Microphase Separation Behavior Research Articles

Microphase separation of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) block copolymers induced by differential interactions with salt

This work describes the microphase separation behavior of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs), a type of new sulfur-containing block copolymer, induced by lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI). PPMTC-b-PEO BCPs with a fixed PEO block length but different PPMTC block lengths were synthesized and doped by LiTFSI. Temperature-variable small-angle X-ray scattering result indicates that microphase separation of the PPMTC-b-PEO BCPs can be induced by differential interactions with LiTFSI. However, the ability of LiTFSI to induce microphase separation in PPMTC-b-PEO BCPs does not monotonically increase with the doping ratio (r = [Li+]/([EO] + [PMTC])). It is observed that stronger microphase separation usually occurs at r = 1/12 and 1/6, but microphase separation is weaker at r = 1/24 and 1/3. In most cases, microphase-separated but disordered structures are obtained. Particularly, ordered lamellar structure is formed at suitable doping ratio and block composition. FTIR result confirms the differential complexation of LiTFSI with PEO and PPMTC. LiTFSI preferentially interacts with PEO at low rs, but also strongly interacts with PPMTC at high rs. This work provides a new method to prepare solid polymer electrolytes with double conductive nano-phases, which may be beneficial to both conducting and mechanical properties.

A comparison of non-isocyanate and HDI-based poly(ether urethane): Structure and properties

DMC-derived poly (ether urethanes) were prepared via isocyanate-free route. The transurethanization reaction of the non-isocyanate route needs higher temperature as compared with the traditional route. There may be some unknown side reactions under high temperature which lead to changes in chemical structure and subsequent thermal and mechanical properties of the novel DMC-derived non-isocyanate polyurethanes (NIPUs). Two 1,6-hexamethylene diisocyanate based polyurethanes (HDIPUs) were prepared as a control. HDIPUs possessed a higher melting point and better mechanical properties than NIPUs. In order to find out the causes of the difference in their thermal and mechanical properties, the structure, crystallization behavior, morphology and microphase separation behavior of NIPUs and HDIPUs were systematically studied and compared in this work. It was found that the structural distinction between NIPUs and HDIPUs was originated from the hard segments. The urea content in the hard segments of NIPUs was much higher than that of HDIPUs. The formation of urea groups was explained by the side reactions during the transurethanization process of NIPUs. Due to the random insertion of urea groups on the hard segments of NIPU, the strength of hydrogen bonding between hard segments and the crystallinity of the hard phase were lower than those of HDIPU. Therefore, the compatibility between the hard phase and the soft phase of NIPU was increased, resulting in poor thermal and mechanical properties.

Preparation and self-assembly of polyferrocenyldimethylsilane-containing tri- and pentablock terpolymers

Functional block copolymers (BCPs) featuring metal moieties are a unique class of materials because of their switching capabilities and pronounced microphase separation behaviour. Within this work, ABC and CBABC tri- and pentablock terpolymers consisting of polystyrene (PS), poly(1,1′-dimethylsilaferrocenophane) (PFS) and a third block segment C either consisting of poly(methyl methacrylate) (PMMA) or poly(2-vinylpyridine) (P2VP) were synthesized via sequential living anionic polymerization. Well-defined polymers having molar masses up to 90 kg mol−1 and low dispersity index values, Đ, below 1.10 were obtained. The multi-functional BCPs were characterized with respect to their constitution and composition by size-exclusion chromatography (SEC) measurements and NMR spectroscopy. Focus of this work was to study the microphase separation of the metal-containing tri- and pentablock terpolymers by (scanning) transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) measurements. Highly ordered structures at the nanoscale were observed comprising lamellar or cylindrical morphologies with more complex core-shell cylindrical morphologies for the organometallic block segment. This structure formation was more pronounced in case of P2VP-containing ABC terblock copolymers. Finally, synthetic approaches for the preparation of CBABC pentablock terpolymers were presented and the obtained bulk morphologies of these polymers were investigated by TEM and SAXS measurements.

Preparation of Fluorosilicone Triblock Copolymers and Microphase Separation Behavior on Surfaces

Fluorosilicone polymer is a new type of structure of the fluorine silicon block polymer. Because it combines the excellent properties of organic silicone and organic fluorine compounds, it has a wide range of uses and becomes a hot issue in the field of materials. In the paper, A series of novel poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-block-poly(dimethylsiloxane)-block-poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)s (PHFBMA-b-PDMS-b-PHFBMA) were synthesized by atom transfer radical polymerization (ATRP) with different molecular weight prepared polydimethylsiloxane macroinitiator as raw materials. The effects of the fluorine and silicone content on the hydrophobic and oleophobic properties of prepared triblock copolymers were also investigated. The structure and composition of the copolymers were analyzed and identified by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). The average molecular weight and molecular weight distribution of the prepared PHFBMA-b-PDMS-b-PHFBMA were evaluated by gel permeation chromatography (GPC). The surface energy of the triblock copolymers was calculated from the contact angle reaches as low as 10.43 mN/m through the Owens-Wendt-Rabel-Kaelble method, with the fluorine content of triblock polymer was 19.0 wt%. Atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) indicated that there were Obvious nanoscopically microphase separation on the surface of the prepared triblock copolymers and the fluoride contents in the block polymer of the fluorine silicon block were more likely to migrate to the surface.

Acoustic damping flexible polyurethane foams: Effect of isocyanate index and water content on the soundproofing

ABSTRACTHigh‐efficiency sound absorbing flexible polyurethane foams (FPUFs) are manufactured using nonpolar polyester resin, methylene diphenyl diisocyanate, and other reagents by one‐shot bulk polymerization. In this study, the impact of the isocyanate index (90, 100, and 110) and water content (2.5 and 5%) on the microphase separation and soundproofing behavior of FPUFs are examined using atomic force microscopy, Fourier transform infrared spectroscopy, optical microscope, and an impedance tube device. The results reveal that the increase of the isocyanate index and water content leads to the increase of the cell size, cell size distribution, open‐cell content, cell wall roughness, and microphase separation. Also, maximum sound absorption coefficient (α) reaches to 0.98 and the average of α in the frequency range of 1500–4000 Hz increases from 0.7 to 0.87 by increasing the water content from 2.5 to 5% and isocyanate index from 90 to 110; therefore, acoustic damping performance enhances up to 26.24% due to the synergic effects of microphase separation on the viscose media formation, open‐cell content, cell wall roughness, cell size, and cell size distribution. In conclusion, FPUFs with an optimal amount of microphase separation and drainage flow can be a promising candidate for sound insulating materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47363.

Chain-End Functionalization with a Saccharide for 10 nm Microphase Separation: “Classical” PS-b-PMMA versus PS-b-PMMA-Saccharide

Microphase-separated structures of block copolymers (BCPs) have attracted much attention as template materials for bottom-up nanofabrication. At the same time, chain-end modification has become a leading facile and efficient technique for fine-tuning the morphologies of microphase-separated structures generated from BCPs. Herein, we describe the preparation of well-defined polystyrene-block-poly(methyl methacrylate)s (PS-b-PMMAs) bearing highly hydrophilic mono/oligosaccharide moieties at their PMMA chain ends (SM-mono/oligosaccharides) as well as the impact of the mono/oligosaccharide on microphase separation behavior. PS-b-PMMAs were terminal-selectively transesterified using the titanium alkoxide of 6-azido-1-hexanol to introduce azido groups into the side chains of the terminal MMA units. The azido-functionalized PS-b-PMMAs were subsequently click reacted with ethynyl-functionalized mono/oligosaccharides to yield SM-mono/oligosaccharides. Small-angle X-ray scattering and microscopy experiments reveal ...

Hydrogen Bonding Aggregation in Acrylamide: Theory and Experiment

Hydrogen bonding plays a role in the microphase separation behavior of many block copolymers, such as those used in lithography, where the stronger interactions due to hydrogen bonding can lead to a smaller period for the self-assembled structures, allowing the production of higher resolution templates. However, current statistical thermodynamic models used in descriptions of microphase separation, such as the Flory–Huggins approach, do not take into account some important properties of hydrogen bonding, such as site specificity and cooperativity. In this combined theoretical and experimental study, a step is taken toward the development of a more complete theory of hydrogen bonding in polymers, using polyacrylamide as a model system. We begin by developing a set of association models to describe hydrogen bonding in amides. Both models with one association constant and two association constants are considered. This theory is used to fit IR spectroscopy data from acrylamide solutions in chloroform, thereby determining the model parameters. We find that models with two constants give better predictions of bond energy in the acrylamide dimer and more realistic asymptotic behavior of the association constants in the limit of high temperatures. At the end of the paper, we briefly discuss the question of the determination of the Flory–Huggins parameter for a diblock copolymer with one self-associating hydrogen bonding block and one non-hydrogen bonding block by means of fitting the scattering function in a disordered state.

Diblock Polymer Brush (PHEAA- b-PFMA): Microphase Separation Behavior and Anti-Protein Adsorption Performance.

In this paper, a series of amphiphilic diblock polymers of poly(hydroxyethylacrylamide)- b-poly(1H,1H-pentafluoropropyl methacrylate) (PHEAA- b-PFMA) were grafted from silicon wafer via surface-initiated atom transfer radical polymerization (SI-ATRP). Surface wettability and chemical compositions of the modified surfaces were characterized by contact angle goniometer and X-ray photoelectron spectroscopy (XPS) respectively. Molecular weight and polydispersity of each block were measured using gel permeation chromatography (GPC). The topography and the microphase separation behavior of PHEAA- b-PFMA surfaces were investigated by atomic force microscope (AFM). The results show that only when the grafting density (σ) and thickness of PHEAA brush were in the range of 0.9-1.3 (chain/nm2) and 6.6-15.1 nm, respectively, and the ratio of PFMA/PHEAA varied from 89/42 to 89/94, could the diblock copolymer phase separate into nanostructures. Further, the antiprotein adsorption performance of the modified surfaces against BSA, fibrinogen, and lysozyme was studied. The results indicated the modified surfaces could reduce the protein adsorption compared to the pristine silicon wafer. For Fibrinogen, the antiadsorption effect of PHEAA- b-PFMA-modified surfaces with microphase segregation was better than that of corresponding PHEAA modified surfaces. The results provide further evidence that surface composition and microphase segregation of fluorinated moieties of block copolymer brushes significantly impact protein adsorption behaviors.

Domain Structures of Poly(3-dodecylthiophene)-Based Block Copolymers Depend on Regioregularity

Microphase-separation behavior of conjugated–amorphous block copolymers (BCPs) is driven by a complex interplay between Flory–Huggins interaction (χ), liquid crystalline (LC) interaction, and crystallization. Herein, in order to elucidate the influence of LC interaction on the morphology of the BCPs, we report the effects of regioregularity (RR) on the microphase separation and molecular packing structures of poly(3-dodecylthiophene)-block-poly(2-vinylpyridine) (P3DDT-b-P2VP). To decouple the effect of LC interactions from crystallization kinetics, we investigate the morphological behavior of the P3DDT-b-P2VP at above the melting temperature of P3DDT (∼160 °C). Both electron microscopy and X-ray scattering show an abrupt reduction in the domain spacing of both lamellar and cylindrical phases as the RR of P3DDT block increases. Specifically, lower RR (i.e., 85, 79, and 70%) BCPs have larger domain spacings than high RR (94%) by 50% (lamellar) or 80% (cylindrical), even though the overall molecular weights ...

Circular assembly of colloidal nanoparticles at the liquid-air interface mediated by block copolymers.

The self-assembly of colloidal nanoparticles (NPs) mediated by block copolymers (BCPs) is an efficient way for fabricating nanocomposite superstructures with precise geometric control. Here we report a generalized liquid-air interfacial strategy by exploiting the versatility in tuning the specific affinities between the grafted polymeric ligands and BCPs, enabling the circular assembly of NPs on a liquid surface to afford unique ring-like superstructures. Fe3O4 NPs act as the model system; however, CoFe2O4 and Au NPs are also demonstrated using the proposed assembly method. Functionalizing NPs with a specific polymeric ligand is the key to achieve the circular assembly of NPs, while both the subphase and the solvent annealing temperature have profound influence on the microphase separation behaviors of BCPs and therefore the morphology of the resulting NP assemblies. Moreover, the co-assembly of two types of NPs grafted with distinct polymeric ligands enables unprecendented heterogeneous concentric rings, with each ring consisting of one type of NP.

Synthesis and microphase separation behavior of random, mixed cylindrical brush copolymers bearing polystyrene and poly(ε-caprolactone) side chains

A series of mixed, random cylindrical brush copolymers bearing polystyrene (PS) and poly(ε-caprolactone) (PCL) side chains were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). These novel cylindrical brush copolymers have been characterized by means of nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). It was found that the mikto-armed cylindrical brush copolymers were microphase-separated in bulks and that the morphologies were dependent on the mass ratios of PS to PCL side chains. One of the cylindrical brush copolymers was employed to incorporate into epoxy thermoset to investigate effect of the mikto-armed cylindrical brush architecture on the reaction-induced microphase separation behavior. Depending on the concentration of the cylindrical brush in epoxy, the thermosets can display the morphologies with the spherical, worm-like and lamellar PS microdomains dispersing in continuous thermosetting matrices.

Rheological characterization of nanostructured material based on Polystyrene-b-poly(ethylene-butylene)-b-polystyrene (SEBS) block copolymer: Effect of block copolymer composition and nanoparticle geometry

Block copolymer (BCP) nanocomposite systems are of broad interest; however, reports on the role of nanoparticles on microphase separation behavior are rare. The goal of present study is to investigate the preparation of composite nanostructured materials containing Multi-Walled Carbon Nanotubes (MWCNTs) or graphene nanoplates. BCP nanocomposites based on the linear triblock copolymer, Polystyrene-b-poly(ethylene-butylene)-b-polystyrene (SEBS), with different morphological structure were prepared by melt mixing. The results of temperature sweep experiments showed an enhancing effect of both MWCNT and graphene nanosheets on increasing the microphase separation temperature as well as accelerating its kinetic, resulting from the confinement of BCP segments, with graphene nanosheets providing a more severely confined geometry for polystyrene segments in contrast to MWCNTs. Additionally, DMTA results indicated a promotion of the BCP microphase separation by incorporation of nanoparticles. Transient flow measurements followed by time sweep test suggested the existence of a special 3D network microstructure caused by nanoparticles/domain interactions.

Microphase separation and crystallization behaviors of bi-phased triblock terpolymers with a competitively dissolved middle block

A series of poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-polystyrene (PCL-b-PnBA-b-PS) triblock terpolymers with fixed PCL and PnBA block lengths but different PS block lengths were prepared. In all of these triblock terpolymers the PnBA block can be competitively dissolved in both the PCL and PS phases to form bi-phase structures in the melt, as revealed by atomic force microscopy (AFM). Due to the “competitive dissolution effect” of the PnBA middle block, the microphase separation and crystallization behaviors of these triblock terpolymers are different from those of common diblock copolymers to some extent. As revealed by the Flory-Huggins parameters, more PnBA segments tend to dissolved in the PS phase. Therefore, the volume fraction of the PS-rich phase (fPS-rich) is evidently larger than the calculated volume fraction of the PS block (fPS), and the phase boundaries between two different structures shift to lower fPS. There also exists a thick interphase layer between the PS-rich and PCL-rich phases due to competitive dissolution of the PnBA block. However, confined crystallization can only occur at a larger fPS-rich, though the measured glass transition temperature (Tg) is high for the PS block. This can be attributed to a high fraction of the soft zone surrounding the PCL-rich phase and the lower volume fraction of the hard zone.

Cross-linked low dielectric nanoporous polycarbosilane derived from benzocyclobutene-containing poly(carbosilane)-b-polylactide block copolymer

Low dielectric materials show great application potential in future microelectronic industry. In this study, benzocyclobutene-functionalized polycarbosilane derived block copolymer, poly(carbosilane-b-lactide), was synthesized via sequential anionic polymerization of silacyclobutene and ring-opening polymerization of lactide. The block copolymer revealed microphase-separation behavior to form a well-defined morphology. Simultaneously, the sacrifice of polylactide blocks by thermal decomposition and thermally-induced reaction of benzocyclobutene produces cross-linked nanoporous polycarbosilane (PBCS). The dielectric constant of this nanoporous material reaches to around 2.1.

Photoalignment of Vertically Oriented Microphase Separated Lamellae in LC-LC Diblock Copolymer Thin Film.

The microphase separation and photoalignment behavior of a diblock copolymer consisting of two kinds of side chain liquid crystalline (LC) polymers are investigated. Here, the mesogens of photoresponsive azobenzene and non-photoresponsive cyanobiphenyl are introduced in the side chains. The azobenzene and cyanobiphenyl mesogens orient homeotropically and planarly, respectively, in a thin film state. The combination of these contrasting orienting properties leads to a formation of vertically oriented lamella in the microphase separation structure. Irradiation with linearly polarized light onto this polymer film induces a highly oriented microphase separation structure having regularly elongated stripe morphology with 30 nm periodicity. The nearly defect-free morphology of this LC-LC diblock copolymer after the photoalignment is a distinct feature when compared with those of coil (amorphous)-LC diblock copolymer films possessing the same azobenzene side chain.

Controlling the morphology and crystallization of a thiophene-based all-conjugated diblock copolymer by solvent blending.

We report the crystallization and microphase separation behavior of an all-conjugated poly(3-hexylthiophene)-b-poly[3-(6-hydroxy)hexylthiophene] (P3HT-b-P3HHT) block copolymer in mixed solvents and demonstrate how the conformations of P3HT and P3HHT chains influence the photophysical properties of the copolymer. It is shown that the balance among π-π stacking of P3HT, P3HHT and microphase separation of the copolymer can be dynamically shifted by controlling the rod-rod interactions of the copolymer via changing the block ratio and solvent blending. A series of nanostructures such as well-ordered nanofibers, spheres and lamellar structures are formed and their formation mechanisms and kinetics are discussed in detail. The variations in P3HT-b-P3HHT conformations are concomitant with a hybrid photophysical property depending on the competition between intrachain and interchain excitonic coupling, resulting in the transformation between J- and H-aggregation. Overall, this work demonstrates how the P3HT-b-P3HHT conformations crystallize and phase-separate in the solution and solid state, and the correlation between their structures and photophysical properties, which improves our understanding of all-conjugated rod-rod block copolymer systems.

Hydrogen-bonding induced abnormal microphase separation behavior of poly(ethylene oxide)-b-poly(tert-butyl acrylate-co-acrylic acid) block copolymers

Hydrogen (H)-bonding interaction was introduced into a poly(ethylene oxide)-b-poly(tert-butyl acrylate) (PEO-b-PtBA) block copolymer (BCP) by partial hydrolysis of tBA units into acrylic acid (AA) ones, in order to compete with the segregation force between the PEO and PtBA blocks. It was found that, as the hydrolysis degree (Dhyd) of the PtBA block increased, the structure of the PEO-b-P(tBA-co-AA) BCPs underwent the change from hexagonally packed cylindrical (HEX) into body-centered cubic spherical (BCC), then into HEX. The first HEX-to-BCC transition at lower Dhyd arose from the enhanced compatibility between the PEO and P(tBA-co-AA) blocks induced by the H-bonding interaction. When a PEO-b-P(tBA-co-AA) BCP with a HEX structure was heated, the BCC-to-HEX order-order transition (OOT), which was opposed to that in the common BCPs with an upper critical ordering temperature (UCOT) phase diagram, could be achieved because the H-bonding interaction was weakened at higher temperature. The second BCC-to-HEX at higher Dhyd was interpreted in terms of the enhanced chain rigidity and the chain arrangement approximately parallel to the microdomain interface induced by H-bonding interaction. The variation of the H-bonding interaction with temperature and the conformational change of the PEO block induced by H-bonding interaction were verified with FT-IR.

Local Grafting of Ionic Liquid in Poly(vinylidene fluoride) Amorphous Region and the Subsequent Microphase Separation Behavior in Melt.

Polymer-based nanostructures can be generally created by self-assembly of block copolymers that are commonly synthesized by living radical polymerization. In this study, a new strategy is proposed to fabricate block-like copolymers by using the template of binary phase structure of semicrystalline polymers. Poly(vinylidene fluoride) (PVDF) is thermodynamically miscible with an unsaturated ionic liquid (IL) (1-vinyl-3-ethylimidazolium tetrafluoroborate) in the melt and IL molecules are expelled out from the crystalline parts during the crystallization of PVDF. Therefore, the IL molecules are only located at the amorphous region of PVDF crystals. The electron beam irradiation of the IL incorporated PVDF leads to the local grafting of IL molecules onto the PVDF molecular chains in the amorphous region, so block-like grafting polymer chains of crystalline PVDF-b-(amorphous PVDF-g-IL)-b-crystalline PVDF can be achieved. The subsequent heating of the irradiated sample induces the microphase separation of PVDF-g-IL from the ungrafted PVDF chains.

Quantitative Monitoring of Microphase Separation Behaviors in Cationic Liposomes Using HHC, DPH, and Laurdan: Estimation of the Local Electrostatic Potentials in Microdomains.

Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N',N'-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical membrane property analyses, focusing on membrane fluidity and membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For DOPC/DOTAP = (7/3), the membrane was in the liquid-disordered phase and the density of cationic molecules was 0.41 cation/nm(2). For DOPC/DC-Ch = (7/3), the membrane was heterogeneous and the densities of cationic molecules in liquid-disordered and liquid-ordered phases were 0.25 and 1.24 cation/nm(2), respectively. We thereby conclude that the DC-Ch molecules can form nanodomains when these molecules are concentrated to 59%.

Diblock copolymers of polystyrene‐b‐poly(1,3‐cyclohexadiene) exhibiting unique three‐phase microdomain morphologies

ABSTRACTThe synthesis and molecular characterization of a series of conformationally asymmetric polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐b‐PCHD) diblock copolymers (PCHD: ∼90% 1,4 and ∼10% 1,2), by sequential anionic copolymerization high vacuum techniques, is reported. A wide range of volume fractions (0.27 ≤ ϕPS ≤ 0.91) was studied by transmission electron microscopy and small‐angle X‐ray scattering in order to explore in detail the microphase separation behavior of these flexible/semiflexible diblock copolymers. Unusual morphologies, consisting of PCHD core(PCHD‐1,4)–shell(PCHD‐1,2) cylinders in PS matrix and three‐phase (PS, PCHD‐1,4, PCHD‐1,2) four‐layer lamellae, were observed suggesting that the chain stiffness of the PCHD block and the strong dependence of the interaction parameter χ on the PCHD microstructures are important factors for the formation of this unusual microphase separation behavior in PS‐b‐PCHD diblock copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1564–1572