A multi‐matrix kinetic Monte Carlo framework enabling the design of sequence‐controlled star block copolymers

Novel star block copolymers containing poly(N-vinylimidazolium salt) as a poly(ionic liquid) segment and poly(N-isopropylacrylamide) (poly(NIPAAm)) as a thermoresponsive segment were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Two R-designed tetrafunctional chain transfer agents (CTAs), including a xanthate-type CTA and a dithiocarbamate-type CTA, were compared for the polymerization of 1-ethyl-3-vinylimidazolium bromide (VEI-Br), which is an ionic liquid-type monomer. The dithiocarbamate-type tetrafunctional CTA was the most efficient CTA for the controlled synthesis of four-armed poly(VEI-Br) stars with low polydispersity values and controlled molecular weights. Star block copolymers with inner thermoresponsive segments connected to their core were synthesized by the RAFT polymerization of VEI-Br, using poly(NIPAAm) stars. In contrast, the RAFT polymerization of NIPAAm using poly(VEI-Br) stars afforded star block copolymers, with block arms consisting of outer block copolymer segments of thermoresponsive poly(NIPAAm). Thermally induced phase separation behavior and assembled structures of star block copolymers were studied in aqueous solution. Four-arm star block copolymers comprising poly(N-vinylimidazolium salt) as a poly(ionic liquid) segment and poly(NIPAAm) as a thermoresponsive segment were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Stimuli-responsive properties and temperature-responsive self-assembly process of these star block copolymers were studied in aqueous solution. Chain architectures, the sequence and comonomer composition of the diblock arms, and salt concentration had a significant effect on their thermally induced phase separation behavior and assembled structures.

n free surface flows, shallow water models simplify the flow conditions by assuming a constant velocity profile over the water depth. Recently developed Shallow Water Moment Equations allow for variations of the velocity profile at the expense of a more complex PDE system. The resulting equations can become stiff depending on the friction parameters, which leads to severe time step constraints of standard numerical schemes. In this paper, we apply Projective Integration schemes to stiff Shallow Water Moment Equations to overcome the time step constraints in the stiff regime and accelerate the numerical computations while still achieving high accuracy. In different dam break and smooth wave test cases, we obtain a speedup of up to 55 with respect to standard schemes.

Structures of amphiphilic block copolymers in their liquid and solid states

A series of star block copolymers were prepared through nitroxide‐mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core‐first polymerization. Eight N‐alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q8M POSS) with 1‐(2‐(allyloxy)‐1‐phenylethoxy)‐2,2,6,6‐tetramethylpiperidine (allyl‐TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa‐N‐alkoxyamines POSS (OT‐POSS) were used as platform to synthesize star polystyrene‐POSS ((PS)8‐POSS) homopolymer and diblock copolymers of poly(styrene‐block‐4‐vinylpyridine)‐POSS ((PS‐b‐P4VP)8‐POSS) and poly(styrene‐block‐acetoxystyrene) ((PS‐b‐PAS)8‐POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS‐b‐PAS)8‐POSS, the poly(styrene‐block‐vinyl phenol) ((PS‐b‐PVPh)8‐POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self‐assembled structures of these star block copolymers based on POSS were characterized by 1H NMR, FTIR, SEC, TEM, and SAXS analyses.magnified image

Water-soluble poly(N-vinyl-1,2,4-triazole) star and amphiphilic star block copolymers by RAFT polymerization

Well-defined photo and pH-sensitive amphiphilic star block copolymers were synthesized by copper based atom transfer radical polymerization, which consisted of a hydrophilic pH sensitive shell and photosensitive hydrophobic core structure. For this, photosensitive n-butyl acrylate (nBA) star polymer was synthesized with a multi-functionalized initiator including Pd-coordinated porphyrin in combination with CuBr and 4,4′-dinonyl-2,2′-bipyridyl (dNbpy) (PDI < 1.09). This hydrophobic photosensitive nBA star polymer was then used as a macroinitiator and polymerized with N,N′-dimethylamino ethyl methacrylate (DMAEMA) in the CuCl/CuCl2/dNbpy catalytic system to synthesize PnBA-PDMAEMA star block copolymer, where the PDMAEMA block segment worked as a base exterior. For the arm chain consisted of an acid exterior block segment, the nBA star polymer macroinitiator was polymerized with tert-butyl acrylate (tBA) in the CuBr/dNbpy catalytic system to synthesize the PnBA-PtBA star block copolymer followed by a treatment with strong acid for deprotecting the tert-butyl groups in the PtBA block segment to give PnBA-poly(acrylic acid) (PAA) star block copolymer. Both amphiphilic photosensitive star block copolymers showed well defined molecular weights with narrow polydispersities (PDI < 1.23). Open image in new window

Copper(I)‐mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n‐butyl methacrylate) [P(n‐BMA)] and poly[(2‐dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n‐BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2‐bromo‐2‐methylpropionic acid 4‐methoxyphenyl ester, 1,4‐(2′‐bromo‐2′‐methyl‐propionate)benzene, and 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow‐polydispersity polymers for which the number‐average molecular weight increased fairly linearly with time with good first‐order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2‐dimethylamino)ethyl methacrylate to obtain well‐defined [P(n‐BMA)x‐b‐PDMAEMAy]z diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22–7.13 × 10−3 g L−1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. © 2002 John Wiley &amp; Sons, Inc. J Polym Sci Part A: Polym Chem 40: 439–450, 2002; DOI 10.1002/pola.10122

The chemical modification (namely the epoxidation) of a star shaped block copolymer (BCP) based on polystyrene (PS) and polybutadiene (PB) and its effect on structural and mechanical properties of the polymer were investigated. Epoxidation degrees of 37 mol%, 58 mol%, and 82 mol% were achieved by the reaction of the copolymer with meta-chloroperoxy benzoic acid (m-CPBA) under controlled conditions. The BCP structure was found to change from lamellae-like to mixed-type morphologies for intermediate epoxidation level while leading to quite ordered cylindrical structures for the higher level of chemical modification. As a consequence, the glass transition temperature (Tg) of the soft PB component of the BCP shifted towards significantly higher temperature. A clear increase in tensile modulus and tensile strength with a moderate decrease in elongation at break was observed. The epoxidized BCPs are suitable as reactive templates for the fabrication of nanostructured thermosetting resins.

The water-soluble ABA-type block copolymer composed of a hydrophobic poly(2-hydroxyethyl methacrylate) and a hydrophilic poly(ethylene oxide) was synthesized. The correlation between the structure of the block copolymer in dilute aqueous solution and its hydrophobic interaction was studied in comparison with random copolymers whose hydrophobic groups are statistically distributed along the chain. Fluorometric measurements using ANS as a probe for hydrophobic region were carried out on the aqueous solution of the block copolymer in the monomolecular state. The hydrophobic domain structure of the monomolecular block copolymer is discussed with respect to the change in the thermodynamic parameters for the binding process of ANS to the polymer chain. The binding ability of the block copolymer for an ANS molecule was found to be larger than that of corresponding random copolymers. This indicates that the mode of the arrangement of hydrophobic groups along the chain affects the hydrophobic interaction and that the block copolymer forms the large hydrophobic region which results from the aggregation of these hydrophobic blocks. It was observed that the temperature dependence of the binding constant of the block copolymer displayed a sharp transition within a narrow temperature range, indicating that the structural change takes place within a molecule. The thermodynamic parameters for both states of the block copolymer below and above the transition temperature were determined independently from the temperature dependence of the binding constant. This means that the hydrophobic domain of the block copolymer becomes larger in the lower temperature range than in the higher, presumably because of the segregation between the hydrophobic and the hydrophilic blocks.

A Monte Carlo study of the compatibilization of A/B polymer blends has been performed using the bond fluctuation model. The considered compatibilizers are copolymer molecules composed of A and B blocks. Different types of copolymer structures have been included, namely, linear diblock and 4-block alternating copolymers, star block copolymers, miktoarm stars, and zipper stars. Zipper stars are composed of two arms of diblock copolymers arranged in alternate order (AB and BA) from the central unit, along with two homogeneous arms of A and B units. The compatibilization performance has been characterized by analyzing the equilibration of repulsion energy, the simulated scattering intensity obtained with opposite refractive indices for A and B, the profiles along a coordinate axis, the radial distribution functions, and the compatibilizer aggregation numbers. According to the results, linear alternate block copolymers, star block copolymers, and zipper stars exhibit significantly better compatibilization, with zipper stars showing slightly but consistently better performance.

Thermal and thermo-oxidative behaviour of butadiene–styrene copolymers with different architectures

γ-Radiation-induced changes in the supermolecular structure of dimethylphenylsilsesquioxane block copolymers were studied with the use of electron microscopy. It was found that the supermolecular structure of the block copolymers was altered by irradiation. The character of changes depends on the size of a soft, dimethylsiloxane block, as well as on the total amount of the blocks in the copolymer molecule. A variation in the properties of block copolymers upon γ-irradiation was also detected by the technique of differential scanning calorimetry.

Polystyrene (PSt) with end-terminal bromine (Br-PSt-Br) was synthesized by the atom transfer radical polymerization of styrene with the difunctional initiator 1,2-bis(2′-bromobutyryloxy)ethane in combination with CuBr and bipyridine. The Br-PSt-Br reacted with silver perchlorate at −78 °C, and the resulting macromolecular initiator was used to initiate the polymerization of tetrahydrofuran. Triblock poly(tetrahydrofuran)-polystyrene-poly(tetrahydrofuran) (PTHF-PSt-PTHF) diol was obtained after propagation at −15 °C. The conversion of the polymerization was measured by gas chromatography. The structures of the triblock copolymer PTHF-PSt-PTHF diol were characterized by 1H NMR and gel permeation chromatography. The mechanism of cationic ring-opening polymerization is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 337–344, 2000

Recent studies of the structure and properties of block copolymers of polystyrene and polybutadiene are reviewed, with special emphasis on the effect of the structure and of the formation conditions for the samples on the interrelated physico-mechanical properties. Problems associated with the macro- and micro-layering of block copolymer solutions are examined in detail. Work on the analysis of block copolymer structures from measurements of sorption characteristics is reviewed in the light of an assumed relaxation mechanism for the sorption and swelling processes. The prospects of controlling the structure and properties of block copolymers are shown to be good. The bibliography contains 190 references.

Adriamycin release from flower-type polymeric micelle based on star-block copolymer composed of poly(γ-benzyl l-glutamate) as the hydrophobic part and poly(ethylene oxide) as the hydrophilic part