DPUR particle

When the process is carried out according to Method la it may be assumed that the kind of initiating system (water-soluble initiator or redox system) does not have any significant effect on the morphology of hybrid dispersion particles since the polymerisation proceeds mainly on the surface of DPUR particles and monomer droplets and in the micelles of emulsifier. In the case of water-soluble initiator (potassium persulphate) the polymerisation starts in water where the ion-radicals are formed from the monomer molecules dissolved in water. These ion-radicals can diffuse to DPUR particles, monomer droplets and emulsifier micelles. After this happens the system will consist of ... 

When polymerisation is carried out after initial swelling of DPUR particles in monomers (Method lb), then formation of separate particles of acrylic/styrene polymer is also possible, but much less probable since the amoimt of monomer present in the system as monomer droplets is very low in this case (assmning that the amount of monomer used to swell DPUR particles was not higher than the maximmn amount resulting from the equilibrium swell curve (see Section 6.5.4)). It can be anticipated that in this method of MDPUR synthesis many more hybrid particles of much more uniform structure will be formed than when the monomers are continuously added to the reaction system (Method la), especially when a... 

In this case it can be assumed that polymerisation will proceed in a similar way as described previously for Method lb. The only difference may be that both structure and size of DPUR particles formed from the prepolymer-ionomer diluted with monomers will differ from the standard case, i.e., when NMP is used as diluent for prepolymer-ionomer. Moreover, some fraction of the monomer molecules may be so closely trapped in the crosslinked polyurethane-urea structure in DPUR particles that their participation in polymerisation will be difficult. This may lead to a decrease in average MW of acrylic/ styrene polymer which will be formed inside DPUR particles. 

The maximum degree of swelling of DPUR particles with monomers was determined using the equilibrium swelling method described in Section 6.4.3. 

Table 6.6 Composition of MDPUR-ASD prepared accordii to method lb (polymerisation of monomers in DPUR after swelling DPUR particles with monomers) ...

Investigations of the Course of Swelling of DPUR Particles with Monomers... 

S.4.2 Determination of the Maximum Degree of Swelling of DPUR Particles... 

Investigations of swelling of DPUR particles with monomers indicate that although all monomer being fed into the system may theoretically enter DPUR particles, since the maximum degree of swelling is more than twice that of the monomer/ DPUR solids w/w ratio used commercially in synthesis of hybrid dispersions, in practice there will always be a natural tendency of the system to reach equilibrium between monomer droplets, non-swollen DPUR particles and swollen DPUR particles. Therefore, when hybrid dispersions are prepared according to method la, lb or 2 (see Section 6.3.2) the result will always be a mixture of particles of hybrid structure with DPUR and ASD particles, as has been explained in Section 6.3.2.1). 

Particle size distribntion and zeta potential determined for one of the DPUR from Table 6.1 are shown in Figures 6.10 and 6.11, respectively. TEM photographs of the particles of the same dispersion are shown in Figure 6.12. 

Figure 6.10 Particle size distribution for typical DPUR synthesised in this study (DPUR...

Figure 6.12 Particles of typical DPUR synthesised in this study (DPUR 237 from Table 6.1). Photograph was taken using TEM technique. Reproduced with permission from Professor I. A. Grickova at Lomonosov...

Figure 6.26 Changes of particle size distribution in the course of swelling of DPUR...

This experiment was aimed at clarifying what is the maximum amount of monomer that would he able to swell polyurethane-urea, i.e., would be able to take part in the formation of hybrid dispersion particles, assuming that enough time is allowed to achieve equilibrium. Films made from DPUR 25 8 were used in this experiment. The following resnlts were obtained ... 

In this study, aqueous hybrid polyurethane-urea-acrylic/styrene polymer dispersions were obtained using four different methods. The dispersions are stable and their viscosity, and pH as well as average particle size and particle size distribution are similar to those observed for DPUR. Most of the hybrid dispersions formed transparent films of good mechanical properties, water resistance and organic solvent resistance. 

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