Miktoarm copolymers

Relatively few theoretical studies have been devoted to the conformational characteristics of asymmetric star polymers in solution. Vlahos et al. [63] studied the conformational properties of AnBm miktoarm copolymers in different solvents. Analytical expressions of various conformational averages were obtained from renormalization group calculations at the critical dimensionality d=4 up to the first order of the interaction parameters uA> uB> and uAB between segments of the same or different kind, among them the radii of gyration of the two homopolymer parts < S > (k=An or Bm) and the whole miktoarm chain < /im > > the mean square distance between the centers of mass of the two homopolymer parts A and B < > and the mean square distance between the center of... 

Fig. 3. Expansion factor oG of the mean square distance between the two centers of mass as a function of Ob for miktoarm copolymers AxBf x with x=2 and various values of f-x. ua=ub= >uab — /8 (reproduced with permission from [63])...

Fig. 8. a Comparison of the spinodal curves %Nt(fA) for diblock and different ABn miktoarm copolymers with n=2,3, and 4. The experimental results from an AB2 ( ) and the two AB3 ( , Q) miktoarm stars are shown together with the investigated temperature range (vertical lines), b Critical values of %Nt plotted as a function of the number of arms of the B blocks. The dependence of the optimal composition corresponding to the minima of the spinodal curves are also shown. The line is only a guide to the eye (reproduced with permission from [78])... 

Fig. 12. Schematic representation of proposed arrangement of A/B junctions on a triply periodic IMDS of constant mean curvature for SB-4 miktoarm copolymer of Fig. 11 (reproduced with permission from [62])...

The homopolymer arms in miktoarm stars are predicted, by the renormalization method, to expand monotonically, reaching a limit which is dictated by the increase in the size of the other kind of homopolymer arms. The whole molecule seems to increase in size monotonically with molecular weight and functionality. The same behavior is predicted for any part of the molecules consisting of two or more arms of different homopolymers. This work was expanded with the study of A2B and A3B miktoarm copolymers. The dimensionless ratio 6q, which expresses quantitatively the effect of heterointeractions between unlike units on the conformational properties of copolymers, was calculated by an intrinsic viscosity analysis. It is defined as... 

ABC, AB2, ACz, and ABD miktoarm copolymers, where A is PEG, B is poly(D-lactide) (P(D)IA), C is poly(L-lactide) (P(L) LA) and D is PS, were prepared via ROP and NMP and their combination. The first step involved coupling of a hydroxyl funaional monomethyl ether PEG oligomer to a carboxylic acid funaional carbonate 23. The cyclic carbonate of the... 

Figure 12 (a) Structural analogy between a phospholipid molecule (left) and an AB2 3-miktoarm copolymer (right) to form a bilayer vesicle (b) chemical structure of PEGm-f (PLLA )2. Reprinted from Yin, H. Kang, S.-W. Bae, Y. H. Macromo/ecw/es 2009, 42, 7456.2 ... 

Figure 1 Example block copolymer architectures available, (a) Linear diblock copolymer, (b) linear multiblock copolymer, (c) miktoarm copolymer, (d) star copolymer, (e) linear-graft copolymer, and (f) cyclic diblock copolymer. In all cases, the different colors represent different block chemistries.

The production of a mixture was unfortunate. However, the presence of the p-(PtBA)2(PM-MA)2 contaminant should not stop the self-assembly of p-(PtB A)(PMMA)2 in the solid state, or in block-selective solvents. It will only shift the phase diagrams of p-(PtBA)(PMMA)2 somewhat. As far as the preparation of materials from the self-assembly of miktoarm copolymers is concerned, the presence of this contaminant is therefore of no consequence. 

In conclusion, we have been able to use the assembly or association and reaction strategy to prepare miktoarm copolymers. For this particular system, we could separate the pure miktoarm star polymers from their precursors by fractionation precipitation. We are now working on the preparation of p-ABC and p-ABCD polymers from this technique and are exploring the applications of the p-ABC or p-ABCD polymers produced. 

The miktoarm star block copolymers (Fig. 5.14b and d) exhibited morphologies quite different from those observed for their linear analogs. The TEM for the (PCL2)39-( -(PS2)6i miktoarm copolymer (where the subscripts outside the brackets indicate the composition in wt%, while the superscript denotes the number average molecular weight of the entire block copolymer), see Figure 5.14b, exhibits a cylindrical... 

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