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Abstract The synthesis and processing of π‐rich polymers found in novel electronics and textiles is difficult because chain stiffness leads to low solubility and high thermal transitions. The incorporation of “shape‐shifting” molecular cages into π‐rich backbone provides an ensemble of structural kinks to modulate chain architecture via a self‐contained library of valence isomers. In this work, we report the synthesis and characterization of (bullvalene‐co‐phenylene)s that feature smaller persistence lengths than a prototypical rigid rod polymer, poly(p‐phenylene). By varying the amount of bullvalene incorporation within a poly(p‐phenylene) chain (0–50 %), we can tune thermal properties and solution‐state conformation. These features are caused by stochastic bullvalene isomers within the polymer backbone that result in kinked architectures. Synthetically, bullvalene incorporation offers a facile method to decrease structural rigidity within π‐rich materials without concomitant crystallization. VT NMR experiments confirm that these materials remain dynamic in solution, offering the opportunity for future stimuli‐responsive applications. 

Solid-state nuclear magnetic resonance (ssNMR) has been playing an indispensable role in revealing the interplay of structure and molecular dynamics in polymers at different states. In this Perspective, we first provide an overview about the fundamental spin interactions in ssNMR and then highlight some recent progress on sensitivity-enhanced ssNMR spectroscopy and in situ NMR. Moreover, we highlight ssNMR applications in the field of polymer crystallization, molecular dynamics, chemical reactions, supramolecular polymers, energy materials, and so on. Finally, our personal perspective is given on the future development at the crossroad of ssNMR and polymer science. 

In the earlier theoretical research, impact of entanglement on folding during crystallization was minimized. The combination of 13C isotope labeling and NMR spectroscopy allows us to quantitatively determine stem to stem distance as well as chain folding distance, hence, we are able to probe chain-level structure. Our recent work indicated that polymer chains are possible to fold prior to crystallization. In this poster, we would like to investigate the folding structure of a semi-crystalline polymer in melt-grown crystals (mgc) by using solid-state NMR spectroscopy and SAXS measurement. First, various 13C enriched poly(L-lactic acid) (PLLA) samples with different molecular weights (Mw = 2.5k – 300k g/mol) across critical entanglement length (Mc = 16k g/mol) were prepared in order to observe the molecular weight dependence of folding structure of PLLA. We revealed that entanglements influence the folding number during crystallization. Second, we attempt to observe the entanglement effect through diluting entanglement density, i.e., blending the PLLA above and below the Mc with different ratio and molecular weight. Based on the experimental results, we would like to highlight the impact of entanglements on folding of semicrystalline polymer in the melt-grown crystal. 

Highly branched polyethylene (PE) thermoplastic elastomer (TPE)s can be synthesized using Brookhart-type α-diimine nickel and palladium catalysts, which show a range of branching number and identity. In this work, we aim at elucidating the structure-property relationship of various PE-TPEs through solution-state and solid-state 13C NMR spectroscopy and mechanical tensile testing. By applying solid-state NMR spectroscopy, DSC, and XRD, it was revealed that small degrees of crystallinity (< 5%) yields polyethylenes that are sufficiently reinforced to exhibit TPE behavior. Across PE samples with similar branching numbers, we relate the effects of branch identity, crystallinity, and molecular weight on the tunable mechanical properties. The structure-property relationship of the PE-TPEs will be discussed. 

Recycling different plastics post-consumers causes downgraded performance due to the physical and chemical property differences conflicting with one another. These properties stem from the incompatibility of the blends to crystallize and blend. As there are millions of tons of waste every year, the ability to effectively blend two plastics such as polyethylene and polypropylene becomes crucial. In this poster, a molecular-level study of polyolefin blend co-crystallization will be explored by utilizing solid-state NMR spectroscopy. It is through NMR spectroscopic techniques and the use of selectively activating various parts of the blend through isotopes that aspects of the arrangement can be made. We will conduct studies into the co-crystallization of the blends utilizing deuterated polymers to access the chain-to-chain interface differences. This will give us the ability to see the relative extent of interaction as well as providing overall system kinetics. From these experiments, a diagram of the co-crystallization structure can be made as well as a defined system to analyze crystallization 

Stereoregularity significantly influences the crystallization, mechanical, and thermal properties of polymers. In this work, we investigate crystallization behaviors and molecular dynamics of atactic (a)-, isotactic (i)-, and syndiotactic (s)-hydrogenated poly(norbornene) (hPNB)s by using small-angle X-ray scattering and solid-state (ss) NMR. a-hPNB exhibits a much higher crystallinity (Φc) (82%) and long period (L) (80 nm) than i- and s-hPNB (50–55% and 17–21 nm). Moreover, in the s-hPNB crystalline region, chain dynamics is not thermally activated up to the melting temperature (Tm), while in the crystalline regions of i- and a-hPNB, small amplitude motions occur in a slow dynamic regime of 10–2–102 s. The molecular dynamics follows Arrhenius behavior in a-hPNB up to the crystal–crystal transition temperature (Tcc), while these dynamics are surprisingly saturated in i-hPNB under these conditions. Temperature dependence of the molecular dynamics leads to different crystal–crystal transitions between i- and a-hPNBs: i-hPNB changes the trans conformation to the gauche one due to the localized bond rotations where chain dynamics is restricted, whereas a-hPNB keeps a nearly trans conformation and conducts fast chain dynamics due to the amplified C–C bond rotations in the high-temperature phase. Such fast chain dynamics leads to unique crystallization behaviors of hPNB, specifically in the atactic configuration due to configurational disorder coupled with conformational flexibility.