Amorphous homopolymers

Although no longer of significant commercial interest, the characteristics of some of the amorphous homopolymers commercially available at one time or another are illustrated in Table 4. No crystalline polymers are known to have been commercialized. This lack of commercial success results from the economically competitive situation concerning vinyl ether polymers versus other, more readily available polymers such as those based on acryUc and vinyl ester monomers. 

The above discussion indicates that only one poly(aryl ether) has been explored as a membrane material (the commercial, amorphous, homopolymer P-1700 produced by Union Carbide). The present program expands these studies to Include other poly(aryl ethers). 

Many amorphous homopolymers and random copolymers show thermorheologically simple behavior within the usual experimental accuracy. Plazek (23,24), however, found that the steady-state viscosity and steady-state compliance of polystyrene cannot be described by the same WLF equation. The effect of temperature on entanglement couplings can also result in thermorheologically complex behavior. This has been shown on certain polymethacrylate polymers and their solutions (22, 23, 26, 31). The time-temperature superposition of thermorheologically simple materials is clearly not applicable to polymers with multiple transitions. The classical study in this area is that by Ferry and co-workers (5, 8) on polymethacrylates with relatively long side chains. In these the complex compliance is the sum of two contributions with different sets of relaxation mechanisms the compliance of the chain backbone and that of the side chains, respectively. 

Since the relaxation mechanisms characteristic of the constituent blocks will be associated with separate distributions of relaxation times, the simple time-temperature (or frequency-temperature) superposition applicable to most amorphous homopolymers and random copolymers cannot apply to block copolymers, even if each block separately shows thermorheologically simple behavior. Block copolymers, in contrast to the polymethacrylates studied by Ferry and co-workers, are not singlephase systems. They form, however, felicitous models for studying materials with multiple transitions because their molecular architecture can be shaped with considerable freedom. We report here on a study of time—temperature superposition in a commercially available triblock copolymer rubber determined in tensile relaxation and creep. 

PDD readily copolymerizes with tetrafluoroethylene and other monomers containing fluorine, such as VDF, CTFE, vinyl fluoride, and PVE via free radical copolymerization, which can be carried out in either aqueous or nonaqueous media. It also forms an amorphous homopolymer with a Tg of 335°C (635°F).2... 

When looking al amorphous homopolymers, DMA has about 1000 times the sensitivity of differential scanning calorimetry, which can show very little below the glass transition. Even the new modulated DSCs are still about 100 times less sensitive, but they arc able to distinguish certain overlapping phenomena. Whether modulated DMA will ever be of interest we shall have to wait and see, (The temperature ramp is modulated at perhaps 0.1 Hz and amplitude of a few degrees on top of the 5°C per minute ramp.) (Fig. 10.)... 

The physical structure of solid amorphous homopolymers is a matter of considerable dispute. All proposed structures can be considered to derive from two limiting types the coil model and the bundle model. 

Tables in this chapter contain published pressure-volume-temperature data for amorphous homopolymers. Measurements below the melting temperatures for semi-crystalline materials are not included because of the potentially large variance among samples with differing degrees of crystallinity. Rogers [1] and Zoller [2] have also compiled equation-of-state data for amorphous polymers.

In column fractionation (157,158) the polymer is precipitated onto an inert support, which is placed at the top of a packed column (159). A solvent mixture of increasing solvent power is pumped through the column a temperature gradient is often maintained. This is known as Baker-Williams fractionation (160). This technique is applicable to all amorphous homopolymers and crystalline ho-mopol5miers above the melting point. For copol5miers and more complex compositions, the same technique may be employed, but the analysis is considerably more difficult. 

The crystallization of homopolymers in binary blends is more complicated as compared with that of neat homopolymers. This is because the second homopolymer, usually amorphous homopolymer, may accelerate the crystallization by working as a diluent or decelerate it by disturbing the diffusion of... 

In miscible binary blends, amorphous homopolymers are completely accommodated within amorphous layers of the lamellar morphology formed after the crystallization of crystalline homopolymers. Stein et al. [51], for example, observed the lamellar morphology formed in a miscible blend of PCL and poly(vinyl chloride) (PVC) using SAXS as a function of composition. They found that PVC existed in amorphous layers of the lamellar morphology to yield a linear increase in the amorphous layer thickness with increasing PVC composition, whereas the crystalline layer thickness remained constant irrespective of composition. Wenig et al. [52] obtained similar results for a miscible blend of poly(2,6-dimethylphenylene oxide) (PPO) and isotactic polystyrene (iPS). However, a different result was reported for a miscible blend of iPS and atactic polystyrene [53], where the amorphous layer thickness was almost constant irrespective of composition. Stein et al. [51] explained this difference in... 

Figure 10.6 (a) Cloud points and melting points for a binary crystalline/amorphous homopolymer blend having an UCST-type... 

The idea described above for glassy amorphous homopolymers can be extended to include miscible amorphous polymer blends, such as PS/PPO. Furthermore, a low degree of covalent cross-links can be considered as equivalent to entanglements for controlling the deformation mode. The strand density of cross-linked polymers is defined as the sum of the entanglement density and the covalent cross-link density [18] as... 

Often, one is interested in comparing the viscosities of flexible, amorphous homopolymers with different molecular weights and which have the same chemical structure or different chemical structures. Since the viscosities of polymers depend on both temperature and molecular weight, it is essential to suppress, if not eliminate completely, the effect of temperature on viscosity for such purposes. When the... 

Sakurai K., MacKnight W. J., Lohse D. J., Schulz D. N., and Sissano J. A. (1994) Blends of amorphous-crystalline block copolymers with amorphous homopolymers. 2. Synthesis and characterization of poly(ethylene-propylene) diblock copolymer and crystallization kinetics for the blend with atactic polypropylene. Macromolecules 27 4941-4951. 

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