We report growing a polymer chain from the backbone of a bottlebrush polymer in the neat polymerization condition produces nanostructured polymer monoliths with ordered morphologies based on the Janus bottlebrush architecture. We installed a norbornene unit at the end of the polylactide macro-chain transfer agent (PLA-CTA) by single unit monomer insertion. We polymerized the resulting macromonomer via ring-opening metathesis polymerization to produce the PLA bottlebrush polymer, where a trithiocarbonate moiety remains on the backbone per every repeating unit. Neat polymerization of styrene in the presence of the PLA bottlebrush polymer proceeded in a grafting-from manner following the reversible addition–fragmentation chain transfer mechanism, resulting in a monolithic solid containing the doubly grafted PLA and polystyrene (PS) side chains. Polymerization-induced microphase separation (PIMS) spontaneously occurred, driven by the incompatibility between PLA and the growing PS segment. In contrast to the significant disordered fraction in PLA-b-PS produced with the linear PLA-CTA, the PLA/PS Janus bottlebrush polymer showed improved order across the investigated composition range. Formation of the asymmetric lamellae up to >80 vol % of PS indicated a strong preference for the lamellar symmetry of the Janus architecture. The in situ structured monoliths even exhibited narrower scattering peak widths compared to the solution-cast and annealed sample, suggesting the utility of the Janus PIMS process for facile preparation of ordered nanostructured materials with uniform domain size.

We report the synthesis and self-assembly of brush–linear diblock copolymers with variable side-chain length and density. Poly(pentafluorophenyl acrylate-g-ethylene glycol)-b-polystyrene ((PPFPA-g-PEG)-b-PS) brush–linear diblock copolymers are prepared by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization of PPFPA and PS, followed by postpolymerization reaction between the precursor PPFPA-b-PS diblock copolymer and amine-functionalized PEG. By controlling the PEG chain length and the degree of substitution, we obtained brush–linear diblock copolymers with different side-chain lengths and densities. The solid-state morphologies of the diblocks are then examined by small-angle X-ray scattering (SAXS). At low PEG side-chain density, the segregation of PEG and PS away from PPFPA leads to the formation of PEG and PS lamellar domains with PPFPA in the interface. At high PEG side-chain density, the segregation is between the PPFPA-g-PEG brush block and the PS linear block, and the domain morphology is determined by the composition of the brush block. A partial experimental phase diagram is presented, and it illustrates the importance of both side-chain length and density on the microdomain morphology of brush–linear diblock copolymers.

We report the synthesis of thiopropionic acid-functionalized polymethacrylate-b-polystyrene (PMATA-b-PS) as a template for patterning Ag nanoarrays. Reversible addition-fragmentation chain transfer (RAFT) polymerization of silyl-protected propagyl methacrylate followed by chain extension with styrene produced a block copolymer precursor. Deprotection of the trimethylsilyl group and subsequent thiol-yne reaction afforded the target, PMATA-b-PS. While the entire series of the precursor was in the disordered phase, microphase separated morphologies were identified from PMATA-b-PS, indicating an increased interaction parameter (χ) as a result of introducing the acid groups. As a preliminary result, we show that an Ag nanoparticle array can be fabricated by selectively associating Ag+ ions to the PMATA cylinders in the thin film of PMATA-b-PS and removing the organic polymer layer by oxygen plasma treatment.

We report that an alternating semifluorinated copolymer of chlorotrifluoroethylene (CTFE) and vinyl ether (VE) is an attractive platform for the synthesis of heterograft copolymers consisting of two distinct side chains. The radical terpolymerization of CTFE with PLA-tethered vinyl ether (PLAVE) synthesized by ring-opening polymerization and isobutyl vinyl ether (IBVE) as a spacer produced PLA-grafted fluorinated copolymer via a “grafting-through” manner. Two PLAVEs with different molar masses (2 and 10 kg mol–1) were successfully incorporated, and the grafting density could be controlled by varying the [PLAVE]/[IBVE] initial molar ratio. From the chlorine atoms in the CTFE repeating units, atom transfer radical polymerization (ATRP) of styrene was further employed to grow PS side chains following a “grafting-from” mechanism per each (CTFE-alt-VE) repeating unit dyad. First-order kinetics was observed for the styrene polymerization and supported controlled growth of PS. The resulting heterograft copolymers possessed regularly spaced PS chains and statistically distributed PLA chains on the backbone, generating a nanoscopic disordered morphology via microphase separation driven by incompatibility between PLA and PS. By copolymerization of styrene and divinylbenzene (DVB) in neat ATRP condition, a cross-linked polymer monolith with the disordered bicontinuous morphology could be also prepared via polymerization-induced microphase separation. The cross-linked precursor was converted into a mesoporous polymer with pore size of 3.7–10.4 nm by removal of PLA. The mesopore size was tunable by adjusting the PLA molar mass and styrene/DVB molar ratio.

We report a route to synthesize polylactide-b-poly(ether sulfone)-b-polylactide (PLA-b-PES-b-PLA) containing PES and PLA, which provide a mechanically robust framework and a sacrificial template for pore formation, respectively. High-molar mass PES terminated with fluorine groups was synthesized by the step-growth nucleophilic aromatic substitution (SNAr) reaction, and the chain ends were transformed into benzylic hydroxyl groups by chain end modification. Growth of the PLA using the hydroxyl groups as initiating sites via chain-growth ring opening transesterification polymerization (ROTEP) produced the target triblock copolymer. Although the step-growth polymerization produced a PES middle block with high dispersity, small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses indicated the formation of an ordered lamellar morphology. We further demonstrated that a nanoporous PES with slit-like pores could be obtained by selective removal of the PLA.

We investigated the microphase separation behavior of well-defined poly(arylene ether sulfone)-b-polylactide (PES-b-PLA) diblock copolymers. PES was synthesized by the nucleophilic aromatic substitution polymerization of 4-fluoro-4′-hydroxydiphenyl sulfone potassium salt in the presence of an allyl-functionalized initiator, which follows a chain growth condensation polymerization mechanism. A hydroxyl group installed via a thiol-ene reaction was utilized as the initiating site for the ring opening polymerization of d,l-lactide, producing the target polymer. The polymers were further purified by preparative size-exclusion chromatography and analyzed by small-angle X-ray scattering with temperature variations from room temperature to 150 °C. The PES block was glassy in the employed temperature range, but the PLA chains provided sufficient mobility for ordering of the block copolymer when PES was the minor fraction. An order-disorder transition (ODT) with changing temperature could not be located because PLA was not stable above 170 °C. From the degree of polymerization values of the polymers near the ODT, the Flory–Huggins interaction parameter, χ, could be roughly estimated as 0.12 at 150 °C. This high χ value suggests that engineering plastic-containing block copolymers could be useful in advanced lithographic and filtration applications.

A series of polystyrene‐b‐(poly(2‐(2‐bromopropionyloxy) styrene)‐g‐poly(methyl methacrylate)) (PS‐b‐(PBPS‐g‐PMMA)) and polystyrene‐b‐(poly(2‐(2‐bromopropionyloxy)ethyl acrylate)‐g‐poly(methyl methacrylate)) (PS‐b‐(PBPEA‐g‐PMMA)) as new coil‐comb block copolymers (CCBCPs) were synthesized by atom transfer radical polymerization (ATRP). The linear diblock copolymer polystyrene‐b‐poly(4‐acetoxystyrene) and polystyrene‐b‐poly(2‐(trimethylsilyloxy)ethyl acrylate) PS‐b‐P(HEA‐TMS) were obtained by combining ATRP and activators regenerated by electron transfer (ARGET) ATRP. Secondary bromide‐initiating sites for ATRP were introduced by liberation of hydroxyl groups via deprotection and subsequent esterification reaction with 2‐bromopropionyl bromide. Grafting of PMMA onto either the PBPS block or the PBPEA block via ATRP yielded the desired PS‐b‐(PBPS‐g‐PMMA) or PS‐b‐(PBPEA‐g‐PMMA). 1H nuclear magnetic resonance spectroscopy and gel permeation chromatography data indicated the target CCBCPs were successfully synthesized. Preliminary investigation on selected CCBCPs suggests that they can form ordered nanostructures via microphase separation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2971–2983

We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition–fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel–Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer.

Interfacial polymerization of an acid chloride-containing block polymer and a multivalent amine in the presence of a macroporous support was explored as a means to generate a nanoporous thin film composite (TFC) membrane potentially useful for ultrafiltration. When polylactide-b-poly(styrene-co-vinylbenzoyl chloride) (PLA-b-P(S-co-VBC)) in an organic phase and m-phenylenediamine (MPD) in an aqueous phase were used as the reactive block polymer and the amine, respectively, a block polymer thin film was successfully formed on a polysulfone support. This nanostructured film could be converted into a nanoporous layer by subsequent PLA etching under mild basic conditions. While most organic solvents used to dissolve PLA-b-P(S-co-VBC) damaged the support and decreased permeability of the resulting membrane, use of a mixture of methyl isobutyl ketone and acetonitrile produced a TFC membrane with high permeability.

Detailed experiments designed to optimize and understand the solvent vapor annealing of cylinder-forming poly(styrene)-block-poly(lactide) thin films for nanolithographic applications are reported. By combining climate-controlled solvent vapor annealing (including in situ probes of solvent concentration) with comparative small-angle X-ray scattering studies of solvent-swollen bulk polymers of identical composition, it is concluded that a narrow window of optimal solvent concentration occurs just on the ordered side of the order–disorder transition. In this window, the lateral correlation length of the hexagonally close-packed ordering, the defect density, and the cylinder orientation are simultaneously optimized, resulting in single-crystal-like ordering over 10 μm scales. The influences of polymer synthesis method, composition, molar mass, solvent vapor pressure, evaporation rate, and film thickness have all been assessed, confirming the generality of this behavior. Analogies to thermal annealing of elemental solids, in combination with an understanding of the effects of process parameters on annealing conditions, enable qualitative understanding of many of the key results and underscore the likely generality of the main conclusions. Pattern transfer via a Damascene-type approach verified the applicability for high-fidelity nanolithography, yielding large-area metal nanodot arrays with center-to-center spacing of 38 nm (diameter 19 nm). Finally, the predictive power of our findings was demonstrated by using small-angle X-ray scattering to predict optimal solvent annealing conditions for poly(styrene)-block-poly(lactide) films of low molar mass (18 kg mol–1). High-quality templates with cylinder center-to-center spacing of only 18 nm (diameter of 10 nm) were obtained. These comprehensive results have clear and important implications for optimization of pattern transfer templates and significantly advance the understanding of self-assembly in block copolymer thin films.

The viscosity of poly(styrene)-b-poly(lactide) [PS-b-PLA] solutions in a neutral solvent was characterized by magnetic microrheology. The effect of polymer concentration on the viscosity of the block polymer solutions was compared with that of the PS and PLA homopolymers in the same solvent. The viscosity of PS-b-PLA solution, unlike the homopolymer solutions, showed a steep increase over a narrow concentration range. The steep rise was concomitant with microphase separation into an ordered cylindrical microstructure as determined by small-angle X-ray scattering. Hence microrheology proved effective as a means of characterizing the order–disorder transition concentration. During an in situ drying experiment, changes in local viscosity through the depth of a block copolymer solution were characterized as a function of drying time. Early in the drying process, the viscosity rose steadily and was uniform through the depth, a result consistent with steadily increasing and uniform polymer concentration. However, later in the drying process as the overall polymer concentration approached that required for microphase separation, the viscosity of the polymer solution near the free surface became an order of magnitude higher than that near the bottom of the container. The zone of high viscosity moved downward as drying proceeded, consistent with a microphase separation front.