Regular chain, defined

However, significant exceptions to all these attributes occur. The regularity of the amide linkages along the polymer chain defines two classes of polyamides AB and AABB. 

When A A or B B, the symmetry is lower and the only possible line repetition groups are s(M/N) and tc for isotactic and syndiotactic polymers, respectively, in both cis and trans configurations. In these cases, two independent torsion angles in the main chain define the regular conformation (Oi and 02 in Figure 2.15). 

Constitutional repeating unit in a regular macromolecule, a regular oligomer molecule, a regular block, or a regular chain, the configuration of which is defined at least at one site of stereoisomerism in the main chain. 

Double helical structures may be constructed from complementary single-stranded polynucleotide chains sharing a common helical axis according to the procedure outlined below. The two strands of the complex are assumed to be regular helices defined by a common set of backbone and glycosyl torsion angles. The data presented here are limited to model poly(dA) poly(dT) double helices stabilized by Watson-Crick base pairs between anti parallel strands. 

The discussion of the influence of the interphase need not be limited to just linear polyethylenes. Interphases of several nm have been reported in polyesters and poly-hydroxy alkanoates. One major difference between the interphase of a flexible polymer like polyethylene and semi-flexible polymers like PET, PEN and PBT is the absence of regular chain folding in the latter materials. The interphase in these semi-flexible polymers is often defined as the rigid amorphous phase (or rigid amorphous fraction, RAF) existing between the crystalline and amorphous phases. The presence of the interphase is more easily discerned in these semi-flexible polymers containing phenylene groups, such as polyesters. 

For the linear chain, any connected cluster (/x, v) is simply a set of consecutive sites n, n + 1,... n + m. Numerical results for ansatze using connected-cluster patterns involving up to M = 4 sites, for alternate chains, and up to M = 5 sites, for regular chains, have been obtained so far. The hierarchy of patterns have been defined as... 

The structure of an usual crystal, or of the perfectly regular chain of a theoretical CP, is specified completely by a small number of parameters, whatever the size of the system. Defects in these perfect structures, such as a dislocation or a soliton, are well defined in the same way. Except for PDAs, which are not considered in this section, this is not true of a real CP sample. It is usually disordered at all scales in a variable way, up to macroscopic dimensions for instance, the morphologies of the two surfaces of a fibrillar PA film are different (see, e.g., Fig. 5 in Ref. 17), or that of an electrochemically synthesized CP film varies continuously along its thick-... 

The folding of polypeptide chain regions into regular structures defines die secondary structure of a protein. The tertiary folding between these regions involves both covalent disulfide bonds and non-covalent bonds. The quaternary structure exists in proteins that contain... 

In a different study, gel-drawn ultrahigh molecular weight PE was analyzed by SFM. The images showed different well-defined levels of the underlying fibrillar morphology (132). These include bundles of microfibrils (diameter between 4 and 7 /um), microfibrils (diameter between 0.2 and 1.2 / m), nanofibrils, and regular chain patterns on the molecular level (Fig. 19). 

For hazard and associated risk issues and problems, the regular chain of command may not respond fast enough to respond to the critical nature of the issue. Historical examples of these issues are the Challenger and Columbia space shuttle disasters. An open door policy and procedures that allow unresolved high hazard and risk information to move rapidly to senior leadership should be in place. Essentially, a way to short circuit and bypass normal communication channels is needed. Refer to Chapter 9, Risk Perception—Defining How to Identify Personal Responsibility . 

The main classes of plasticizers for polymeric ISEs are defined by now and comprise lipophilic esters and ethers [90], The regular plasticizer content in polymeric membranes is up to 66% and its influence on the membrane properties cannot be neglected. Compatibility with the membrane polymer is an obvious prerequisite, but other plasticizer parameters must be taken into account, with polarity and lipophilicity as the most important ones. The nature of the plasticizer influences sensor selectivity and detection limits, but often the reasons are not straightforward. The specific solvation of ions by the plasticizer may influence the apparent ion-ionophore complex formation constants, as these may vary in different matrices. Ion-pair formation constants also depend on the solvent polarity, but in polymeric membranes such correlations are rather qualitative. Insufficient plasticizer lipophilicity may cause its leaching, which is especially undesired for in-vivo measurements, for microelectrodes and sensors working under flow conditions. Extension of plasticizer alkyl chains in order to enhance lipophilicity is only a partial problem solution, as it may lead to membrane component incompatibility. The concept of plasticizer-free membranes with active compounds, covalently attached to the polymer, has been intensively studied in recent years [91]. 

---