Hyperbranching, block copolymers

We are currently initiating three research projects that include (1) the synthesis of reflective liquid crystal/polymer composite films, (2) a study of microphase separation in hyperbranched block copolymers, and (3) the design and synthesis of polar organic thin films, which is the subject of this proposal. (47 words aim for 41 words)... 

For the synthesis of linear hyperbranched block copolymers an analogy may be drawn to the linear dendrimer block copolymers. In a pioneering paper, the group of Kricheldorf suggested the use of terminally functional linear polymers as monoftmctional terminating agents or macro-cores for the synthesis of linear hyperbranched block copolymers. However, since a major side reaction is the well-known cydiza-tion of the focal A-group in the synthesis of hb polymers by polycondensation (see above), preparation of a block copolymer with narrow polydispersity cannot be achieved in this manner. 

Tian, H.Y., Deng, C., Lin, H., Sun, J., Deng, M., Chen, X. and Jing, X. (2005) Biodqpadable cationic PEG-PEl-PBLG hyperbranched block copolymer synthesis and micelle characterization. Biomaterials, 26,4209-4217. 

Compared to linear multiblock copolymers, the study on the phase behavior of hyperbranched multiblock copolymers has received less attention due to the lack of model samples. To the best of our knowledge, only a handful of work reported the related results [44, 77]. Namely, Hutchings et al. comparatively studied the phase behaviour of hyperbranched block copolymer hyper-(PS-PI)n and its linear precursor PS-PI-PS [44]. The TEM results indicated that the tendency of phase separation was strongly suppressed by the branching structure, as shown in Fig. 1.7 unfortunately, the structure of the studied hyperbranched samples were still not as perfect as we defined before [44]. 

Similar to the synthetic process of macromonomer polystyrene homopolymer, we have also synthesized Seesaw-type macromonomer triblock copolymer [1]. This is because we have been interested in the phase behaviors of long linear multiblock copolymer chains in selective solvents for many years [18, 19]. Therefore, we intentionally prepared Seesaw-type macromonomer triblock copolymers to construct hyperbranched block copolymers and study their solution properties. 

Fig. 3.11 IR spectra of PfBA23"PS 14-P/BA23. where a before and b after azidation c after clicking reaction to form hyperbranched block copolymer hyper-(PrBA23-PSi4- PfBA23)73 and d after hydrolysis of tert-butyl groups to form hyperbranched block copolymer hyper-(PAA23-PS14- PAA23)73...

Fignre 4.13 shows four relatively narrowly distributed hyperbranched block copolymers < 1.40) resulted from the precipitation fractiona-... 

Fig. 4.12 Initial macromonomer concentration dependence of SEC curves of resultant hyperbranched block copolymers, hyper-(PtBA23-PSi4-PtBA23)n, after 24 h polycondensation of triblock PtBA23-PSi4-PtBA23 in DMF at 35 °C...

F. 4.13 SEC curves of four fractions of hyperbranched block copolymer hyper-(P/BA23-PSi4-P/BA23)n with different overall molar masses, which were obtained by precipitation fractionation... 

Solution Properties of Hyperbranched Block Copolymer Hyper-(PtBA-PS-PtBA)n and Hyper-(PAA-PS-PAA) ... 

Previously, we successfully prepared narrowly distributed amphiphilic hyperbranched block copolymer hyper-(PtBA36-PS55-PtBA36)600- In this section, we ll see how these ultialarge hyper-(P/BA36-PS55-P/BA36)6oo chains fold and associate... 

Experimental Details About Hyperbranched Block Copolymers... 

A PEG-PEl-PBLG hyperbranched block copolymer was prepared by amine-initiated NCA polymerization from the primary amine groups of poly(ethylene imine) (PEI), which had been coupled to a PEG chain via a diisocyanate. The hyperbranched block copolymers form micelles in aqueous solution with a large hydrophobic core and a cationic corona further stabilized by the PEG chains (see Fig. 21). The micelles can form complexes with DNA via electrostatic interaction, and enzymatic degradation of the micelles was shown in vitro. The copolymers therefore might be useful as new vectors for gene delivery [38]. 

Fig. 21 (a) PEG-PEI-PBLG hyperbranched block copolymer and (b) cationic micelle. Symbol "Oplus" Represents protonated PEI in aqueous condition. Reprinted with permission from [38]. Copyright (2005) Elsevier... 

Scheme 36 Synthetic approach to a linear-hyperbranched block copolymer using polystyrene-Woc/f-poly[(hydroxyethyl)ethylene] (PS-O-(PB-OH)) as initiating core . Reprinted with permission from Barriau, E. Garcfa Marcos, A. Kautz, H. Frey, H. Macromol. Rapid Commun. 2005,26,862. Copyright Weley-VCH Verlag GmbH co. KGaA.

Application of hyperbranched block copolymers as templates for the generation of nanoporous organosilicates. High Perform. Polym. 13 SI 1-S19 Hedrick, J. L., Hawker, C. J., Trollsas, M., Remenar, J., Yoon, D. Y., and Miller, R. D., 1998, Templating nanoporosity in organosilicates using well-defined branched macromolecules. Mat. Res. Symp. Proc. 519 65-75. 

Scheme 29 Synthesis of amphiphilic linear-hyperbranched block copolymer of PEG and HBPA...

Rezaei, S. J. T, Abandansari, H. S., Nabid, M. R., Niknejad, H. [2014]. pH-responsive unimolecular micelles self-assembled from amphiphilic hyperbranched block copolymer for efficient intracellular release of poorly water-soluble anticancer drugs,/. Colloid Interfaces Sci., 425, 27-35. 

---