Fundamental solution and single‐chain properties of polylactides

Dorgan, John R.; Janzen, Jay; Knauss, Daniel M.; Hait, Sukhendu; Limoges, Bradford R.; Hutchinson, Matthew H.

doi:10.1002/polb.20577

Cited by 142 publications

(142 citation statements)

References 33 publications

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“…The standard model for branched polymers was modified to account for the strong steric interactions that occur in bottlebrushes due to the high grafting density of the side chains, as was done previously for similar bottlebrush block polymers (25). Gaussian chains were used to represent the N = N A + N B + N C (LSO) or N = N A + N B + N A′ (LSL′) side chains, and the volumes and unperturbed end-to-end lengths of the side chains were set to known literature values (26,27). For the backbone, a worm-like chain of fixed persistence length was used to handle the strong lateral tension that occurs due to sidechain crowding.…”

Section: Resultsmentioning

confidence: 99%

Manipulating the ABCs of self-assembly via low-χ block polymer design

Chang

Bates

Lee

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χ ij ). In this article, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χ AC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology, which we designate LAM P . Transmission electron microscopy indicates that LAM P exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM 3 ) with ABCB periods. Complementary small-angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations and predicts that LAM P is thermodynamically stable below a critical χ AC , above which LAM 3 emerges. Both experiments and theory expose close analogies to ABA′ triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. These conclusions provide fresh opportunities for block polymer design with potential consequences spanning all self-assembling soft materials.block polymer | self-assembly | polymer nanostructure | domain spacing | LAM P B lock polymers are a diverse class of soft materials capable of self-assembling into complex periodic nanostructures. Synthetic command over composition, dispersity, sequence, and molecular architecture enables control over the mesoscopic order and macroscopic thermal, mechanical, rheological, and transport properties (1-4). The phase behavior of "simple" linear AB diblock copolymers is universally parameterized by the segregation strength χ AB N and relative volume fraction f, where χ AB represents the effective Flory-Huggins binary interaction parameter and N is the total volume-averaged degree of polymerization. Mixing behavior, captured through the mean-field concept of χ AB , is central to block polymer self-assembly: the competing demands of minimizing interfacial energy and maximizing configurational entropy only favor microphase separation when A-B interactions are repulsive (χ AB > 0) (5, 6). Extension to higher-order multiblock polymers introduces additional interaction parameters (χ ij ) that impact self-assembly and properties (7). For example, introducing a mutually incompatible C block (χ AC > 0, χ BC > 0) generates a host of new morphologies dictated by the chain connectivity (ABC, ACB, or BAC) and intrinsic χ ij -values (8, 9). In this rich phase space, designing multiblock polymers with a combination of miscible and immiscible blocks can also access new structures and impart useful functions (10, 11). Perhaps the best-known examples of such systems are linear ABA′ triblock copolymers (χ AB > 0, χ AA′ ≈ 0): their high-value industrial applications as thermoplastic elastomers are entirely enabled by A/A′ mixing and chain connectivity, which together create physically cross-linked materials with ex...

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Section: Resultsmentioning

confidence: 99%

Manipulating the ABCs of self-assembly via low-χ block polymer design

Chang

Bates

Lee

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Figure 10.1 shows the K H values so determined (vertical axis intercepts) to vary over a wide range, from lowest to highest, by a factor of 25! From this analysis [3], it was concluded that the state of the literature regarding Mark-Houwink parameters for PLA was inadequate.…”

Section: Viscometry Of Plamentioning

confidence: 99%

“…Different definitions of the mean squared ''monomer'' step length Because of the confused state of the literature, a careful study [3] was performed to determine appropriate physical constants for PLA under dilute solution conditions. The results of this important study are summarized here with attention focused on the most important results useful for characterizing PLA.…”

Section: Viscometry Of Plamentioning

confidence: 99%

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Rheology of Poly(Lactic Acid)

Dorgan

2010

Poly(Lactic Acid)

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The readers of this chapter are expected to come from a wide variety of backgrounds with varying degrees of expertise in polymer materials science. Accordingly, a detailed understanding of the rheological properties of polymers is, for many readers, an unknown subject. With these factors in mind, the first topic to be addressed is, What is rheology and why is it important?Simply stated, rheology is the study of the flow and deformation of matter. Rheology is a subfield of continuum mechanics that combines elements of both solid and fluid mechanics. Polymer rheology is a highly advanced science that reveals very important features of polymeric materials like PLA. In particular, the viscometry of dilute polymer solutions is an effective means of determining fundamental properties of polymer molecules; these include the molecular weight and the characteristic ratio (subjects to be discussed in detail in this chapter). More important, the melt rheology of polymeric materials reflects the relationship between molecular structure and dynamic properties. Of these properties, the viscosity and elasticity of the molten polymer are of primary importance in processing of plastics into useful articles. For example, both the shear thinning viscosity and the strain hardening extensional behavior of PLA are of great importance in plastic processing operations such as extrusion and fiber spinning. With this very cursory discussion of the nature and importance of rheology in mind, the attentive reader will ask, Is there anything particularly unique about the rheology of PLA?Indeed, the melt rheology of PLA is distinct from other commodity plastics in at least one important respect. Namely, the chemical stability of PLA can be adversely affected rather easily compared to most other polymeric molecules. At processing temperatures typically needed for semicrystalline PLA, namely, those above the melting temperature, both hydrolysis and pyrolysis can become important. Fortunately, commercially available PLAs are typically stabilized against thermal degradation. However, it is impossible to overstate the importance of drying PLA sufficiently prior to processing (or measuring its rheological properties!). Rheological measurements can provide direct evidence for the loss in molecular weight of improperly stabilized PLA in the molten state. Accordingly, in examining rheological data on PLAs, it is of particular importance to understand what, if any, chemical changes have taken place during the preparation and testing of the samples. In this regard, there is a clear link to dilute solution viscometry that can provide information about molecular weight in a simple test requiring only elementary equipment. As a final remark on the unique nature of PLA rheology, we can state that rheological measurements are particularly useful for assessing the effectiveness of both chemical stabilization against thermal degradation and of drying procedures meant to preclude hydrolytic degradation.This chapter is organized to provide a short yet detailed un...

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“…For PLA-THF, K =1.74·10 -4 and a = 0.736 [35]. Figure 1 display SEM micrographs of PLA/HT nanocomposites.…”

Section: Viscometrymentioning

confidence: 99%

Structure-properties relationships in melt reprocessed PLA/hydrotalcites nanocomposites

Scaffaro¹,

Sutera²,

Mistretta³

et al. 2017

Express Polym. Lett.

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Abstract. In this work the effect of multiple reprocessing was studied on molecular structure, morphology and properties of poly(lactic acid)/hydrotalcites (PLA/HT) nanocomposites compared to neat PLA. In addition, the influence of two different kinds of HT -organically modified (OM-HT) and unmodified (U-HT) -was evaluated. Thermo-mechanical degradation was induced by means of five subsequent extrusion cycles. The performance of the recycled materials was investigated by mechanical and rheological tests, differential scanning calorimetry (DSC), intrinsic viscosity measurements and SEM observation. The results indicated that the best morphology was achieved in the systems incorporating OM-HT. On increasing the extrusion reprocessing cycles, the properties showed behavior due to two opposite effects: i) chain scission due to thermo-mechanical degradation and ii) filler dispersion effect resulting from multiple processing. In particular, at low reprocessing cycles, both tensile and rheological properties seem to be mainly affected by HT dispersion, especially when OM-HT was added. After five reprocessing cycles, on the contrary, chain scission, i.e. thermo-mechanical degradation, dominated. As regards the effect of the presence of organic modifier in HT, the results indicated that this variable apparently did not affect the macroscopic performance of the nanocomposites, especially at high reprocessing cycles.

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Fundamental solution and single‐chain properties of polylactides

Cited by 142 publications

References 33 publications

Manipulating the ABCs of self-assembly via low-χ block polymer design

Manipulating the ABCs of self-assembly via low-χ block polymer design

Rheology of Poly(Lactic Acid)

Structure-properties relationships in melt reprocessed PLA/hydrotalcites nanocomposites

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