Block copolymers inclusion complexes

The crystallinity of the PHB block in the copolymers increases as compared with that of the pure PHB precursor, presumably being caused by the presence of the soft PEG block. In contrast, the crystallinity of the PEG block in the copolymers decreases as compared with that of the PEG precursor because of the presence of a hard PHB block, which restricted the crystallization of the PEG blocks. Triblock copolymers with lower PHB contents such as EHE(20-05-20), EHE(50-08-50), and EHE(50-38-50) are water-soluble (the numbers in parentheses show the indicative molecular mass of the respective block in 100 gmoL ). Amphiphilic triblock copolymers can self-assemble to form micelles in an aqueous medium, and these micelles contain dense cores of the insoluble blocks, surrounded by diffuse outer shells formed by the soluble blocks. Li et al. (2005a, b) prepared a series of water-soluble EHE triblock copolymers and studied the micelle formation of the copolymers. Inclusion complexes of biodegradable amphiphilic EHE triblock copolymers with a-cyclodextrin or y-cyclodextrin were prepared from an aqueous medium. The formation of inclusion complexes led to an increase in the thermal stability of both cyclodextrins and the triblock copolymers (Li et al. 2003b). 

Interestingly, this behavior of the reaction mixture can be prevented by employing another principle of particle stabilization steric protection. Inclusion of pegylated comonomer (PEG-AEPD) into the reaction mixture did enable the formation of nonaggregating DNA particles. It also caused the particles to form worm -like structures (as judged by transmission electron microscopy) that have previously been observed with DNA complexes formed from block copolymers of PEL and PEG [98]. 

Summary The analysis of supramolecular structures containing polymers, and the discussion about the effect of polymeric materials with different chemical structures that form inclusion complexes is extensively studied. The effect of the inclusion complexes at the air-water interface is discussed in terms on the nature of the interaction. The entropic or enthalpic nature of the interaction is analyzed. The description of these inclusion complexes with different cyclodextrines with several polymers is an interesting way to understand some non-covalent interaction in these systems. The discussion about the generation and effect of supramolecular structures on molecular assembly and auto-organization processes is also presented in a single form. The use of block copolymers and dendronized polymers at interfaces is a new aspect to be taken into account from both basic and technological interest. The effect of the chemical structure on the self-assembled systems is discussed. 

Keywords Supramolecular system Block copolymer Self-assembled system Inclusion complexes Cyclodextrin Air-water interface Non-covalent interaction Auto-organization... 

To get a better insight into the dynamics of prepared ICs, more advanced NMR experiments were carried out [19]. Distinctive cross-polarization parameters were observed for guest polymer and host a-cyclodextrin in the inclusion complex. For a-CD, as expected from the relatively rigid molecule, the intensity quickly rises to a maximum, and then quickly decays. The behaviour is quite different for the PCL-PEO-PCL block copolymer, which has a slow rise in intensity followed by a slower decay. Maximum intensity was observed at 1 ms and 0.5 ms CP-time for PCL-PEO-PCL and a-CD. To evaluate the domain size... 

The inclusion complex formation between PEO blocks of the Pluronic copolymers and a-CD in the hydrogels was confirmed with wide-angle X-ray diffraction studies of the hydrogels [68], The effect of a-CD to aid the gelation of... 

Hydrogels formed by PEO block copolymers have previously been proposed as sustained release matrix [85,86], The a-CD-PEO hydrogel delivery system differs in that the gelation relies on the formation of a polymer inclusion complex induced by the PEO-threaded CDs. The properties of the supramolecular hydrogel can be fine-tuned with the composition, molecular weight and chemical structure of the polymer or copolymers. 

J5] have been reported. Recent work by Thomas and Harris [36-38 and Hollingsworth [JS] have shown that the inclusion phenomenon is much more complex, varied, and interesting than had been realized all along, and the latest review on urea/thiourea/selenourea inclusion compounds was published by them in 1996 [38b. The formation, characterization, and segmental mobilities of block copolymers in crystals of their urea inclusion compounds have been reported recently [39]. 

The inclusion complexes formed by a-CD and y-CD with PCL have been characterized by DSC, FTIR and X-ray diffraction [3,11]. These studies showed that complexes are formed and adopt channel structures. PCL and PEO chains of the triblock copolymer are included in both a- and y-CD/ICS, while the PS chains in the diblock copolymer are excluded from the channels of a-and y-CD/ICs. In the bulk PCL-PS diblock the PCL blocks do not crystallize, and so rubbery, amorphous PCL blocks are bonded to glassy, amorphous PS blocks. Figure 1 shows the 100 MHz solid-state NMR spectra for a-CD, PCL and the a-CD/PCL inclusion complex. The signals from PCL are easily identified and are well resolved from the a-CD signals in the complex. The chemical shifts for PCL in the inclusion complex are similar to those observed in the semicrystalline sample, suggesting that the PCL in a-CD channels adopts an extended all-trans conformation [3]. We can observe similar characteristics in the complex between PCL and y-CD. However, the cross polarization dynamics indicates that the maximum intensity for the PCL peaks was observed with a 4 ms cross polarization time, rather than the shorter 1 ms contact time used for the a-CD complex. 

An outstanding approaeh for the development of drug delivery systems has been recently presented by Zhang and Ma [99], In this work, the use of a P-cyclodextrin (P-CD) containing DHBC has been proposed for the inclusion of many hydrophobic substances. In their work, the synthesis of a bloek eopolymer with a PEG block and a polyaspartamide block carrying some P-CD units has been described. The P-CD imits are used as host sites for a plethora of hydrophobic small molecules, like pyrene and comnarine, as well as for hydrophobic polymers. However, the formation of inclusion complexes leads to the creation of located hydrophobic areas within the copolymer domain, which, in turn, has as a result the formation... 

The hypothesis is also supported by the number of a-CD rings threaded on a PEO chain and capped by bulky groups at the two ends [44], In the case of PEO-PHB-PEO block copolymer (PEO Mn = 5,000), the PEO segments covered by a-CD rings should be shorter than 2,000 from each end because of the steric hindrance effect, and the partial inclusion complexation of a-CD with PEO block with hydrophobic interaction of PHB blocks resulted in a strong network and a novel supramolecular hydrogel (Fig. 7c) [17]. 

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