PEO-related block copolymers

Mortensen, K., PEO-related block copolymer surfactants. Colloids and Surfaces A -Physicochemical and Engineering Aspects 2001, 183, 277-292. 

The diblock copolymers synthesized (Table 1) are structurally related to the commercially available poly(oxyethylene-alkyl ether) systems (Brij that are built from PEO blocks and hydrocaibon chains. These systems have been successfidly lied as templates in the synthesis of mesostructured silicate materials [2]. PDMS-PEO-based block copolymers are also known to exhibit a two-phase morphology in a certain set of solvents, which may be ascribed, to a first approximation, to the large difference in the solubility parameters of the PDMS and PEO blocks [5]. 

PEO-polypeptide block copolymers, another combination potentially interesting for biomedical applications, were also shown to produce stable monolayers with very interesting features relating to the orientation of peptide helices at the interface, additionally influenced by the presence of poly(ethylene glycol), PEG [48]. In particular, PEG seems to adsorb partly at the interface, and thus inhibits the perfect perpendicular arrangement of the polyleucine helices. On the other hand, the helical conformation of peptide segments is unaffected by the monolayer packing state, as shown by CD spectroscopy. 

Statistical and block copolymers based on ethylene oxide (EO) and propylene oxide (PO) are important precursors of polyurethanes. Their detailed chemical structure, that is, the chemical composition, block length, and molar mass of the individual blocks may be decisive for the properties of the final product. For triblock copolymers HO (EO) (PO)m(EO) OH, the detailed analysis relates to the determination of the total molar mass and the degrees of polymerization of the inner PPO block (m) and the outer PEO blocks (n). 

A related product is formed from the analogous reaction using hydroxyl-terminated PEO with aromatic diacids to form a segmented aromatic polyester block copolymer that is sold under the trade name Hytrel. 

The formation of disordered mesotunnels may be related to the change of hydrophobic/hydrophilic property of the block copolymers with temperature. When the hexagonal mesostructure is formed at low temperature, the hydrophilic PEO chains have strong interaction with the silica species and are partially occluded into silica wall [15]. The high temperature process would result in volume expansion of the block copolymer because the PEO chains become hydrophobic. The microporous void space in the wall would be attacked by the copolymer and become expanded, resulting in formation of the mesotunnels. It is also expected that by addition of TMB, the number and size of the mesotunnels increase because of larger volume expansion of the block copolymer caused from TMB. 

The most successful example is the control of window size of caged mesoporous silica materials synthesized with block copolymer as templates. The pore-entrance diameter of SBA-16 increases as a function of synthesis or hydrothermal-treatment temperature. This is likely to be related to the known phenomenon of the decrease in hydrophilicity of PEO blocks as the temperature increases. In the mesostructure of the F127-silica composite, the cores of the (spherical) micelles are constituted by PPO blocks, whereas the micelle corona, which consists of PEO blocks, interacts with the silica framework. At lower temperature, PEO blocks are expected to favorably interact with hydrophilic silica species and thus to have a tendency to be intimately mixed with the silica framework. When the F127-silica composite is subjected to the treatment at higher temperatures,... 

The block copolymer molecular mass (related strongly to the block lengths) determines the thickness of the vesicular membranes was experimentally proved for a series of PEO-fe-PBD polymers [24], Microscopy images evidenced an increase in the wall thickness upon increasing the polymer molecular mass in the range from 3,600 to 20,000g mol-1. 

Polyethylene oxide) and poly(N-alkylacrylamide)s are known to undergo a temperature-dependent phase change whereupon they separate from an aqueous phase at increased temperatures [14]. This inverse temperature dependence, i.e., the occurrence of a lower critical solution temperature, can be related to an entropi-cally favorable decrease in hydrogen bonding between water and the polymer with increasing temperature. In order to exploit this physical property for catalyst recovery, Bergbreiter et al. attached phosphines covalently to commercially available PEO or PEO-b-PPO-b-PEO block copolymers [Schemes 1 and 2 PPO = polypropylene oxide)] [9a],... 

One type of gel which has been extensively investigated in relation to pharmaceutical applications is that formed by certain PEO-PPO-PEO block copolymers (153). These systems are particularly interesting since even a concentrated polymer solution is quite low-viscous in nature at low temperature, whereas a very abrupt gelation (liquid crystal formation (25, 187, 188)) occurs on increasing the temperature. The precise value of the transition temperature depends on the polymer molecular weight, composition and concentration, the concentration and nature of the drug, etc., but by... 

Figure 3 shows typical TEM pictures of such gold colloid containing block copolymer films which were obtained after reduction of PS-b-PEO/LiAuCU complexes in toluene either by BHs/methanol or by N2H4(aq). It was generally observed that reduction with BHs/methanol led to bimodal products containing very small (1.5 nm) and larger (ca. 15 nm) particles in each micelle core (Figure 3A). In contrast, reduction with hydrazine hydrate led to particles with sizes mostly between 6 and 15 nm (Figure 3B). Size and location of the particles was, however, not directly related to a micellar film structure.

Figure 5 A Relation between LiAuCU loading and obtained particle size for PS-b-PEO block copolymers in toluene (1 wt%), and B particle size distribution of colloids protected by PS(610)-b-PEO(80) for different salt loadings.

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