High-Performance Polyurea Improved by Reactive Nanocluster for Antibiofouling.

Polyurea has found applications in protective coatings. Yet, the too fast polymerization and lack of functions limit its application. Herein, we report a high-performance polyurea via the stepwise polymerization of an isocyanate (NCO)-terminated prepolymer consisting of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPG-b-PEG-b-PPG) with a nanocluster synthesized via the hydrolysis of N-phenylaminomethyltriethoxysilane. Such a nanocluster contains low-reactivity secondary amines, so the polymerization of polyurea can be slowed down (over 1 h), which improves its wetting and adhesion to a substrate. The residual silanol groups on the nanocluster further increase the adhesion. Such polyurea exhibits high adhesion on various substrates, including glass, ceramic, steel, copper, titanium, wood, and natural rubber (∼2.35-14.64 MPa). Besides, the nanoclusters can cross-link the prepolymer into a tough network, endowing the polyurea with a high mechanical strength of ∼25 MPa, much higher than the traditional polyaspartic ester polyurea. On the other hand, the PEG segments enable the polyurea to have good fouling resistance against proteins (fibrinogen absorption was reduced by over 90%), bacteria (RBA of S. aureusE. coli and Pseudomonas sp. was less than 10%), as well as diatom (diatom density was less than 100 cells/mm2). The polyurea is expected to find applications in biomedical engineering and marine antifouling.

Non-isocyanate Polyurethane Coating with High Hardness, Superior Flexibility, and Strong Substrate Adhesion.

Flexible hard coatings with strong adhesion are critical requirements for several foldable devices and marine applications; however, only a few such coatings have been reported. Herein, we report a non-isocyanate polyurethane (NIPU) coating prepared by the epoxy-oligosiloxane nanocluster-amine curing reaction and cyclic carbonate-amine polyaddition, where the former provides the coating with ceramic-like hardness and polymer-like flexibility while the latter polymerization results in NIPU with strong substrate adhesion. The coating is transparent (>92% transmittance), hard (5-7 H), and flexible (2 mm bending diameter). It has strong adhesion to various substrates including aluminum alloy, titanium, steel, glass, ceramic, epoxy, and polyethylene terephthalate (2-8 MPa), which can be attributed to the high density of polar groups in NIPU. Moreover, we can facilely endow the coating with anti-icing, self-cleaning, and anti-smudge capabilities by incorporating amine-terminated low-surface-tension polydimethylsiloxane (PDMS) to replace a part of the amine curing agent. Particularly, the mechanical properties of NIPU coatings are only slightly affected by the introduction of low-content PDMS since it intends to enrich on the surface. The novel coating has promising future for use in fields of foldable devices and marine applications.

Degradable Vinyl Polymers for Combating Marine Biofouling.

Marine organisms such as barnacle larvae and spores of algae adhere to underwater surfaces leading to marine biofouling. This phenomenon has numerous adverse impacts on marine industries and maritime activities. Due to the diversity of fouling organisms and the complexity of the marine environment, it is a huge challenge to combat marine biofouling, which limits the development and utilization of marine resources. Since the International Marine Organization banned the use of tributyltin self-polishing copolymer (SPC) coatings in 2008, the development of an environmentally friendly and efficient anti-biofouling polymer has been the most important task in this field. Tin-free SPC is a well-established and widely used polymer binder for anti-biofouling coating today. Being a nondegradable vinyl polymer, SPC exhibits poor anti-biofouling performance in static conditions. Even more, such nondegradable polymers were considered to be a source of microplastics by the International Union for the Conservation of Nature in 2019. Recently, numerous degradable polymers, which can form dynamic surface through main chain scission, have been developed for preventing marine biofouling in static conditions. Nevertheless, the regulation of their degradation and mechanical properties is limited, and they are also difficult to functionalize. A new polymer combining the advantages of vinyl polymers and degradable polymers is needed. However, such a combination is a challenge since the former are synthesized via free radical polymerization whereas the latter are synthesized via ring-opening polymerization.In this Account, we review our recent progress toward degradable vinyl polymers for marine anti-biofouling in terms of polymerization methods and structures and properties of polymers. First, we introduce the strategies for preparing degradable vinyl polymers with an emphasis on hybrid copolymerization. Then, we present the synthesis and performance of degradable and hydrolyzable polyacrylates, degradable polyurethanes with hydrolyzable side groups, and surface-fragmenting hyperbranched polymers. Polymers with degradable main chains and hydrolyzable side groups combine the advantages of SPC and degradable polymers, so they are degradable and functional. They are becoming new-generation polymers with great potential for preparing high-efficiency, long-lasting, environmentally friendly and broad-spectrum coatings to inhibit marine biofouling. They can also find applications in wastewater treatment, biomedical materials, and other fields.

Combining a bio-based polymer and a natural antifoulant into an eco-friendly antifouling coating.

Biodegradable polymers are promising binders and carriers for natural antifoulants. In the present study, an antifouling (AF) coating was developed by adding a non-toxic AF compound (butenolide) to a bio-based and biodegradable poly(lactic acid)-based polyurethane. Mass loss measurement showed that the polymer degraded in seawater at a rate of 0.013 mg cm-2 day-1. Measurements showed that butenolide was released from the coatings into seawater over a period of at least three months. Both the concentration of butenolide in the coatings and the ambient temperature determined the release rate of butenolide. The results further demonstrate that incorporating rosin into the coatings increase the self-renewal rate of the polymer and facilitated the long-term release of butenolide from the coating. The results show that poly(lactic acid)-based polyurethane is a suitable polymer for butenolide-based AF coatings.

Specific Ion Effects on the Enzymatic Degradation of Polymeric Marine Antibiofouling Materials.

It is expected that the widely dispersed ions in seawater would have strong influence on the performance of polymeric marine antibiofouling materials through the modulation of enzymatic degradation of the materials. In this work, poly(ε-caprolactone)-based polyurethane and poly(triisopropylsilyl methacrylate-co-2-methylene-1,3-dioxepane) have been employed as model systems to explore the specific ion effects on the enzymatic degradation of polymeric marine antibiofouling materials. Our study demonstrates that the specific ion effects on the enzymatic degradation of the polymer films are closely correlated with the ion-specific enzymatic hydrolysis of the ester. In the presence of different cations, the effectiveness of the enzyme to degrade the polymer films is dominated by the direct specific interactions between the cations and the negatively charged enzyme molecules. In the presence of different anions, the kosmotropic anions give rise to a high enzyme activity in the degradation of polymer films induced by the salting-out effect, whereas the chaotropic anions lead to a low enzyme activity in the degradation of the polymer films owing to the salting-in effect. This work highlights the opportunities available for the use of specific ion effects to modulate the enzymatic degradation of polymeric antibiofouling materials in the marine environment.

Dynamic surface antifouling: mechanism and systems.

Marine biofouling is a global problem today. High efficiency and eco-friendly antifouling systems are in pressing need. In recent years, we have proposed the concept of dynamic surface antifouling (DSA). That is, a continuously changing surface can effectively prevent marine fouling organisms from landing and adhesion. Based on this strategy, we developed coatings with dynamic surfaces by using degradable polymers including polyester-polyurethane, modified polyester and poly(ester-co-acrylate). They exhibit tunable renewability, and excellent antifouling and mechanical performance. Moreover, the polymers can serve as carrier and controlled release systems of antifoulants so that they have long service life. This paper reviews the progress and trends in marine anti-biofouling, and presents the mechanism and systems of DSA.

Biodegradable Polymer with Hydrolysis-Induced Zwitterions for Antibiofouling.

Persistent protein resistance is critical for marine antibiofouling. We have prepared copolymer of 2-methylene-1,3-dioxepane (MDO), tertiary carboxybetaine ester (TCB), and 7-methacryloyloxy-4-methylcoumarin (MAMC) via radical ring-opening polymerization, where MDO, TCB, and MAMC make the polymer degradable, protein resistible, and photo-cross-linkable, respectively. Our study shows that the polymer can well adhere to the substrate with controlled degradation and water adsorption rate in artificial seawater (ASW). Particularly, the polymer film can generate zwitterions via surface hydrolysis in ASW. Quartz crystal microbalance with dissipation measurements reveal that such hydrolysis-induced zwitterionic surface can effectively resist nonspecific protein adsorption. Moreover, the surface can inhibit the adhesion of marine bacteria Pseudomonas sp. and Vibrio alginolyticus as well as clinical bacterium Escherichia coli.