Crystallization and morphology of isotactic poly(methyl methacrylates)

Lemieux, Even; Prud’homme, Robert E.

doi:10.1007/bf00264144

Cited by 6 publications

(7 citation statements)

References 4 publications

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“…The obtained T g suggests the presence of a syndiotactic PMMA fraction for which the crystallization process is slow, leading to very low degrees of crystallinity. However, it is accompanied by a spherulitic structure, with the semicrystalline regions [ 63 ], characterized by self-generated fields of lamellas or fibrils in the different regions of polymers [ 64 ], affecting the mechanical properties of polymers [ 65 ].…”

Section: Resultsmentioning

confidence: 99%

The Role of Electrical Polarity in Electrospinning and on the Mechanical and Structural Properties of As-Spun Fibers

et al. 2020

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Electric field strength and polarity in electrospinning processes and their effect on process dynamics and the physical properties of as-spun fibers is studied. Using a solution of the neutral polymer such as poly(methyl methacrylate) (PMMA) we explored the electrospun jet motion issued from a Taylor cone. We focused on the straight jet section up to the incipient stage of the bending instability and on the radius of the disk of the fibers deposited on the collecting electrode. A new correlation formula using dimensionless parameters was found, characterizing the effect of the electric field on the length of the straight jet, L˜E~E˜0.55. This correlation was found to be valid when the spinneret was either negatively or positively charged and the electrode grounded. The fiber deposition radius was found to be independent of the electric field strength and polarity. When the spinneret was negatively charged, L˜E was longer, the as-spun fibers were wider. The positively charged setup resulted in fibers with enhanced mechanical properties and higher crystallinity. This work demonstrates that often-overlooked electrical polarity and field strength parameters influence the dynamics of fiber electrospinning, which is crucial for designing polymer fiber properties and optimizing their collection.

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Section: Resultsmentioning

confidence: 99%

The Role of Electrical Polarity in Electrospinning and on the Mechanical and Structural Properties of As-Spun Fibers

et al. 2020

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“…41−43 In our studies, the iso-PMMA may have had the highest packing density among the polymer chains, as compared to the syn-and a-PMMAs, due to the higher crystallinity of the iso-PMMA as a result of the regular configurational arrangements of the pendant methyl methacrylate substituents along the polymer backbone. 29,31,34,44−48 This higher packing density induced by the polymer crystalline structures efficiently reduced the free volume in the polymer film, 49,50 which acted as a path for I leakage upon application of E. That is, the I leakage behavior displayed in Figure 2 was related to the stereostructure of the PMMA, which affected the crystalline structures and the molecular packing density in the bulk PMMA films. The dielectric strength, therefore, increased in the following order, a-, syn-, and iso-PMMAs.…”

Section: Resultsmentioning

confidence: 98%

“…18,19 As the free volume in the polymer dielectrics decreases due to close packing among the polymer chains, the motions of each polar functionality in response to the electric field may be restricted due to steric hindrance. 42,49,50 This effect decreases the C i of the polymer film, which explains why the iso-PMMA exhibited the lowest C i and the highest V th among the three stereoisomers.…”

Section: Resultsmentioning

confidence: 99%

Gate-Bias Stability Behavior Tailored by Dielectric Polymer Stereostructure in Organic Transistors

Lee

Min

Park

et al. 2015

ACS Appl. Mater. Interfaces

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Understanding charge trapping in a polymer dielectric is critical to the design of high-performance organic field-effect transistors (OFETs). We investigated the OFET stability as a function of the dielectric polymer stereostructure under a gate bias stress and during long-term operation. To this end, iso-, syn-, and atactic poly(methyl methacrylate) (PMMA) polymers with identical molecular weights and polydispersity indices were selected. The PMMA stereostructure was found to significantly influence the charge trapping behavior and trap formation in the polymer dielectrics. This influence was especially strong in the bulk region rather than in the surface region. The regular configurational arrangements (isotactic > syntactic > atactic) of the pendant groups on the PMMA backbone chain facilitated closer packing between the polymer interchains and led to a higher crystallinity of the polymer dielectric, which caused a reduction in the free volumes that act as sites for charge trapping and air molecule absorption. The PMMA dielectrics with regular stereostructures (iso- and syn-stereoisomers) exhibited more stable OFET operation under bias stress compared to devices prepared using irregular a-PMMA in both vacuum and air.

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“…In this contribution, we present a time‐resolved study of the melting behavior of polylactide by means of a joint small angle light scattering (SALS) and DSC analysis. SALS is a powerful tool to disclose the crystal morphology of semicrystalline thermoplastics, in particular under conditions where time‐resolved structure characterization is a challenge for POM . Accordingly, SALS was also used to determine changes in polylactide morphology during crystallization and in one further case it was applied to characterize the isothermal crystallization of polylactide in terms of spherulite growth rates .…”

Section: Introductionmentioning

confidence: 99%

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Schmidt

Keuker‐Baumann

Meyer

et al. 2019

J Polym Sci B Polym Phys

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Small angle light scattering (SALS) and differential scanning calorimetry DSC have been applied to investigate the melting of spherulites isothermally crystallized polylactide. At an isothermal crystallization temperature high enough, pure α-phase crystals are formed. Exposed to a temperature gradient, the crystals first melt and then recrystallize before they finally melt. With decreasing crystallization temperature, an increasing fraction of polylactide is crystallizing in the less stable α 0 -phase.α 0 -crystals also melt upon increasing the temperature but recrystallize to the more stable α-phase. A constant spherulite size is revealed by SALS for both processes, the α/α and α 0 /α meltrecrystallization, until completion of the final melting, thereby supporting integrity of the spherulites throughout the entire processes. Joint DSC and SALS experiments demonstrate that the depolarized scattering invariant correlates with the heat flow recorded by DSC and thus offer an alternative measure for the degree of crystallinity. The following mechanism is identified for both processes: initial melting and recrystallization overlay each other. Crystallinity is not fully recovered upon recrystallization because only part of the original lamellae survives the melt-recrystallization, though with an increased thickness. While lamellae are melting and reforming or simply transforming their phase, the spherulites survive the process until final melting.

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Crystallization and morphology of isotactic poly(methyl methacrylates)

Cited by 6 publications

References 4 publications

The Role of Electrical Polarity in Electrospinning and on the Mechanical and Structural Properties of As-Spun Fibers

The Role of Electrical Polarity in Electrospinning and on the Mechanical and Structural Properties of As-Spun Fibers

Gate-Bias Stability Behavior Tailored by Dielectric Polymer Stereostructure in Organic Transistors

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

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