Highly Efficient Preparation of Length and Width-Controllable Donor-Acceptor Nanoribbons via Polymerization-Induced Crystallization-Driven Self-Assembly of Fully Conjugated Block Copolymers.

Despite the high potential of one-dimensional (1D) donor-acceptor (D-A) coaxial nanostructures in bulk-heterojunction solar cell applications, the preparation of such 1D nanostructures using π-conjugated polymers has remained elusive. Herein, we demonstrate the first example of D-A semiconducting nanoribbons based on fully conjugated block copolymers (BCPs) prepared in a highly efficient procedure with controllable width and length via living crystallization-driven self-assembly (CDSA). Initially, Suzuki-Miyaura catalyst-transfer polymerization was employed to successfully synthesize BCPs containing two types of acceptor shells as the first block, followed by a donor poly(3-propylthiophene) core as the second block. The limited solubility and high crystallinity of the core induced a polymerization-induced crystallization-driven self-assembly (PI-CDSA) of the BCPs into nanoribbons during polymerization, providing a tunable width (7.6-39.6 nm) depending on the length of the polymer backbone. Surprisingly, purifying as-synthesized BCPs via simple precipitation directly yielded short and uniform seed structures, greatly shortening the overall protocol by eliminating the time-consuming process of initial aging and breaking down to the seed required for the conventional CDSA. With this new highly efficient method, we achieved length control over a broad range from 169 to 2210 nm, with high precision (Lw/Ln < 1.20). Furthermore, combining self-seeding and seeded growth from two different D-A-type BCPs enabled continuous living epitaxial growth from each end of the nanoribbons, resulting in B-A-B triblock D-A semiconducting comicelles with controlled length.

Size-Tunable Semiconducting 2D Nanorectangles from Conjugated Polyenyne Homopolymer Synthesized via Cascade Metathesis and Metallotropy Polymerization.

Size-tunable semiconducting two-dimensional (2D) nanosheets from conjugated homopolymers are promising materials for easy access to optoelectronic applications, but it has been challenging due to the low solubility of conjugated homopolymers. Herein, we report size-tunable and uniform semiconducting 2D nanorectangles via living crystallization-driven self-assembly (CDSA) of a fully conjugated polyenyne homopolymer prepared by cascade metathesis and metallotropy (M&M) polymerization. The resulting polyenyne with enhanced solubility successfully underwent living CDSA via biaxial growth mechanism, thereby producing 2D nanorectangles with sizes precisely tuned from 0.1 to 3.0 µm2 with narrow dispersity mostly less than 1.1 and low aspect ratios less than 3.1. Furthermore, living CDSA produced complex 2D block comicelles with different heights from various degrees of polymerization (DPs) of unimers. Based on diffraction analyses and DFT calculations, we proposed an interdigitating packing model with an orthorhombic crystal lattice of semiconducting 2D nanorectangles.

Risk Assessment of Tractor-Related Hazards Based on Accident Cases.

Annually, tractor accidents are estimated to account for more than 100 deaths in South Korea. Periodic accident surveys have served as an essential means for the National Institute of Agricultural Sciences (NAS) to develop strategies to prevent tractor accidents. In this study, hazards leading to accidents were identified, and their risks were assessed based on survey results to establish a more effective accident prevention strategy. Risk assessment for hazards proceeded as follows: hazard identification, frequency estimation, number of equivalent fatalities (NEF) estimation, and finally risk evaluation. Hazards were identified by analyzing 588 accident cases from NAS surveys and performing an expert review of the analysis results by implementing a Delphi survey. The frequency and NEF of each hazard were estimated by multiplying its probabilities and the statistical results of the NAS surveys. Each hazard was plotted in a frequency-NEF (FN) diagram and evaluated according to its position. Fifty-four hazards were identified, and their frequencies and NEF values were estimated. The risk evaluation results, based on the FN diagram, revealed that no hazard was located in the "unacceptable" area, and two hazards (carelessness and not looking ahead carefully) were in the "as low as reasonably practicable" area. Thus, it is critical to mitigate the effects of these two hazards. With the risk assessment method used in this study, personnel who are engaged in the prevention of tractor accidents, such as policymakers, extension specialists, and researchers, can quantitatively predict how many cases or fatalities can be reduced by eliminating a certain hazard.