Monodisperse Cyclic Polymer Mechanochemistry: Scission Kinetics and the Dynamic Memory Effect with Ultrasonication and Ball-Mill Grinding.

A series of monodisperse cyclic and linear poly(d,l-lactide)s (c-PLA and l-PLA, respectively) were prepared with various degrees of polymerization (DP) using an iterative convergent synthesis approach. The absence of a molecular weight distribution provided us a chance to study their mechanochemical reactivity without obstructions arising from the size distribution. Additionally, we prepared l- and c-PLAs with identical DPs, which enabled us to attribute differences in scission rates to the cyclic polymer architecture alone. The polymers were subjected to ultrasonication (US) and ball-mill grinding (BMG), and their degradation kinetics were explored. Up to 9.0 times larger scission rates were observed for l-PLA (compared to c-PLA) with US, but the difference was less than 1.9 times with BMG. Fragmentation requires two backbone scission events for c-PLA, and we were able to observe linear intermediates (formed after a single scission) for the first time. We also developed a new method of studying the dynamic memory effect in US by characterizing and comparing the daughter fragment molecular weight distributions of l- and c-PLAs. These results provide new insights into the influence of the cyclic polymer architecture on mechanochemical reactions as well as differences in reactivity observed with US and BMG.

Motion Responses by Occupants in Out-of-Seat Positions During Autonomous Emergency Braking.

The occupant's posture can be changeable to an inadvertent or unintentional out-of-seat position (OOSP) depend on their convenience. Understanding for OOSP has been demanded, but it is not sufficient; especially when AEB is activated. The aim of the current study was to characterize the motion responses of an occupant in various OOSPs when AEB is activated and to identify if there were any additional risks of injury or discomfort to the occupant. The normal seat position (NSP) and three OOSPs were defined to compare the difference of human responses, and six healthy males were participated. Particularly, the maximum rotation angles of the neck in OOSP2 and OOSP3 differed significantly around 1.3 ± 0.3 and 1.4 ± 0.2 times higher respectively than from in the NSP (p < 0.05). Occupants assuming OOSP3 exhibited motion characteristics were not restrained effectively and characterized a hovering and falling upper body and a slipping pelvis. This study has identified, for the first time, a potential risk of injury or discomfort when AEB is activated while an occupant is in an OOSP. This study may serve as fundamental data for the development of safety system that can improve restraint and counteract any deterioration in occupant safety.