Semicrystalline polycarbonate, thermal

Obtain DSC thermal curves of several semicrystalline polymers such as polymethylmethacrylate (PMMA), polystyrene, polycarbonate, high-density (HD) polyethylene, and low-density (LD) polyethylene, and look for the glass transition in these polymers. The DSC run may need to be repeated twice with rapid cooling between runs. Many as received polymers will show a small peak on top of the glass transition on the first run due to relaxation effects in the polymer. The second run should not show this peak, but only a step change in the baseline. Compare your values of to literature values. Deviations may indicate the presence of plasticizers or other additives in the polymer. 

Homopolymers derived from MDI and azelaic acid are semicrystalline engineering plastics with a Tg of 135°C and a Tm of 290°C (88). Copoljrmers of MDI with azelaic acid, containing 20-30 mol% of adipic acid show a eutectic Tm of approximately 240°C. These amorphous or slightly crystalline copolymers have mechanical properties comparable to transparent nylons or polycarbonates. Although injection molded samples are transparent, they will crystallize and turn opaque. Copolyamides derived from MDI and aromatic dicarboxylic acids are more difficult to prepare. Because of the very high Tm (420°C) of the isophthalic acid/MDI block it was necessary to prevent the formation of any appreciable ciystalline blocks, which was accomplished by prereacting a portion of the isophthalic acid (15-20 mol%) with 2,4-TDI. In this manner crystallization of the isophthalic acid/MDI blocks was surpressed (89). Thus, copolyamides containing IPA/azelaic acid (50 50) are obtained with thermal and mechanical properties similar to poly-sulfone. 

Poly(p-phenylenevinylene) (PPV) could be obtained in the form of nanotubes, nanorods and nanofilms by the chemical vapor deposition (CVD) polymerization of a,a -dichloro-/7-xylene followed by thermal dehydrochlorination. The polymerizations were conducted on the inner surface of or inside the nanopores of alumina or polycarbonate membrane filters or on the surface of silicon wafers. The PPVs thus obtained could be thermally converted to the corresponding carbonized tubes, rods, and films. We also could obtain nanopatterns and nanowells of PPV and carbon on silicon wafers by utilizing nanolithographed poly(methyl methacrylate) patterns. The PPV films obtained on the silicon wafers are semicrystalline and produce highly conducting (a 0.7 x 10 Scm ) graphitic films even when treated only at 850 C. Field-emission properties of some of the graphitic nanotubes are also described in this report. 

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