Random-type amphiphilic copolymers

Fig. 1 Vesicle construct formed from poly(L-lysine)-i)-poly(L-leucme) polypeptides where the poly(L-leucine) block corresponds to the a-helical hydrophobic segments and the poly (L-lysine) block corresponds to the random coil hydrophilic segments. Note that this is one specific example and not all vesicle constructs have a-helical and random coil blocks. Moreover, the amphiphilic copolymer can be comprised of either a pure block copolypeptide or a macromolecule consisting of a polypeptide and another type of polymer. Adapted from [20] with permission. Copyright 2010 American Chemical Society...

Siloxane amphiphilic copolymers are a class of silicone surfactants consisting of a methylated siloxane hydrophobe attached to one or more polar chains such as poly(oxyalkylene). The blocks in the copolymer can be arranged in a linear fashion (as in A-B-type block copolymer) or, as in graft copolymers, one type of blocks can be attached (usually randomly) to a linear, backbone chain of the other type of blocks. Siloxane amphiphiUc copolymers are of special interest since their hydrophile-hydrophobe balance can be easily tailored by changing the length of the corresponding blocks [26-28]. 

Polymeric surfactants can be homopolymers, random amphiphilic copolymers, and of the A-B (diblock), A-B-A (triblock), and BA (graft) types [23]. The A chain is referred to as the stabilizing chain (soluble in the medium), and the B chain is referred to as the anchor chain (insoluble in the medium with strong affinity to the surface). The simplest type of a polymeric surfactant is a homopolymer, such as PEO and poly(vinyl pyrrolidone) (PVP). Homopolymers are not the most suitable surfactants and it is better to use polymers with some groups that have affinity to the surface. The most employed copolymers are random amphiphilic copolymers, like poly(vinyl alcohol), diblocks of polystyrene-block-poly(vinyl alcohol) (PS-b-PVA), poly(ethylene oxide)-block-polystyrene (PEO-b-PS), and triblocks of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO, Pluronic) (PPO resides at the hydrophobic surface, leaving the two PEO chains dangling inaqueous solution), andpoly(ethyleneoxide)-block-polystyrene-block-poly(ethylene oxide) (PEO-b-PS-b-PEO). The graft copolymer is referred to as a comb stabilizer Atlox 4913,... 

A polymer is considered to be a copolymer when more than one type of repeat unit is present within the chain. There are a variety of copolymers, depending on the relative placement of the different types of repeat units. These are broadly classified as random, block, graft, and alternating copolymers (see Fig. 2.1 for structural details Cheremisinoff 1997 Ravve 2000 Odian 2004). Among these stmctures, block copolymers have attracted particular attention, because of their versatility to form well-defined supramolecular assemblies. When a block copolymer contains two blocks (hydrophobic and hydrophilic), it is called an amphiphilic diblock copolymer. The immiscibility of the hydrophilic and lipophilic blocks in the polymers provides the ability to form a variety of assemblies, the stmctures and morphologies of which can be controlled by tuning the overall molecular weight and molar ratios of the different blocks (Alexandridis et al. 2000). 

The synthesis of a miktoarm star copolymer of the type AnBn has been also demonstrated. The synthesis was performed via ATRP using divinylbenzene, as the core cross-liking agent. PEO macroinitiator chains were utilized for the polymerization of divinylbenzene forming a star polymer, with a random number of branches. The above star polymer was used as a multi-functional initiator for the polymerization of methacrylate monomers. Therefore, the synthesis of an amphiphilic miktoarm star copolymer was realized [54]. Finally, the hydrolysis of the protected methacrylate block led to the preparation of the desired DHBCs, namely the PEOn-PMAA stars. SEC analysis of the preeursor PEOn-PMMA copolymer revealed a relatively broad molecular weight distribution. Nevertheless, this is a good example for the synthesis of A Bn double hydrophilic star copolymers. 

The macromonomer has a hydrophilic PEG segment, and hence its GROP-type copolymerization with PhOZO proceeded randomly to give an amphiphilic graft copolymer PPhOZO-g-PEG, showing good surfactant nature with a y value of 28.8 dyn cm ... 

An appropriate overall amphiphilic balance in a polymer chain may be a key to successful sensitive phase separation. This concept was evidenced by phase separation behavior of a polymer with an alcohol pendant having a fine balance between hydrophilidty and hydrophobicity. Ahydroxybutyl group is a rearrangement of an ethoxyethyl unit, and is expected to have a similar overall amphiphilic balance. Aqueous solutions of 23 (Figure 17) underwent rapid phase separation at 42 ° The corresponding polymer with branched alcohol pendants showed a lower critical temperature. Another type of polymers with fine-tuned amphiphilidty would be random copolymers of hydrophobic... 

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