Intramolecular phase separation

Fast growing Interest in block copolymers originates from the Intramolecular phase separation, which Is responsible for some unique properties involving many potential applications. In this field again major progress has been accomplished due to the availability of the "living" anionic polymerization techniques. 

The chief reason for the interest in graft copolymers originates from the incompatibility between polymer chains of different chemical nature. Intramolecular phase separation results, because grafts and backbone repell each other, and these compounds exhibit a marked tendency to form mesomorphic phases like block copolymers and soaps do. When these species are mixed with a solvent that exhibits a preferential affinity for one of the components (grafts or backbone) the incompatibility may be enhanced. This intramolecular phase separation has led to a number of applications. If small amounts of a graft copolymer are included into a homopolymer of the same nature as the grafts (or the backbone), surface modifications can result as described below. 

In all three cases, it can be assumed that the grafts are distributed at random along the polystyrene backbone chain. These species exhibit a strong tendency to intramolecular phase separation as it could be expected with backbones and grafts of different chemical nature. Moreover, they display quite different affinities to solvents. Applications of these compounds are searched for as materials of biomedical interest. 

The multiblock side chains not only increase the stmaural components, but also introduce new morphology and properties. AB-type diblock side chains may include block segment combinations of soft-hard, hydrophilic-hydrophobic, and crystalline-amorphous, and, therefore, the entire bmshes resemble intramolecularly phase-separated cylindrical micelles. 

Among a variety of present stmctures, core-shell molecular bmshes that contain diblock copolymers in the side chains are of special interest. A judicious choice of the two blocks in the side chains may result in an intramolecular phase separation in solution due to their unlike interactions with the solvent. This can aeate a ID channel in the core surrounded by a protective shell. The anisotropically shaped core can be practically used as a nanoreactor to synthesize and accommodate ID inorganic or hybrid nanostmctures. According to the chemical nature of the core and shell, the templates can be classified roughly into three forms, namely, amphiphilic, bishydrophilic, and self-templating core-shell molecular bmshes. 

Intramolecular Phase Separation Within Cylindrical Copolymer Brushes with... 

In summary, there is ample evidence for the occurrence of intramolecular phase separation in cylindrical copolymer bmshes. Since the phase separation is restricted to a length scale of a few nanometers, direct proof is extremely difficult to achieve. In addition, the computer simulations outlined in Sect. 3.5 will show that statistical... 

Fig. 29 Proposed scenario for the intramolecular phase separation and subsequent ordering, in order to explain the X-ray scattering peak corresponding to a mean distance of 17.25 nm of correlated scattering objects [95]...

In most cases the different constituent blocks are incompatible, giving rise to intramolecular phase separation, but the chemical connectivity restricts the special dimension of phase segregation to the nanoscale. As a result, at sufficiently high molecular weight, monodisperse block copolymers form a rich variety of self-assembled structures or an array of periodic nanostructures with a periodicity of 10-100 nm, commonly referred to as microphase-separated structures. By changing the relative composition, the compatibility between the component polymers, and the architecture of the copolymer molecules, the size and type of nanostructures can be precisely controlled [1-6]. 

The norbornadiene dimer exo-trans-exo-pentacyc ote-tradeca-5,11-diene has been employed as a crosslinking agent for the controlled synthesis of these star-shaped copolymers in the catalytic presence of W(CHr-Bu)(NAr)(0/-Bu)2 or Mo(CHr-Bu)(NAr)Or-Bu)2 [66], Star polymers in which the arms are block copolymers of different polarities can be prepared by this method, as well as star polymers in which the composition of the arms is different, as are the solubility characteristics and stereochemical regularity. Heterostars thus obtained, in which the number of the different arms will be approximately equal, may exhibit interesting intramolecular phase separations. 

Based on those results we reasoned that a strong intramolecular phase separation is the origin of the Cub phase, and we tried the MD simulation of a liquid crystal with perfluorinated alkyl chains at both ends of a rodlike molecule, PFMI6 (the molecular structure is shown in Fig. 10.40) [108, 109]. We simulated a system composed of 256 PFMI6 molecules at two temperatures, in the smectic C (SmC) phase at 530 K, and in the cubic phase at 570 K. 

Many graft copolymers have been made by free radical copolymerization of co-styryl or co-methacryloyloxy macromonomers and various comonomers. Special interest has been devoted to amphiphilic copolymers involving a hydrophilic backbone and hydrophobic grafts, or vice versaf Poly(perfluoroalkyl methacrylate) and poly(stearyl methacrylate) are typical examples of hydrophobic polymers, whereas poly(hydroxyethyl methacrylate) or poly(vinylpyrrolidone) are examples of nonionic hydrophilic chains. Such graft copolymers have found a number of applications as surface modifiers or coatings because of their ability to give intramolecular phase separation (surface accumulation phenomena ). 

Other imperfections are developed in the process of crosslinking network defects (unreacted functionalities, intramolecular loops, chain entanglements), inhomogeneity in crosslink distribution, or heterogeneity of the network due to phase separation. These four types of network imperfections are interdependent and a sharp borderline between them does not exist. 

An example of this case is a vinyl (A2 ) - divinyl (A4) polymerization. The assumption of an ideal polymerization means that we consider equal initial reactivities, absence of substitution effects, no intramolecular cycles in finite species, and no phase separation in polymer- and monomer-rich phases. These restrictions are so strong that it is almost impossible to give an actual example of a system exhibiting an ideal behavior. An A2 + A4 copolymerization with a very low concentration of A4 may exhibit a behavior that is close to the ideal one. But, in any case, the example developed in this section will show some of the characteristic features of network formation by a chainwise polymerization. 

The room temperature Raman spectra of the intramolecular modes between 100 cm and 2000 cm are reported for alkali-metal doped A,C films. For A = K, Rb, and Cs, phase separation is observed with the spectra of C,jo> K jC oj RbaC joj... 

In experimental studies, where the loss of fluidity is taken as marking the gel point, the conversion at the observed gel point is almost always found to be higher than that (calculated) at the theoretical gel point. This can be explained by the model proposed by Bobalek et al (1964) for the gelation process, as shown in Fig. 5.8. According to this model, at the theoretical gel point, a number of macroscopic three-dimensional networks (gel particles) form and undergo phase separation. The gel particles so formed remain suspended in the medium and increase in number as reaction continues. At the experimentally observed gel point, the concentration of gel particles reaches a critical value and causes phase inversion as well as a steep rise in viscosity. The lower value of pc predicted by the statistical approach is also attributed to the occurrence of some wasteful intramolecular cy-clization reactions not taken into account in the derivation and also in some cases to the limited applicability of the assumption of equal reactivity of all functional groups of the same type, irrespective of molecular size. 

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