Hydrophobic comonomers

Morishima etal. [29 — 31] prepared amphiphilic copolymers of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) with various hydrophobic comonomers, and studied the tendency of their self-aggregation and the nature of the hydrophobic microdomains thus formed in aqueous solution. Chart 1 shows some of these amphiphilic copolymers. Here, the value of x indicates the mol% content of hydrophobic comonomer units. 

A number of diblock copolymers of NIPAM and hydrophobic comonomers have been prepared by various groups and assessed in terms of micellar structure, thermosensitivity, and applications. For example, PS-fo-PNIPAM was shown to form either micelles consisting of a PS core and a PNIPAM corona, or vesicles. The assemblies were colloidally stable at elevated temperature [262-266]. 

For self-emulsification the molar mass of the EUP must be within a certain range. If the molar mass is too high, the solubility of the EUP is too low. If the molar mass is too low, the solubilizing efficiency is insufficient. With an EUP from maleic anhydride (MA) and hexanediol-1,6 (HD) and acid terminal groups, the optimal molar mass for the solubilization of a hydrophobic comonomer, such as styrene (S), was found to be between about 1700 and 2200 [116]. 

The rate of pinocytosis (cellular uptake) may be influenced by molecular weight [131], charge [22] and incorporation of hydrophobic comonomers [21] among others. 

As mentioned in Sect. 2.2.3, the biodistribution of HPMA copolymers depends on many factors. Molecular weight influences the uptake in the isolated tissue of yolk sac [266] as well as the elimination in vivo [124, 125,267,268]. Nonspecific increase in the rate of polymer uptake can be achieved by incorporation of positively charged or hydrophobic comonomers into the HPMA copolymer structure, such as methacryloyloxyethyltrimethylammonium chloride [22], N-methacryloyltyrosinamide [21], or N-[2-(4-hydroxyphenyl)ethyl]acrylamide [267]. The incorporation of hydrophobic moieties may influence the solution properties of the HPMA copolymer conjugates [132,134,269]. The interaction with the cellular surface may depend on the association number and the stability of the micelles. 

MACA as a hydrophobic comonomer can be used to modify PNIPAM. Copolymers, PNIPAM-co-MACA with different amounts of MACA can be synthesized by free-radical copolymerization of NIPAM and MACA in a mixture of methanol and chloroform with AIBN as the initiator. The resulting copolymers after purification can be dried in vacuum at 40 °C for 24 h. Hereafter, these copolymers are denoted as PNIPAM-co-x-MACA, where x denotes the molar percent of MACA. As expected, their solubility in water decreases as the MACA content or the solution temperature increases. It is also expected that the copolymer chains with a higher MACA content would have a lower LCST in comparison with PNIPAM homopolymer chains. In order to prepare a true solution, one has to dissolve these copolymers in water at low temperatures. The chemical structure of PNIPAM-co-MACA is as follows (Scheme 7). 

Recently, we surprisingly found that even hydrophobically modified PNIPAM-co-MACA comonomer chains can form stable mesoglobules at higher temperatures [142]. Moreover, opposite to our expectation, the PNIPAM copolymer with a higher content of hydrophobic comonomer could... 

The comonomer distribution can be alternated by controlling the synthesis conditions, such as the copolymerization at different reaction temperatures at which the thermally sensitive chain backbone has different conformations (extended coil or collapsed globule). In this way, hydrophilic comonomers can be incorporated into the thermally sensitive chain backbone in a more random or more segmented (protein-like) fashion. On the other hand, short segments made of hydrophobic comonomers can be inserted into a hydrophilic chain backbone by micelle polymerization. One of the most convenient ways to control and alternate the degree of amphiphilicity of a copolymer chain, i.e., the solubility difference of different comonomers in a selective solvent, is to use a thermally sensitive polymer as the chain backbone, such as poly(N-isopropylacrylamidc) (PNIPAM) and Poly(N,N-diethylacrylamide) (PDEA). In this way, the incorporation of a hydrophilic or hydrophobic comonomer into a thermally sensitive chain backbone allows us to adjust the degree of amphiphilicity by a temperature variation. 

On the other hand, hydrophobic comonomers, such as 2,-methacryloyl-aminoethylene)-3a, 7a, 12a -trihydroxy-5/3-cholanoamide (MACA) and styrene (St), can be incorporated into the thermally sensitive chain backbone by copolymerization of different comonomers in a common organic solvent, which results in a random distribution of hydrophobic comonomers on the chain backbone, or by micelle copolymerization in water with the help of surfactant micelles in which hydrophobic comonomer molecules are concentrated, which leads to evenly distributed short hydrophobic segments on the chain backbone. 

Considering the competition between intrachain contraction and interchain association, we have to discuss an overlooked viscoelastic effect in the formation of stable mesoglobules in dilute solutions. Otherwise, it would be difficult to understand why copolymer chains with a high content of hydrophobic comonomers could form smaller interchain aggregates. In the micro-phase separation, copolymer chains in solutions contract and associate. The collision between contracted and associated chains would not be effective if the collision (or contact) time (rc) is much shorter than the time (re) needed to establish a permanent chain entanglement between two ap-... 

Synthesis and Characterization. The transition temperature (Tc) of NIPAAm copolymers can be modified by a hydrophilic or hydrophobic comonomer. This phenomenon has already been explained on the basis of inter-molecular and intramolecular hydrogen bond formation between the solvent (water) and polymer chains [6,7],... 

To obtain amphiphilic polymers, different concepts are conceivable to introduce amphiphilic moieties into the polymer backbone. They are schematically summarized in Figure 5. Polymers of type A and B can be realized, if a polymerizable group is introduced into the hydrophobic group (type A) or hydrophilic group (type B) of a conventional surfactant, which exhibit the liquid crystalline state in solution. Copolymerization of a hydrophilic and a hydrophobic comonomer yields amphiphilic copolymers of type C. According to the convention, these polymers may be called "amphiphilic side-chain polymers"... 

Copolymers of type C offer an additional feature changing the composition of the hydrophilic and the hydrophobic comonomers, the hydrophilic/hydrophobic balance of the copolymers can be easily varied without changing the chemical structure of the starting material (28). Table 1 displays the results of non-ionic copolymers. In the case of a suitable monomer... 

The concept of polymeric soil release agents has been around for well over 25 years. The initial polymer chemistries (polyethylene terephthalate-polyoxyethylene terephthalate, PET-POET) were designed to deposit on fabrics and facilitate oily soil removal upon subsequent washing [98,133,134], The limitation of this chemistry was its effectiveness on synthetics (polyester) alone, with limited benefits being observed on cotton and synthetic blends. In recent years the focus has shifted to delivering soil release on cotton. Two classes of polymer chemistries have been disclosed in the recent patent literature for cotton soil release one based on hydrophobically modified polycarboxylates derived from acrylic acid and hydrophobic comonomers at defined molar ratios [188] and the other based on modified polyamines [189-193],... 

Y. Kaneko, R. Yoshida, K. Sakai, Y. Sakurai and T. Okano, Temperature-responsive shrinking kinetics of poly(Y-isopropylacrylamide) copolymer gels with hydrophilic and hydrophobic comonomers, J. Membr. Sci., 1995, 101, 13 Y.H. Lim, D. Kim and D.S. Lee, Drug releasing characteristics of thermo- and pH-sensitive interpenetrating polymer networks based on poly(W-isopropylacrylamide), J. Appl. Polym. Sci., 1997,... 

Copolymerization. Synthetic HMWSPs can be prepared according to this approach by the copolymerization of a vinyl or epoxide monomer (4) with a small amount of a specific hydrophobic monomer that is copolymer-izable with the primary monomer as shown in Scheme II. The hydrophobe content of the polymers can be tailored by controlling the amount of the hydrophobic comonomer used in the polymerization process. The nature of the group (i.e., ether, ester, carbamate, etc.) connecting the long-chain... 

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