Rigid backbones

The recurring para-substituted benzene rings and sulfur atoms form a symmetrical rigid backbone. 

The next stop is to cool the nylon below its Tg without removing the stress, retaining its molecular orientation. The nylon becomes rigid with a much higher elastic modulus in the tension direction [15,000 to 20,000 MPa (2 to 3 x 106 psi)]. This is nearly ten times the elastic modulus of the unoriented nylon-66 plastic. The stress for any elastic extension must work against the rigid backbone of the nylon molecule and not simply unkink molecules. This procedure has been commonly used in the commercial production of man-made fibers since the 1930s via DuPont. 

In reality, the universal calibration curve is not quite universal. Certain exceptions exist, such as polymers with very rigid backbones. However, the... 

In the diphosphines bis(diphenylphosphino)alkyne and tr<2 x-l,2-bis(diphenylphosphino)ethy-lene, due to the rigid backbone, the orientations of the lone pairs are restricted, so that these ligands cannot point inwards and set up the metals for anion bridging. The reaction of Ph2PC=CPPh2 with AgSbF6 in a 1 1 molar ratio gives a mixture of the 1 2, 2 2, and 3 2 complexes (Equation (6)) ... 

Bis[2-(diphenylphosphino)phenyl]phenylphosphine (TP) is a very inflexible ligand with a rigid backbone and gives the trinuclear complex [Au3Cl3(TP)] (452), that has a compact unsymmetrical structure in the solid state which is retained in solution owing to the fixation of the gold atoms through intermetallic contacts.2651... 

Further exploitation of the molecular shape feature has led more recently to the design of another series of clathrate hosts by substituting on the allene rigid backbone bulky groups 22>, Representative compounds of this new host family are 20 and 21. The allene 20 (R = t-butyl) shows an interesting clathration behaviour upon crystallization from various environments, including alicyclic and aromatic compounds, heterocycles, cyclic ketones and eyclohexaneamine 26>. 

The BDPMI (27) system can also be considered to be a DIOP variant, as an imidazole ring forms the rigid backbone [119-121], Excellent stereoselectivity is seen with this system for the reductions of arylenamides. 

An aromatic system can also provide a rigid backbone, as seen with Phane-Phos (28a) [122-124],... 

Stars, combs with three-functional branching points along a locally rigid backbone, and planar surface-brushes can also be considered as assemblies of linear chains tethered to df-dimensional objects [9] (df=0, chains tethered to a point, or stars, df=l, chains tethered to a line, combs, and df=2, chains tethered to a surface, brushes). Excellent introductions and reviews on the molecular properties of these different molecular architectures are contained in [2-4,6-9]. 

Bidentate boranes with an o-phenylene backbone constitute some of the simplest examples of polydentate Lewis acids with rigid backbones. They can be prepared by the reaction of boron halides with a 1,2-dimetallated benzene derivative. Thus, the reaction of 1,2-bis(chloromercurio)benzene (5) with boron trichloride affords 1,2-bis(dichloroboryl)benzene (6, Scheme 3). ... 

Polymer chain composed of a rigid backbone to which many lateral side-groups are attached, giving the repeating unit a board-like shape. 

Note 1 The rigid backbone often has a polyester, polyamide or poly(ester-amide) type of structure. Examples are ... 

Some engineering thermoplastics, such as PC or PET, exist, due to their inherently high melt viscosity caused by rigid backbone chains, as supercooled liquids when solidified at moderate cooling rates, with a supermolecular structure exhibiting no long-range translation symmetry. However, both PC and PET... 

The AB monomer in structure 13 was polymerized in CHP in the presence of sodium hydride to yield low molecular polymer [50]. The rigid backbone apparently led to poor solubility and the polymer precipitated before high... 

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