From Microphase Separation to Self-Organized Mesoporous Phenolic Resin through Competitive Hydrogen Bonding with Double-Crystalline Diblock Copolymers of Poly(ethylene oxide-b-ε-caprolactone)

Abstract

A series of immiscible crystalline–crystalline diblock copolymers, poly(ethylene oxide)-b-(ε-caprolactone) (PEO-b-PCL), were synthesized through ring-opening polymerization and then blended with phenolic resin. FT-IR analyses demonstrate that the ether group of PEO is a stronger hydrogen-bond acceptor with the hydroxyl group of phenolic resin than is the carbonyl group of PCL. Phenolic, after being cured with hexamethylenetetramine (HMTA), results in the excluded and confined PCL phase based on analyses by differential scanning calorimetry (DSC). This effect leads to the formation of a variety of composition-dependent nanostructures, including disorder, gyroid and short-cylinder structures. The self-organized mesoporous phenolic resin was found only at 40–60 wt % phenolic content by an intriguing balance of the contents of phenolic, PEO, and PCL. In addition, the mesoporous structure was destroyed at higher PCL/PEO ratios in the block copolymers, as determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) experiments. In addition, the large and long-range order of bicontinuous gyroid-type mesoporous carbon was obtained from mesoporous gyroid phenolic resin calcined at 800 °C under nitrogen.

Fabrication and Characterization of Inorganic Silver and Palladium Nanostructures within Hexagonal Cylindrical Channels of Mesoporous Carbon

“…Silver nitrate (AgNO 3 ) and palladium(II) nitrate dehydrate were purchased from Aldrich (St. Louis, MO, USA). The phenolic was synthesized through a condensation reaction with H 2 SO 4 , producing a material with an average molecular weight (M n = 500) similar to those described previously [6], EtOH (95%) and tetrahydrofuran (THF, >99%) were purchased from ECHO (Kaohsiung, Taiwan). Diblock copolymers were prepared through the ring-opening polymerization (ROP) of ε-CL in the presence of PEO 114 and Sn(Oct) 2 .…”

“…To prepare the mesoporous carbon, we first used a simple ring-opening polymerization (ROP) to synthesize an amphiphilic diblock copolymer PEO-PCL, with a specific weight ratio of each segment (EO 114 CL 84 ; NMR M n = 14,600; PDI = 1.31) [5,6]. Next, we combined the EO 114 CL 84 , phenolic resin, and PEO-POSS at a unique weight ratio (EO 114 CL 84 :phenolic resin:PEO-POSS = 50:50:22) and subjected the mixture to EISA and calcination steps to fabricate an hexagonal cylindrical mesoporous phenolic resin [9].…”

“…Evaporation-induced self-assembly (EISA) has been developed aggressively as a strategy for the fabrication of mesoporous nanostructures because of its broad applicability to soft templating using various block copolymer templates [1][2][3][4][5][6][7][8][9][10][11][12]. Prior to its development, the pore sizes of mesoporous carbons were limited to approximately 5-10 nm as a result of the need for copolymer templates of low molecular weight [13,14].…”

“…Prior to its development, the pore sizes of mesoporous carbons were limited to approximately 5-10 nm as a result of the need for copolymer templates of low molecular weight [13,14]. The EISA method made it feasible to regulate pore structures and pore sizes and allowed the preparation of various mesoporous materials from water-insoluble systems, including mesoporous silicas [2,7,8,10,[15][16][17][18], mesoporous resins [3,6,9,11], mesoporous TiO 2 [19][20][21], and mesoporous carbons [2,4,12,16,[22][23][24]. The typical procedure used to prepare ordered mesoporous carbons, so-called "template synthesis" [25][26][27][28][29][30], involves the use of mesoporous silicas as hard templates, impregnation of carbon precursors into their mesochannels, carbonization under an inert gas, and finally dissolving the hard template of the "ordered mesoporous silica" through etching in HF (aq) .…”

“…In previous studies, we employed EISA-with the diblock copolymer poly(ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) as the template, phenolic resin as the matrix precursor, and hexamethylenetetramine (HMTA) as the curing agent-to prepare a series of mesoporous phenolic resins [6]. Moreover, we blended in the star octakis-PEO-functionalized polyhedral oligomeric silsesquioxane (PEO-POSS) to induce higher ordering of the mesostructures as well as mesophase transformations of the mesoporous phenolic structures [9].…”