Main-chain structure

From the viewpoint of synthetic polymer chemistry, although the formation of stereospecific polymers (isotactic and syndiotactic) is very popular, the present polymer is the first example having a double syndiotactic structure. In ad tion, the polymer consists of an alternating zigzag-linear main chain structure. 

In order to study this question in a more systematic way, we have recently optimized 144 different structures of ALA at the HF/4-21G level, covering the entire 4>/v )-space by a 30° grid (Schafer et al. 1995aG, 1995bG). From the resulting coordinates of ALA analytical functions were derived for the most important main chain structural parameters, such as N-C(a), C(a)-C, and N-C(a)-C, expanding them in terms of natural cubic spline parameters. In fact, Fig. 7.18 is an example of the type of conformational geometry map that can be derived from this procedure. 

The substituents on the phenyl group can also sterically influence the chiral recognition ability. The main-chain structures of 23a and 23x look similar, but the conformations of side groups are not the same. Three aromatic groups of... 

Although the main-chain conformations of polysilanes have been described as random coil, 73- (deviant helical), 157 (transoid helical), and 2i (all anti, planar) structures, it is now generally accepted that most polysilanes tend to adopt helical main-chain structures, regardless of side groups and temperature.39 It... 

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

In this part, two series of 44 copolymers with coiled main-chain structures and 45 copolymers with stiff main-chain conformations were described. It was concluded that both optically inactive 42 and 43 adopt helical conformations with an equal proportion of P and M screw senses by means of UV and CD spectra as well as molecular mechanics calculations. A marked positive cooperative induction effect of the preferential screw sense in 44 and 45 copolymers was found. However, there is a marked difference in the helical cooperativity between 44 and 45, probably because of the differences in their global and local conformations. This difference can be related to the persistence of the helical conformation against defects allowing change of... 

Fig. 6.1 Main chain structures of the native (grey) and the intermediate states (black). The intermediate state shown here was the most stable state observed in the simulation whose residence time was about 0.15 psec. Only the average NMR structure of the native conformation is shown here.

By using this method, the chemical shifts of the resonances in the spectra of a sulfur vulcanized natural rubber (Fig. 32 expanded aliphatic region in shown in Fig. 33 [top]) are assigned to various units of the polymer network, which arise from structural modifications induced by the vulcanization 194,196 200). Different sulfidic structures are found for unaccelerated and accelerated sulfur vulcanizations, respectively. With increasing amount of accelerator (as compared to the sulfur), the network structure exhibits less crosslinking, fewer main chain structural modifications, and fewer cyclic sulfide structures 197). 

We turn to the relaxation processes observed in smectic polymers with different attachment of mesogenic groups to the macromolecular backbone and compare dielectric behaviour of smectic and nematic polymers having identical mesogenic groups but different main chain structure. 

Table 2 shows the present state-of-the-art for the electrical conductivity of doped conjugated polymers. The magnitude of the electrical conductivity in polymers is a complex property determined by many structural aspects of the system. These include main-chain structure and 7T-overlap, molecular... 

Highly efficient green photoluminescence has also been realized from SCPs. Copolymers 11 (Fig. 5) derived from 2,7-fluorene and 2,3,4,5-tetraphenylsilole show absolute PL quantum yields up to 84%.28 A well-defined alternating copolymer 12 with a repeating unit made up of ter-(2,7-fluorene) and 2,5-silole possesses an absolute PL quantum yield >80%.29 SCPs 13 with a main chain structure of 3,6-carbazole-2,7-fluorene-2,5-silole also show absolute PL quantum yields up to 86%.30 An energy transfer copolymer 14 of 2,7-dibenzosilole and... 

Cyclolinear carbosilane polymers with disilacyclobutane rings in the main-chain structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding l,3-dibutenyl-l,3-disilacyclobutanes in the presence of Grubbs catalyst (Scheme 13) <2003PP789, 2004MM5257, 2004PP118>. 

Retrieve pdb hies of lysozyme from different species including chicken (ILYZ.pdb), swan (lGBS.pdb), pheasant (lGHL.pdb), and turkey (lLZY.pdb), and compare their main chain structures. Write a new pdb hie for the superimposed structures of chicken and turkey lysozymes. 

The 13C NMR examination of CBS cured SBR was performed on unfilled, silica filled, and carbon black filled samples [41], Several different SBR samples with respect to styrene content and cis, trans, and vinyl BR content were used. The unfilled SBR samples gave 3 major peaks that appeared at 51.0, 50.2, and 49.3 in a spectrum similar to BR vulcanisation. Unfortunately, peaks below 45 ppm are obscured by the different main chain structural peaks of SBR. A difference was seen in the rate of formation of these peaks in filled samples with silica inhibit the vulcanisation rate compared to carbon black filled samples. 

Abstract. This article reviews mainly the results of our recent research on the relationship between the structure and the luminescence properties of PPV derivatives. PPV derivatives are particularly useful in an effort toward the establishment of such relationship because their chemical structures can be manipulated very systematically. Attachment of a wide variety of substituents, inclusion of kinky structural units, modification of main chain structures by inclusion of hole- and/or electron-transferring structures, and blending of polymers having different optical and electronic properties are representative approaches. The device characteristics of the light-emitting diodes (LEDs) fabricated from these polymers are discussed in relation to their structures. In certain cases, their photoluminescence (PL) properties are compared with their electroluminescence (EL) properties. 

Murayama8> studied a series of resins from diglycidyl ether of Bisphenol A (DGEBA) cured with varying quantities of diaminodiphenylmethane (DDM). These cured resins had the same main chain structure, but differed in the degree of crosslinking. Izumo 25) performed similar studies by using diethylenetriamine (DETA) as a... 

The values of log K2 are nearly the same, which indicates that the resins are almost the same in physical properties, although their main chain structures are different... 

Those relations between Tg and log q(E. are nearly linear except of Sue A, as shown in Fig. 9. The values of and K2 derived from Eq. (11) are very close to those for the diamine and dihydrazide-cured resins, as shown in Table 1. As e(E.) becomes smaller, the differences in main chain structures have almost no effect on Tg, but only the increase of e(E. can increase Tg. 

The uniformity of the polymer structure obtained is determined by the exact reaction conditions used, with the initiator having a large influence [11]. Polymers with main chain structural uniformities greater than 99% units 15 and less than 1% units 31 (Fig. 6) have been obtained using AlClj, H2SO4, or CF3CO2H as initiators [11],... 

The polymers evaluated are shown in Fig. 1. These twelve polymers cover typical types of organosilicon polymers, such as polysiloxane, ladder type polysiloxane, polysilane, polymethacrylate, polysilyl-styrene, and novolak. Polymers and were supplied by Shin-etsu Chemical Co., Ltd. Actually, polymer" 2 evaluated contains very small amount of vinylsiloxane for crosslinking by deep UV irradiation after coating, because the pure polysiloxane is a fluid at room temperature and is impossible to measure the etching depth. These polymers have Si-0 bonds in the main chain structure. Polymer was purchased from Shin Nisso Kako Co., Ltd. and was purified in house. Polymers 4 to 12 were synthesized in house. Polymers 1J and 12 have Si-0 bonds in side chain structure. Thermal Si02 1J was evaluated as a reference. ... 

Free-radical and anionic polymerizations of TAD-DOL—MA (30) proceed exclusively via a cyclization mechanism, and the obtained polymer seems to have a helical conformation with an excess helicity.92-94 The main chain structure of poly(TADDOL—MA) with cyclized units (poly-30) is different from that of all other polymethacrylates discussed here. Similar monomers have been synthesized and polymerized.95... 

---