The Order–disorder Transition Temperature Research Articles

Amphiphilic olefin block copolymers synthesized by successive coordinative chain transfer and ring-opening polymerizations

Introducing polarity is a necessity for widening the application scope of polyolefins specifically for developing biocompatible products. To this end, we exploit a two-step polymerization process to synthesize poly(ethylene‑b‑caprolactone) PE‑PCL block copolymers, which contain both polar and non-polar segments. First ethylene is polymerized by a generic metallocene catalyst in the presence of ZnEt2 as the chain transfer agent according to the coordinative chain transfer polymerization (CCTP) technique. Terminal zinc atoms are subsequently replaced by hydroxyl groups (PE‑OH) by exposing dormant polymer chains to oxygen. Afterward, ring-opening polymerization (ROP) of ε‑caprolactone is initiated by PE‑OH to form PE‑PCL block copolymers. Successful formation of both blocks is verified by FTIR and NMR spectroscopy. The presence of PCL blocks greatly lowers the crystallinity of ethylene sequences according to XRD and DSC results. Moreover, a second type of PE crystals with more chain folds and lower lamella thickness is found in block copolymers, which is absent in the equivalent physical blend. The diverse crystal structure of block copolymers suggest that phase separation exists between PE and PCL segments. The SEM image of the equivalent physical blend confirms the tendency of PCL and PE chains to phase separate, and infers a compatibilization in the presence of PE‑PCL block copolymers. This phase separation is detected by rheological measurements, as well, where block copolymers show deviations from Maxwell behavior in the terminal relaxation zone at low frequencies. Rheology results also show that the order-disorder transition temperature (TODT) of these block copolymers is higher than 180 °C. These results provide a clear picture from the morphology and utility of such block copolymers specifically for compatibilizing blends of polar polymers and non-polar polyolefins, which significantly broaden the utility of polyolefins.

Order-to-Disorder Transition of Cylinder-Forming Block Copolymer Films Confined within Neutral Interfaces

We present the phase behavior of cylinder-forming block copolymer (BCP) films confined within neutral interfaces through theory and experiment. The Langevin field-theoretic simulation (L-FTS) is utilized to account for the compositional fluctuation effect on the order-to-disorder transition (ODT), and the ultraviolet divergence in the L-FTS result is eliminated by renormalization of the Flory–Huggins parameter χ, allowing accurate comparison of thickness-dependent (χN)ODT, where N is the polymerization index. The L-FTS is accelerated by utilizing a deep learning method, and we managed to achieve a 50–60% reduction in simulation time. The L-FTS results show that (χN)ODT decreases as the film thickness decreases at a very large value of the invariant polymerization index N̅, and BCPs undergo a phase transition from disordered to cylindrical phases through a spherical phase as predicted by the self-consistent field theory calculation. By performing the L-FTS at experimentally relevant low N̅, we show that the BCPs undergo a direct transition from disordered to cylindrical phases, and the (χN)ODT value of cylinder-forming BCPs confined within neutral interfaces increases as the film thickness decreases. To verify and complement the theoretical results, we investigate the ODT temperature (TODT) of cylinder-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films supported on a neutral mat of P(S-r-2VP) random copolymers using grazing-incidence small-angle X-ray scattering. Our film experiments with low-N̅ PS-b-P2VP confirm the direct transition from disordered to cylindrical phases and the decrease in TODT with decreasing thickness below the onset thickness above which the TODT levels off.

Influence of Charge Fraction on the Phase Behavior of Symmetric Single-Ion Conducting Diblock Copolymers.

A series of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)]-block-polystyrene (PsOEGMA-PS) diblock copolymers were synthesized as a model system to probe the effect of charge fraction on the phase behavior of charged-neutral single-ion conducting diblock copolymers. Small-angle X-ray scattering (SAXS) experiments showed that increasing the charge fraction does not alter the ordered phase morphology (lamellar) but increases the order-disorder transition temperature (TODT) significantly. Additionally, the effective Flory-Huggins interaction parameter (χeff) was found to increase linearly with the charge fraction, similar to the case of conventional salt-doped diblock copolymers. This indicates that the effect of counterion solvation, attributed to the significant mismatch between the dielectric constant of each block, provides the dominant effect in tuning the phase behavior of this charged diblock copolymer. We therefore infer that electrostatic cohesion (local charge ordering induced by Coulombic interactions), which is predicted to suppress microphase separation and lead to asymmetric phase diagrams, only plays a minor role in this model system.

Detection of the Order-to-Disorder Transition in Block Copolymer Electrolytes Using Quadrupolar 7Li NMR Splitting

The order-to-disorder transition temperature (TODT) in a series of mixtures of polystyrene-b-poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is identified by the disappearance of a quadrupolar 7Li NMR triplet peak splitting above a critical temperature, where a singlet is observed. The macroscopic alignment of ordered domains required to produce a quadrupolar splitting occurs due to exposure to the NMR magnetic field. Alignment is confirmed using small-angle X-ray scattering (SAXS). The TODT determined by NMR is consistent with that determined using SAXS.

Origins of low-symmetry phases in asymmetric diblock copolymer melts

Cooling disordered compositionally asymmetric diblock copolymers leads to the formation of nearly spherical particles, each containing hundreds of molecules, which crystallize upon cooling below the order-disorder transition temperature (TODT). Self-consistent field theory (SCFT) reveals that dispersity in the block degrees of polymerization stabilizes various Frank-Kasper phases, including the C14 and C15 Laves phases, which have been accessed experimentally in low-molar-mass poly(isoprene)-b-poly(lactide) (PI-PLA) diblock copolymers using thermal processing strategies. Heating and cooling a specimen containing 15% PLA above and below the TODT from the body-centered cubic (BCC) or C14 states regenerates the same crystalline order established at lower temperatures. This memory effect is also demonstrated with a specimen containing 20% PLA, which recrystallizes to either C15 or hexagonally ordered cylinders (HEXC) upon heating and cooling. The process-path-dependent formation of crystalline order shapes the number of particles per unit volume, n/V, which is retained in the highly structured disordered liquid as revealed by small-angle X-ray scattering (SAXS) experiments. We hypothesize that symmetry breaking during crystallization is governed by the particle number density imprinted in the liquid during ordering at lower temperature, and this metastable liquid is kinetically constrained from equilibrating due to prohibitively large free energy barriers for micelle fusion and fission. Ordering at fixed n/V is enabled by facile chain exchange, which redistributes mass as required to meet the multiple particle sizes and packing associated with specific low-symmetry Frank-Kasper phases. This discovery exposes universal concepts related to order and disorder in self-assembled soft materials.

Phase Behavior of Poly(2-vinylpyridine)-block-Poly(4-vinylpyridine) Copolymers Containing Gold Nanoparticles

We studied the phase behavior of the poly(2-vinylpyridine)-block-poly(4-vinylpyridine) copolymer (P24VP) containing gold nanoparticles, by rheometry, small-angle X-ray scattering, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Although both blocks of P24VP exhibited attractive interaction to gold precursors, unusual phase behavior was observed depending on the amount of gold nanoparticles. As the amount of gold nanoparticles increased, the order-to-disorder transition temperature (TODT) of P24VP with gold nanoparticles decreased first, then increased, and finally decreased again. To explain this phenomenon, we prepared two block copolymers: polystyrene-block-poly(2-vinylpyridine) copolymer (PS2VP) and polystyrene-block-poly(4-vinylpyridine) copolymer (PS4VP) containing gold nanoparticles. With increasing the amount of gold particles, the TODT of PS2VP increased continuously, whereas that of PS4VP gradually decreased. For PS4VP containing gold nanoparticles, because P4...

Effects of Tailored Dispersity on the Self-Assembly of Dimethylsiloxane–Methyl Methacrylate Block Co-Oligomers

The effect of dispersity on block polymer self-assembly was studied in the monodisperse limit using a combination of synthetic chemistry, matrix-assisted laser desorption ionization spectroscopy, and small-angle X-ray scattering. Oligo(methyl methacrylate) (oligoMMA) and oligo(dimethylsiloxane) (oligoDMS) homopolymers were synthesized by conventional polymerization techniques and purified to generate an array of discrete, semidiscrete, and disperse building blocks. Coupling reactions afforded oligo(DMS-MMA) block polymers with precisely tailored molar mass distributions spanning single molecular systems (Đ = 1.0) to low-dispersity mixtures (Đ ≈ 1.05). Discrete materials exhibit a pronounced decrease in domain spacing and sharper scattering reflections relative to disperse analogues. The order-disorder transition temperature (TODT) also decreases with increasing dispersity, suggesting stabilization of the disordered phase, presumably due to the strengthening of composition fluctuations at the low molar masses investigated.

Phase Structure of the Exact Graft Copolymer Synthesized by Iterative Methodology Based on Living Anionic Polymerization

Exact graft copolymer (EGC) is a type of copolymer with precisely defined molecular parameters, including the number of grafts per molecule (n), the length of the grafts (lg), and the separation distance between the junction points (ε) in the backbone. In the present study, the phase structure of the EGC composed of poly(2‐vinyl pyridine) backbone and polystyrene graft with n = 2 and n = 3 under fixed ε and lg is systematically investigated to seek a general understanding on the effect of the graft architecture on the domain spacing of the microphase‐separated structure and the order–disorder transition temperature (TODT). It is found that the TODT associated with the fluctuation‐induced ODT of the EGC increases with increasing n due to the increase of the total molecular weight. Nevertheless, the domain spacing does not exhibit a monotonic change with n, as the EGC with n = 2 shows the largest domain spacing compared with that of EGC with n = 3 and the corresponding linear diblock copolymer. The experimental observation on the domain spacing is explained by a thermodynamic model considering the packing mode of the constituting chains under the junction constraint. image

Improved self‐assembly of poly(dimethylsiloxane‐b‐ethylene oxide) using a hydrogen‐bonding additive

ABSTRACTBlock copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub‐10 nm nanopatterns in the growing field of directed self‐assembly for next generation lithographic applications. A library of PDMS‐b‐PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χ measured in our samples was 0.21 at 150 °C, which resulted in phase‐separated domains with periods as small as 7.9 nm, suggesting that PDMS‐b‐PEO is a prime candidate for sub‐10 nm nanopatterning. To suppress PEO crystallization, PDMS‐b‐PEO was blended with (l)‐tartaric acid (LTA) which allows for tuning of the self‐assembled morphologies. Additionally, it was observed that the order‐disorder transition temperature (TODT) of PDMS‐b‐PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self‐assembly. To understand the mechanism of this phenomenon, we present a novel field‐based supramolecular model, which describes the formation of copolymer‐additive complexes by reversible hydrogen bonding. The mean‐field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS‐b‐(PEO/LTA suprablock). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2200–2208

Birefringence Analysis of the Effect of Electric Fields on the Order–Disorder Transition Temperature of Lamellae Forming Block Copolymers

A detailed birefringence analysis of the effect of strong dc electric fields on the order–disorder transition temperature (TODT) of lamella forming block copolymers is reported. The setup presented here enabled the measurement of the TODT with high temperature resolution while the birefringence measurements were nondestructive and straightforward compared to alternative methods. A downward shift in the transition temperature was found for all samples upon application of the electric field. The data indicate that the dominating parameter that evokes the mixing of block copolymers when exposed to electric fields is the difference in dielectric permittivity Δϵ between the block copolymer constituents. The extent to which the TODT is shifted is furthermore influenced by the degree of polymerization N. Shifts in the transition temperature of up to 7 °C were found upon application of an electric field of 5 kV/mm.

Rheological Study of Order-to-Disorder Transitions and Phase Behavior of Block Copolymer–Surfactant Complexes Containing Hydrogen-Bonded Small Molecule Additives

Dynamic mechanical measurements were used to investigate the effect of small molecule additives on the order-to-disorder transitions (ODTs) of Pluronic, poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–PEO triblock copolymer surfactant melts. The small molecule additives contain multiple functional groups (carboxyl or hydroxyl), which selectively interact with the PEO component of Pluronic via hydrogen bonding, thereby effectively increasing χ of the system and leading to microphase separation in otherwise disordered melts. The ODTs of these Pluronic/small-molecule-additive complexes can be detected by rheology since, upon increasing temperature, crossing the order-to-disorder transition temperature (TODT) results in a sharp decrease in the low frequency storage and loss moduli (G′ and G″, respectively). The crystallization of the PEO component is suppressed with increasing additive loading due to strong hydrogen bond interactions. The TODT is strongly composition dependent and increases up to 145 °...

Phase behavior and ionic conductivity of dendron–coil–dendron block copolymer/ionic liquid electrolytes

In this paper, we report the thermal, morphological, lower critical solution temperature (LCST), and ion-conducting properties of electrolytes based on a dendron–coil–dendron block copolymer (BCP) and ionic liquids (ILs). The BCP consists of ionophilic poly(ethylene oxide) middle and ionophobic dendron ends with crystalline octadecyl peripheries. The two ILs that were employed, 1,2-dimethyl-3-propylimidazolium tetrafluoroborate ([PMMIM][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), had identical molecular weights but different molecular structures in the imidazolyl cation. Electrolyte (1) with [PMMIM][BF4] exhibited crystalline lamellar and disordered micellar phases as a function of temperature. On the other hand, electrolyte (2) with [BMIM][BF4] showed an additional ordered hexagonal columnar liquid crystalline (LC) phase in between the crystalline lamellar and the disordered micellar phases. Infrared absorption studies suggest that the induction of the ordered LC phase is attributed to the strong hydrogen-bonding between PEO and [BMIM]. Furthermore, it was found that electrolyte (2) suddenly started to become turbid near the order-to-disorder transition temperature (TODT). This indicates that the LCST of 2 is identical to the TODT, above which liquid–liquid separation occurred gradually. The ionic conductivity curve of 1 increased continuously as the temperature increased. In contrast, 2 displayed a sudden drop in conductivity upon changing from the crystalline lamellar to the columnar phase, which was due to the variation of the ionophilic domain dimensionality from two to one. The calculated activation energy for ionic conduction in each phase was revealed to be affected by the translational motion and polarity of the ion-carrying medium.

Directed Assembly of Lamellae Forming Block Copolymer Thin Films near the Order–Disorder Transition

The impact of thin film confinement on the ordering of lamellae was investigated using symmetric poly(styrene-b-[isoprene-ran-epoxyisoprene]) diblock copolymers bound by nonpreferential wetting interfaces. The order-disorder transition temperature (TODT) and the occurrence of composition fluctuations in the disordered state are not significantly affected by two-dimensional confinement. Directed self-assembly using chemical patterning is demonstrated near TODT. These results establish the minimum feature size attainable using directed self-assembly of a given diblock copolymer system.

Orientation-Dependent Order-Disorder Transition of Block Copolymer Lamellae in Electric Fields.

Electric fields have been shown to stabilize the disordered phase of near-critical block copolymer solutions. Here, we use in situ synchrotron small-angle X-ray scattering to examine how the initial orientation of lamellar domains with respect to the external field (φ) affects the shift in the order-disorder transition temperature (TODT) of lyotropic solutions of poly(styrene-b-isoprene) in toluene. We find a downward shift of the transition temperature, which scales with lamellar orientation as ΔTODT ∼ cos2 φ, in accordance with theory.

Salt-induced microphase separation in poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer

In the present work, a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer was doped with LiClO4 at various salt concentrations. The morphology of the hybrids was characterized with time-resolved small-angle X-ray scattering (SAXS). It is observed that LiClO4 can induce microphase separation of the miscible PCL-b-PEO in the melt. With increase in doping ratio, the morphology of the hybrids changes from cylinder into lamella. The order–disorder transition temperature (TODT) and domain spacing increase with doping ratio in the low salt concentration range, but decrease at higher salt concentrations. FT-IR, UV and DSC results show that LiClO4 preferentially interacts with PEO at low doping ratios, but also associates with PCL at high doping ratios. The effective Flory–Huggins interaction parameters (χeff) for the hybrids were calculated. It is found that at low salt concentrations the χeff increases linearly with doping ratio due to selective interaction between PEO and LiCLO4, but the competitive interaction of LiClO4 with PCL and PEO at high salt concentration can lead to decrease of χeff.

Simulation study on the liquid‐crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3‐bis(azidomethyl) oxetane

AbstractThe liquid‐crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3‐bis(azidomethyl) oxetane] (BAMO) and 3‐nitratomethyl‐3′‐methyloxetane (NMMO) were investigated by the dissipative particle dynamics method. The results show that these copolymers, with moderate BAMO block lengths (x's), experienced the disorder, nematic, and smectic phases with decreasing temperature. The nematic phase was suppressed when the rod length was too long or short. After the formation of the smectic phase, the fluidity had a sharp decline. The temperature forming the smectic phase was defined as the order–disorder transition temperature (TODT) and depended strongly on x. A simple scaling rule, TODT ≈ e−x, between TODT and x was constructed. The effect of the soft NMMO block fraction on the fluidity emerged before the formation of the smectic phase. These results can help researchers design and synthesize new energetic copolymers with an appropriate melting temperature range for use as binders of solid propellants. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Order–Disorder Transition of Nanocomposites: Polystyrene-block-Poly(methyl methacrylate) with Palladium Nanoparticles

We studied how the palladium nanoparticles, (Pd)ns, incorporated into poly(styrene)-block-poly(methyl methacylate) (PS-b-PMMA) block copolymer (bcp), alter its order–disorder transition (ODT). The (Pd)ns were incorporated into the lamellar template of PS-b-PMMA by the thermal reduction of Pd(acac)2, dissolved uniformly in the bcp before the reduction, at 230 °C where both the neat PS-b-PMMA and the PS-b-PMMA incorporated with (Pd)ns (nanocomposite) are in the disordered state. The ODT behavior of the neat bcp and the nanocomposites are investigated by small-angle X-ray scattering as a function of temperature. We found that: (i) the average size and size distribution of (Pd)ns did not change at all during the heating and cooling processes across the ODT; (ii) the incorporation of a very small amount (1 wt %) of (Pd)ns significantly increased the ODT temperature (TODT) by ∼8 °C and the lamellar spacing D by ∼1%. These trends were found to be completely opposite to those previously reported on the (Pd)ns inc...

Thermorheological behavior of coexisting physical networks: combining SAFIN and SAMIN organogels

Organogels, like their hydrogel analogs in aqueous media, consist of chemically or physically cross-linked networks that endow simple (or even viscoelastic) organic liquids with solid-like characteristics. Of particular interest here are physical networks composed of either low-molar-mass organic gelators, which tend to form self-assembled fibrillar networks (SAFINs) by site-specific interactions such as hydrogen bonding and/or π–π stacking, or microphase-separated triblock copolymers, which form self-assembled micellar networks (SAMINs) due primarily to bridged midblocks that connect neighboring micelles. In this study, we combine these two physical networks by mixing the gelator 1,3:2,4-dibenzylidene-D-sorbitol with a series of midblock-swollen triblock copolymers differing in molecular weight to produce coexisting SAFIN/SAMIN networks in two midblock-selective solvents differing in polarity. The thermorheological properties of the resultant mixed network systems are investigated for three cases: (i) the order–disorder transition temperature (TODT) of the SAMIN is much lower than the dissolution temperature (Td) of the SAFIN, (ii) TODT < Td and (iii) TODT ≈ Td. Employing dynamic rheology, we show how these transitions are affected by the order in which self-organization occurs.

Manipulating ordering transitions in interfacially modified block copolymers

We report a synthetic strategy that allows us to manipulate the interfacial region between blocks and control ordering transitions in poly(isoprene-b-styrene) [P(I-S)] block copolymers. This interfacial modification is accomplished by combining a semi-batch feed with anionic polymerization techniques. Using this approach, we are able to control the segmental composition and molecular interactions in our phase-separated block copolymers, independent of molecular weight and block constituents. A library of copolymers is prepared with various interfacial modifications to examine the effect of interfacial composition on copolymer self-assembly. The morphological characteristics of the self-assembled structures are investigated using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and dynamic mechanical analysis (DMA). Normal and inverse tapered block copolymers, containing approximately 15–35 vol% tapered material, show a measurable decrease in the order–disorder transition temperature (TODT) relative to the corresponding non-tapered diblock copolymers, with the inverse tapered materials showing the greatest deviation in TODT. Additionally, TODT was inversely related to the volume fraction of the tapered region in both normal and inverse tapered copolymer materials.

Self-Assembled Poly(4-vinylpyridine)−Surfactant Systems Using Alkyl and Alkoxy Phenylazophenols

Para-substituted alkyl and alkoxy phenylazophenols (PAP’s) have been synthesized and used as hydrogen-bonded side chains for poly(4-vinylpyridine)-based comb-shaped supramolecules akin to the well-studied poly(4-vinylpyridine)/pentadecylphenol systems. In this paper we report the self-assembly of these new materials as investigated by DSC and simultaneous SAXS/WAXS. The systems exhibit smectic ordering with a periodicity in the range of 3.0−4.2 nm. The periodicity length scale, the order−disorder transition temperature (TODT), and the glass transition temperature Tg of the self-assembled systems all increase with increasing alkyl chain length. The correlation between TODT and Tg observed is argued to be the consequence of the increasing segregation in the self-assembled systems with increasing alkyl tail length of the amphiphiles.