Surfactant monomers, homogeneous distribution

In these studies, polymeric nanocapsules with encapsulated dsDNA (790 base pairs) were produced via anionic polymerization of n-butylcyanoacrylate (BCA) carried out at the interface of homogeneously distributed aqueous droplets in inverse miniemulsion which are in a second step then redispersed in an aqueous continuous phase. The obtained capsules were characterized in terms of size, size distribution, morphology, polymer molecular weight, and encapsulation efficiency of DNA. The effects of surfactant type and concentration, viscosity of the continuous phase, monomer amount, and water-to-oil ratio were investigated and results are discussed in this paper. 

Copolymerization of a water-soluble monomer and a surfactant monomer can be performed in organic solution or in aqueous media in the presence or absence of noiqrolymeriz le surfactants (19,38-41). In aqueous media, micelle or emulsion polymerization may occur, by which copolymers with a blocky sequence distribution of tte surfactant comonomer unit may be obtained (19,22,38-40,42). In contrast, homogeneous polymerization in organic solution may yield copolymers with a random distribution. The association behavior of the copolymer depends strongly on the sequence distribution of surfactant comonomer units (19,20,26,39,43,44). To obtain copolymers with a random distribution of and DEmMA (Chart 1), homogeneous solution polymerization... 

In the semibatch experiments, the particle size distributions of the final latexes were affected by the residual surfactant in the seed latex, which tended to facilitate homogeneous nucleation during the entire feed period. The monomer feedrate determined the polymerization rate and had little effect on copolymer composition. The polymer compositions for the runs with different monomer feeding modes tended to be identical at very low feedrate. 

The Eqs. (5.210) and (5.211) describe the diffusion of monomers and micelles as before. The physical meaning of Eq. (5.212) is not so obvious. It can be regarded as the equation of the local balance of surfactants in micelles. If the initial distribution of micelles is homogeneous and only the monomer concentration is perturbed, the first relaxation proeess can lead to the dependence of the aggregation numbers on space coordinates and time even in absence of a concentration gradient of the total number of micelles. Surfactants can be transferred not only as a result of the monomer diffusion but due to the diffusion of aggregates of different aggregation numbers. This effect is described by equation (5.212). 

The mixed sur ctant systems have found rather extensive use for industrial production of PVC latexes. A major advantage of the method is that a separate homogenization stq) is avoided. The relatively large size and the broad size distribution of the spontaneously formed monomer droplets are maintained in the final latex. Disadvantages of the process are the requirements made with respect to the structure of the fatty alcohol and ionic surfactant, and to the absolute amounts and the ratio between the two components. Also, the method only permits a limited variation of the size and size distribution of the final latex. 

Micro-emulsion Swollen monomer micelles dispersed in a continuous phase fairly large concentrations of surfactants required initiator dissolved in continuous phase Polymerisation initiated in the course of nucbation of monomer micelbs process characterised by continuous nucleation during entire reactbn fast rate of polymerisation (< 30 min) Particbs of very small si (diameter <100 nm) and narrow distribution polymer with ultra-high molecular weight (> 10 g/mol) copolymers with well-defined, homogenous composition... 

Micro-emulsion is another variant of emulsion polymerisation. Such emulsions are thermodynamically stable systems including swollen monomer micelles dispersed in a continuous phase. In general, they require fairly large concentrations of surfactants to be produced compared with the other dispersed polymerisation systems. Hence, the interfacial tension of the oil/water is generally close to zero. Polymers with ultra-high molecular weight, i.e. above 10 g/mol, can be obtained, as can copolymers with a very well-defined, homogenous composition. Whereas polymerisation can take 24-48 h in the normal emulsion process, it proceeds at a fast rate in micro-emulsion, as total conversion can be obtained in less than 30 min. Polymer particles of very small size (diameter < 100 nm) and narrow distribution can be obtained by this process. 

Microsuspension polymerization, in which a monomer-soluble initiator is used. Polymerization takes place within the fine droplets in which the monomer is dispersed by passing a coarse emulsion of monomer, initiator, and surfactant through a mechanical homogenizer (24-26). The resulting particle size distribution is Gaussian between 0.2 and 1.2 /xm. 

Those who are interested in the recipes (e.g., monomers, surfactants, costabilizers, and initiators), preparation (e.g., homogenization equipments and processes), and characterization (e.g., monomer droplet size and droplet size distribution and colloidal stability) of monomer miniemulsions are referred to references 12 and 13. 

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