C Polystyrene

Fig. 4. Comparative thermogravimetric analyses of polymers in nitrogen A, poly(vinyl chloride) B, poly(methyl methacrylate) C, polystyrene D,...

Many of the most floppy polymers have half-melted in this way at room temperature. The temperature at which this happens is called the glass temperature, Tq, for the polymer. Some polymers, which have no cross-links, melt completely at temperatures above T, becoming viscous liquids. Others, containing cross-links, become leathery (like PVC) or rubbery (as polystyrene butadiene does). Some typical values for Tg are polymethylmethacrylate (PMMA, or perspex), 100°C polystyrene (PS), 90°C polyethylene (low-density form), -20°C natural rubber, -40°C. To summarise, above Tc. the polymer is leathery, rubbery or molten below, it is a true solid with a modulus of at least 2GNm . This behaviour is shown in Fig. 6.2 which also shows how the stiffness of polymers increases as the covalent cross-link density increases, towards the value for diamond (which is simply a polymer with 100% of its bonds cross-linked. Fig. 4.7). Stiff polymers, then, are possible the stiffest now available have moduli comparable with that of aluminium. 

The results of intrinsic viscosity measurements for four polymer-solvent systems made at the -temperature of each are shown in Fig. 141. The four systems and their -temperatures are polyisobutylene in benzene at 24°C, polystyrene in cyclohexane at 34°C, poly-(di-methylsiloxane) in methyl ethyl ketone at 20°C, and cellulose tricapry-late in 7-phenylpropyl alcohol at 48°C. In each case a series of poly-... 

FIGURE 8.3. SEM images of non-spherical building blocks (A-C) polystyrene spheroids of various aspect ratios (D) silver nanocubes, (E) iron oxide (a-Fe203) peanuts and (F) Xe nanorods. 

Block copolymers, polyclhylcnc-fr/oc/c-polystyrene (PE-fc-PS) and PP-fo-PS, were prepared by the polymerization of styrene with terminally lithiated PO macroinitiators [31]. 

FIGURE 2.23 Scheme for fabrication of plastic microdevices from silicon master using an intermediate soft mold, (a) Silicon structures are fabricated using conventional photolithography and reactive ion etching, (b) PDMS is cured in situ over the silicon master, (c) Polystyrene is hot embossed onto the PDMS mold or polymerized in situ from partially polymerized styrene, (d) Polystyrene replica is separated from the mold [85]. Reprinted with permission from Springer Science and Business Media. 

Fig. I. Kinetics of carbon radical decay a-polyvinylacetate, b-polyinethylmetacrylate (curve 3-quadruplet spectrum, curves 1—5-quintiplet spectrum), c-polystyrene...

Fig. 4. Kinetics of peroxide radical decay a-polymethylmetacrylate, b-polyvinyiacetate c-polystyrene (oxygen pressure - 760 mm Hg, — — — 0,1 mm Hg)...

Fig. 2 Typical synthesis of a polystyrene-Z /6>ck-polysilane-Z7/6>c -polystyrene by a polymer coupling reaction...

Conditions a) SnC, NaNs b) NaCN, MeOH c) polystyrene MMT-CI resin, DMAP, pyridine d) t-butyidimethylsilyl chloride, Imidazole e) PMea f) diisopropylethylamlne g) Set A amine building blocks, diisopropylethylamlne, 0 °C to rt h) Set B amine building blocks, diisopropylethylamlne, 75-80 °C i) 1M tetra-n-butylammonium fluoride in THF j) 2% trifluoroacetic acid in 1,2-dichloroethane, 1 min... 

Glass and plastic vessels (but not nitrocellulose centrifuge pots) can be dried in an oven at the following temperatures, which depend on the thermal stability of the material polyvinyl chloride 70 °C polystyrene 70 °C polyethylene 80 °C high density polyethylene 120 °C polyallomer 130 °C polypropylene 130 °C polycarbonate 135 °C teflon 180 °C and glass 200 °C. 

FIGURE 25.26 Schematic representation of (a) a simple asymmetric filter and alternative designs of a hierarchical asymmetric filter using (b) preformed alumina spheres and (c) polystyrene-derived voids. (From DeFriend, K.A., and Barron, A.R., J. Membr ScL, 212, 29, 2003.)... 

C. Polystyrene Grafted onto Polyethylene Film or Tubing... 

Treatment of polymers by superheated water at high temperatures can result in their decomposition/hydrolysis to monomers or lower oligomers [6]. At lower temperatures the polymer is stable and the small amounts of monomers, initiators, low oligomers and other small compounds can be extracted from polymers with superheated water [6]. For example, at 200°C styrene, alkylbenzene contaminants and styrene dimers were extracted from polystyrene without destroying the polymer. Although stable at 200°C, at 250°C polystyrene was decomposed into substituted benzenes [6]. 

Fig. 13.12. The distance dependence of the force of interaction between crossed mica plates coated by polystyrene in cyclohexane at 24 °C polystyrene molecular weight l,6x 10 2,1 x 10 (after Klein, 1982).

Both first- and second-order transitions are observed in polymers. Melting and allotropic transformations are accompanied by latent-heat effects and are known as first-order transitions. During second-order transitions, changes in properties occur without any latent-heat effects. Below the second-order-transition temperature (glass transition temperature) a rubberlike material acts like a true solid (see Chapter 1). Above this temperature the fixed molecular structure is broken down partially by a combination of thermal expansion and thermal agitation. The glass transition temperature of polystyrene is 100°C below 100°C polystyrene is hard and brittle, and above 100°C it is rubberhke and becomes easily deformed. 

Polystyrene Dispersions. On account of their glass transition temperature T of ca. lOO C, polystyrene dispersions do not form films at room temperature. These rigid polymers can only be applied with means of heat drying (e.g., to stiffen fabrics and nonwovens). Film formation is not required in agents used to protect floor coverings and paper coatings (plastic pigments) in this case polystyrene is therefore applied in the form of a dispersion at room temperature. 

Other experiments. In the same semi-batch equipment one experiment was performed using methanol to precipitate the PPE instead of CO2. In another experiment a Styrene-Butadiene-Styrene (SBS) triblock copolymer was precipitated from cyclohexane by adding CO2 as an anti-solvent. This synthetic rubber contains blocks with a glass transition temperature of 100°C (polystyrene) and blocks with a glass transition temperature of approximately -100°C (polybutadiene). 

In the first approach, prolinamides have been supported on micelleforming species, dendrimers (32a-c), polystyrene (26, 31a-d), poly-vinylidene chloride, phenolic polymers, ionic liquids, silica (28, 29), other inorganic supports (30), ° and polymer-modified small peptides. Supported prolinamide catalysts have also been prepared by acrylic and styrene (27) copolymerisation. 

---