Debate, macromolecular

Yet as the many sided debate went on, Wallace Carothers started a series of investigations in 1928 which would eventually establish the macromolecular concept. His objective from the beginning was to prepare polymers of known structure through the use of established reactions of organic chemistry (85). In the brilliant years before his untimely death in 1937, he studied the preparation and properties of polyesters, polyanhydrides, polyamides, and polychloroprene (28). 

Nevertheless, the existence of the famed maximum in the dendrimer [>7] vs G relationship, and whether this behavior could be a characteristic fingerprint property of this type of macromolecular architecture, was questioned recently [19, 23], In fact, so was the linearity of the dependence of dendrimer molecular radii on M1/3 [19], so that whether this may be the beginning of yet another controversy, remains to be seen. Perhaps the future may bring an interesting debate on these subjects, but until new data become available, one should refrain from drawing premature conclusions because the exciting architectural beauty of idealized dendrimer structures has already proven itself to easily tempt the most astonishing hypotheses that may not be readily substantiated by reality. 

One of the dominant issues in coal structure to re-emerge in the past decade is the two-phase concept of coal structure. A very spirited discussion of this topic was a feature of the 1989 symposium (48-52V Peter Given played a central role in the recent work on the two-phase concept, particularly in fostering the usage of the terms "mobile phase" and "macromolecular network" (23.53-551 and in organizing the "debate in print" (54V which has become a landmark papers in coal structure. In particular, the debate in print (24) was cited by all of die contributors to the 1989 discussion of the mobile phase (48-52V Given s work on the mobile phase was a... 

Proton n.m.r. investigations of coals swollen in deuterated pyridine showed that the free induction decay /FID/ consists of Gaussian and Lorentzian components related to two populations of protons which have widely different degrees of rotational mobility (1-5). The Gaussian component of FID has been unanimously ascribed to the macromolecular part of the coal matter that is supposed to have very limited rotational mobility. These publications as well as the ensuing debates (6-9) however, reflected the controversy regarding the nature of the Lorentzian /mobile/ protons in coals. 

In the debate about existence of pre-ordered states in the polymer melt, as advocated recently, polyolefins with chiral side chains may well become a major investigation tool. Indeed, the macromolecular amplification induces a pre-organization, or at least a preferred helical conformation in the polymer melt or solution. As such, these polymers display very precisely the behavior that is assumed by some of the recent crystallization schemes or scenarios. Furthermore, for the P4MH1 systems considered so far at least, the confor-mationally racemic character of the stable crystal structure implies that half of the stems must change their helical hands at some stage in the crystallization process - which may greatly delay the formation of this stable crystal structure, as illustrated by P(S)4MH1. 

Water behaves differently in different environments. Properties of water in heterogenous systems such as living cells or food remain a field of debate. Water molecules may interact with macromolecular components and supramolecular structures of biological systems through hydrogen bonds and electrostatic interactions. Solvation of biomolecules such as lipids, proteins, nucleic acids, or saccharides resulting from these interactions determines their molecular structure and function. 

Tg will be much reduced. Therefore, as low a temperature as conveniently obtainable was planned for a series of experiments, reported by Rigbi74 (It may incidentally be noted that stresses in the macromolecular network do develop on swelling in solvent, but as long as no external stress is applied, the meaning of the expression stress softening becomes debatable. Nevertheless, this semantic problem will not be discussed here). 

Our knowledge of the aliphatic structures in coals is currently inadequate. In many low-rank coals, there is a significant amount of long-chain aliphatic material. There is a debate as to whether this material is bound to the coal macromolecular structure or whether it is simply tangled up with it and thus trapped. 

Both chemical and macromolecular structures are important determinants in the selection of the SEC method(s) used for the analysis and characterization of cellulose. Each structure is briefly discussed however, each is also the subject of much research and debate. For detailed discussions, refer to the literature (e.g.. Refs. 111-124). 

It is debatable whether the two-phase model describes the relationships correctly. The concept of a phase has to be used with caution in the interpretation of the physical structure of macromolecular substances because equilibrium states do not usually exist, and the borderlines between crystalline and amorphous phases are not distinct. As the electron micrographs (particularly Figure 5-Id) show, different sta tes of order can, in fact, occur alongside each other in a particular sample. The individual methods for determining crystallinity thus cover varying degrees of order, and will... 

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