A linear polyester was synthesized from furfural-based monomer through solvent-free polymerization using sunlight and the polymer structure was confirmed by a single crystal X-ray structure of a partially polymerized intermediate.
Two stereoregular 2D polyesters were synthesized by using topochemical polymerization of symmetric four-armed monomers. The monomers contain reactive carbon–carbon double bond(s) on each arm. The critical assemblies with multiple preorganized reactive centers were characterized by powder and single crystal X-ray diffraction. The solvent-free polymerization could be carried out with sunlight or UV irradiation. The locally confined photopolymerization process dimerized all of the olefins within the 2D bricklayer packing, which led to the formation of 2D polymers in the solid state. The process was monitored by FT-IR, and the products were confirmed by solid state NMR. After hydrolysis of the 2D polyester, the newly formed carbon–carbon single bonds during the [2 + 2] photocyclization were directly revealed by the single crystal structure of the hydrolysis product. Ultrathin sheets of the 2D polymer were observed under SEM and TEM after exfoliation.
Irreversible adsorption at polymer/substrate interfaces has been reported to influence glassy properties in thin films. However, consideration has yet to be extended to the nanocomposite geometry, wherein a large interfacial area and high processing temperatures afford especially favorable conditions for irreversible adsorption at the polymer/nanoparticle interface. Here, we present an approach for directly measuring the site-specific glassy properties at the polystyrene (PS)-adsorbed layer interface in PS−silica nanocomposites. We achieved this using a stepwise assembly approach to localize fluorescent dyes within the nanocomposite adsorbed layer, subsequently measuring the glass transition temperature (T g ) via fluorescence. We found that PS adsorption within nanocomposites strongly influenced the local T g . By measuring the thickness of the PSadsorbed layers atop nanoparticles via transmission electron microscopy, we found a correlation between adsorbed layer T g and thickness. Our results provide compelling evidence that adsorbed layer formation within polymer nanocomposites can have a profound impact on local interfacial properties.
While ultraviolet light is hailed for its renewability, nontoxicity, and lack of resulting waste products, photochemistry is relatively out of reach for many researchers and industries because conventional ultraviolet radiation sources are not always accessible. For example, the availability of sunlight varies with weather conditions, geographical location, and daylight duration. The use of commercial incandescent light as an alternative to conventional ultraviolet radiation was explored in this article. The classic [2 + 2] photocycloaddition of trans-cinnamic acid was tested under controlled conditions in the solid state, and it was found that 150 W light bulbs provided satisfactory results and 1.5 cm away from the light source was a viable distance for the photoreaction. A [2 + 2] cycloaddition of 10 mg trans-cinnamic acid finished in as few as 4 h. Gram-scale synthesis was also achieved in 40 h by using a 500 W floodlight bulb. The incandescent floodlight also effectively facilitated a cutting-edge photopolymerization in 24 h to produce a two-dimensional (2D) polymer. The use of reliable, inexpensive, and nonhazardous incandescent light in place of sunlight or even ultraviolet lamps for certain photoreactions will allow for the wider study and development of photochemistry.
Glassy polymer films with extreme stability could enable major advancements in a range of fields that require the use of polymers in confined environments. Yet, from a materials design perspective, we now know that the glass transition temperature (T g ) and thermal expansion of polymer thin films can be dramatically different from those characteristics of the bulk, i.e., exhibiting confinement-induced diminished thermal stability. Here, we demonstrate that polymer brushes with an ultrahigh grafting density, i.e., an ultradense brush morphology, exhibit a significant enhancement in thermal stability, as manifested by an exceptionally high T g and low expansivity. For instance, a 5 nm thick polystyrene brush film exhibits an ∼75 K increase in T g and ∼90% reduction in expansivity compared to a spin-cast film of similar thickness. Our results establish how morphology can overcome confinement and interfacial effects in controlling thin-film material properties and how this can be achieved by the dense packing and molecular ordering in the amorphous state of ultradense brushes prepared by surface-initiated atom transfer radical polymerization in combination with a self-assembled monolayer of initiators.
Polyladderane, the first polymer to contain the ladderane functional group, was synthesized from a gemini monomer through photoreaction in the solid state. The modular design of the gemini monomers used to create polyladderane allowed specific structural modification, resulting in the formation of two distinct polymer products. Monomers were synthesized by connecting two photoreactive units, either sorbic acids (monomer I) or 2-furanacrylic acids (monomer II), with a 1,4-butanediol linker. Single-crystal X-ray diffraction analysis of the monomers confirmed that they packed in the desired head-to-tail orientation and within a viable distance for photoreaction by electronically complementary interaction. Pre-organized gemini monomers were irradiated with UV light and monitored by FT-IR. Two polyladderanes with cis,anti,cis-[3]-ladderane as a characteristic functional group were constructed stereospecifically in 24-36 hours.
Annealing a supported polymer film in the melt state results in the growth of an irreversibly adsorbed layer, which has been shown to influence thin film properties such as diffusion and glass transition temperature. Adsorbed layer growth is attributed to many simultaneous interactions between individual monomer units and the substrate, stabilizing chains against desorption. In this study, adsorbed layers of polystyrene (PS), poly(methyl methacrylate) (PMMA), and their random copolymers are isolated by select solvents. While PS adsorbed layer thickness is largely unaffected by the choice of washing solvent, the PMMA adsorbed layer completely desorbs when washed with tetrahydrofuran and chloroform, as opposed to toluene. Scaling relationships between adsorbed layer thickness and degree of chain adsorption at the substrate enable the use of adsorbed layer thickness to probe specific polymer‐substrate interactions. Composition‐dependent desorption trends indicate non‐preferential adsorption between styrene and methyl methacrylate repeat units at the substrate, despite differences in substrate interaction strength. This insight contributes to the developing mechanism for the adsorption of random copolymers during melt‐state annealing, further extending the ability to predict processing‐inducted changes to the properties of polymer thin films to heterogeneous systems.
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