Oil prepolymerization

Figure 4. Effect of oil prepolymerization on morphology of 15/85 epoxidized lunaria oil-dimer acid/polystyrene network SINs. Acid values A, 98 B, 75 C, 55.

Figure 5, Effect of oil prepolymerization (morphology) on dynamic moduli of epoxidized lunaria oil SINs.

High Impact Polystyrene by Prepolymerization in a Water-in-Oil Emulsion Followed by Suspension Polymerization... 

The rubber particle size in the final product increases several fold if the prepolymerization is carried out in the presence of a dilute aqueous solution of an alkane sulfonate or polyvinyl alcohol in place of pure water. The addition of a surface-active agent converts the coarsely dispersed oil-water mixture—obtained as above in the presence of pure water—into an oil-in-water emulsion. In this case even prolonged stirring during prepolymerization does not decrease the rubber particle size appreciably in the final product. The stabilization of the droplets of the organic phase in water by the emulsifier obviously impedes or prevents agitation within the polymeric phase. Figure 1 shows the influence of these three prepolymerization methods (under otherwise equal reaction conditions) on the dispersion of rubber particles in polystyrene. 

Simultaneous IPNs are formed by homogeneously mixing together monomers, prepolymers, linear polymers, initiators, and crosslinkers, The monomers and prepolymers are simultaneously polymerized by independent reactions that differ enough to avoid interfering with each other. For example, a polyure-thane/polymethacrylate and a polyurethane/polystyrene were made in a process in which both monomers were prepolymerized, dissolved together, and reacted to form an IPN. Another urethane system was made from castor oil reacted with toluene diisocyanate and sebacic acid polyesters. The resultant urethane prepolymer was then mixed with polystyrene to form an IPN. 

Linseed oil is prepolymerized at 60°C under oxygen. The resulting linoxyn is then homogenized at 150 C to a tough gel with colophonium or copal resin. This gives linoleum cement, which is mixed with fillers and dyes, rolled onto a jute backing, and hardened to linoleum. 

The radical prepolymerization occiurs in the oil-in-oil emulsion state. As the reaction proceeds, the copolymer of styrene and acrylonitrile is produced, and when the ratio between the produced copolymer and polybutadiene rubber reaches 1 1, the phase inversion occurs. Thereafter, styrene/acrylonitrile copolymer is present in the continuous phase, and polybutadiene rubber is present in the dispersed phase. In general, the phase inversion is terminated when the polymerization conversion rate reaches about 15%. The particle size is varied depending on the change in stirring rate, the viscosity ratio between the rubber phase and the monomer phase, and the interfacial tension. 

In contrast (Fig, 2E), when the oil was prepolymerized (but not to the point of gelation) prior to addition of the styrene, such PS domains were evident, as found previously for a castor-oil-based SIN (9) and high-impact polystyrene (HIPS) (16). It is evident from Figs. 2A and 2B that when the oil is not prepolymerized prior to adding the styrene-DVB the resulting elastomer phase exhibits a lower rubber-phase volume fraction (RPVF) than is the case when the oil is prepolymerized. 

For the 10/90 SINs, the values of (elastomer phase) and Tg2 (plastic phase) shown in Table 4 tena to be lower than those of the homopol3nners (9,10). The observed trend suggest that molecular mixing between the plastic and rubber phases is more extensive for the case of no prior prepolymerization. Similarly for 15/85 SINs (see Table 5), the Tg behavior changes with the acid value (depending on the type of oil) until the rubber becomes the discontinuous phase, shown in Figs. 5 and 6. However, after exceeding this critical value, the 15/85 compositions exhibit an anomalous upward... 

As seen in Fig. 9, with one exception (ELO not prepolymerized), the relaxation times are increased over that of the homopolymer PSN control. While the exact reason is not known, the general phenomenon probably involves a reduction of free volume, and analogous tendencies have been noted for epoxies (20, 23, 23a). Often this is caused by the visiting molecule (the oil) taking up free volume in the host (the epoxy), thus raising Tg. 

Initially, styrene monomer is completely miscible with the oil prepolymer, but as the styrene polymerizes to high molecular weight polystyrene, the two components phase separate from each other. At this point, it is thought that the oil-rich phase is continuous, and the polystyrene-rich phase discontinuous. If the oil is not prepolymerized, a phase inversion will occur, as in Figures 4-A and 4-B. For extensive prepolymerization, the oil remains continuous, but the domains are smaller. As described below, the morphology of Figure 4-C yielded the highest impact resistance. 

The pure polystyrene phase in the highly prepolymerized system should have no shift in Tg, since no miscibility is expected between the high molecular weight oil and polystyrene, which is observed (Figure 5, A.V. = 47). The oil-polyester phase in this case contains more polystyrene than in the non-prepolymerized case, causing a more pronounced shift in the oil-polyester Tg. This is due to the trapping effect of the gel, since some of the polystyrene to polymerize inside of the oil-polyester phase may not be able to nucleate a phase domain, or diffuse to an already formed domain. 

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