H-shaped Block Copolymer Research Articles

Dissipative Particle Dynamics Study on Interfacial Properties of Ternary H-Shaped Copolymer–Homopolymer Blends

Dissipative particle dynamics (DPD) simulations is used to study the effect of Am/2BmAm/2 and H-shaped (Am/4)2Bm(Am/4)2 block copolymers on the interfacial properties of ternary blends. Our simulations show the following: (i) The capacity of block copolymers to diminish interfacial tension is closely linked to their compositions. With identical molecular weights and concentrations, H-shaped block copolymers outperform triblock copolymers in mitigating interfacial tension. (ii) The interfacial tension within the blends correlates positively with the escalation in H-shaped block copolymer molecular weight. This correlation suggests that H-shaped block copolymers featuring a low molecular weight demonstrate superior efficacy as compatibilizers when contrasted with those possessing a high molecular weight. (iii) Enhancing the concentration of H-shaped block copolymers fosters their accumulation at the interface, leading to a reduction in correlations between immiscible homopolymers and a consequent decrease in interfacial tension. (iv) As the length of the homopolymer chains increases, there is a concurrent elevation in interfacial tension, suggesting that H-shaped block copolymers perform more effectively as compatibilizers in blends characterized by shorter homopolymer chain lengths. These findings elucidate the associations between the efficacy of H-shaped block copolymer compatibilizers and their specific molecular characteristics.

Single gyroid in H-shaped block copolymers

Single gyroid in H-shaped block copolymers

Dissipative particle dynamics simulations of H-shaped diblock copolymer self-assembly in solvent

We examine the self-assembly of H-shaped block-copolymers as the function of the middle block to branch length ratio and interaction between the middle and branch blocks differing in their solvophobicity. The work shows that the examined H-shaped polymers readily transition from uniform mixing of the polymer species to domain formation and a variety of advanced assembly configurations including vesicles, onion-like, and multicompartment aggregates. We identify the polymer conformational and packing changes involved to extract governing interactions and molecule features giving rise to the different assembly structures. The findings are discussed in terms of the H-shaped polymer architecture and polymer assemblies. We conclude that the assembly structure is governed by the molecular level local curvature induced by the varying conformations of the polymers. The findings highlight that for H-shaped polymers the degree of polymerization and polymer chemistries in terms of solvation and mixing characteristics of the blocks are keys to controlling the assembling structures.

Synthesis of H-shaped complex macromolecular structures by combination of atom transfer radical polymerization, photoinduced radical coupling, ring-opening polymerization, and iniferter processes

Three controlled/living polymerization processes, namely atom transfer radical polymerization (ATRP), ring opening polymerization (ROP) and iniferter polymerization, and photoinduced radical coupling reaction were combined for the preparation of ABCBD-type H-shaped complex copolymer. First, a-benzophenone functional polystyrene (BP-PS) and poly( methyl methacrylate) (BP-PMMA) were prepared independently by ATRP. The resulting polymers were irradiated to form ketyl radicals by hydrogen abstraction of the excited benzophenone moieties present at each chain end. Coupling of these radicals resulted in the formation of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) with benzpinacole structure at the junction point possessing both hydroxyl and iniferter functionalities. ROP of e-caprolactone (CL) by using PS-b-PMMA as bifunctional initiator, in the presence of stannous octoate yielded the corresponding tetrablock copolymer, PCL-PSPMMA- PCL. Finally, the polymerization of tert-butyl acrylate (tBA) via iniferter process gave the targeted H-shaped block copolymer

A2BA2 Block Copolymers of Poly(N-isopropylacrylamide) (A) and Poly(ethylene glycol) (B): Synthesis and Thermal Gelation Properties of Aqueous Solutions

A2BA2 block copolymers of poly(N-isopropylacrylamide) (A, PNIPAM) and poly(ethylene glycol) (B, PEG) were synthesized by SET-LRP for the first time. The 1H-NMR and GPC analyses showed that the block copolymers prepared had in average 3.5–3.8 PNIPAM arms/macromolecule and low polydispersities (Mw/Mn=1.25–1.35). The thermogelation behavior of their 20 wt% aqueous solutions was investigated by DSC, dynamic rheometry and the tube inversion method as a function of the molecular weight of both PEG block and PNIPAM arms. The results showed that both phase transition temperature, as determined by DSC, and gelation temperature, determined by the tube inversion method, increased with the PEG block length and decreased with the MW of the PNIPAM arms, while the forming gels were more stable for longer PEG chains. By comparing the thermoresponsive properties of the H-shaped block copolymers synthesized with those of some linear PNIPAM-PEG-PNIPAM triblock copolymers of similar molecular weights of both PNIPAM side blocks and PEG middle chain, almost identical results were obtained, indicating practically no influence of the shape of the PNIPAM blocks from this point of view.

Chemoenzymatic synthesis amphiphilic H-shaped copolymer and its self-assembly behavior

ABA triblock copolymers were synthesized by dihydroxyl-capped PEO initiated enzymatic ring-opening polymerization (eROP) of e-CL in the presence of biocatalyst Novozyme 435. The chains ended with hydroxyl of block copolymers were modified by the esterification of 2,2-dichloro acetyl chloride (DCAC) to obtain the tetrafunctional macroinitiator, which was used in the ATRP of 4-vinylpyridine (4-VP). CuCl/HMTETA was used as the catalyst system in the ATRP of 4-VP to acquire the H-shaped block copolymers (PVP)2-b-PCL-b-PEG-b-PCL-b-(PVP)2. The H-shaped block copolymers were characterized by FTIR, NMR, and GPC. Copolymers with high molecular weights (Mn = 46121 g/mol) and low polydispersities (Mw/Mn = 1.30) were prepared. Moreover, the morphology of the copolymer was examined with dynamic light scattering (DLS) and atomic force microscopy (AFM). Spherical micelles with a diameter of 70 nm in aqueous solution were obtained.

Study of morphology and phase diagram of the H-shaped (AC)B(CA) ternary block copolymers using self-consistent field theory

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymer systems, the micro-phase morphologies of the H-shaped (AC)B(CA) ternary block copolymer system are studied in three-dimensional (3D) space. By systematically varying the volume fractions of the components A, B, and C, six triangle phase diagrams of this H-shaped (AC)B(CA) ternary block copolymer system with equal interaction energies among the three components are constructed from the weaker segregation regime to the strong segregation regime, In this study, thirteen 3D micro-phase morphologies for this H-shaped ternary block copolymer system are identified to be stable and seven 3D microphase morphologies are found to be metastable.

Synthesis and self-assembly of reactive H-shaped block copolymers

The H-shaped block copolymers (PTMSPMA)2-PEG(PMPSTMSPMA)2 with two compositions, (EG)91-b-(TMSPMA)92 and (EG)455-b-(TMSPMA)176 have been successfully synthesized by atom transfer radical polymerization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The initiation system applied was composed of 2,2-bis(methylene α-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br2PEGBr2) with M n = 4000 or 2000, CuBr and 2,2′-bipyridine. The macroinitiator, Br2PEGBr2, was prepared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene α-bromoisobutyrate)propionyl chloride. The NMR spectroscopy and GPC measurements were used to characterize the structure and molecular weight and molecular weight distribution of the resultant copolymers. The H-shaped block copolymers Sam 1 and Sam 2 were self-assembled in DMF/water mixtures and then the trimethoxysilyl groups in PTMSPMA were cross-linked by condensation reaction in the presence of triethylamine. Stable large-compound vesicles with 10 nm diameter of cavities were formed for Sam 1 which contains a short PEG chain. However, the self-assembling of the Sam 2 in the selective solvents resulted in big vesicles aggregates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Sam1 with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles.

Chemozymatic synthesis and characterization of H-shaped triblock copolymer

The synthesis of well-defined H-shaped block copolymer based on the enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP) is described. The dihydroxyl polycaprolactone (PCL) was synthesized by the eROP of e-caprolactone (e-CL) in the presence biocatalyst Novozyme 435 and initiator ethylene glycol. Subsequently, the resulting PCL was converted to tetrafunctional macroinitiator by the esterification with 2,2-dichloro acetyl chloride (DCAC). The H-shaped block copolymer was then synthesized by the ATRP of styrene. The polymers were characterized by NMR and GPC. Linear first-order kinetics, linearly increasing molecular weight with conversion, and low polydispersities observed from the ATRP of St showed that the polymerization was well controlled. (PSt)2-b-PCL-b-(PSt)2 block copolymers with varying molecular weight and controllable composition were obtained.

Ring-shaped morphology in H-shaped block copolymer thin films

The formation of ring-shaped structures in an H-shaped block copolymer [a poly(ethylene glycol) backbone with polystyrene branches, i.e., (PS)2PEG(PS)2] thin film was investigated when it was annealed in saturated PEG-selective acetonitrile vapor. Our results clearly indicate that ring formation is determined by the initial morphology of the spin-coated film, the solvent vapor selectivity and the environmental temperature of the solvent-annealing process. Only the films with the initial core–shell cylindrical structure in strongly PEG-selective acetonitrile vapor could form the ring-shaped structures. Environmental temperature has an influence on the formation mechanisms. It was proven that the rings arising from the core–shell cylindrical structure of the pristine spin-coated (PS)2PEG(PS)2 film were caused by the migration of the PEG shells to the top surface in the process of PEG-selective vapor annealing at the environmental temperature of 15 °C. While at a higher environmental temperature (25 °C), the degree of swelling of the film and the chains’ mobility increased and the formation mechanism of the rings in this situation was similar to that in dilute solution.

Synthesis of symmetric H-shaped block copolymer by the combination of ATRP and living anionic polymerization

A novel fluorescent dye labeled H-shaped block copolymer, (PMMA-Fluor-PS) 2-PEO-(PS-Fluor-PMMA) 2, is synthesized by the combination of atom transfer radical polymerization (ATRP) and anionic polymerization (AP). To obtain the designated structure of the copolymer, a macroinitiator, 2,2-dichloro acetyl-PEO-2,2-dichloro acetyl (DCA-PEO-DCA), was prepared from DCAC and poly(ethylene oxide). The copolymer was characterized by 1H NMR, GPC and fluorescence spectroscopy.

Comparing the Morphology and Phase Diagram of H-Shaped ABC Block Copolymers and Linear ABC Block Copolymers

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymers, we have investigated the morphology of H-shaped ABC block copolymers (A2BC2) and compared them with those of the linear ABC block copolymers. By changing the ratios of the volume fractions of two A arms and two C arms, one can obtain block copolymers with different architectures ranging from linear block copolymer to H-shaped block copolymer. By systematically varying the volume fractions of block A, B, and C, the triangle phase diagrams of the H-shaped ABC block copolymer with equal interactions among the three species are constructed. In this study, we find four different morphologies (lamellar phase (LAM), hexagonal lattice phase (HEX), core-shell hexagonal lattice phase (CSH), and two interpenetrating tetragonal lattice (TET2)). Furthermore, the order-order transitions driven by architectural change are discussed.

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS) 2–PEO–(PMMA) 2 has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl–PS) 2–CHCOOCH 2CH 2OH with an active hydroxyl group. The chlorine was removed to yield the (PS) 2–CHCOOCH 2CH 2OH ((PS) 2–OH). The hydroxyl group of the (PS) 2–OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS) 2–PEO–OH. The (PS) 2–PEO–OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS) 2–PEO–OCCHCl 2 ((PS) 2–PEO–DCA). The asymmetric H-shaped block polymer (PS) 2–PEO–(PMMA) 2 was prepared via ATRP of MMA at 130 °C using (PS) 2–PEO–DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS) 2–PEO–(PMMA) 2, were confirmed by 1H NMR, GPC and FT-IR.

Self-Assembly of H-Shaped Block Copolymers

We have systematically studied the effect of the solvent nature on the self-assembly of H-shaped block copolymers with a poly(ethylene glycol) backbone and polystyrene branches, i.e., (PS)2PEG(PS)2. Two copolymers with different molecular weights (MW) and compositions, copolymer 1 and copolymer 2, were used, where copolymer 2 has a higher MW and higher PEG fraction than those of copolymer 1. In nominally neutral (nonselective) solvents, it is found that very subtle variation in the solvent affinity can remarkably influence the morphologies of the films spin-coated from the corresponding solutions. For example, as the solvent was changed from PS-affinitive to PEG-affinitive, the films of copolymer 1 changed from a disordered state into PEG cylinders. In contrast, the films of copolymer 2 changed from wormlike patterns into PEG spheres. Besides, the surface morphologies also showed some dependence on the solution concentration: with decreasing concentration, the PEG cylinders were changed into PEG spheres and a disordered state. In PEG-selective solvent (e.g., acetonitrile), copolymer 2 formed typical spherical micelles. In contrast, copolymer 1 formed a mixture of spheres and cylinders, which could be transformed into vesicles and lamellae upon dilution. The polymer−solvent interactions and their effects on the copolymer chain conformation are discussed.

Synthesis and characterization of H-shaped copolymers by combination of RAFT polymerization and CROP

A novel trithiocarbonate, S,S′-bis(1-(((5-ethyl-2,2-dimethyl-1,3-dioxane-5-yl)methoxy)carbonyl)propyl) trithiocarbonate (CTA-H), was synthesized in the presence of the anion-exchange resin with OH − form. And then it was used as the chain transfer agent in RAFT polymerizations of styrene (St), the polymers with controllable molecular weights and narrow molecular weight distributions were synthesized. After the terminal acetonide groups was deprotected in the presence of a cation-exchange resin with H + form, the polystyrene (PSt) with two hydroxyl groups in both chain ends was easily afforded. Then it was used as macro initiator in the cation ring open polymerization (CROP) of 1,3-dioxepane (DOP), and the well-defined H-shaped block copolymers, (PDOP) 2PSt(PDOP) 2, were successfully prepared. The H-shaped structure was characterized by its IR, GPC and 1H NMR spectra, and also those of the hydrolysis products.

Swelling behavior of ordered miktoarm star block copolymer–homopolymer blends

We report the morphological characterization of asymmetric miktoarm star block copolymers of the (PS-b-PI)nPS type where n=2,3 (denoted 2DB and 3DB miktoarm stars, respectively) and a symmetric super H-shaped block copolymer of the (PS-b-PI)3PS(PI-b-PS)3 type (denoted SH) which were synthesized by anionic polymerization. The initial volume fraction of PS (φPS) for each copolymer was 0.51–0.56, giving a lamellar morphology. Addition of homopolystyrene (hPS) with a molecular weight lower than the respective PS blocks in the neat materials lead to a transition from the lamellar structure to hexagonally packed cylinders. Addition of low molecular weight homopolyisoprene (hPI) on the other hand, only resulted in swollen lamellae even when the overall composition was highly asymmetric (80/20). Changes in the lamellar spacing as well as in the respective PS and PI layer thickness were measured by SAXS. The transition from lamellae to cylinders with increased PS content occurred without the observation of an intervening cubic morphology for the 2DB and 3DB miktoarm stars. However, blends with 30 and 35% hPS ((φPS)total=0.68–0.70) with the super H-shaped block copolymer lead to the observation of lamellar-catenoid structures.

Microphase Separation in Super-H-Shaped Block Copolymer Colloids

Block copolymers of the A3BA3 type with a short connector block B exhibit features known in multi-arm star polymers in addition to their block copolymer nature. We have studied the ordered state morphology and the order-to-disorder transition (ODT) in three model super H-shaped block copolymer melts of the A3BA3 type. From the three asymmetric nonlinear block copolymers (0.07 < fB < 0.35, B is polystyrene (PS)) one is in the homogeneous disordered phase (fPS = 0.072), another is in the ordered phase (fPS = 0.345), and the third (fPS = 0.118) undergoes an order-to-disorder transition in a temperature range accessible by SAXS and rheology. In the former experiment the ODT has been identified from the discontinuous changes in the peak intensity and width, whereas in the latter it has been identified by the discontinuous drop of the storage modulus. The SAXS results have shown a peculiar T dependence of the peak position q*, which is attributed to the starlike nature of the system. TEM and SAXS identify the morphology of the fPS = 0.118 sample as spheres organized in a body-centered-cubic (bcc) lattice with each domain consisting of about 40 connector blocks (PS), whereas in the fPS = 0.345 sample, PS cylinders are packed in a hexagonal lattice. At some temperatures in the vicinity of the TODT two states with very different viscosities exist and large amplitude deformation and/or temperature results in a transformation from the high (state I) to the low viscosity state (state II). To identify the associated structural changes, we have compared the viscoelastic response of each state to the corresponding structural profiles. We found that the viscoelastic response in state I is controlled by the relaxation of grains whereas in state II it is controlled by the relaxation of individual domains in the absence of long range order. At low shear rates, below the grain relaxation, we identify a flow regime that is a consequence of the colloidal nature of these block copolymers.

Synthesis of model super H-shaped block copolymers

Block copolymers are materials of great technological importance,' finding application as ther- moplastic elastomers, as compatibilizers for polymer blends, in the modification of surface and interfacial properties, etc. Most of our fundamental understanding has been gained by the study of well-defined and nearly monodisperse linear diblockand, to a lesser extent, triblock copolymers. Very little is known about the influence of the chain architecture on properties. In previous papers the synthesis of model miktoarm (from the Greek word