Amphiphilic polymers comonomers

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"... 

Thus in the emulsifier-free emulsion copolymerization the emulsifier (graft copolymer, etc.) is formed by copolymerization of hydrophobic with hydrophilic monomers in the aqueous phase. The ffee-emulsifier emulsion polymerization and copolymerization of hydrophilic (amphiphilic) macromonomer and hydro-phobic comonomer (such as styrene) proceeds by the homogeneous nucleation mechanism (see Scheme 1). Here the primary particles are formed by precipitation of oligomer radicals above a certain critical chain length. Such primary particles are colloidally unstable, undergoing coagulation with other primary polymer particles or, later, with premature polymer particles and polymerize very slowly. 

Recently, Siu et al. [139] studied the effect of comonomer composition on the formation of the mesoglobular phase of amphiphilic copolymer chains in dilute solutions. The copolymer used was made of monomers, N,N-diethylacrylamide (DEA) and N,N-dimethylacrylamide (DMA). like PNI-PAM, PDEA is also a thermally sensitive polymer with a similar LCST, but PDMA remains water-soluble in the temperature range (< 60 °C) studied. At room temperature, copolymers made of DMA and DEA are hydrophilic, but become amphiphilic at temperatures higher than 32 °C. Before the association study, each P(DEA-co-DMA) copolymer was characterized by laser light scattering to determine its weight average molar mass (Mw) and its chain size ( Rg) and (R )). The copolymer solutions (6.0 x 10 A g/mL) were clarified with a 0.45 xm Millipore Millex-LCR filter to remove dust before the LLS measurement. 

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. 

As the polymer concentration increases, interchain association inevitably occurs, but some amphiphilic chains can undergo a limited interchain association to form a stable mesoglobular phase that exists between microscopic single-chain globules and macroscopic precipitation. As expected, when the solvent quality changes from good to poor, intrachain contraction and interchain association occur simultaneously and there exists a competition between these two processes. Such a competition depends on the comonomer composition and distribution on the chain backbone and also depends on the rate of micro-phase separation. When intrachain contraction happens quickly and prior to interchain association, smaller mesoglobules are formed. A proper adjustment of the rates of intrachain contraction and interchain association can lead to polymeric colloidal particles with different sizes and structures. 

Perfluoroalkyl groups are also introduced into block copolymers with methacrylates, acrylates, and styrene (B-46 to B-53), which can be synthesized in scCC>2 or in the bulk.95,315 Amphiphilic block copolymers based on glycopolymer segments (B-54 and B-55) are synthesized by copper-catalyzed polymerizations.321,322 Comonomers with a polyhedral oligomeric silsesquioxane unit afforded hybrid polymers between organic and inorganic components (B-56 and B-57).326... 

This review introduces the method of active ester mtheris, and discusses its application to the preparation of a variety erf specialty polymers, including amphiphilic gels, graft copolymers, and side chain reactive and liquid crystalline polymers. The polymerization and copolymerization of activated acrylates by solution and suspension techniques are discussed, and polymer properties such as comonomer distribution, molecular weights, C-NMR spectra and gel morphology are reviewed. Potential applications of these polymers are also highlighted, and the versatility of active ester synthesis as a new dimension of creativity in macromolecular chemistry is emphasized. 

Multifunctionality can be introduced not only through copolymerization but also by polymer analogous reactions in a postpolymerization modification step, often in combination with the introduction of additional comonomers during the polymerization process. Well-known technical examples are copolymers of polyvinyl alcohol and polyvinyl acetate with different amounts of vinyl acetate (see Section 3.1.3), which all derive from homopoly(vinyl acetate) and are the result of acetate hydrolysis to a different extent. The content of remaining vinyl acetate groups defines the hydrophilicity/hydrophobicity of the copolymer and thus the amphiphilic and stabilizing character of the material. 

Further, the ability to synthesize random copolymers with various hydrocarbon monomers allows the anchor-soluble balance to be tuned while maintaining solubility even with high incorporations of hydrocarbon comonomers [29]. Because of the amphiphilic nature of such copolymers, it was predicted that these materials would selfassemble into micelles consisting of a highly fluorinated corona segregating the lipophilic core from the compressed CO2 continuous phase. Thus, PFOA-F-PS block copolymers were synthesized via controlled free-radical techniques (Fig. 9.3), and it was confirmed (by smaU-angle neutron scattering) that these copolymers spontaneously assemble into multimolecular micelles in solution [40]. In addition to amphiphilic materials, which physically adsorb to the surface of polymer particles in dispersion polymerizations, fluorinated acrylates can be utihzed as polymerizable comonomers in the stabilization of C02-phobic polymer colloids [41]. 

The use of phospholipids to mimic cell walls has been one commercially successful coating strategy. To create a polymer surface with phospholipid-type properties, two routes are possible. The polymer surface can be modified by the attachment of the biological molecule of interest, as described in the modification of polymer surfaces with phosphorylcholine (72-74), amphiphilic molecules (75) or liposomes. Alternatively, phosphorylcholine moieties have been incorporated into artificial surfaces by using polymerizable precursors the most representative monomer is 2-methacryloxyethylphosphorylcholine (MFC) 16, 17). Block copolymers of phosphorylcholine with other hydrophobic comonomers like lauryl methacrylate (75) also have been found to be effective. 

A styryl-type macromonomer having a water-soluble ROZO segment (Scheme 47) or having an amphiphilic ROZO block copolymer (Scheme 51) was extensively used as surfactant for the emulsion or dispersion polymerization. Polymerization of St or MMA in the presence the macromonomer as stabilizer (less than 3 wt% for the total monomer) in water took place with a radical initiator to give stable monodisperse polymer particles with a micron-size diameter. The macromonomer acted as both comonomer and stabilizer actually the copolymerization occurred. Therefore, the system is micelle forming but soap-free. Hydrophilic PMeOZO segments are preferential on the particle surface. 

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