Asymmetric block copolymers ring polymers

Unfortunately, neither an accurate location of the transition temperature nor a study of the order of the transition has been possible so far. The value of e at the transition increases with increasing deviation of/from 1/2, which is qualitatively consistent with theoretical predictions. Unfortunately, the Monte Carlo data are too crude to allow any quantitative test of the theory. Also Fig. 7.39 reveals small but systematic deviations from the scaling with the variable eN, but again the data are too crude to 

4 Block copolymers in reduced geometry thin films, interfaces, etc. 

A very interesting problem is the adsorption of block copolymers at the interface between incompatible homopolymers,which lower the interfacial tension and therefore act as compatibilizing agents in such blends. This phenomenon has been studied theoretically (e.g.. Refs 200-203, 207), experimentally (e.g.. Ref. 206), and by Monte Carlo simulation. In the last work the A, B homopolymers are not included explicitly in the simulation, however, and their existence shows up only indirectly via suitable energy parameters which differ in the A-phase (for z T/2) from those in the B-phase (for z Ljl). The A-B interface hence is sharp on the scale of the lattice spacing and treated as strictly localized. Wang et al treat L lattices with lattice sizes up to = 50 and up to 400 chains of composition Na= Nb = ox variable / with N = 10 up to /= 3/4, and discuss the description of the block copolymer adsorption at the A-B interface in terms of Langmuir-type isotherms. 

L = 24 and a repulsive interaction = ab/2 at the two hard Lx L walls). All snapshots refer to tAslksT = 0.6, and show only A-monomers as block dots, while neither B-monomers nor vacancies are shown, and also the bonds connecting the monomers are not displayed. Part (a) refers to Z) = 30, part (b) to Z = 14, part (c) to Z) = 24. (From Kikuchi and Binder..  

For some problems, however, the shortness of the chains is still a limitation, as well as the lattice structure (which prevents the study of critical dynamics, later stages of spinodal decomposition, etc., where the fluid nature of real polymer melts and blends is essential). While future work could clearly address questions such as mixtures of block copolymers and homopolymers, asymmetry effects (different stiffness of chains, etc.) and interfacial structure, one needs to develop complementary molecular dynamics methods for the study of dynamical phenomena in mixtures and block copolymer melts. 

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The first report of ROMP activity by a well-characterized Mo or W species was polymerization of norbornene initiated by W(CH-t-Bu)(NAr)(0-f-Bu)2 [122]. In the studies that followed, functionality tolerance, the synthesis of block copolymers, and ring-opening of other monomers were explored [30, 123]. Two important issues in ROMP concern the cis or trans nature of the double bond formed in the polymer and the polymer s tacticity. Tacticity is a consequence of the presence of two asymmetric carbons with opposite configuration in each monomer unit. The four ROMP polymers (using polynorbornene as an example) that have a regular structure are shown in Scheme 3. 

Fig. 24 Self-assembled morphologies of an asymmetric diblock copolymer confined to cylindrical pores obtained by a simulated annealing method as a function of the ratio Dp/Lo> where Lq is the period of the BCP, for different wall-polymer interactions. The parameter Dp/f-o is given underneath each morphology. The outmost circles in the top views indicate the wall of the cylindrical pores. For some large diameters, the inner ring is shown separately, a The pore wall attracts the majority blocks b the pore wall attracts the minority blocks c neutral pore walls. Reproduced from [213]. (2006) American Physical Society...

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