Acrylic copolymers, lipophilicity

The lipophilicity of PSA polymers, which is markedly affected by chemical composition, may influence drug solubility (Table 5). In general, acrylic copolymers have medium lipophilicity compared with other PSA polymers, and have the most excellent drug solubility. A suitable lipophilicity of copolymers can be obtained by changing the compositional content of comonomers. The lipophilicity of acrylic copolymers can be roughly estimated by the theoretical calculation of the hydrophobic parameters of copolymers according to the hydrophobic fragments of each comonomer, or the calculation of the octanol-water partition coefficients (log PC). ... 

Silicone copolymer and SIS rubber (i.e., with a high lipophilic additive, paraffin) have a higher lipophilicity than acrylic copolymer. Hence, both bases give a much lower drug solubility than common acrylic copolymers. 

Theoretically, a chemical enhancer, which has a lipophilicity similar to the PSA matrix, will have the highest affinity for the adhesive matrix, thus having the lowest skin absorption. This would often happen with the same concentration of enhancers, but shows the different enhancing effects in the different PSA matrices. Table 6 shows the different enhancing effects of IPM in various acrylic adhesives with different lipo-philicities. Here, the concentration of FB is saturated in every adhesive, and the amount of IPM is fixed to be 38% in acrylic copolymers. In relation to be the... 

Acrylic adhesive Lipophilicity of copolymer Permeation flux (pg/cm /hr) Enhancement ratio... 

De Simone et al. synthesized poly(fluoroalkyl acrylate)-based block copolymers for use as lipophilic/C02-philic surfactants for carbon dioxide applications [181]. The particle diameter and distribution of sizes during dispersion polymerization in supercritical carbon dioxide were shown to be dependent on the nature of the stabilizing block copolymer [182]. 

EP 1402877 03/2004 Tepe/Rohm and Haas Composition containing at least one lipophilically modified copolymer (acrylic residues) and a colloidal inorganic clay. Thickener for high surfactant concentrations (>18%)... 

Studies have demonstrated that the degree of lipid absorption depends on the lipophilicity of the polymer (17). Enhanced lipid absorption was observed in block copolymers in which the lipid polar and hydrocarbon segments associated simultaneously with hydrophilic and lipophilic polymer chain regions, respectively. These results are supported by studies that have demonstrated the sorption of lipids by acrylic hydrogels to be inversely proportional to the hydrophilicity of the polymer (18). 

A considerable amount of work has focused on the design and synthesis of macromolecules for use as emulsifiers for lipophilic materials and as polymeric stabilizers for the colloidal dispersion of lipophilic, hydrocarbon polymers in compressed CO2. It has been shown that fluorinated acrylate homopolymers, such as PFOA, are effective amphiphiles as they possess a lipophilic acrylate-like backbone and C02-philic, fluorinated side chains, as indicated in Figure 4.5-1 [100]. Furthermore, it has been demonstrated that a homopolymer which is physically adsorbed to the surface of a polymer colloid precludes coagulation due to the presence of loops and tails [110]. These fluorinated acrylate homopolymers can be synthesized homogeneously in CO2 as described in an earlier section. The solution properties [111,112] and phase behavior [45] of PFOA in SCCO2 have been thoroughly examined. Additionally, the backbone of these materials can be made more lipophilic in nature by incorporating other monomers to make random copolymers [34]. 

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]. 

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