Block copolymer-homopolymer mixture

Electron spectroscopy has been utilized by a number of investigators to study the surface behavior of block copolymers and block copolymer/homopolymer mixtures (17-19,24,25). 

Block copolymer/homopolymer mixtures have been of considerable interest because they can be easily modified to yield desired properties in polymeric materials such as pressure sensitive adhesives. Phase behavior of these mixtures is generally quite complicated because two different natures of transition can occur at the same time macrophase and microphase separation. If the molecular weight of a... 

Instead of the familiar sequence of morphologies, a broad multiphase window centred at relatively high concentrations (ca. 50-70% block copolymer) truncates the ordered lamellar regime. At higher epoxy concentrations wormlike micelles and eventually vesicles at the lowest compositions are observed. Worm-like micelles are found over a broad composition range (Fig. 67). This morphology is rare in block copolymer/homopolymer blends [202] but is commonly encountered in the case of surfactant solutions [203] and mixtures of block copolymers with water and other low molecular weight diluents [204,205]. 

Macrophase separation after microphase separation has been observed in an AB block copolymer/homopolymer C blend (Hashimoto et al 1995). Blends of a PS-PB starblock copolymer (75wt% PS) and PVME homopolymer were prepared by solvent casting. Binary blends of PS and PVME exhibit a lower critical solution temperature (LCST), i.e. they demix at high temperatures. The initial structure of a 50% mixture of a PS-PB diblock and PVME shown in Fig. 6.20(a) consists of worm-like micelles. Heating led to macrophase separation as evident... 

The homopolymer of DMP dissolves readily in methylene chloride but precipitates on standing as a crystalline polymer-CH2Cl2 complex, providing a method for distinguishing between block copolymers and mixtures of homopolymers. Random copolymers prepared by methods a and b form stable solutions in methylene chloride. Copolymers with a 1 1 ratio of DMP and DPP prepared by methods c and d also yield stable methylene chloride solutions. Since the NMR spectrum shows that the DMP portion of these materials is present as a block and the solubility in methylene chloride shows that DMP homopolymer is absent, these copolymers have the block structure. They can be separated by crystallization from m-xylene into an insoluble DPP-rich fraction and a soluble DMP-rich fraction, both fractions having the NMR spectra characteristic of block copolymers. A typical 1 1 copolymer prepared by adding DMP to growing DPP polymer yielded 35% of insoluble material... 

The product from Run A was found to be completely soluble in s-tetrachloroethane at room temperature, whereas poly(chloro-p-xylyl-ene) is insoluble in this solvent at all temperatures. These marked changes in solubility characteristics are considered excellent evidence for the formation of random copolymers rather than block copolymers or mixtures of homopolymers. 

Thus, how should block copolymers between styrene and a vinyl ether be prepared Starting with styrene or with a vinyl ether In the former system, the propagating styryl cation is intrinsically more reactive but present at much lower concentration. A rough estimate of the ratio of cation reactivities is = 103 but the ratio of carbocations concentrations is = I0 S. Thus, the ratio of apparent rate constants of addition is 10-2. Macromolecular species derived from styrene should add to a standard alkene one hundred times slower than those derived from vinyl ethers. Thus, one cross-over reaction St - VE will be accompanied by =100 homopropagation steps VE - VE. Therefore, in addition to a small amount of block copolymer, a mixture of two homopolymers will be formed. Blocking efficiency should be very low, accordingly. 

In the case of diblock copolymer melts, which are the simplest model system for the elucidation of structure formation processes involving BCPs in nanoporous hard templates, only the two immiscible blocks have to be considered as components. Self-consistent field methods were applied to study the morphologies of liquid diblock copolymer/homopolymer mixtures that were considered as a model system for triblock copolymers in sol solutions [182], of pure diblock copolymer melts [200-202], and of order-disorder transitions in diblock copolymer melts [203]. For example, Li et al. found for a model diblock copolymer that forms cylinders in the bulk... 

In general, graft copolymers consist of a polymer backbone to which another polymer is chemically attached as side chains. The backbone and side chain polymers may be homopolymer, random copolymers, block copolymers or mixtures of the various types. For example, most graft copolymers of cellulose consist of a homopolymer backbone (cellulose) and another homopolymer (e.g. polystyrene) or a random copolymer (e.g. polystyrene-co-acrylic acid). 

If the noise term is turned off, the system is driven towards the nearest saddle point. Therefore, the same set of equations can be used to find and test mean-field solutions. The complex Langevin method was first applied to dense melts of copolymers [74], and later to mixtures of homopolymers and copolymers [80] and to diluted polymers confined in a slit under good solvent conditions [77]. Figure 2 shows examples of average density configurations (p ) for a ternary block copolymer/homopolymer system above and below the order/disorder transition. 

Such definitive forecasts do not result from the theories of Leibler or Hong and Noolandi. However, the latter theory describes in detail the phase diagram for copolymer — homopolymer mixtures and is therefore pertinent to the X-ray work of Roe Similarly, Leibler s theory provides a detailed description of a microphase separation mechanism and thus is of value in the interpretation of experiments investigating this phenomenon. Small angle neutron scattering data reported to date has been maitily concerned with pure styrene-diene block copolymers which are fully microphase separated and thus examined D, dj, and interfadal layer thickness as a function of molecular weight and composition and therefore comparison has usually been made with the MIA theory of Helfand. 

The behavior of ternary polymer mixtures containing a diblock copolymer with homopolymer and toluene as a function of mixture composition and temperature were investigated to obtain experimental phase diagram for solvent/copolymer/ homopolymer mixture. In order to avoid the complications associated with the microphase separation of block copolymers, the molar mass of block copolymer was kept low in our experiment (Madbouly Wolf, 2002). 

Similar to core-shell structures reported in hydrogen-bonded block copolymer/homopolymer systems, core-shell micelle formation through electrostatic interaction were also reported. These complexes were generally formed at equimolar ratio of polycations and polyanions. But non-stoichiometric mixtures can also be employed to increase the stability... 

Table 3.4 Temperature Coordinate and Relative Height (in Parenthesis) for the Two Loss Tangent Maxima Observed in Mixtures of Isoprene-Butadiene Block Copolymers with Homopolymers of These Two Repeat Units in the Same Proportion ...

The catalysts described in Table XII cannot be used to make tailored-block copolymers because of reaction (19). The latter continues in the absence of monomer resulting in detachment of chains from the transition metal centers forming hydride (XX). Introducing a second monomer would lead to realkylation of the chain centers giving a homopolymef of the second monomer. Hence mixtures of homopolymers would be obtained with little block-copolymer formation. 

The transformation of the chain end active center from one type to another is usually achieved through the successful and efficient end-functionalization reaction of the polymer chain. This end-functionalized polymer can be considered as a macroinitiator capable of initiating the polymerization of another monomer by a different synthetic method. Using a semitelechelic macroinitiator an AB block copolymer is obtained, while with a telechelic macroinitiator an ABA triblock copolymer is provided. The key step of this methodology relies on the success of the transformation reaction. The functionalization process must be 100% efficient, since the presence of unfunctionalized chains leads to a mixture of the desired block copolymer and the unfunctionalized homopolymer. In such a case, control over the molecular characteristics cannot be obtained and an additional purification step is needed. 

Employing similar procedures, PPO-fc-POEGMA block copolymers and POEGMA-fc-PPO-fc-POEGMA triblock copolymers were prepared from the corresponding PPO macroinitiators [129]. The polymerizations were performed in a isopropanol/water (70/30) mixture at 20 °C using CuCl and bpy. The methacrylate monomer was almost quantitatively polymerized, and the polydispersities were lower than 1.25 in most cases. Less than 5% PPO homopolymer contamination was detected by SEC analysis. 

A second method for preparing block copolymers is a crosscoupling process. A low molecular weight coupling reagent is added to a mixture of poly(phenylene oxide) and a second homopolymer with phenolic hydroxyl endgroups such as 7 (9) or 8 (10) in the presence of sodium hydroxide and catalyst. 

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