Styrenic phase

Another study that focussed on the glass transition temperature of such composites revealed that the a-relaxation in the acrylonitrile/ styrene phase is broadened towards higher glass transition temperatures. It is believed that the shift arises due to the interaction located at the boundary layer between polymer and CNTs (51). 

In HIPS, desirably the PS is the continuous phase including a discontinuous phase of rubber particles. The size and distribution of the rubber particles in the continuous PS phase can affect the properties of the HIPS. In blends of PS with other materials, the distribution of the noncontinuous phase in the continuous poly(styrene) phase is often similarly important (2). The impact strength of HIPS can go up to sevenfold of that of general purpose PS. 

Figure 2 shows that the different methods of preparation give the same results. The butadiene phase is dark, the styrene phase pale. 

Further details of the phase separation of polymer mixtures were obtained by analyzing the high styrene phase sedimented at a weight concentration gB of benzene (Table II). 

In accordance with general experience with immiscible polymers, the styrene phase contains very little polybutadiene. In the same manner, only very little polystyrene can then be dissolved in the polybutadiene phase. The aggregates of the block polymers are certainly also free... 

For formulations rich in styrene, phase separation takes place in the course of polymerization (Hsu and Lee, 1991). In this case it would be necessary to account for the different compositions of both phases and the partition of the initiators and radicals between them. 

Under these conditions of irradiation, the oxidation of the acrylonitrile component does not proceed, as shown by the invariance of the band (2237 cm-1) of acrylonitrile units. The calculated photooxidation rate of a model ABS is also reported in Figure 30.5. In this reference system, no interaction occurs between the photooxidation of the elastomeric and styrenic phases. The photochemical evolution of the model ABS has been determined for various irradiation times the increase in absorbance of the BR homopolymer has been added to that of the PS homopolymer and corrected by a multiplicative factor that takes into account the percentage of each component in the experimental ABS blends. 

The comparison of the photooxidation rates reported in Figure 30.5, along with analysis of FTIR and UV spectra, suggests that the BR component was implicated as the prime site for the photooxidation of ABS and that the photooxidation of the styrenic phase was enhanced by the presence of the polybutadiene in ABS, compared with PS homopolymer. 

These experimental results confirm that the oxidation of the styrenic phase in ABS is enhanced by the presence of polybutadiene, compared with PS homopolymer. 

In secondary steps, radical species formed in BR photooxidation are able to initiate the oxidation of the neighbouring styrenic moieties the photooxidation of the styrenic phase is enhanced by the presence of polybutadiene in ABS, compared with PS homopolymer. Butadiene grafting sites, containing tertiary allylic carbon atoms (A), are preferentially oxidized in tertiary hydroperoxides in the first stages of ABS photooxidation rather than in secondary allylic carbon atoms (B) ... 

The study of the birefringence of the Kraton single crystal and of the effect of stress applied along and perpendicular to the extrusion directfon has shown that the birefringence is entirely due to form birefringence and that the di ersed styrene phase and the butadiene matrix consist of randomly oriented chains Thisresults have been confirmed by infra-red dichroism studies ... 

The cross-linking process used for the poly(divinylbenzyl)styrene phase produces rigid, spherical particles with a well-controlled pore size. This makes them ideal for use in size exclusion chromatography and indeed they are amongst the most important materials in use for this separation technique. 

We cannot give a proved interpretation for this behavior. However, the following assumption of continued particle formation is not unlikely. In the case of emulsion polymerization of styrene with normal emulsifier concentrations (I to 3%), the phase of particle formation is probably over at a conversion of about 20%. This is due to the fact that the emulsifier concentration at this point falls off below the critical value for micelle formation (c.m.c.) therefore no micelles are further available. At higher emulsifier concentrations (5 to 6% with respect to water), this does not happen during the whole polymerization process (9). Particle formation therefore should be possible throughout the reaction. According to Bovey (9) this is not the case, because disappearance of the pure styrene phase at about 30% conversion stops particle formation. As far as we know, this... 

In lamellar styrene-diene diblock copolymers, SANS studies showed that the segment Rg contracts to 70% of the unperturbed value parallel to the interface and expands to 160% of the unperturbed value perpendicular to the interface (Hasegawa et al 1985, 1987). These values were found for both the styrene and diene blocks. A smdy of stretching SIS block copolymers having spherical styrene phases showed that the deformation in the direction of stretch was greater than affine, while the deformation perpendicular to the stretch was much less (Richards and Welsh, 1995). 

For both O/W and W/O systems, the amount of monomer is usually restricted to 5-10 wt% with respect to the overall mass, and that of surfactant(s) lies within the same range or even above. Nevertheless, there have been a few studies in which the formulation deviated from these conditions. For instance, surfactant concentrations of 2 wt V() were reported [56-58,69,124,125]. However, in this case the amount of monomer was also very low (< 2 wt%) so that the systems must be considered as micellar solutions rather than true microemulsions. Conversely, a 1994 study of Gan et al. [82] reported the polymerization of styrene up to 15 wt% using only about 1 wt V(> dodecyltrimethylammonium bromide surfactant (DTAB) in a Winsor I-like system. This system consists of a microemulsion (lower) phase topped off with pure styrene. The polymerization takes place in the microemulsion phase, while the styrene phase acts as a monomer reservoir. Such a polymerization process is novel, but it yields latices of large particle size ( 100 nm) that can be more easily obtained by conventional emulsion polymerization. 

Four types of phase behavior characteristic of the PS/P(MMA-S) system have been described and illustrated in some detail in the previous section and further, the average particle sizes have been tabulated as a function of molecular weight and weight percent of PS initially present in the PS/MMA-S mixture and of the composition of the final P(MMA-S) copolymer resulting after polymerization. In the section we will discuss these results in terms of the ternary polystyrene/poly(methyl methacrylate-styrene)/methyl methacrylate-styrene phase diagram, dealing with (1) the four types of phase relationships, (2) particle size, and lastly (3) multiple emulsions or subinclusions within the dispersed phase. 

Butene-C(3-ethylene Ethylene-co-styrene Phase contrast optical microscopy I had 15 mol% butane II had 1.0-3.9 moI% styrene Hu et al. (2005)... 

Figure 8.4 Transmission electron micrographs of HIPS showing the styrene dispersed within the butadiene phase that is in turn dispersed within the styrene phase. The isoprene phase is stained black.

Thin films of blended deuterated polystyrene (dPS) and poly(vinyl methyl ether) (PVME) were imaged as a fimction of the dPS PVME ratio. Near the critical composition of 35% dPS, an imdulating, spinodal-like structure was observed, whereas for compositions away from the critical mixture ratio, regular mounds or holes (< dPS < < crit and < dPS > (pent, respectively) were present. These variations were assigned to surface tension effects (120). Blends of PBD, SBR, isobutylene-brominated p-methylstyrene, PP, PE, natural rubber, and isoprene-styrene-isoprene block rubbers were imaged (Fig. 18). Stiff, styrenic phases and rubbery core-shell phases were evident as the authors utilized force-modulated afm to determine detailed microstructure of blends, including those with fillers such as carbon-black and silica (121). 

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