Precision, Tunable Deuterated Polyethylene via Polyhomologation

Boron-Catalyzed C1 Copolymerization of Arsonium and Sulfoxonium Ylides toward Unrepresented Structures and Fluorescence Properties

The first synthesis of well-defined poly(methylene-co-1,1-diphenylpropenenylene) (C1-co-C1'), equivalent to poly(ethylene-co-diphenylbutadiene) copolymers was accomplished by C1 copolymerization of novel diphenylpropenyl triphenyl arsonium ylides (Ph2AY) and dimethylsulfoxonium methylide (Me2SY) using B-thexylborepane as initiator. All polymerization conditions, including feed ratio, temperature, and reaction time, were optimized. A series of photoluminescent poly(ethylene-co-diphenylbutadiene)s were synthesized at different feed ratios, opening a new synthetic horizon for poly(ethylene-co-disubstitutedbutadiene) copolymers. Notably, a new C1 segment, arising from a double bond rearrangement, was confirmed by NMR, resulting in an unprecedented two-monomer three-structure random terpolymer. An unexpected red-shift phenomenon in the fluorescence spectra was observed with increasing the ratio of Ph2AY in the copolymer. This shift is attributed to the aggregation of diphenylbutadiene segment, similar to through-space conjugation (TSC), likely induced by a decrease in the crystallinity of copolymers. Furthermore, another disubstituted allylic triphenyl arsonium ylides, (E)-2-phenylbutenyl triphenyl arsonium ylide (MePhAY) was also synthesized and investigated. These additional compounds expand the knowledge and the potential applications of such copolymerization techniques in advanced materials.

Organoboron-mediated polymerizations

The scientific community has witnessed extensive developments and applications of organoboron compounds as synthetic elements and metal-free catalysts for the construction of small molecules, macromolecules, and functional materials over the last two decades. This review highlights the achievements of organoboron-mediated polymerizations in the past several decades alongside the mechanisms underlying these transformations from the standpoint of the polymerization mode. Emphasis is placed on free radical polymerization, Lewis pair polymerization, ionic (cationic and anionic) polymerization, and polyhomologation. Herein, alkylborane/O2 initiating systems mediate the radical polymerization under ambient conditions in a controlled/living manner by careful optimization of the alkylborane structure or additives; when combined with Lewis bases, the selected organoboron compounds can mediate the Lewis pair polymerization of polar monomers; the bicomponent organoboron-based Lewis pairs and bifunctional organoboron-onium catalysts catalyze ring opening (co)polymerization of cyclic monomers (with heteroallenes, such as epoxides, CO2, CO, COS, CS2, episulfides, anhydrides, and isocyanates) with well-defined structures and high reactivities; and organoboranes initiate the polyhomologation of sulfur ylides and arsonium ylides providing functional polyethylene with different topologies. The topological structures of the produced polymers via these organoboron-mediated polymerizations are also presented in this review mainly including linear polymers, block copolymers, cyclic polymers, and graft polymers. We hope the summary and understanding of how organoboron compounds mediate polymerizations can inspire chemists to apply these principles in the design of more advanced organoboron compounds, which may be beneficial for the polymer chemistry community and organometallics/organocatalysis community.

Synthesis of Deuterated and Sulfurated Polymers by Inverse Vulcanization: Engineering Infrared Transparency via Deuteration

The synthesis of deuterated, sulfurated, proton-free, glassy polymers offers a route to optical polymers for infrared (IR) optics, specifically for midwave IR (MWIR) photonic devices. Deuterated polymers have been utilized to enhance neutron cross-sectional contrast with proteo polymers for morphological neutron scattering measurements but have found limited utility for other applications. We report the synthesis of perdeuterated d14-(1,3-diisopropenylbenzene) with over 99% levels of deuteration and the preparation of proton-free, perdeuterated poly(sulfur-random-d14-(1,3-diisopropenylbenzene)) (poly(S-r-d14-DIB)) via inverse vulcanization with elemental sulfur. Detailed structural analysis and quantum computational calculations of these reactions demonstrate significant kinetic isotope effects, which alter mechanistic pathways to form different copolymer microstructures for deutero vs proteo poly(S-r-DIB). This design also allows for molecular engineering of MWIR transparency by shifting C-H bond vibrations around 3.3 μm/3000 cm-1 observed in proteo poly(S-r-DIB) to 4.2 μm/2200 cm-1. Furthermore, the fabrication of thin-film MWIR optical gratings made from molding of deuterated-sulfurated, proton-free poly(S-r-d14-DIB) is demonstrated; operation of these gratings at 3.39 μm is achieved successfully, while the proteo poly(S-r-DIB) gratings are opaque at these wavelengths, highlighting the promise of MWIR sensors and compact spectrometers from these materials.

Selective deuteration along a polyethylene chain: Differentiating conformation segment by segment

To improve the circularity and performance of polyolefin materials, recent innovations have enabled the synthesis of polyolefins with new structural features such as cleavable breakpoints, functional chain ends, and unique comonomers. As new polyolefin structures become synthetically accessible, fundamental understanding of the effects of structural features on polymer (re)processing and mechanical performance is increasingly important. While bulk material properties are readily measured through conventional thermal or mechanical techniques, selective measurement of local material properties near structural defects is a major characterization challenge. Here, we synthesized a series of polyethylenes with selectively deuterated segments using a polyhomologation approach and employed vibrational spectroscopy to evaluate crystallization and melting of chain segments near features of interest (e.g., end groups, chain centers, and mid-chain structural defects). Chain-end functionality and defects were observed to strongly influence crystallinity of adjacent deuterated chain segments. Additionally, chain-end crystallinity was observed to have different molar mass dependence than mid-chain crystallinity. The synthesis and spectroscopy techniques demonstrated here can be applied to range of previously inaccessible deuterated polyethylene structures to provide direct insight into local crystallization behavior.

Polyethylenes functionalized with ureidopyrimidone: synthesis, thermomechanical properties and shape memory behavior

In this contribution, we reported an approach to functionalize polyethylene with quadruple hydrogen bonds.