An organized combination of stiff and elastic domains within a single material can synergistically tailor bulk mechanical properties. However, synthetic methods to achieve such sophisticated architectures remain elusive. We report a rapid, facile, and environmentally benign method to pattern strong and stiff semicrystalline phases within soft and elastic matrices using stereo-controlled ring-opening metathesis polymerization of an industrial monomer, cis -cyclooctene. Dual polymerization catalysis dictates polyolefin backbone chemistry, which enables patterning of compositionally uniform materials with seamless stiff and elastic interfaces. Visible light–induced activation of a metathesis catalyst results in the formation of semicrystalline trans polyoctenamer rubber, outcompeting the formation of cis polyoctenamer rubber, which occurs at room temperature. This bottom-up approach provides a method for manufacturing polymeric materials with promising applications in soft optoelectronics and robotics.
The development of facile synthetic strategies to access well-defined polymers promises to provide advanced soft materials with functionality that rivals that observed from nature. To this end, ring-opening metathesis polymerization (ROMP) presents a compositionally simple and rapid strategy for controlled polymerization, yet it has received far less attention relative to radical counterparts. This limited attention arises in part from scattered reports on optimization strategies and a narrow monomer scope. Contemporary ROMP methods favor the use of exo-norbornene derivatives and highly reactive nonchelated Ru-alkylidenes, such as Grubbs Catalysts. In contrast, endo-norbornene derivatives, from which analogous exo-forms are often generated, present a more accessible alternative, yet examples of their utility in ROMP remain scarce. Herein, a systematic examination of ROMP with endo-norbornene monomers using stable chelated Ru-alkylidene initiators is presented. Through initiator screening and polymerization optimization, the ROMP process is shown to be versatile and robust, providing rapid access to polymers with excellent molecular weight control, low dispersities (Đ < 1.1), good functional group tolerance, and high chain-end fidelity that enabled the preparation of block copolymers via sequential monomer addition. Furthermore, the process is oxygen-tolerant, allowing for ROMP to be performed under ambient conditions on the bench, which was showcased in synthesizing mechanically robust endonorbornene imide thermoplastics with high glass transition and decomposition temperatures. This report provides a comprehensive overview of the scope and limitations of endo-norbornene ROMP with chelated initiators, serving as a user guide for the polymer chemistry community to develop well-defined next-generation functional plastics.
During the course of studying silicon-containing diblock copolymers, it was discovered that poly(3,5di(trimethylsilyl)styrene)-block-poly(3,4-methylenedioxystyrene) (PDTMSS-b-PMDOS) showed very unusual thermal properties. The material can be recovered as a free-flowing powder despite heating above 250 °C. To better understand this behavior, homopolymers of the 3,5-disubstituted styrenes, poly(3,5-di(trimethylsilyl)styrene) (PDTMSS) and poly(3,5-di-tert-butylstyrene) (PDtBS), were prepared. These polymers are soluble in common organic solvents and formed clear, glassy thin films upon spin coating. These homopolymers were studied by differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), dynamic mechanical analysis (DMA), and temperature-programmed ellipsometry. These experiments document the lack of a conventional glass transition in these materials below their decomposition temperature. A series of statistical copolymers of PDTMSS and PDtBS with styrene was synthesized and studied by DSC in an attempt to establish the T g of the homopolymers by model-based extrapolation.
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