Poly , atactic room temperature

Figure 2 X-ray diffractograms recorded at room temperature, (a) Metallocene-synthesized isotactic poly(propylene), mmmm — 0.996 crystallized at 145°C. (b) Atactic poly(propylene). Reproduced with permission from Ref. [43], Copyright John Wiley Sons, Inc., 1999.

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

A common example of a plasticized polymer is poly(vinyl chloride). The common atactic form has a Tg of about 80 °C, well above room temperature. Without a plasticizer, vinyl is stiff and brittle. Dibutyl phthalate (see the structure at left) is added to the polymer to lower its glass transition temperature to about 0 °C. This plasticized material is the flexible, somewhat stretchy film we think of as vinyl raincoats, shoes, and even inflatable boats. Dibutyl phthalate is slightly volatile, however, and it gradually evaporates. The soft, plasticized vinyl gradually loses its plasticizer and becomes hard and brittle. 

FIGURE 7-21 Room temperature infrared spectra of atactic polystyrene (a-PS) and atactic poly(methyl methacrylate) (a-PMMA) (recorded by Dr. Maria Sobkowiak). 

Polymerizations of polar monomers, like acrylic and methacrylic esters with alkyllithium initiators, yield the greatest amount of steric control. Almost all isotactic poly(methyl methacrylate) foims at low temperatures. Addition of Lewis bases such as ethers or amines reduces the degree of isotactic placement. Depending upon the temperature, atactic or syndiotactic polymers form. Also, butyllithium in heptane yields an isotactic poly(A, A -dibutylacrylamide) at room temperature. ... 

Poly(methacrylamide) could subsequently be dehydrated to poly(methacrylonitrile) using a large excess of oxalyl chloride and dimethyl formamide in methylene chloride at 0°C, warming to room temperature overnight as indicated in Scheme I. To date, this reaction has only been followed by infrared spectroscopy on the atactic material. Appearance of a peak at 2238 cm" is indicative of formation of nitrile groups in this polymer. 

This group comprises substituted polyacrylamides and their substituted derivatives and atactic poly(methyl vinyl ether), obtained at room temperature by cationic mechanism, which at this temperature is water insoluble and shows phase transition an 38 °C. 

Amorphous polymers of commercial importance include polymers which are glassy or rubbery at room temperature. Many amorphous thermoplastics, such as atactic polystyrene and poly (methyl methacrylate), form brittle glasses when cooled from the melt. The glass transition temperature, Tg or glass-rubber transition, is the temperature above which the polymer is rubbery and can be elongated and below which the polymer behaves as a glass. Thermal analysis of amorphous polymers shows only a glass transition temperature whereas crystalline poly-... 

In a suitable reaction vessel, a solution of 180gm (2.1 moles) of freshly distilled methacrylic acid in 900 ml of distilled water is sparged with oxygen-free nitrogen. Then 5.4 gm (0.05 mole) of a 30 7 o hydrogen peroxide solution is added. The mixture is maintained between 80 and 90" C for 5 hr. The gelled polymer system is allowed to cool to room temperature. The polymer is dissolved in distilled methanol and precipitated with diethyl ether. The resulting polymer is air dried, powdered, and then dried under reduced pressure. Yield 178 gm (99 7o) of atactic poly(methacrylic acid). 

Figured. Crystal structures of atactic poly (vinyl alcohol) at WOK, 200K, and room temperature obtained by the least-squares refinements. Broken lines indicate X-ray structure at room temperature. (Reproduced with permission from reference 7, Copyright 1997, Wiley-InterScience)...

The possible effect of spatial order on carbazole groups has been a subject of discussion. Isotactic poly[2-(N-carbazolyl)ethyl acrylate] exhibits a room-temperature hole mobility of 1.7 x 10 m V s at 2xlO Vm which is considerably higher than that of the atactic polymer or PVK [80]. On the other hand, these values are very close to those obtained for NIPC/polycarbonate at a comparable concentration of the transport-active molecule, i.e, a system with no order. Experiments with other carbazole polymers have shown that changing the backbone (e.g. carbon vinyl to siloxy) [45], or spacing of carbazole groups from the chain, has only a secondary effect. 

Simpler initiating systems based on the association of conventional anionic initiators, typically sodium or potassium alkoxides (ROMt), with trialkylaluminum (R3AI) behave very similarly to porphyrin salts associated to bulky Lewis acid systems. For instance, sodium isopropoxide in combination with triisobutylaluminum in hydrocarbon solvents yields rapid POx polymerization at room temperature or below." The chain transfer reactions are also strongly reduced in these conditions, thus allowing the synthesis of regioregular atactic poly(POx), with relatively high molar masses (up to SOOOOgmol" ). 

Figure 6 C CP-MAS spectra of poly(vinyl alcohol) at room temperature. (A) syndiotactic, (B) isotactic and (C) atactic. Line spectra represent the spectra in DMSO-dg solution at 353 K. Reproduced with permission of American Chemical Society from Terao T, Maeda S and Saika A (1983) Macromolecules 1535.

Fig. 15. The as recorded intensity function /g p ( ) for a sample of atactic poly(methyl methacrylate) recorded at room temperature.

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