Multiblock and di-/tri-block copolymers are successfully synthesized for the first time via the metal-free terpolymerization of propylene oxide (PO), ʟ-lactide (LA) and CO2 in one-pot/one-step and one-pot/two-step protocols respectively. Firstly, triethyl borane (TEB) and bis(triphenylphosphine)iminium chloride (PPNCl) Lewis pair is employed in the ring-opening polymerization of LA, wherein the catalytic efficiency is significantly correlated to the TEB/PPNCl feed ratio. Next, a series of TEB/base pairs are selected to synthesize the PO/LA/CO2 terpolymer (PPCLA) in one-pot/one-step strategy. In PPCLA synthesis, LA exhibits the fastest reaction rate but severe transesterification is almost unavoidable, resulting in low molecular weight products. In order to prepare high-molecular-weight terpolymers, a one-pot/two-step methodology has to be applied. By this method, the copolymerization of PO/CO2 proceeds first to form poly(propylene carbonate) (PPC) macroinitiators, which triggers the polymerization of LA to polylactide (PLA), leading to PLA-PPC or PLA-PPC-PLA block copolymers. The synthesized PLA-PPC-PLA block copolymers display improved thermal stability compared with PPC.
Because lithium-ion batteries cannot meet increasing demand for power density, lithium metal batteries are expected as the next generation of rechargeable batteries. As one of lithium metal batteries, lithium-sulfur (Li-S) batteries have attracted extensive attention because of their ultrahigh power density (2600 Wh kg−1) and low cost of sulfur. In order to overcome problems of active material loss, volume expansion and dendritic growth of Li metal in Li-S batteries, researchers have adopted several methods such as adding electrolyte additives, electrode modification and separator modification. Among them, separator modification shows significant advantages in inhibiting the shuttle effect of lithium polysulfides. This paper reviews research progress of inhibiting the shuttle effect of Li-S batteries by the means of the separator modification in recent years, including direct design of new type of separator and physical/chemical modification of separator surface. Through extensive reading and summarizing of the research results of the separator modification of Li-S batteries, we give the possible development direction of Li-S batteries at the end of the paper.
Safety concern of lithium-ion battery, attributed to using volatile and flammable liquid electrolytes, could be addressed by using solid electrolytes. Solid electrolytes including inorganic solid electrolytes, polymer solid electrolytes and organic/inorganic composite electrolytes have the common drawbacks in low ion-conductivity. Much efforts have been devoted to increase the specific ion conductivity, especially for inorganic solid electrolyte whose intrinsic conductivity is close to liquid electrolyte. However, most solid-state electrolyte membranes in lithium-ion batteries are thick, resulting in long ion-conduction pathway, low energy density and high cost. In this review, the advantages and disadvantages of different kinds of solid electrolytes were analyzed, and the promising strategies of ultra-thin solid electrolyte preparation were summarized and prospected. Applied organic-inorganic composite, continuous phase enhancement and in situ integration have been devoted to reducing thickness of electrolyte membrane and improving battery performance. On the basis of the technical requirement of lithium-ion batteries, this review aims to provide a guidance in terms of rational design and synthesis of ultra-thin solid electrolytes for the further research that addresses the safety issues and improves cycling performance of batteries.
CO2-based aliphatic polycarbonates (APCs) are not widely commercialized due to the poor performance and high cost, compared to the traditional synthetic materials. In this paper, poly(ethylene carbonate) diol (PECD) was synthesized from CO2 and ethylene oxide (EO), and the comprehensive properties were characterized. Furthermore, the preparation and properties of waterborne polyurethane dispersion (WPU) derived from PECD were studied. The result showed that PECD had high reactivity, narrow molecular weight distribution index and excellent thermal stability. The obtained WPU exhibited superior tensile performance, adhesion properties and surface hardness. Due to the low cost of EO and CO2, PECD is expected to be widely used in the preparation of polyurethanes.
The acquisition of high-performance biodegradable plastics is of great significance in addressing the problem of environmental pollution of plastics. Polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are the most promising biodegradable polymers and have excellent functional properties. However, low elongation at break and impact strength of PLA and low tensile modulus and flexural strength of PBAT hinder their application. A large number of studies focus on improving the performance of PLA and PBAT and broadening their applications. In terms of polymer modification, this paper summarized recent progresses in both chemical and physical modification methods for PLA and PBAT, respectively. The properties of PLA can be improved by co-polymerization, grafting, cross-linking and blending. The properties of PBAT can be improved mainly through blending with other degradable polymers, natural macromolecules and inorganic materials. This review can provide the reference and ideas for the modification of biomass-based biodegradable plastics like PLA and fossil-based biodegradable plastics like PBAT.
