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Vitrimers usually show decreased mechanical properties after welding, recycling or remolding processes due to the hysteresis of topology network rearrangement. Herein, we propose a strategy for developing self-strengthening vitrimers whose mechanical properties increase upon network rearrangement. Such vitrimers are constructed based on the exchangeable β-hydroxyl ester network formed by two immiscible polymers, epoxidized poly-isoprene (EPIP) and poly-(thioctic acid) (PTA). A radical capture agent, 1,3-diisopropenylbenzene (DIB), is introduced into vitrimers. DIB is miscible with EPIP while immiscible with PTA, yet it can react with PTA by capturing the free radicals released by the dynamic disulfide bonds of PTA at high temperature, thereby improving the compatibility between EPIP and PTA during network rearrangement. As a result, more β-hydroxyl ester linkages are formed between EPIP and PTA, and the density of the crosslinking network in the vitrimers increases after repeated remolding process, which result in improved mechanical properties after network rearrangement. This strategy of compatibility driven self-strengthening can be easily extended to other vitrimers composed of immiscible components. [ABSTRACT FROM AUTHOR]

Abstract: Stereocomplex (SC) crystallization between poly( l‐lactide) (PLLA) and poly( d‐lactide) (PDLA) exhibits tremendous potential to improve the properties of polylactide (PLA), but the practical processing of SC‐type PLA (SC‐PLA) is significantly hindered by the insufficient melt stability and serious degradation after complete melting of SC crystallites over 240 °C. In a previous work, powder metallurgy inspired low‐temperature (180–210 °C) compression sintering is proposed to fabricate SC‐PLA products from its nascent powder. However, its industrial application is still challenging mainly due to the low production efficiency (half an hour is required) as well as the weak ability to fabricate products with complex shapes. In this work, an effort to rapidly fabricate complex‐shaped SC‐PLA products using low‐temperature injection molding technology is reported, where SC‐PLA nascent powder is partially melted. To ensure appropriate powder flowability, small amounts of glyceryl monostearate are incorporated as a lubricant. The results show that, both the self‐nucleation and flow‐induced nucleation effects facilitate the SC crystallization across the interfaces between adjacent unmelted powder particles, which considerably shortens the sintering cycle to about 2 min. In this way, complex‐shaped SC‐PLA products (such as gears) with superb performance are successfully fabricated by injection molding for the first time. [ABSTRACT FROM AUTHOR]