Hydrophobic Modification of Hydrophilic Polymers

Given the shortcomings of an approximate analytical treatment and the difficulties with the laboratory measurements, it is conceivable that computer simulations might help greatly in verification of the qualitative arguments presented above. 

In this model, the solvation free energy, A/ s, required to transfer an M-site molecule from vacuum to polar solvent (e.g., in water) is approximated by the 

To give a visual impression of the simulated system. Fig. 7 presents a typical snapshot of an amphiphilic copolymer having a 256-unit hydrophilic backbone with 64 attached hydrophobic side groups. Already from this picture, it is seen that, using the synthetic strategy described above, one can indeed end up with a copolymer having a dense hydrophobic core surrounded by a hydrophilic shell. 

From the picture presented in Fig. 7, one can expect that the sequential hydrophobization of a polymer coil should lead to a copolymer with a non-random sequence distribution. This is indeed the case. As an example, let us consider the average number fractions of blocks consisting of i neighboring amphiphilic monomers, (f), occurring in a copolymer chain. Some results are shown in Fig. 8 on a semilogarithmic scale. 

copolymers of the same composition can have quahtatively different sequence distributions depending on the solvent in which the chemical transformation is performed. In a solvent selectively poor for modifying agent, hydrophobically-modified copolymers were found to have the sequence distribution with LRCs, whereas in a nonselective (good) solvent, the reaction always leads to the formation of random (Bernoullian) copolymers [52]. In the former case, the chemical microstructure cannot be described by any Markov process, contrary to the majority of conventional synthetic copolymers [ 10]. 

In a dilute solution, when the polymer is in a coil state (Fig. 6a), the diffusion of hydrophobic particles into the coil is normally faster than the chemical reaction [53]. In this case, the local concentration of particles H inside the coil is practically the same as in the bulk. Therefore, we expect that at the initial stage, the reaction will lead to a random copolymer some of the P monomeric units will attach to H reagent and thereby they will acquire amphiphilic (A) properties P + H —A (Fig. 6b). As long as the number of modified A units is not too large, the chain remains in a swollen coillike conformation (Fig. 6b). However, when this number becomes sufficiently large, the hydrophobically modified polymer segments would tend to form 

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