DPUR particle Swelling

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... 

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). 

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 ... 

---