Glass Transition Temperature, Free Volume, and Curing Kinetics of Unsaturated Polyester

C, S; Lin, Hsiu-Li; Yu, T. Leon

doi:10.1295/polymj.25.897

Cited by 13 publications

(5 citation statements)

References 16 publications

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“…In the literature, at least for the last three decades, DSC studies are used to more accurately calculate the percentage of the crosslinking degree [ 33 , 34 , 35 , 36 ]. However, the reported studies usually refer to the system with a complete crosslinking reaction, which, as stated before, will not occur for the used resin nor for the tested temperatures.…”

Section: Resultsmentioning

confidence: 99%

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Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

et al. 2020

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This work intends to study the effect of the curing parameters on the mechanical properties of a polyester resin without a complete curing reaction process. For this purpose, cures at room temperature, 40 °C, and 60 °C, and post-cures at 40 °C and 60 °C, with different exposure times, were considered. Three-point bending tests were performed to assess the bending properties and both stress relaxation and creep behavior. The degree of crosslinking was estimated by evaluating the C = C ester bond, by Fourier infrared spectroscopy and complemented with the thermal characterization made by differential scanning calorimetry. The results showed that higher curing temperatures are preferable to methods involving curing and post-curing, which can be confirmed by the higher degree of conversion of unsaturated ester bonds at 60 °C. Compared to the resin cured at room temperature, the bending strength increased by 36.5% at 40 °C and 88.6% at 60 °C. A similar effect was observed for bending stiffness. In terms of stress relaxation and creep strain, the lowest values were obtained for samples cured at 60 °C.

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Section: Resultsmentioning

confidence: 99%

“…This indicates that the system presents free styrene molecules that are not crosslinked. They contribute to a high free volume of the system [ 33 ], which, consequently, presents a low (T g1 ). Even with a post-cure step at 40 °C (specimens 2–5) this endothermal transition occurred.…”

Section: Resultsmentioning

confidence: 99%

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

et al. 2020

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“…e g o unsaturated polyester/styrene increases with the extent of curing reaction. Ma et al 20 had reported that Tg of the partially cured resins can be related to conversion a by eq 11:…”

Section: Resultsmentioning

confidence: 99%

Glass Transition Temperature Profile of the Curing Reaction of Unsaturated Polyester Resin

1996

Polym J

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ABSTRACT:The curing reaction of unsaturated polyester/styrene system was investigated by differential scanning calorimetry (DSC). Between gelation and vitrification (where T 8 of the curing system equals to the curing temperature), the propagation of the curing reaction is kinetically controlled whilst the termination reaction is diffusion controlled. After vitrification, both the propagation and termination reactions are diffusion controlled. The variation of T 8 during the curing reaction was calculated from the curing profile obtained from DSC measurements by using an empirical equation developed in a previous work. The experimental data indicated that there exist a critical point such that the time-temperature shifts of T 8 vs. ln(cure time) data at different cure temperatures formed a master curve between critical point and vitrification at an arbitrary reference temperature and yielded a single Arrhenius activation energy. These results indicated that polymerization between critical point and vitrification was T, dependent only.KEY WORDS Unsaturated Polyester / Glass Transition Temperature / Differential Scanning Calorimetry / Unsaturated polyester resin is one of the most important thermosetting resins for preparing molding compounds (SMC and BMC), resin transfer molding (RTM), hand lay up fiber reinforced plastics, and filament winding fiber reinforced plastics, etc. 1 • 2 Recently, the processing of thermosetting unsaturated polyester resins has received increasing attention from industry, especially from the automotives and aerospace industries.Curing of unsaturated polyester resins generally involves the transformation of low molecular weight amorphous solids by means of chemical reactions. The curing process is of particular importance in the making of structural composites, coatings, adhesives, and electronic encapsulants. An useful framework for understanding and conceptualizing the changes that occur during cure of a thermostting system is the isothermal time-temperature-transformation curves. 3 The curing of styrene-unsaturated polyester resins is a free radical polymerization. The reaction of styrene with unsaturated polyester includes not only kinetic reaction but also gelation and network formation. Several researchers 4 • 5 reported that before gelation "microgel" structure formed through intra-molecular cross-linking among the pendant C = C bonds of the polyester molecule. As the polymerization proceeds, the microgel particles growth both in particle sizes and numbers and the system gelled at a critical conversion where the microgel particles started to overlap. After gelation the termination between the free radical polymer chains becomes diffusion controlled, the rate coefficient for termination begins to decrease markedly and the reaction rate increases rapidly. During curing the glass transition temperature (T 8 ) of the system increases. As T 8 becomes higher than the cure temperature, the polymer network goes into the glassy state and the diffusion of monomer molecules in the polymer d...

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“…On the other hand, T g gradually increased by the heating treatment at 150 °C and 170 °C. According to the literature, [24,25] the T g for crosslinked polymers was associated with the degree of cross-linking reaction or the molecular weight between the cross-links. The swelling tests and time-resolved rheology clearly indicated the formation of cross-linked structures at these conditions, which indicated the correlation with the increase in T g .…”

Section: Variation Of Thermal and Mechanical Propertiesmentioning

confidence: 99%

Seamless, Self‐Transformation of Thermoplastic Polyesters into Vitrimers Through Bond Exchange‐Triggered Cross‐Linking

Isogai,

Hayashi

2024

Macromol. Rapid Commun.

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In this study, a seamless, self‐transformation system of linear thermoplastic polyesters into the sustainable cross‐linked polymers, vitrimers, is demonstrated. The key is the use of polyesters bearing abundant hydroxyl side groups, which are synthesized via the reaction using dithiol molecules bearing ester units and diepoxy molecules. The polymerization reaction progresses efficiently at relatively low temperature due to the click nature of the thiol‐epoxy reaction, which provides the hydroxyl side groups along the polyester chain. The tin catalyst (stannous octoate) is added in the initial polymerization, and the catalyst also works to cross‐link the polyesters via intermolecular transesterification bond exchange simply by heating at high temperatures. By adjusting the degrees of cross‐linking, the mechanical properties as well as the thermal properties are well tuned. The bond exchange can still be activated in the final cross‐linked sample; and thus, the material behaves as vitrimers, exhibiting mechanical recyclability. The application of a new type of hot melt adhesive, where the post‐coating tuning/enhancement of adhesion strength is realized, is also demonstrated. On the whole, the present system is very simple but proposes a new application window of bond exchange concept into self‐transformation polymers.

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Glass Transition Temperature, Free Volume, and Curing Kinetics of Unsaturated Polyester

Cited by 13 publications

References 16 publications

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

Glass Transition Temperature Profile of the Curing Reaction of Unsaturated Polyester Resin

Seamless, Self‐Transformation of Thermoplastic Polyesters into Vitrimers Through Bond Exchange‐Triggered Cross‐Linking

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