Tuning Mesoporosity in Cross-Linked Nanostructured Thermosets via Polymerization-Induced Microphase Separation

Abstract

Using the synthetic approach of polymerization-induced microphase separation (PIMS), we prepared cocontinuous and cross-linked nanostructured monoliths from bulk polymerizations of styrene and divinylbenzene (DVB) in the presence of polylactide macro-chain-transfer agents (PLA-CTAs). The resulting monolithic precursors were converted to cross-linked mesoporous materials following hydrolytic degradation of the PLA domain, the morphology and porosity of which were characterized through a combination of small-angle X-ray scattering, scanning electron microscopy, and nitrogen sorption experiments. This report highlights the concept, functionality, and limitations of PIMS for the generation of mesoporous materials through variation of reaction parameters found to strongly influence the porous properties of the matrix: the cross-linker-to-monomer ratio, reaction temperature, molar mass and mass fraction of PLA-CTA, and the reactivity of the DVB isomer. Increases in the cross-linker-to-monomer ratio (≥40 mol % DVB) induced formation of smaller mesopores within the matrix in addition to the principal pore mode largely defined by the molar mass and mass fraction of the PLA-CTA. Higher reaction temperatures and the increased relative reactivity of the p-DVB isomer are shown to influence the matrix integrity, ultimately achieving surface areas as high as 796 m2 g–1 using 8 kg mol–1 PLA-CTA. In combination, these parameters suggest methods to circumvent limitations of pore collapse associated with concomitant reductions in the molar mass of PLA-CTA.

Nanostructure Control in 3D Printed Materials

“…As such, it appeared that increasing the mac-roCTA weight percentage insignificantly affected the macroCTA domain lengths. This data is consistent with the literature, [26,52] which report that the characteristic length scale of the macroCTA domains in bicontinuous morphologies are primarily influenced by the macroCTA molecular weight and the cross-linker concentration. Tanδ profiles of the 3D printed objects using 28.2 wt% and 43.9 wt% PBA 48 -CTA showed two distinct peaks at −31 and 80 °C, which are attributed to the glass transitions of the PBA-rich phase and the net-P(AA-stat-PEGDA) phase, respectively (Figure S8, Supporting Information).…”

Control of porosity in hierarchically porous polymers derived from hyper‐crosslinked block polymer precursors

“…A significant reduction in pore size was observed in the HPPs with high DVB content, that is, HPP(50‐0‐50) and HPP(67‐0‐33). They also showed much narrower pore size distributions, which was consistent with the literature …”

“…(a)], and was consistent with the disordered bicontinuous morphology generated by the PIMS process. As the molar fraction of DVB decreased, however, a sharper principal peak was observed with a shift in q * towards a lower q , indicating the increased order and domain spacing ( d ) of the bicontinuous morphology, as reported in the literature . A scaled SAXS plot based on the intensity and the position of the principal peaks showed the highest order was achieved at 10 mol % DVB fraction, and reducing the DVB content further produced some heterogeneity, as evidenced by the increase in the scattering intensity at low q in the case of BPP(95‐0‐5) (Supporting Information, Fig.…”

Nanoporous Thermosets with Percolating Pores from Block Polymers Chemically Fixed above the Order–Disorder Transition

“…The removal of PLA was accompanied by a dramatic change of the SAXS pattern of the samples cross-linked below T ODT (Δ T < 0) with a total loss of the scattering characteristic of the lamellar ordering, likely due to the collapsing of the nanoporous structure ( T curing = 160 °C, Δ T = −18 °C, Figure 3 a, dashed line, and T curing = 170 °C, Δ T = −8 °C, Figure S27a ), consistent with previous reports of partial collapsing in nanoporous lamellar microstructure. 29 , 30 Conversely, for all the samples cross-linked above 180 °C, the SAXS patterns retain a broad reflection post etching consistent with a disordered structure ( T curing = 190 °C, Δ T = +12 °C, Figure 3 c, dashed line, and T curing = 200 °C, 210 °C, and 220 °C, Δ T = +22 °C, +32 °C, and +42 °C, Figure S27c–e ) and the domain spacing is within 9–14% of the spacing prior to etching ( Table S10 ). The dramatic difference in stability for the porous microstructures obtained from samples cross-linked above and below T ODT is likely due to a difference in terms of the continuity of their porous network.…”