Bulk and Thin Film Morphological Behavior of Broad Dispersity Poly(styrene-b-methyl methacrylate) Diblock Copolymers

Fine control of the molecular weight and polymer dispersity via a latent monomeric retarder

A latent monomeric retarder was used for a one-shot polymerization with a defined MW and Đ.

Block copolymers containing stable radical and fluorinated blocks with long-range ordered morphologies prepared by anionic polymerization

We report a facile synthetic approach to create stable radical block copolymers containing a secondary fluorinated block via anionic polymerization using a bulky, sterically hindered countercation composed of a sodium ion and di-benzo-18-crown-6 complex. The synthetic conditions described in this report allowed for controlled molecular weights and dispersity (<1.3) of both homopolymers: poly(2,2,6,6-tetramethyl-1-piperidinyloxy-methacrylate) (PTMA) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as well as their block copolymers (PTMA-b-PTFEMA). The stable radical concentration of the polymers was determined by electron spin resonance (ESR) and showed radical content above 70%. An analysis of the microphase morphologies in PTMA-b-PTFEMA thin films via atomic force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS) showed clear evidence of long-range ordering of lamellar and cylindrical morphologies with 32 and 36 nm spacing, respectively. The long-range ordering of the morphologies was developed with the aid of two separate neutral layers: PTMA-ran-PTFEMA-ran-poly(hydroxyl ethyl methacrylate) (PHEMA) and poly(isobutyl methacrylate) (PiBMA)-ran-PTFEMA-ran-PHEMA, which helped us corroborate, along with the Zisman method, the surface energy estimation of PTMA to be 30.1 mJ/m2.

Self-assembly of highly asymmetric, poly(ionic liquid)-rich diblock copolymers and the effects of simple structural modification on phase behaviour

A series of ATRP-synthesized poly(IL) diblock copolymers exhibit morphological phase behavior with shifted phase boundaries and alkyl substituent dependent segregation.

Dispersity and architecture driven self-assembly and confined crystallization of symmetric branched block copolymers

Architectural variety in the form of branching combined with disparate dispersities in block polymers have been exploited to access microphase morphologies outside the conventional phase windows typically observed in uniform linear analogs.

Molecular Weight Distribution Shape as a Versatile Approach to Tailoring Block Copolymer Phase Behavior

The molecular weight distributions (MWDs) of block copolymers significantly impact their morphological phase behavior, but exploiting these features as a means to tune material properties has been limited to the MWD breadth, or dispersity (Đ). Manipulation of the entire MWD has promising potential to address this challenge by providing a convenient and versatile route toward tailoring polymer nanostructure. Herein, we describe the self-assembly of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) where the PS blocks have systematically deviating compositions of molecular weights. We find that controlling the MWD shape, breadth and skew, afforded access to different morphologies in samples with the same molecular characteristics, including Đ. As such, we illustrate the generality and effectiveness of this strategy and anticipate that it will facilitate the increased deployment of disperse polymer compositions in advanced materials applications.

Domain swelling in ARB-type triblock copolymers via self-adjusting effective dispersity

We investigated the domain spacing of an ordered structure formed by polydisperse ARB-type triblock copolymers (triBCPs) with random middle R blocks consisting of A and B monomers. ARB-type triBCPs were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, and the dispersities of all samples were controlled as narrow as ∼1.2. From the bulk and film morphologies, it was found that the domain swelling increases as the content of middle R blocks increases, which implies that the middle R block even with a small content plays a critical role in dilating the domain spacing. Since the random middle R blocks are energetically neutral, they can be segregated into either A or B blocks. The strong stretching theory (SST) suggests that the dispersities of the resulting constituent blocks are maximized to reduce the elastic energy associated with chain stretching, thereby leading to the dilation of domain spacing.

Dispersity under Scrutiny: Phase Behavior Differences between Disperse and Discrete Low Molecular Weight Block Co-Oligomers

An experimental study is presented in which we compare the bulk phase behavior of discrete and (partially) disperse diblock co-oligomers (BCOs) with high χ-low N. To this end, oligomers of dimethylsiloxane (oDMS) and lactic acid (oLA) were synthesized, each having either a discrete number of repeat units or a variable block length. Ligation of the blocks resulted in oDMS-oLA BCOs with dispersities ranging from <1.00001 to 1.09, as revealed by mass spectroscopy and size exclusion chromatography. The phase behavior of all BCOs was investigated by differential scanning calorimetry and small-angle X-ray scattering. Compared to the well-organized lamellae formed by discrete oDMS-oLA, we observe that an increase in the dispersity of these BCOs results in (1) an increase of the stability of the microphase-segregated state, (2) a decrease of the overall degree of ordering, and (3) an increase of the domain spacing.

Application of Bottlebrush Block Copolymers as Photonic Crystals

Brush block copolymers are a class of comb polymers that feature polymeric side chains densely grafted to a linear backbone. These polymers display interesting properties due to their dense functionality, low entanglement, and ability to rapidly self-assemble to highly ordered nanostructures. The ability to prepare brush polymers with precise structures has been enabled by advancements in controlled polymerization techniques. This Feature Article highlights the development of brush block copolymers as photonic crystals that can reflect visible to near-infrared wavelengths of light. Fabrication of these materials relies on polymer self-assembly processes to achieve nanoscale ordering, which allows for the rapid preparation of photonic crystals from common organic chemical feedstocks. The characteristic physical properties of brush block copolymers are discussed, along with methods for their preparation. Strategies to induce self-assembly at ambient temperatures and the use of blending techniques to tune photonic properties are emphasized.

Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers

We demonstrate through isomeric effect the modulation of thermal properties of poly(hydroxystyrene) (PHS)-based block copolymers (BCPs). A minimal structural change of substituting 3HS for 4HS in the BCP results in a drastic decrease in T_g, which in turn enables the thin film assembly of the BCP via thermal annealing. We synthesized a series of poly(3-hydroxystyrene-b-tert-butylstyrene) [P(3HS-b-tBuSt)] and poly(4-hydroxystyrene-b-tert-butylstyrene) [P(4HS-b-tBuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS monomer and tBuSt followed by deprotection. Measured T_g of P(3HS) was ∼20-30 °C lower than P(4HS) of comparable molecular weights. As a result, thermally driven self-assembly of P(3HS-b-tBuSt) BCPs in both bulk and thin film is demonstrated. For P(4HS-b-tBuSt) thermal annealing in thin-film at high temperatures results in poorly developed morphology due to cross-linking reaction of the 4HS block. The smallest periodicity observed for P(3HS-b-tBuSt) was 8.8 nm in lamellar and 11.5 nm in cylindrical morphologies. The functionality of the 3HS block was exploited to incorporate vapor phase metal oxide precursors to generate sub-10 nm alumina nanowires.

How does dense phase CO2 influence the phase behaviour of block copolymers synthesised by dispersion polymerisation?

Using a CO₂ continuous phase for dispersion synthesis of block copolymers can provide a useful handle to control phase behaviour.

Microphase separation in thin films of lamellar forming polydisperse di-block copolymers

Effects of polydispersity in chain lengths on microphase separation in thin films of di-block copolymers are studied using self-consistent field theory (SCFT) and neutron reflectivity experiments.

Phase Behavior of Tapered Diblock Copolymers from Self-Consistent Field Theory

Tapered diblock copolymers are similar to AB diblock copolymers, but the sharp junction between the A and B blocks is replaced with a gradient region in which composition varies from mostly A to mostly B along its length. The A side of the taper can be attached to the A block (normal) or the B block (inverse). We demonstrate how taper length and direction affect the phase diagrams and density profiles using self-consistent field theory. Adding tapers shifts the order-disorder transition to lower temperature versus the diblock, and this effect is larger for longer tapers and for inverse tapers. However, tapered systems' phase diagrams and interfacial profiles do not simply match those of diblocks at a shifted effective temperature. For instance, we find that normal tapering widens the bicontinuous gyroid region of the phase diagram, while inverse tapering narrows this region, apparently due to differences in polymer organization at the interfaces.

3-[1-(4-Bromo-phen-yl)eth-oxy]-2,2,5-trimethyl-4-phenyl-3-aza-hexa-ne

The title compound, C22H30BrNO, is an alk-oxy-amine compound, an effective initiator in nitroxide-mediated free radical polymerization. It was prepared as a mixture of two diasteromers; the crystal for the X-ray analysis showed one of these as a pair of R,S and S,R enanti-omers. The tert-butyl and isopropyl groups are in an almost anti conformation in the crystal [C-N-C-C torsion angle = -168.8 (1)°], and the methyl group of the ethoxy group is in an approximate anti relationship to the tert-butyl group. The dihedral angle between the phenyl and benzene rings is 33.12 (7)°. The Br atom is disordered over two positions, with occupancies of 0.9139 (16) and 0.0861 (16). In the crystal, weak C-H⋯Br contacts link the mol-ecules into chains along [-110].

Highly ordered dielectric mirrors via the self-assembly of dendronized block copolymers

Dendronized block copolymers were synthesized by ruthenium-mediated ring-opening methathesis polymerization of exo-norbornene functionalized dendrimer monomers, and their self-assembly to dielectric mirrors was investigated. The rigid-rod main-chain conformation of these polymers drastically lowers the energetic barrier for reorganization, enabling their rapid self-assembly to long-range, highly ordered nanostructures. The high fidelity of these dielectric mirrors is attributed to the uniform polymer architecture achieved from the construction of discrete dendritic repeat units. These materials exhibit light-reflecting properties due to the multilayer architecture, presenting an attractive bottom-up approach to efficient dielectric mirrors with narrow band gaps. The wavelength of reflectance scales linearly with block-copolymer molecular weight, ranging from the ultraviolet, through the visible, to the near-infrared. This allows for the modulation of photonic properties through synthetic control of the polymer molecular weight. This work represents a significant advancement in closing the gap between the precision obtained from top-down and bottom-up approaches.