Triblock Chains Research Articles

Dynamic Light Scattering Based Microrheology of End-Functionalised Triblock Copolymer Solutions.

Nano-sized particles functionalised with short single-stranded (ss)DNAs can act as detectors of complementary DNA strands. Here we consider tri-block-copolymer-based, self-assembling DNA-coated nanoparticles. The copolymers are chemically linked to the DNA strands via azide (N3) groups. The micelles aggregate when they are linked with complementary ssDNA. The advantage of such block-copolymer-based systems is that they are easy to make. Here we show that DNA functionalisation results in inter-micellar attraction, but that N3-groups that have not reacted with the DNA detector strands also change the phase behaviour of the tri-block polymer solution. We studied the triblock copolymer, Pluronic® F108, which forms spherical micelles in aqueous solutions upon heating. We find that the triblock chains ending with either an N3 or N3-DNA complex show a dramatic change in phase behaviour. In particular, the N3-functionalisation causes the chain ends to cluster below the critical micelle temperature (CMT) of pure F108, forming flower-micelles with the N3-groups at the core, while the PPO groups are exposed to the solvent. Above the CMT, we see an inversion with the PPO chains forming the micellar core, while the N3-groups are now aggregating on the periphery, inducing an attraction between the micelles. Our results demonstrate that, due to the two competing self-assembling mechanisms, the system can form transient hydrogels.

Influence of copolymer chain sequence on electrode latex binder for lithium-ion batteries

Electrode binders have significant influences on lithium-ion battery performance. Good binders should be able to absorb electrolyte to accelerate lithium-ion transport while simultaneously maintaining adequate adhesion and mechanical strength after swelling. Currently, most polymer binders are based on homo or random copolymers so they may only meet one of these requirements, as an improvement in electrolyte swelling ability is detrimental to mechanical strength, and vice versa. This work investigates whether the design of chain sequence can resolve this contradiction. Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization is employed to synthesize copolymer latex with different chain sequences as electrode binders, which are examined in both LiFePO4 cathode and silicon anodes. The results show a triblock copolymer chain sequence gives the best performance. The microphase separation in triblock copolymer distributes functionalities of electrolyte affinity and strength maintenance into disparate blocks and therefore satisfies both requirements simultaneously. The advantages of triblock chain sequence are demonstrated by superior ionic conductivity, mechanical strength after electrolyte absorption, and lithium-ion diffusion coefficient and then lead to better battery performance compared with random counterpart and commercial aqueous binders.

Interstitial micelles in binary blends of ABA triblock copolymers and homopolymers.

We investigate triblock-homopolymer blends of types A1BA2/A and A1BA2/B, using a lattice Monte Carlo method. While the simulated triblock chains are compositionally symmetric in terms of the A-to-B volume ratio, the A1 block is significantly shorter than the A2 block. For the pure A1BA2 melt and the A1BA2 solutions in selective solvent the phase behavior is relatively well known, including existence and stability of the interstitial micelles which were discovered in previous Monte Carlo simulations. In this paper we study the stability of the interstitial micelles as a function of triblock volume fraction in selective homopolymers of either type A or type B, using two significantly different homopolymer chain lengths. We found that adding selective homopolymer of type A shifts the stability of the interstitial micelles into significantly higher temperatures. We also obtained, via self-assembly, intriguing new nanostructures which can be identified as ordered truncated octahedra. Finally, we established that the phase behavior of the triblock-homopolymer blends depends relatively weakly on the chain length of the added homopolymer.

Towards entropy-driven interstitial micelles at elevated temperatures from selective A1BA2 triblock solutions.

We simulate selective A1BA2-A and A1BA2-B triblock solutions (that is, mixtures of the A1BA2 triblock with a solvent of either type A or type B) using a lattice Monte Carlo method. Although the simulated triblock chains are compositionally symmetric in terms of the A to B volume ratio, the A1 block is significantly shorter than the A2 block. For the pure A1BA2 melt the phase behavior is relatively well known, including the existence and stability of the recently discovered interstitial micelles which were found at the very strong segregation limit. In this paper, we investigate the stability of the interstitial micelles as a function of triblock volume fraction in a selective solvent of either type A or type B. The main finding of this paper is that adding a selective solvent of type A shifts the stability of the interstitial micelles into significantly higher temperatures which may provide a pathway towards experimental studies of interstitial micelles in real triblock solutions. We also find that adding selective solvents to the A1BA2 melt gives rise to a variety of nonlamellar nanostructures for temperatures and compositions at which the interstitial micelles are stable.

Multi-shape memory polymers achieved by the spatio-assembly of 3D printable thermoplastic building blocks

Multi-shape memory polymers were prepared by the macroscale spatio-assembly of building blocks in this work. The building blocks were methyl acrylate-co-styrene (MA-co-St) copolymers, which have the St-block-(St-random-MA)-block-St tri-block chain sequence. This design ensures that their transition temperatures can be adjusted over a wide range by varying the composition of the middle block. The two St blocks at the chain ends can generate a crosslink network in the final device to achieve strong bonding force between building blocks and the shape memory capacity. Due to their thermoplastic properties, 3D printing was employed for the spatio-assembly to build devices. This method is capable of introducing many transition phases into one device and preparing complicated shapes via 3D printing. The device can perform a complex action via a series of shape changes. Besides, this method can avoid the difficult programing of a series of temporary shapes. The control of intermediate temporary shapes was realized via programing the shapes and locations of building blocks in the final device.

Experimental and Theoretical Study of the Living Polymerization of N-Silylphosphoranimines. Synthesis of New Block Copolyphosphazenes

The sequential living polymerization of N-silylphosphoranimines for the synthesis of polyphosphazene-b-polyphosphazene diblock copolymers (PP-b-PP) has been studied both experimentally and theoretically. For the experiments, BrMe2P═N–SiMe3, [Cl3P═N═PCl3][X] (X = PCl6–, Cl–), Cl3P═N–SiMe3, ClMe2P═N–SiMe3, and [Me3P═N═PMe2Cl]+ were used as representative model reagents. Density functional theory (DFT) calculations in the gas phase adjusted for solvent effects on ClMe2P═N–SiMe3, [Cl3P═N═PCl3]+, Cl3P═N–SiMe3, and ClMe2P═N–SiMe3 confirmed the experimental observations. The results have shown the necessity of starting with mono-end-capped initiators to avoid the formation of triblock chains. It was also demonstrated that the nature of the nucleophilic N-silylphosphoranimines and the electrophilic cationic end groups of the living polyphosphazenes strongly affects the polymerization reaction, imposing limits to its synthetic potential. Thus, good electron donor N-silylphosphoranimines, i.e. XR2P═N–SiMe3, react b...

Effects of component molecular weight on the viscoelastic properties of thermoreversible supramolecular ion gels via hydrogen bonding

We describe a thermoreversible supramolecular ion gel system consisting of a poly(2-vinylpyridine-b-ethylene oxide-b-2-vinylpyridine) (P2VP-PEO-P2VP) triblock copolymer, a poly(4-vinylphenol) (PVPh) linear homopolymer, and a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMI][TFSA]). Aggregates of intermolecularly hydrogen-bonded PVPh cross-linkers form cross-links, connecting P2VP-PEO-P2VP triblock chains into a transient polymer network through hydrogen bonding with the P2VP endblocks. The viscoelastic properties of the resulting gels are strongly temperature-dependent, as manifested by the 15 orders of magnitude variation in the longest relaxation time (τ1) from the gel temperature (Tgel) down to room temperature. Wide temperature- and frequency-independent rubbery plateaus are distinct, indicating the formation of a well-defined network structure. The applicability of time-temperature superposition to this system is striking, suggesting the invariance of the underlying relaxation mechanism. The terminal relaxation dynamics of these hydrogen-bonded supramolecular networks is dramatically retarded upon increasing the P2VP endblock length. In contrast, their viscoelastic properties are relatively insensitive to the PVPh cross-linker length. These results are consistent with the hypothesis that τ1 is determined by the average lifetime of a P2VP ↔ PVPh association, which is directly related to the number of hydrogen bonds involved. Besides their potential applications in various electrochemical devices, these materials might also be used in surface coatings, where thermally reversible and sensitive viscoelastic properties are highly advantageous.

Folding of Long Multiblock Copolymer (PI-b-PS-b-PI)n Chains Prepared by the Self-Assembly Assisted Polypolymerization (SAAP) in Cyclohexane

The formation of polymeric micelles made of A−B−A triblock chains in a solvent selectively poor for the middle B-block concentrate and exposes two active end groups so that short triblock chains can be effectively coupled together to form a long (A−B−A)n multiblock chain with a controllable block length and sequence. Using this method, we successfully prepared a (PI-b-PS-b-PI)30 multiblock copolymer, starting from a triblock PI-b-PS-b-PI copolymer (Mn = 4.8 × 104 g/mol). The coupling efficiency with and without the self-assembly was compared. The folding of such long multiblock chains (Mn = 1.4 × 106 g/mol) in a dilute solution (10-5 g/mL) was studied by a combination of static and dynamic laser light scattering. The results reveal that such long multiblock chains do not collapse into single-chain globule in a dilute solution even when the solution temperature is much lower than the ϑ temperature. Instead, each PS block collapses into a small globule stabilized by the two attached PI blocks on the chain b...

Synthesis, Folding, and Association of Long Multiblock (PEO23-b-PNIPAM124)750 Chains in Aqueous Solutions

A thermally sensitive ultralong multiblock copolymer, [poly(ethylene oxide)(23)-b-poly(N-isopropylacrylamide)(124)](750) (M-w = 1.78 x 10(7) g/mol and M-z/M-w = 1.49), was prepared using the oxidative coupling of two mercapto groups at the two ends of triblock PNIPAM(62)-b-PEO23-b-PNIPAM(62) (M-n,M-PEO = 1.0 x 10(3) g/mol and M-n,M-PNIPAM = 1.4 x 10(4) g/mol) copolymer chains. The folding of individual multiblock copolymer chains in an extremely dilute solution (10(-6) g/mL) was studied by laser light scattering (LLS). Moreover, the association of multiblock and triblock copolymer chains in relatively concentrated aqueous solutions (10(-3) g/mL) was also comparatively studied by a combination of LLS, fluorescence spectrometry, and microcalorimetry. We found that in the single-chain folding process the average radius of gyration ( ) remains a constant in one heating-and-cooling cycle, but the average hydrodynamic radius ( ) decreases as the solution temperature increases. Our result reveals that the single-chain folding undergoes two stages at similar to 32 and similar to 40 degrees C, presumably due to the successive contraction of thermally sensitive PNIPAM segments in the middle-around each hydrophobic S-S coupling point and near the hydrophilic PEO block. Each PNIPAM block collapses into a small globule (bead) stabilized by the two attached PEO blocks on the chain backbone, a string-bead conformation, which makes the chain thicker and more extended. The association of multiblock chains also undergoes similar two stages to form stable mesoglobules during the heating. In contrast, the triblock chains associate at similar to 30 degrees C to form polymeric micelles.

Effect of Chemical Modification on Macroscopic Phase Separation in Styrene−Isoprene Block Copolymer Driven by Thermooxidative Reactions

Macroscopic phase separation induced by thermooxidative reaction has been observed in a commercial styrene-block-isoprene-block-styrene (SIS) copolymer, Kraton 1107, upon exposure to atmospheric oxygen at elevated temperatures. Unlike styrene-block-butadiene-block-styrene (SBS) copolymers, there is essentially no gel formation (i.e., no cross-linking reaction) in the thermal oxidation of SIS copolymer. In the first phase separation, oxidative reaction causes the breakup of the SIS triblock chains into the SI blocks (containing polystyrene blocks and short isoprene segments) and low molar mass neat polyisoprene, forming an immiscible region with macrophase-separated domains. The continued decline of the molecular weight of polyisoprene and further detachment of isoprene fragments from the SI diblocks suppress the immiscibility region to a lower temperature, causing phase dissolution to occur at the reaction temperature. With progressive oxidation, the chain scission continues to occur while heavily oxidized lower molecular weight polyisoprene derivatives and oily byproducts are formed. Such chemical change in polyisoprene makes the system to be very unstable, thereby driving the macroscopic phase separation for a second time. It may be concluded that the cascading phase separation occurs due to chemical modification of the isoprene units of the SIS blocks as opposed to the cross-linking reaction induced macrophase separation in the SBS blocks.

End-Adsorbed Telechelic Polymer Chains at Surfaces: Bridging and Elasticity

We have studied the interaction of telechelic polymer chain (hydrophobic end-capped poly(ethylene oxide)) layers with hydrophobic polystyrene surfaces in water using the atomic force microscope. There are polymer bridges between the surfaces. The bridging creates an attractive force between surfaces at distances larger than the equilibrium thickness of the layer and a repulsive force at short distances. The attraction is attributed to polymer bridges in which the two end groups of a single triblock chain simultaneously adsorb onto opposing surfaces. The attractive forces depend strongly on the number of the approach-and-retract cycles. The comparison between theoretical and experimental profiles allows an estimation of the adsorption energy of the end groups of the triblock chains on the polystyrene surface.

Morphology of ABC Triblock Copolymers

We present results from theoretical calculations of the morphological phase diagrams for ABC triblock copolymers in the strong segregation limit. The chain conformation free energy is approximated following an approach proposed by Ohta and Kawasaki. Our study focuses on two unique features of the ABC triblock copolymers, namely, the dependence of the morphology on the sequence of the triblock chain and the relative strength of the various interaction parameters. Our results compare favorably with experimental observations. In addition, we predict the existence of some new structures that have yet to be observed experimentally.

Structure and dynamics of polymeric micelles in solution

The association properties of binary and ternary systems of the EPE and PEP (E and P refer to poly(oxyethylene) and poly(oxypropylene), respectively) polymeric surfactants in water and/or xylene were studied by using light scattering and small angle X-ray scattering. The ability of PEP to form micelles in water is greatly reduced when compared with that of EPE, thus demonstrating the profound influence of the triblock chain architecture. The anomalous scattering before the onset of micellization which has puzzled people for a long time is found to be associated with the copolymer composition heterogeneity. The addition of water to the EPE solution in xylene can induce the micelle formation with a transition from spherical to non-spherical shapes of the associated structures at high water content.

End-adsorbed triblock copolymer chains at the liquid-solid interface: bridging effects in a good solvent

Direct force measurement on the interactions of end-adsorbed diblock and triblock copolymer layers against a bare mica surface in toluene are dreported. Only monotonically repulsive forces are observed when a bare mica sheet interacs with a single layer of polystyrene (PS)-poly(ethylene oxide) (PEO) diblock copolymer, end-adsorbed at a toluene/mica interface. In contrast, clearly detectable attractive forces are found for PEO-PS-PEO triblock copolymers under similar conditions. The attraction is attributed to polymer bridges in which the two PEO end blocks of a single triblock chain simultaneously adsodrb onto opposing mica surfaces

Conformations of Block Copolymers Terminally Adsorbed at the Solid-Liquid Interface

Abstract The conformations of end-adsorbed diblock and mblock copolymers of polystyrene (PS) and polyethylene oxide (PEO) adsorbed onto mica from toluene have been studied by the surface force method. The PS-PEO diblock copolymer system forms a semi-dilute brush with the non-adsorbing PS chains adopting an extended configuration away from the surface. Neutron reflectometry indicates that the volume fraction profile of such a system has a broadly parabolic shape, in agreement with theory. In contrast to PS-PEO diblock copolymers which adsorb only in a “tail” conformation, PEO-PS-PEO triblock chains form “loops” as well as “tails” on the mica substrate. Attractive forces are observed when an adsorbed layer of PEO-PS-PEO triblock copolymer is allowed to interact with a bare mica wall, due to the formation of polymer bridges between the two opposing surfaces.

Theory of correlations in partly labelled homopolymer melts

Small-angle neutron scattering by a polymer melt with partly tagged chains is considered. When several types of chain (differently labelled) are present in the system a new long-range correlation effect which modifies the scattering spectrum is predicted. This effect will arise because of the chemical polydispersity of the sample. A general formalism is developed to calculate the scattering intensity and is applied to special cases: diblock and triblock chains. It is shown that even a small chemical polydispersity leads to important long-range fluctuations and modifies the scattering spectrum substantially.

Chain conformations of block copolymers

AbstractAn analytical theory of block copolymer conformations is developed for systematically studying the effects of the chain length, chain architecture, and segment interactions. The main results obtained for AB diblock and ABA triblock chains are as follows: (i) In the absence of AA and BB interactions, both diblock and triblock chains collapse to a dense form if the AB interaction is attractive. In the collapsed coil form, the mean‐square end‐to‐end distance 〈R2〉 is proportional to the square root of the number of segments n1/2. (ii) The diblock chain has a dumbbell form if AA and BB interactions are attractive and AB interaction repulsive, but the triblock chain collapses. In the dumbbell form, 〈R2〉 is proportional to n.