Poly copolymer, dielectric

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Recently siloxane-imide copolymers have received specific attention due to various unique properties displayed by these materials which include fracture toughness, enhanced adhesion, improved dielectric properties, increased solubility, and excellent atomic oxygen resistance 1S3). The first report on the synthesis of poly(siloxane-imides) appeared in 1966, where PMDA (pyromellitic dianhydride) was reacted with an amine-terminated siloxane dimer and subsequently imidized 166>. Two years later, Greber 167) reported the synthesis of a series of poly(siloxane-imide) and poly(siloxane-ester-imide) copolymers using different siloxane backbones. However no physical characterization data were reported. 

The symbols have their usual meanings (] ). From measured values of NTj and ri on a poly (butene-1 sulfone) of degree of polymerization 700 the values of t (in nanosec.) shown in Table III are obtained. The discrepancy between the values of from NT and from ri, particularly marked for the side-chain motions, indicates the inadequacy of the single-Tg model. Nevertheless it is evident that the backbone motions are relatively rapid. (Comparison to polybutene-1 (jW) shows that SO2 groups retard the motion of the copolymer chains by a factor of about 50.) The question now becomes why are these rapid motions NMR-active but dielectrically inactive One possible type of motion which would account for this is shown in Fig. 9. Five backbone bonds and six main-chain atoms are involved, i.e. the sequence C-S-C-C-S-C, with concerted segmental transitions about two C-S bond, allowing interconversion... 

The approach developed in this paper, combining on the one side experimental techniques (dynamic mechanical analysis, dielectric relaxation, solid-state 1H, 2H and 13C NMR on nuclei at natural abundance or through specific labelling), and on the other side atomistic modelling, allows one to reach quite a detailed description of the motions involved in the solid-state transitions of amorphous polymers. Bisphenol A polycarbonate, poly(methyl methacrylate) and its maleimide and glutarimide copolymers give perfect illustrations of the level of detail that can be achieved. 

Arnold CA, Summers JD, Chen YP, Yoon TY, McGrath BE, Chen D, McGrath JE (1989) Soluble polyimide homopolymers and poly (siloxane imide) segmented copolymers with improved dielectric behavior polyimides In Feger C, Khojasteh MM, McGrath JE (eds) Materials chemistry and characterization. Elsevier, Amsterdam... 

The synthesis (9, 10), dynamic mechanical (11), rheological (12), dielectric (13), electrical (14), NMR (15), and thermal (16) behavior of HMS and its isomeric analog, poly-2-methyl-2-ethyl propylene sebacate (MEPS), and copolymers of HMS and MEPS have been reported. 

The JG and the a-Relaxations of Poly(n-butyl methacrylate) in Poly(n-butyl-methacrylate-stat-styrene) Random Copolymers. The copolymers of poly(n-butyl methacrylate) (PwBMA) and polystyrene (PS) is one example [338,339]. Here PnBMA is the lower Tg component A. Neat PnBMA has n = 0.47 and a JG relaxation. On increasing the styrene content from 0 to 66 mol% in the copolymer, a monotonic increase of nA of the PnBMA component leads to a concomitant increase in the separation of the JG relaxation from the segmental relaxation, both of the PwBMA component. This changes were observed in the dielectric relaxation experiment. 

The calculated e(298K) 2.67 for poly(vinyl butyral) as a random copolymer containing 12% by weight of poly(vinyl alcohol), is in close agreement with the experimental value [8] of 2.69 for the low-hydroxyl grade of poly(vinyl butyral). If the presence of hydroxyl groups is neglected and the calculations are carried out for the homopolymer of poly(vinyl butyral), a dielectric constant of 2.42, which is much lower than the observed value, is calculated. 

Recently, n-channel transistors of poly(9,9-di-n-octylfluorene-alt-benzothiadia-zole) (51d) have been reported using thin films fabricated by spin-coating.[298] Electron mobilities ranging from 6 x lO. S x 10 cm V s were observed with the use of a 50 nm BCB polymer layer on top of the Si02 dielectric and Ca electrodes. Alternating copolymers containing 1,3,4-heterodiazoles and fluorenes have also been synthesized and show very low n-channel mobilities (2.2 x 10 cm V s for compound 51e).[299]... 

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