Enhanced T_g-Confinement Effect in Cross-Linked Polystyrene Compared to Its Linear Precursor: Roles of Fragility and Chain Architecture

Abstract

The glass transition temperature (T g) of cross-linked polystyrene (PS) is directly compared to that of its linear precursor polystyrene-co-vinyl­benzo­cyclobutene (PS–VBCB) in bulk and confined states. The VBCB units incorporated into a linear PS precursor cross-link with one another upon annealing at 250 °C. Bulk T g (T g,bulk) is characterized by differential scanning calorimetry (DSC) and ellipsometry, with T g,bulk and T g breadth increasing with increased cross-linking. The T g-confinement effect is characterized by ellipsometry in supported PS–VBCB films before and after cross-linking; T g decreases with decreasing nanoscale thickness in both supported linear and cross-linked polymer films. The magnitude of the confinement effect is greater in cross-linked PS compared to linear precursors; e.g., with PS-VBCB containing 8.5 mol % VBCB, T g – T g,bulk = −2 to −3 °C for a 23 nm thick film of linear polymer whereas T g – T g,bulk = −8 to −9 °C after cross-linking. The larger T g reduction upon confinement in cross-linked PS is correlated with increased bulk fragility after cross-linking as measured by DSC and ellipsometry. Neat linear PS–VBCB copolymers provide an extension to lower fragility of the correlation between the T g-confinement effect and bulk fragility observed previously [ Evans Evans Macromolecules2013466091] for neat linear polymers lacking attractive polymer–substrate interactions; i.e., the strength of the T g-confinement effect increases with increasing bulk fragility. Both cross-linked PS and doped PS films deviate from the relationship for neat linear polymers, the former being weaker and the latter stronger. These results indicate that chain architecture and dopant content modify the relationship between the strength of the T g-confinement effect and bulk fragility observed in many neat, linear polymers.

A Europium(III) Complex with an Unusual Anion–Cation Interaction: A Luminescent Molecular Thermometer for Ratiometric Temperature Sensing

“…Confinement of complex 1 within a polysulfone membrane, 1‐PSU , reduces the complex mobility which hinders the anion‐cation interaction during heating. For the 1‐PSU film, the reduction in the emission intensity of Eu 3+ is not accompanied by any significant changes in the respective profile (Figure ) . In this case, the usually observed and commonly reported temperature‐dependent luminescence intensity was observed, with a linear fit from 60 to 120 °C and a quantum yield, φ, at room temperature, of 54 %.…”

Dependences of Confining Size and Interfacial Curvature on the Glass Transition of Polydimethylsiloxane in Self‐Assembled Block Copolymers

“…Interestingly, we find that when T g of PDMS increases in HEX, LAM, and GYR structures, the T g breadth ( T + – T − , while the T − is the onset of glass transition and the T + is the end point of glass transition) would also exhibit a significant increment, respectively. Jin and Torkelson recently compared the thickness dependence of T g breadth for linear polystyrene‐ co ‐vinylbenzocyclobutene (PS‐VBCB) films before and after cross‐linking, both samples exhibited an increase of T g breadth with decreasing film thickness . A smaller T g breadth in PC films with 635 nm thickness than that with 28 nm thickness is also investigated .…”

“…In Figure , we also find that all samples exhibit an increase of apparent T g breadth with decreasing confining size, which is in agreement with the former results of Torkelson, indicating an increase of apparent T g breadth with decreasing thickness of thin films. In addition, the T + exhibits a significant increase with decreasing confining size, while the T − exhibits only a slight increase with decreasing confining size.…”

“…Jin and Torkelson recently compared the thickness dependence of T g breadth for linear polystyrenecovinylbenzocyclobutene (PSVBCB) films before and after crosslinking, both samples exhibited an increase of T g breadth with decreasing film thickness. [26] A smaller T g breadth in PC films with 635 nm thickness than that with 28 nm thick ness is also investigated. [27] Kawana and Jones indicated that the PS thin films has a broadening of T g breadth with decreasing thickness measured by ellipsometry.…”

Partially bio‐based tri‐ and hexaallyl monomers: Synthesis from naturally occurringmyo‐inositol and polyaddition with dithiols

“…Networked polymers have been used as indispensable materials for a wide range of applications, including adhesives, sealants, and coatings . The synthesis of networked polymers relies on two major strategies: crosslinking of linear polymers with reactive side chains, and polymerization of multifunctional monomers, that is, molecules bearing multiple reactive groups . In the latter strategy, not only appropriate choices of reactive groups, but also their numbers, locations, and the structures of the core part to which those reactive groups are attached, are essential factors in designing multifunctional monomers.…”