New sustainable polymers and oligomers for Cultural Heritage conservation.

The development of "green" chemistry materials with enhanced properties is a central topic in numerous applicative fields, including the design of polymeric systems for the conservation of works of art. Traditional approaches in art restoration comprise polymer thickeners and viscous dispersions to partially control solvents in the removal of soil or aged varnishes/coatings from artifacts. Alternatively, polymeric gel networks can be specifically designed to grant full control of the cleaning action, yielding safe, time- and cost-effective restorations. The selection of polymers and oligomers in gel design is crucial to tune solvent upload, retention, and controlled release over the sensitive artistic surfaces. Starting from an overview of traditional polymer formulations and state-of-the-art gel systems for cleaning works of art, we provide here the design of a new class of gels, focusing on the selection of oligomers to achieve gels with tailored hydrophilicity/hydrophobicity. We evaluated the oligomers Hydrophilic-Lipophilic Balance (HLB) by developing, for the first time, a novel methodology combining SEC and DOSY NMR analysis, which was tested on a library of "green" oligoesters synthesized by polycondensation and poorly explored in the literature. Oligomers with moderate polydispersity were chosen to validate the new protocol as a robust tool for designing polymeric gels even on industrial scale. The methodology is more time-effective than traditional methods, and gives additional insights on the oligomers physico-chemical nature, evaluating their compatibility with different solvents. Then, we used the selected oligoesters with castor oil to obtain a new class of organogels able to upload solvents with varying polarity, which effectively removed different types of unwanted layers typically found in painting restoration. These results validate the oligomers screening approach and the new class of gels as promising chemical processes/materials in art preservation. The methodology can potentially allow evaluation of HLB also for small molecules (e.g., surfactants), opening for the formulation of polymers solutions/gels beyond Cultural Heritage conservation, as in pharmaceutics, cosmetics, food industry, tissue engineering, agriculture, and others.

Highly biocidal poly(vinyl alcohol)-hydantoin/starch hybrid gels: A "Trojan Horse" for Bacillus subtilis.

HYPOTHESIS: Poly (vinyl alcohol) (PVA) cryogels can be functionalized with n-Halamines to confer biocidal features useful for their application as wound-dressing tools. Their efficacy can be boosted by stably embedding a polymeric bacterial food source (e.g., starch) in the gel matrix. The bioavailability of the food source lures bacteria inside the gel network via chemotactic mechanisms, promoting their contact with the biocidal functionalities and their consequent inactivation. EXPERIMENTS: The synthesis of a novel hydantoin-functionalized PVA (H-PVA-hyd) is proposed. The newly synthesized H-PVA-hyd polymer was introduced in the formulation of H-PVA-based cryogels. To promote the cryogelation of the systems we exploited phase-separation mechanisms employing either a PVA carrying residual acetate groups (L-PVA) or starch as phase-segregating components. The permanence of the biocidal functionality after swelling was investigated via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) microscopy. The activated H-PVA-hyd cryogels have been tested against bacteria with amylolytic activity (Bacillus subtilis) and the outcomes were analyzed by direct observation via confocal laser scanning microscopy (CLSM). FINDINGS: The cryogels containing starch resulted in being the most effective (up to 90% bacterial killing), despite carrying a lower amount of hydantoin groups than their starch-free counterparts, suggesting that their improved efficacy relies on a "Trojan Horse" type of mechanism.

Tailoring the properties of poly(vinyl alcohol) "twin-chain" gels via sebacic acid decoration.

HYPOTHESIS: The development of gels capable to adapt and act at the interface of rough surfaces is a central topic in modern science for Cultural Heritage preservation. To overcome the limitations of solvents or polymer solutions, commonly used in the restoration practice, poly(vinyl alcohol) (PVA) "twin-chain" polymer networks (TC-PNs) have been recently proposed. The properties of this new class of gels, that are the most performing gels available for Cultural Heritage preservation, are mostly unexplored. This paper investigates how chemical modifications affect gels' structure and their rheological behavior, producing new gelled systems with enhanced and tunable properties for challenging applications, not restricted to Cultural Heritage preservation. EXPERIMENTS: In this study, the PVA-TC-PNs structural and functional properties were changed by functionalization with sebacic acid into a new class of TC-PNs. Functionalization affects the porosity and nanostructure of the network, changing its uptake/release of fluids and favoring the uptake of organic solvents with various polarity, a crucial feature to boost the versatility of TC-PNs in practical applications. FINDINGS: The functionalized gels exhibited unprecedented performances during the cleaning of contemporary paintings from the Peggy Gugghenheim collection (Venice), whose restoration with traditional solvents and swabs would be difficult to avoid possible disfigurements to the painted layers. These results candidate the functionalized TC-PNs as a new, highly promising class of gels in art preservation.

Environmentally friendly ZnO/Castor oil polyurethane composites for the gas-phase adsorption of acetic acid.

HYPOTHESIS: Acetic acid, a common pollutant present in museums and art galleries, can irreversibly damage works of art. Herein, a sustainable and scalable synthesis of zinc oxide-castor oil polyurethane hybrids (ZnO/COPs), to be used as acetic acid removers in the preventive conservation of Cultural Heritage, is reported. EXPERIMENTS: The adsorption capacities of ZnO/COPs were studied in saturated acetic acid atmosphere, at low acetic acid gas concentration, and inside a wooden crate (naturally emitting acetic acid) representative of those used in the storage deposits of museums and art collections. FINDINGS: Upon exposure, acetic acid interacts with the castor oil polyurethane and diffuses to the surface of ZnO particles where is stably fixed as zinc acetate crystals. Zinc acetate domains form homogeneously on the surface and are distributed evenly within the ZnO/COPs, thanks to weak interactions between the polyurethane matrix and acetic acid that favour the transport of the acid up to reach the zinc oxide surfaces, resulting in a synergistic effect. The ZnO/COPs composites showed significantly enhanced adsorption capacities of acetic acid surpassing those of the activated carbon benchmark, with the advantage of being easily handled and movable, without the health issues and risks associated to the use of non-confined micro/nano-powders.

Effect of Crystallinity on the Properties of Polycaprolactone Nanoparticles Containing the Dual FLAP/mPEGS-1 Inhibitor BRP-187.

Seven polycaprolactones (PCL) with constant hydrophobicity but a varying degree of crystallinity prepared from the constitutional isomers ε-caprolactone (εCL) and δ-caprolactone (δCL) were utilized to formulate nanoparticles (NPs). The aim was to investigate the effect of the crystallinity of the bulk polymers on the enzymatic degradation of the particles. Furthermore, their efficiency to encapsulate the hydrophobic anti-inflammatory drug BRP-187 and the final in vitro performance of the resulting NPs were evaluated. Initially, high-throughput nanoprecipitation was employed for the εCL and δCL homopolymers to screen and establish important formulation parameters (organic solvent, polymer and surfactant concentration). Next, BRP-187-loaded PCL nanoparticles were prepared by batch nanoprecipitation and characterized using dynamic light scattering, scanning electron microscopy and UV-Vis spectroscopy to determine and to compare particle size, polydispersity, zeta potential, drug loading as well as the apparent enzymatic degradation as a function of the copolymer composition. Ultimately, NPs were examined for their potency in vitro in human polymorphonuclear leukocytes to inhibit the BRP-187 target 5-lipoxygenase-activating protein (FLAP). It was evident by Tukey's multi-comparison test that the degree of crystallinity of copolymers directly influenced their apparent enzymatic degradation and consequently their efficiency to inhibit the drug target.

Polyester Stereocomplexes Beyond PLA: Could Synthetic Opportunities Revolutionize Established Material Blending?

This review summarizes the current literature regarding stereocomplexation of different polyesters based on α- as well as ß-hydroxy acids beyond the well-known poly(lactic acid). Representing the initial step toward stereocomplexation, synthetic approaches needed to obtain and analyze isotactic polyesters are summarized. The basic technologies for the preparation and characterization of the respective stereocomplexes (SCs) are described, and published material properties are related to the structure of the respective polyesters. The variety of available SC materials is very limited despite the multiple options provided by state-of-the-art stereoselective monomer synthesis and polymerization methods. A combination of knowledge from the three scientific areas (i.e., organic chemistry, synthetic macromolecular chemistry, and materials science) thus has enormous potential to create novel materials with additional features enabled by the introduction of functional moieties to such materials besides the adjustment of thermal as well as mechanical properties.

Strontium Isopropoxide: A Highly Active Catalyst for the Ring-Opening Polymerization of Lactide and Various Lactones.

Commercially available strontium isopropoxide represents a suitable catalyst/initiator for the ring-opening polymerization (ROP) of lactide (LA), ε-caprolactone, δ-valerolactone, δ-caprolactone, and δ-decalactone. Well-defined polyesters are accessible via the solution polymerization of lactide in toluene with a [LA]:[Sr] ratio of 100:1 at room temperature with or without the addition of dodecanol as coinitiator. Kinetic studies and detailed analysis by means of matrix-assisted laser desorption ionization mass spectrometry reveal pseudo-first-order kinetics of the ROP as well as excellent endgroup fidelity of the polylactide (PLA) with isopropyl and dodecyl α-endgroups. Both isopropanolate moieties as well as the coinitiator each initiate PLA chains, enabling the synthesis of PLA with tailored molar mass. The polymerization of ε-caprolactone and δ-valerolactone confirms the high catalyst activity, which causes quantitative monomer conversion after 1 min polymerization time but broad molar mass distributions. In contrast, the catalyst is well suited for the ROP of the less reactive δ-caprolactone and δ-decalactone. Although kinetic studies reveal initially bimodal molar mass distributions, polyesters with dispersity values Ð < 1.2 and unimodal molar mass distributions can be obtained at moderate to high monomer conversions.

TBD-Catalyzed Ring-Opening Polymerization of Alkyl-Substituted Morpholine-2,5-Dione Derivatives.

In a two-step synthesis, five different alkyl-substituted morpholine-2,5-dione monomers were synthesized from the natural amino acids glycine, alanine, valine, leucine, and isoleucine. The heterocyclic compounds crystallize in a boat-like conformation and are polymerized via 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed ring-opening polymerization (ROP) in tetrahydrofuran. Well-defined polymers could be obtained from the monomers based on valine, leucine, and isoleucine at a feed ratio of M/I/TBD = 100/1/0.5. Kinetic studies of the ROP reveal that the molar masses and dispersities (D < 1.2) could be well controlled, as confirmed by size exclusion chromatography and 1 H NMR spectroscopy. At conversions above 50%, the polymerization rate decreases and the dispersity slightly increases, presumably due to transesterification. Matrix-assisted laser desorption time-of-flight mass spectrometry indicates the presence of polymer chains with α-end groups derived from the initiator.

Bifunctional Initiators as Tools to Track Chain Transfer during the CROP of 2-Oxazolines.

Detailed kinetic studies during the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) are conducted using four bifunctional bromo-type initiators in N,N-dimethylformamide (DMF) at 140 °C. Serving as models to quantify chain transfer to monomer occurring during the CROP initiated by monofunctional initiators, size exclusion chromatography (SEC) resolves a second molar mass distribution with lower molar mass at initial [monomer] to [initiation site] ratios ([M]0 /[I]0 ) of 25, while the resolution is insufficient at [M]0 /[I]0 of 10. Slightly slow initiation is revealed at [M]0 /[I]0 = 25, which prohibits the derivation of chain transfer rates by fitting of the size exclusion chromatography (SEC) data. Although conventional kinetic plots give no indication of significant amounts of chain transfer, the molar mass distributions resolved by SEC can unambiguously be identified as such by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in both the high as well as the low m/z regions of the mass spectra.