Though an excellent protection material, graphene possesses an unpleasant adverse side effect, which refers to the phenomenon that graphene can aggravate metal corrosion. This effect potentially impedes its applications in metal protection. This work aims to demonstrate a facile graphene encapsulation strategy to effectively inhibit the corrosion-promotion activity of graphene. We encapsulated reduced graphene oxide (rGO) with (3-aminopropyl)-triethoxysilane (APTES). The composite of encapsulated rGO (rGO@APTES) has a flake-like structure with high aspect-ratio. Embedding appropriate amounts of rGO@APTES in polyvinyl butyral coating effectively enhances the barrier properties of the coating by suppressing the penetration of aggressive species. Besides, scratch tests further reveal that the corrosion-promotion activity of the graphene incorporated into the coating is completely inhibited. The strategy of graphene encapsulation can be extended to develop new graphene-based materials with superior physical and chemical properties for the protection of metal components.

Selective transformation of CO 2 into biodegradable polycarbonates (CO 2 -based copolymers) by the alternating copolymerization with epoxides represents a most promising green polymerization process. Despite the tremendous progress this field has made, most of the CO 2 -based polycarbonates are known to be amorphous, and their low thermal resistance makes them difficult to use as structural materials. Herein, we report the selective synthesis of highly isotactic CO 2 copolymers from meso-3,5-dioxaepoxides in perfectly alternating nature by the enantiopure dinuclear Co(III)-complex-mediated desymmetrization copolymerization under mild conditions. These isotactic CO 2 -based polycarbonates are typical semicrystalline polymers, possessing melting points (T m ) of 179−257 °C, dependent on the substitute groups at 4-position of the meso-epoxides. As a model monomer of 3,5-dioxa-epoxides, 4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0]octane (CXO) was studied in detail in the asymmetric copolymerization with CO 2 . The isotactic CO 2 /CXO copolymer (PCXC) with >99% enantioselectivity possesses a high T m of 242 °C and a decomposition temperature of 320 °C, while its atactic copolymer has a high T g of up to 140 °C. Moreover, the acid hydrolysis of highly isotactic PCXC was performed to provide stereoregular poly(1,2-bis(hydroxymethyl)ethylene carbonate)s (PCFC) with two hydroxyl groups in a carbonate unit, which showed a remarkable decrease of ∼80 °C in thermal decomposition temperature. This hydroxyl-functionalized CO 2 copolymer accords with an unmet need for a readily degradable biocompatible polycarbonate and was further explored to prepare bush copolymers for biomedical and pharmaceutical applications. This approach was initially demonstrated by the hydroxyl groups appended in polycarbonate backbone of a hydroxyl-functionalized terpolymer serving as macroinitiators for direct graft polymerization via organocatalytic lactide ringopening polymerization to give fully degradable brush polymers with polycarbonate backbones and polylactide side chains. Furthermore, enantiopure dinuclear Co(III)-complex-mediated asymmetric terpolymerization of CO 2 with CXO and cyclohexene oxide (CHO) at various feed ratios was carried out in toluene solution, affording optically active terpolymers poly(CHC-co-CXC) with highly enantioselective ring-opening of the both meso-epoxides. These stereospecific terpolymers were found to be crystallizable and their crystallization capacity could be tuned by changing the feed ratio of the epoxides.

Four novel crystalline stereocomplexed polymers are formed by mixing isotactic (R)- and (S)-polycarbonates in 1:1 mass ratio. They show the enhanced thermal stability and new crystalline behavior, significantly distinct from the component enantiomer. Two stereocomplexed CO2 -based polycarbonates from meso-3,4-epoxytetrahydrofuran and 4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0]octane have high melting temperatures of up to 300 °C, about 30 °C higher than the individual enantiomers. Isotactic (R)- or (S)-poly(cyclopentene carbonate) and poly(cis-2,3-butene carbonate) are typical amorphous polymeric materials, however, upon mixing both enantiomers together, a strong interlocked interaction between polymer chains of opposite configuration occurs, affording the crystalline stereocomplexes with melting temperatures of about 200 °C and 180 °C, respectively. A DFT study suggests that the driving force forming the stereocomplex is the hydrogen-bonding between carbonate units of the opposite enantiomers.