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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. 

The crystallization pathway of long and flexible polymer chains is debatable because of the lack of an initial melt/glass structure. To identify the crystallization pathway, we focus on two binary blends of poly(lactic acid) racemates that form stereocomplex crystals (SCCs). NMR crystallography is used to identify the stereocomplex (SC) structure and SC fraction with or without long-range order. There are significant structural analogies between glass and crystals for both high-molecular-weight (M) and low-M racemates. The observed analogies and kinetics of crystallization indicate that polymer crystallization proceeds via chain segments moving the least possible distance (“freezing in” mechanism) and that topological constraints govern nucleation barriers. 

Branching number, pattern, and distribution of polyethylene (PE) significantly affect the crystalline structures at hierarchical length scales and thus dominate physical properties. Highly branched (HB) PE with over 100 branches per 1000 carbons (100b/1kC) can be synthesized from a sole ethylene feedstock using α-diimine nickel catalysts but results in complex 13C solution-state NMR spectra. In this study, we assign numerous 13C peaks that were unassigned in HBPEs synthesized via three nickel α-diimine catalysts. By application of an additive rule of 13C chemical shifts, several new microstructures are identified. The results successfully reveal new branching microstructures, including (i) the configuration of paired branches, (ii) continual paired branches, and (iii) methylated branch ends. Based on these new assignments, several insights into the chain-walking mechanisms of HBPEs are discussed. 

Chain entanglements play a crucial role in polymer crystallization, yet their effects on crystallization remain not fully understood. Freeze-drying is one way to potentially preserve disentangled states of long polymer chains. In fact, it is known that freeze-drying (FD) significantly accelerates the crystallization kinetics of semicrystalline polymers. However, the chain-level structure of the FD polymer chains without a long-range order (glass) has been a debatable matter. In this study, we investigate the effect of freeze-drying on single chain-level structures of 13CH3 enriched poly(L-lactic Acid) and 13CH enriched poly(D-lactic acid) racemate by using 1H-1H spin diffusion via 13C detection solid-state NMR spectroscopy. Spatial distributions of PLLA and PDLA glassy chains in the range of a few Å – 30 nm are evaluated via 1H-1H spin diffusion. This analysis provides core-shell morphology of single chains where the outer shell layers include both PDLA and PLLA mixture and the inner core possess a single component. 

Semicrystalline polymers exhibit different re-organization behaviors during heating depending on crystal growth methods. Upon heating, solution-grown crystals (SGCs) undergo lamellar doubling while melt-grown crystals (MGCs) show a gradual increase in lamellar thickness. However, the molecular-level mechanisms driving these distinct reorganization processes remain unresolved. In this study, we investigate the morphological development, crystalline chain dynamics, chain packing, and chain-folding structures of poly (L-Lactic Acid) in both SGCs and MGCs upon heating by using solid-state NMR spectroscopy and in-situ Small Angle X-ray Scattering (SAXS). By comparing the hierarchical semicrystalline structures and crystalline chain dynamics in SGCs and MGCs, it is found that the chain-folding structure and the presence or absence of entanglements are key factors influencing the thermal stability and different reorganization mechanisms of mobile polymer crystals. 

Polymer crystallization is a process which connects the initial amorphous state with the final semicrystalline state. It is important to elucidate the amorphous structure which determines the crystallization pathway. In this work, we report quantitative analysis of the spatial proximity of poly(Lactic acid) (PLA) racemate before and after stereocomplex (SC) crystallization by using 13C selective isotope labeling and two-dimensional solid-state (ss) NMR techniques. It is found that i) the PLA racemate forms SC structure prior to crystallization (chiral recognition), ii) fraction of the chiral recognition segments (f) is extremely high, 94% in a low molecular weight (M) racemate while a high M one possesses only f = 10%, and iii) the f value for the former and latter is surprisingly in accordance with the f value after SC crystallization and SC crystallinity, respectively. From the observed analogies between the initial glassy and final crystalline structures, it is concluded that pre-existing chiral recognition fraction governs the formations of SCC. 

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