DDFT is applied to phase formation in homopolymer/copolymer blends in which the copolymer is extremely disperse with a uniform chemical composition distribution. Such systems develop a core/shell structure with a thick interface. This study is motivated by peculiarities in the phase evolution of industrial PP high‐impact copolymers. It is demonstrated that it is possible to reach time and length scales of relevance for realistic industrial blend systems. A rational method for improving the numerical efficiency of the calculations is presented. The model can be applied to a variety of industrially relevant systems with similar “random chemistry” or extreme copolymer dispersity in coatings, crude oil recovery systems, food emulsions, and so forth.
We present a computer study of the association behavior of copolymer chains with a gradient part and soluble tail of variable length. As a simulation method we use dynamic Monte Carlo simulation on a simple cubic lattice with pair interaction parameters. The solvent quality and selectivity is modeled by the variation of pair interaction parameters between nearest neighbors on the lattice. The role of the length of soluble part in the self‐assembly and its effect on the structure of aggregates was the main goal of this work. The size and structure of aggregates were analyzed using an improved topological classification method which has been developed and tested in the present study. The structure and association numbers of aggregates were compared with those of linear diblock copolymers.
Summary: Amphiphilic graft polyphosphazenes (EtTrp/PNIPAm‐PPP) with different mole ratios of hydrophobic groups to hydrophilic segments were synthesized by ring‐opening polymerization and subsequent substitution reactions. The self‐assembly behavior of these graft copolymers was studied in detail by TEM, SEM, CLSM, and AFM. Depending on the copolymer composition and common organic solvent employed in dialysis process, supramolecular aggregates ranging from network, nanospheres, high‐genus particles to macrophage‐like aggregates were produced with graft copolymers.
Hydrogen‐bonded supramolecular copolymers were easily prepared by mixing cyclohexanetricarboxamides with three ( 1 ) and six ( 2 ) alkylsilyl groups, and supramolecular fibers were fabricated. When the composition of 1 and 2 was at or close to equimolarity, the supramolecular copolymer chain was found to have an alternating sequence. This was attributed to the fact that the steric factor of the alkylsilyl side chains effectively controls the unit sequence of the supramolecular polymer chain.
Random copolymers of poly(9,9‐di‐n‐octylfluorene) (PF8) incorporating 0, 8, 12, 15, and 20% dibenzothiophene (DBT), and copolymers with 2, 5, 8, 12, and 15% dibenzothiophene‐S,S‐dioxide (S‐unit) were synthesised. Absorption and emission spectra of thin films indicate that the DBT system shows a linear decrease of toluene vapour induced β phase with increasing DBT content to a 20% cutoff, whilst in the S‐unit copolymers the β phase is present up to 12% co‐monomer content, and at 15% the characteristic absorption peak is absent or masked. These results demonstrate the limits, in thin films, at which the β phase can be formed in widely used PF8 copolymer systems for device applications and clearly show that it is practical to use copolymers having electron or hole transport units in the polyfluorene backbone and still be able to form efficient β phase emission sites.
A series of novel biodegradable random copolymers of 5‐benzyloxy‐1,3‐dioxan‐2‐one (5‐benzyloxy‐trimethylene carbonate, BTMC) and glycolide were synthesized by ring‐opening polymerization. The copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The incorporation of BTMC units into the copolymer chains results in good solubility of the polymers in common solvents. The in vitro degradation rate can be tailored by adjusting the composition of the copolymers.
The in vitro degradation of the homopolymers and poly(BTMC‐co‐GA) copolymers. 相似文献
Summary: Novel biodegradable copolymers derived from succinate, butan‐1,4‐diol, and butan‐1,4‐diamine were synthesized by two‐step polycondensation reactions. The obtained copolymers had a periodical‐sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.
Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine 相似文献
While network‐like assemblies are formed by amphiphilic polyphosphazenes with poly(N‐isopropylacrylamide) and ethyl tryptophan as side groups in aqueous solution, a significant morphology transformation is observed when small molecules that exhibit hydrogen‐bonding interactions with amphiphilic copolymers are introduced during the preparation of polymeric assemblies through a dialysis procedure. Depending on copolymer composition and the content of small molecules introduced, aggregates ranging from general vesicles, high‐genus vesicles, to well‐defined nanospheres can be prepared successfully as clearly evidenced by TEM observation, which suggests this procedure should be a novel approach to prepare composite vesicles.
We report a new method for the synthesis of block copolymers with a pentasilane core by the polymerization of alkyl methacrylate monomers using the pentasilyl dianion as an initiator. The polymerization proceeded with living features and yielded the corresponding block copolymers with controlled molecular weights. The amphiphilic block copolymer was obtained by the polymer reaction, and it formed sphere‐like aggregates in MeOH/H2O solution.
The synthesis of diblock copolymers of aromatic polyether and polyacrylonitrile (PAN) was conducted by chain‐growth condensation polymerization (CGCP) and atom transfer radical polymerization (ATRP) from an orthogonal initiator. When CGCP for aromatic polyether was carried out from a PAN macroinitiator obtained by ATRP with an orthogonal initiator, decomposition of the PAN backbone occurred. However, when ATRP of acrylonitrile was conducted from an aromatic polyether macroinitiator obtained by CGCP followed by introduction of an ATRP initiator unit, the polymerization proceeded in a well‐controlled manner to yield aromatic polyether‐block‐polyacrylonitrile (polyether‐b‐PAN) with low polydispersity. This block copolymer self‐assembled in N,N‐dimethylformamide to form bundle‐like or spherical aggregates, depending on the length of the PAN units in the block copolymer.
Investigations on the self‐assembly of block copolymers in solution have in some way a less well‐studied history than the study of their phase separation in the solid state, and many aspects are yet not completely understood. Here we focus on the behavior of a specific class of copolymers, namely semicrystalline block copolymers, capable of forming cylindrical aggregates in a solvent selective for the non‐crystalline, complementary block. A common model of micellization is proposed, in principle applicable to most of these copolymeric systems.
Perfectly alternating copolymers can be synthesised by reacting diacrylates with terminal dienes using alternating diene metathesis polycondensation (ALTMET). This novel method is very versatile and allows preparation of diverse structures of polymers, including main‐chain liquid crystalline polymers.
Main‐chain liquid crystalline polymer obtained by ALTMET. 相似文献
The self‐assembly of amphiphilic diblock copolymers in block selective solvents is well documented in the scientific literature. It gives rise to micelles in which the insoluble blocks form a core, which is surrounded by a corona that contains the soluble blocks. Another method to trigger micellization consists in introducing additional non‐covalent interactions such as electrostatic interactions or hydrogen bonding in an initially soluble block copolymer. The non‐covalent complexes that result from these interactions should be insoluble in order to induce micellization. Such insoluble complexes can be generated by mixing, in a non‐selective solvent for all the individual blocks, two block copolymers or a block copolymer and a homopolymer, that contain mutually interacting blocks. This mixing process may, therefore, lead to insoluble non‐covalent complexes, which further aggregate into micellar cores stabilized by the uncomplexed blocks. Such a strategy has been successfully implemented in both aqueous and non‐aqueous solvents to create interesting stimuli‐responsive systems, mainly using ionic interactions and hydrogen bonding. This feature article will summarize these approaches.
Summary: Like in many other cases, block copolymers bearing alkoxysilyl groups in one segment self‐assemble into aggregates. However, they may allow one to study the sol‐gel reaction by making use of the gelable groups located in the domains of the aggregates, therefore, the gelation process can be made in a selected domain of the nanoscale. As a result, the organic nanostructure is transformed into an organic/inorganic hybrid. The process of using covalently grafted alkoxysilane groups along the block copolymer precursors is applicable not only to the aggregates formed in solution, but also to the other forms of aggregates in melts, thin films, and interfaces. In this feature article, this emerging field is introduced, mainly focusing on the gelation that occurs inside the preformed block copolymer aggregates in solution. The morphologically fixed hybrid nanoparticles, such as spheres, hollow particles, and complex hollow particles, are presented and discussed. This technology has great potentials in the fields of nanomaterials and nanotechnologies, since various organic/inorganic hybrid nanoparticles and nanostructures can be effectively generated using this process.
Gelation in preformed block‐copolymer aggregates generates controlled structures. 相似文献
Highly dispersed ZnO nanoparticles with variable particle sizes were successfully prepared within an amphiphilic hyperbranched polyetherpolyol matrix via decomposition of an organometallic precursor in the presence of air leading to stable nanocomposites. The high degree of stabilization during and after the synthesis by the polymer permits control over the nanoparticle size and therefore, due to the quantum‐size‐effect, the particle properties. Furthermore, these polymer‐inorganic nanocomposites can easily be dispersed in apolar solvents to yield highly transparent, stable solutions.
A new type of polymeric hybrid coating is created by layer‐by‐layer deposition of polyelectrolyte multilayers (PEM) onto nano‐patterned polymer brushes (NPB). The PEM is a hydrogen‐bonded multilayer consisting of poly(acrylic acid) and poly(acrylamide) and the NPB is derived from a surface reactive rod‐coil block copolymer, polystyrene‐block‐poly[3‐(triethoxysilyl)propylisocyanate]. The thickness of the PEM coating is optimized with respect to the height of the NPB mounds, to yield PEM/NPB hybrid coatings with unique nano‐embossed or nano‐porous structures that can be interchangeable by heating and moisture annealing. The hybrid coating is patternable by the micro‐contact printing method. The results demonstrate that the combination of surface‐bound, hydrophobic NPB layer with hydrophilic PEM films at the nanoscopic level offers a new organic hybrid coating with novel surface properties.
Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.
The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.
Summary: A new computational algorithm for dynamic lattice Monte Carlo simulations of the associative behavior of heteroarm copolymers in selective solvents was developed and optimized for efficient and relatively fast simulation studies. The algorithm is based on the Siepmann and Frenkel variant of the bias self‐avoiding walk procedure. Simultaneously, a new criterion for recognition of an associate was proposed. The first results on the micellization of heteroarm star copolymers are presented.
