study will open several novel insights related to the use of such biocompatible and biodegradable metal-free polyesters in targeted drug delivery, tissue engineering and other biomedical applications.

Glycidyl Triazolyl Polymers: Poly(ethylene glycol) Derivatives Functionalized by Azide-Alkyne Cycloaddition Reaction

Glycidyl triazolyl polymer (GTP), which is the product of the Huisgen dipolar cycloaddition reaction between glycidyl azide polymer and alkyne derivatives, is featured here. GTP is the multifunctionalized poly(ethylene glycol) (PEG). The drawback of PEG is that linear PEG has the functional group only at both ends. The low loading capability of the functional groups limits the possibilities of PEG applications. GTP facilitates the synthesis of multifunctionalized PEG derivatives. In this article, 74 examples of GTP homopolymers and copolymers are introduced. The synthetic protocols and work-up processes of GTP are summarized. In addition, application studies are reviewed: for example, stimuli-responsive and self-healing materials, materials for electrical memory devices, ion-conductive materials, and biomedical materials. Finally, some issues on GTP synthesis and future directions for GTP-based polymer materials are proposed.

Light-induced cross-linking and post-cross-linking modification of polyglycidol

The photoinduced radical generation process has received renewed interest due to its economic and ecological appeal. Herein the light-induced cross-linking of functional polyglycidol and its post-cross-linking modification are presented. Linear polyglycidol was first functionalized with a tertiary amine in a two-step reaction. Dimethylaminopropyl functional polyglycidol was cross-linked in a UV-light mediated reaction with camphorquinone as a type II photoinitiator. The cross-linked polyglycidol was further functionalized by quaternization with various organoiodine compounds. Aqueous dispersions of the cross-linked polymers were investigated by means of DLS and zeta potential measurements. Polymer films were evaluated by DSC and XPS.

Novel Antibacterial Polyglycidols: Relationship between Structure and Properties

Antimicrobial polymers are an attractive alternative to low molecular weight biocides, because they are non-volatile, chemically stable, and can be used as non-releasing additives. Polymers with pendant quaternary ammonium groups and hydrophobic chains exhibit antimicrobial properties due to the electrostatic interaction between polymer and cell wall, and the membrane disruptive capabilities of the hydrophobic moiety. Herein, the synthesis of cationic⁻hydrophobic polyglycidols with varying structures by post-polymerization modification is presented. The antimicrobial properties of the prepared polyglycidols against E. coli and S. aureus are examined. Polyglycidol with statistically distributed cationic and hydrophobic groups (cationic⁻hydrophobic balance of 1:1) is compared to (i) polyglycidol with a hydrophilic modification at the cationic functionality; (ii) polyglycidol with both-cationic and hydrophobic groups-at every repeating unit; and (iii) polyglycidol with a cationic⁻hydrophobic balance of 1:2. A relationship between structure and properties is presented.

Homoserine Lactone as a Structural Key Element for the Synthesis of Multifunctional Polymers

The use of bio-based building blocks for polymer synthesis represents a milestone on the way to "green" materials. In this work, two synthetic strategies for the preparation of multifunctional polymers are presented in which the key element is the functionality of homoserine lactone. First, the synthesis of a bis cyclic coupler based on a thiolactone and homoserine lactone is displayed. This coupler was evaluated regarding its regioselectivity upon reaction with amines and used in the preparation of multifunctional polymeric building blocks by reaction with diamines. Furthermore, a linear polyglycidol was functionalized with homoserine lactone. The resulting polyethers with lactone groups in the side chain were converted to cationic polymers by reaction with 3-(dimethylamino)-1-propylamine followed by quaternization with methyl iodide.

Functional PEG building blocks via copolymerization of ethylene carbonate and tert-butyl glycidyl ether

Functional poly(ethylene glycol) building blocks were synthesized with ethylene carbonate as a new source for ethylene oxide repeating units.

Activated anionic ring-opening polymerization for the synthesis of reversibly cross-linkable poly(propylene oxide) based on furan/maleimide chemistry

Controlled anionic copolymerization of propylene oxide and furfuryl glycidyl ether was developed for the synthesis of reversibly cross-linkable polyethers.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Polyglycidol-based metal adhesion promoters

Hydrophilic adhesion promoters that facilitate intimate binding between metals and polymers are an important class of materials with a wide variety of applications in biomedical coatings. Currently, non-poly(meth-)acrylate based hydrophilic polymeric adhesives are unavailable. Here, we report the preparation of such adhesion-promoters based on linear polyglycidol for biomedical applications. The adhesion promoting polymer is prepared from partly phosphonoethylated polyglycidol in three steps. First, the remaining hydroxyl groups of the polyglycidol backbone are reacted with acryloyl chloride; secondly, the phosphonate groups are chemoselectively dealkylated using bromotrimethylsilane. Finally, the bis(trimethylsilyl)phosphonate intermediate is converted to the phosphonic acid through ethanolysis. The reaction conditions of each synthetic step are optimized individually and the products are characterized by ¹H, ³¹P NMR and SEC analysis. The optimized reaction conditions are applied to establish a straightforward one-pot reaction, resulting in an ethanolic formulation of the adhesion promoter, which can be used immediately for the coating application. Special attention is paid to the stability of the intermediates, the chemoselectivity of the reactions and the shelf-life of the product. ¹H NMR spectroscopy reveals hydrolytic instability of the product under ambient conditions; however, the polymers are sufficiently stable in dry ethanol for at least 14 days. The combination of this hydrophilic polymer with acrylate and phosphonic acid groups constitutes a versatile platform technology for the preparation of thin primer coatings on metal substrates for biomedical applications. The phosphonic acid residues assure strong binding to stainless steel wires and the acrylates can be addressed by UV light to enable crosslinking, thus improving mechanical stability and adhesion between the substrate and a biomedical hydrogel coating. The quality of the adhesion promotion to stainless steel wires is verified by using a lubricious, hydrogel top coat and by evaluating friction and wear resistance of this total coating system. Constant values for friction and wear are obtained, proving the applicability of phosphonic acid-functionalized polyglycidols as metal adhesion promoters for biomedical applications.

Polymerization of 5-alkyl δ-lactones catalyzed by diphenyl phosphate and their sequential organocatalytic polymerization with monosubstituted epoxides

One-pot sequential organocatalytic polymerization reactions of 5-alkyl δ-lactones and monosubstituted epoxides were carried out using the base→acid “catalyst switch” strategy, leading to well-defined polyether–polyester block copolymers with various alkyl substituents.

A green and sustainable phosphine-free NHC-ruthenium catalyst for selective oxidation of alcohols to carboxylic acids in water

An efficient novel protocol is applied for direct synthesis of carboxylic acids from primary alcohols through catalytic dehydrogenation. This reaction occurs in water as the solvent and as the oxygen-atom source and no toxic oxidizing agent is involved.

Synthesis and characterization of glycidyl-polymer-based poly(ionic liquid)s: highly designable polyelectrolytes with a poly(ethylene glycol) main chain

Glycidyl-polymer-based poly(ionic liquid)s with different spacers and ionic moieties were synthesized by click functionalization of a glycidyl azide polymer.

Lipases in polymer chemistry

Lipases are highly active in the polymerization of a range of monomers. Both ring-opening polymerization of cyclic monomers such as lactones and carbonates as well as polycondensation reactions have been investigated in great detail. Moreover, in combination with other (chemical) polymerization techniques, lipase-catalyzed polymerization has been employed to synthesize a variety of polymer materials. Major advantages of enzymatic catalysts are the often-observed excellent regio-, chemo- and enantioselectivity that allows for the direct preparation of functional materials. In particular, the application of techniques such as Dynamic Kinetic Resolution (DKR) in the lipase-catalyzed polymerization of racemic monomers is a new development in enzymatic polymerization. This paper reviews selected examples of the application of lipases in polymer chemistry covering the synthesis of linear polymers, chemoenzymatic polymerization and applications of enantioselective techniques for the synthesis and modification of polymers.

Side chain thiol-functionalized poly(ethylene glycol) by post-polymerization modification of hydroxyl groups: synthesis, crosslinking and inkjet printing

Thiol functionalized PEG-based polymers were synthesized by post polymerization reactions of hydroxyl functionalized polymers. Applications of the polymers in cell culture and inkjet printing were demonstrated.

Reactivity ratios, and mechanistic insight for anionic ring-opening copolymerization of epoxides

Reactivity ratios were evaluated for anionic ring-opening copolymerizations of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator. The chemical shift for the benzylic protons of the initiator, as measured by (1)H NMR spectroscopy, were observed to be sensitive to the sequence of the first two monomers added to the initiator during polymer growth. Using a simple kinetic model for initiation and the first propagation step, reactivity ratios for the copolymerization of AGE and EGVGE with EO could be determined by analysis of the (1)H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be r(AGE) = 1.31 ± 0.26 and r(EO) = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were r(EGVGE) = 3.50 ± 0.90 and r(EO) = 0.32 ± 0.10. These ratios were consistent with the compositional drift observed in the copolymerization between EO and EGVGE, with EGVGE being consumed early in the copolymerization. These experimental results, combined with density functional calculations, allowed a mechanism for oxyanionic ring-opening polymerization that begins with coordination of the Lewis-basic epoxide to the cation to be proposed. The calculated transition-state energies agree qualitatively with the observed relative rates for polymerization.