Do we need to know and can we determine the complete macrostructures of synthetic polymers?

Gurarslan, Rana; Tonelli, Alan E.

doi:10.1016/j.progpolymsci.2016.09.001

Cited by 9 publications

(7 citation statements)

References 30 publications

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“…For example, it is not clear to what degree, if any, that both butadiene-rich and styrene-rich chain segments contribute to the averaged T g 's observed for the ITB-10, -20, and -30 copolymers. Variable-temperature solid-state 1 H MAS NMR affords chain-specific resolution over essentially the same temperature range as the DSC data, since molecular motion associated with the onset of the glass transition eliminates homonuclear dipolar interactions between the abundant 1 H spins in the copolymers leading to narrow and resolved spectral lines in the isotropic region of the spectrum. Prior to the onset of chain reorientations, the proton signal appears as a featureless, broad Gaussian signal extending over a 50 kHz region.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

“…1 H and 13 C solution NMR measurements were collected on a Bruker 400 MHz spectrometer, using chloroform or THF as the solvent, from which copolymer compositions and sequence effects were calculated. 1 H solution data were strictly quantitative, while 13 C solution data were acquired with NOE (nuclear Overhauser enhancement). Quantitative spin-counting MAS spectra using the previously published internally calibrated method 22,29 were obtained at room temperature on the solid copolymers, using a Bruker Avance-400 spectrometer operating at a magnetic field strength of 9.4 T, and 6−7 kHz MAS (magic-angle spinning) speeds.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Figure 4. Selected solution1 H NMR spectra comparing DB-20 to three ITB copolymers, as indicated by color. In the absence of color, the spectra are arranged top to bottom in the same order as the legend.…”

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confidence: 99%

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Multiblock Inverse-Tapered Copolymers: Glass Transition Temperatures and Dynamic Heterogeneity as a Function of Chain Architecture

et al. 2017

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Systematic variation of the size and number of inverse-tapered blocks in styrene–butadiene copolymers results in a wide range of accessible glass-transition temperatures (T g), including T g’s approaching that predicted by the Fox equation. Composition-weighted average T g’s are expected for miscible blends or random copolymers, but such behavior has not previously been reported for block copolymers made from immiscible styrene and butadiene segments. In this work, 50:50 wt % multiblock copolymers with M n = 120 000 kg/mol were synthesized using an inverse-tapered block design for all blocks except the end blocks. The total composition and molecular weight were held constant, but the type and number of blocks were systematically varied in order to compare contributions from the inverse-tapered chain interfaces to the overall glass transition behavior. Discrete copolymers of similar block number and length were investigated as controls to help separate contributions from the inverse-tapered design and the molecular weight of individual blocks. Some copolymers were intentionally designed such that individual block molecular weights were between the entanglement molecular weight (M e) of polystyrene (PS) and polybutadiene (PB). A range of intermediate glass transitions was observed, but the inverse-tapered copolymers that satisfied this latter condition were the only copolymers that exhibited a T g near a composition-weighted average. Solid state NMR reveals dynamic heterogeneity among monomeric components through chain-level identification of relatively large amounts of rigid PB segments and mobile PS chain segments versus that observed in discrete block analogues where essentially all PB segments are mobile and all PS segments are rigid. NMR revealed subtle differences in the temperature-dependent segmental chain dynamics of different inverse-tapered blocks, which were not obvious from the calorimetric studies but which presumably contribute to the longer length scale T g behavior.

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Section: ■ Results and Discussionmentioning

confidence: 97%

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Multiblock Inverse-Tapered Copolymers: Glass Transition Temperatures and Dynamic Heterogeneity as a Function of Chain Architecture

et al. 2017

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“…This procedure would result in ester bonds that are connected either to the methylene groups in AA and DEG or to the rigid virtual bonds replacing the cyclobutane and cyclohexane rings in TMCBD and DMCHC. This would allow us to utilize the RIS models developed for aliphatic polyesters whose ester groups are connected by methylene or oxyalkane sequences [20,38,42,43] or phenyl groups (poly (ethylene terephthalate)) [47] to account for the ester bonds formed by TMCBD and DMCHC.…”

Section: Resultsmentioning

confidence: 99%

“…[24][25][26][27][28][29][30][31][32] More recently we have extended our Kerr effect observations to polymers whose complete macrostructures were controlled and varied by careful syntheses, and found that the Kerr effect can distinguish between polymers containing the same types and quantities of short-range microstructures, as determined, for example, by 13 C-NMR, but which are located in different positions along their backbones. [33][34][35][36][37][38] For this reason, we employed Kerr effect observations of the complex aliphatic co-and homopolyesters in an attempt to begin to determine microstructures of longer range than are evidenced by NMR.…”

Section: Introductionmentioning

confidence: 99%

Attempted Determination of the Structures of Complex Aliphatic Copolyesters

Shen

Nichol

et al. 2017

Macro Chemistry & Physics

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Attempts at the microstructural characterization of biodegradable aliphatic polyesters made via melt‐polymerization of three distinct diacids or diesters and three structurally distinct diols are described. Probes sensitive to local, short‐range microstructures (13C‐NMR) and potentially sensitive to overall, global, complete polymer architectures (Kerr effect) are employed. Solution 13C‐NMR reveals the copolyesters possess largely random comonomer sequences, without, however, complete elucidation of even their shortest comonomer sequences. The limited structural sensitivity of NMR prevents development of meaningful structure–property relations. Observed Kerr effects, on the other hand, clearly demonstrate sensitivity to the presence of distinct microstructures of longer range than are observed by 13C‐NMR. To identify the details of these longer‐range structural elements, will, however, require the ability to estimate the Kerr constants of these aliphatic copolyesters when they are assumed not only to possess the types and amounts of short‐range microstructures identified experimentally by 13C‐NMR, but which are located at different positions along their chains. This ambitious goal requires extensive experimental and calculational efforts, which are currently just beginning and will be described subsequently.

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Conformation and Configuration

Tonelli

2023

Encyclopedia of Polymer Science and Technology

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The unique feature of polymers is the flexibility of their long chains, achieved by rotation about their many backbone bonds, which enable them to assume an extremely large number of different Conformations. This is the source of their unique material behaviors, such as rubber‐like elasticity and their time and processing dependencies. Polymer conformations and material properties depend upon their Configurations, among which are the mode of enchainment of diene monomers, regiosequences (directions of monomer insertion), the stereosequences (stereochemical arrangements of atoms in the polymer chain), co‐monomer sequences of vinyl polymers, branches, and cross‐links. Polymer configurations cannot be altered without breaking and reforming their covalent bonds. In this article, we describe how the conformational characteristics of polymers can be rigorously treated, with account explicitly taken of their configurations, and how various conformationally averaged chain properties can be connected to the behaviors of their materials to allow improved structure–property relations. As examples, because 13 C NMR resonances depend on local polymer microstructures, the average bond conformation probabilities calculated for each microstructure can be used to assign their resonances. The applied to its dilute solution (the Kerr‐Effect) is very sensitive to the Configuration/Macrostructure of the overall polymer chain. When compared to the molar Kerr constants (mK) calculated for chains possessing the microstructures determined by 13 C NMR, the Macrostructures or complete molecular architectures of polymer chains may be revealed.

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Do we need to know and can we determine the complete macrostructures of synthetic polymers?

Cited by 9 publications

References 30 publications

Multiblock Inverse-Tapered Copolymers: Glass Transition Temperatures and Dynamic Heterogeneity as a Function of Chain Architecture

Multiblock Inverse-Tapered Copolymers: Glass Transition Temperatures and Dynamic Heterogeneity as a Function of Chain Architecture

Attempted Determination of the Structures of Complex Aliphatic Copolyesters

Conformation and Configuration

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