Molecular Engineering of Nanostructures in Disordered Block Polymers

Abstract

A series of symmetric poly­(methyl methacrylate-stat-styrene)-block-polylactide (P­(MMA-s-S)-b-PLA) diblock terpolymers with nearly constant molar masses yet varying block interaction parameters were synthesized as a model system to probe the extent and utility of composition fluctuations in the disordered state. A combination of differential scanning calorimetry, dynamic mechanical analysis, and small-angle X-ray scattering revealed that a broad range of segregation strengths ranging from what we ascribe to essentially a mean-field disordered to a fluctuating disordered to an ordered system could be readily obtained by tuning the molar fraction of styrene in these diblocks. The P­(MMA-s-S)-b-PLA diblocks were annealed above their order–disorder transition temperatures (T ODT) and rapidly quenched to low temperatures to trap the disordered state via vitrification, as confirmed by scanning electron microscopy. Small-angle X-ray scattering and N2 sorption analysis post-removal of PLA demonstrated that a transition from a very weakly structured, mean-field-like melt to a bicontinuous fluctuating disordered state occurred with increasing segregation strength. This work demonstrates that the extent of microphase segregation as well as the domain continuity of the disordered block polymer melt can be tuned using both synthetic design and thermal stimuli, guiding the design of disordered block polymers with targeted nanostructures that have potential technological utility.

Nano- to macro-scale control of 3D printed materials via polymerization induced microphase separation

“…For all three loadings of PBA-CTA, the breadth of SAXS peaks increased with higher PBA-CTA X n , suggesting that materials 3D printed using higher PBA-CTA X n consisted of domains with less sharp compositional interfaces. To further examine this, the SAXS curves were fitted using the Teubner-Strey (T-S) model 47 – 49 , which has been broadly applied for structural analysis of phase-separated polymers 50 , 51 , including polymer materials prepared by PIMS approaches 44 . Three structural parameters are determined from the T-S model fitting: the domain spacing ( d TS ), the correlation length ( ξ ), and the amphiphilicity factor ( f a ).…”

Co-Casting Highly Selective Dual-Layer Membranes with Disordered Block Polymer Selective Layers

“…The SML block polymer used as the selective layer was synthesized by a reversible addition−fragmentation chain-transfer copolymerization of MMA and S from a PLA macro chain transfer agent following a previously reported procedure. 25 The diblock terpolymer architecture of SML-48 is appealing for the cocasting strategy outlined in this work as the segregation strength (χN) can be precisely tuned by adjusting the composition of the P(MMA-s-S) block. As a result, the disordered state can be readily accessed at temperatures appropriate for convenient membrane casting while still allowing the average pore size to be tailored for the intended application.…”

“…To demonstrate that porous materials could be produced from this diblock, a monolithic sample of SML-48 was annealed in the disordered state at 150 °C and rapidly quenched in liquid nitrogen to kinetically trap disordered state composition fluctuations. 25 Following quenching, the PLA domains were selectively removed by immersing the monolith in a 2 M solution of NaOH in H 2 O/MeOH (40/60 v/v) overnight at room temperature. Room-temperature SAXS of the etched monolith displayed an increase in the scattered intensity as compared to the unetched precursor, while the scattering vector of the principal scattering peak, q*, remained unchanged (Figure 1).…”

“…Previous work has reported average pore sizes ranging from 10−20 nm for SML block polymers with similar T ODT 's, where smaller pores are accessed by increasing the molar fraction of styrene and decreasing the overall molar mass. 25 Preparation and Characterization of As-cast Dual-Layer Membranes. The preceding sections have primarily utilized temperature as the stimulus for accessing the disordered state in the block polymer selective layer, where the selection of quench temperatures above T ODT resulted in segregation strengths, χN, that were lower than the critical value of approximately 10.5.…”

“…Recently our group has reported that the fluctuating disordered state in block polymers can be kinetically trapped by either cross-linking above the order–disorder transition (ODT) temperature ( T ODT ) or by rapidly cooling from above the T ODT to below the glass transition temperature ( T g ). − Upon the selective removal of one domain, a bicontinuous network of pores within a supporting glassy matrix was obtained. The resulting pores were shown to have a narrow size distribution, while their disordered and bicontinuous nature eliminated the need for domain alignment during UF membrane fabrication …”