Length sequence, mean

When measuring vinyl polymer tactlclty, one prefers the longest complete n-ad distribution available as well as the translated simplest comonomer distribution, possibly m versus r. An alternative exists to the m versus r distribution In the form of number average or mean sequence lengths. If any vinyl homopolymer Is viewed conceptually as a copolymer of meso and racemic dyads, mean sequence lengths can be determined for continuous runs of both meso and racemic configurations (32), that Is,... 

In addition to viewing a vinyl homopolymer conceptually as a copolymer of meso and racemic dyads, one may also consider the mean sequence length of "like" configurations (M). In this Instance, the polymer chain Is seen as a succession of different lengths of co-orlented configurations from one to "n", the longest sequence of like configurations, that Is,... 

As was true in the case of mean sequence lengths for meso and racemic dyads, the necessary relationships can be used to develop corresponding equations for any particular n-ad distribution. A favorable point concerning the concept of "like" configurations is that it attaches a physical significance to the racemic distribution. 

The mean sequence lengths may offer a better way to present the simple comonomer distribution than meso, racemic distributions because they do reflect the polymer sequential structure. 

In addition, mean sequence lengths may be useful in evaluating statistical fits. For example. 

Mean sequence lengths can also be used to write average configurational structures, that is. 

The sequence distributions are clearly non-Bernoulllan in this case although they could satisfy conformity to Markovian behavior as indicated by equations 11-13. The following average structure is suggested by these observed mean sequence lengths. 

When describing polymer tactlcity, one should attempt to obtain the highest complete "n-ad" distribution available as well as a simple "comonomer" distribution. In connection with such a measurement, the mean sequence lengths may offer a viable alternative to the simple m versus r distribution. Useful relationships, which are helpful in establishing particular statistical behaviors, are available. 

The copolymerization equation can also be derived from the mean sequence lengths, I, of Mj and M2 units in the chains. The number of M, monomer additions per single M2 addition will evidently be given by the corresponding rate ratio, and the sequence will be longer by one unit than the rate ratio... 

It is seen to be given by the copolymerization eqn. (67), derived once more without any assumption of the existence of a stationary state. The whole procedure reminds us of the derivation of eqn. (67) from mean sequence lengths [see eqn. (68) and (69)]. The population of an Mj sequence of degree of polymerization Pn can be determined by means of the relation... 

The series of copolymers of 1-vinyl naphthalene with methyl methacrylate used in a recent study is shown in Table 3 ete the fonctions are the mole fraction of naphthalene chromophores in the copolymer, fn the fraction of linkages between naphthalene species in the polymer chain, f n, and the mean sequence length of aromatic species, 1 . Fluorescence decays in the monomer and excimer emission... 

Similarly, one can speak about mean sequence-length and its dispersity in statistical copolymers, about mean tacticity and its dispersity in the stereoiegular polymers, and so on. 

In radical polymerizations, the mean sequence length can be calculated, given certain assumptions (cf. Section 22.1.4). As a rule, it is not directly obtainable from experiments. However, in many copolymers, the fraction /ab of all the ab groups (i.e., a bonded to b and b to a) can be determined by nuclear magnetic resonance spectroscopy / b is defined by... 

As might be anticipated the equilibrium requirement that the largest sequence of A units crystallize, and do so in extended form is extremely difficult to attain experimentally. To account for the size of the crystallites that actually form, attention is focused on the mean sequence length (0, and the melting of crystallites of the same thickness. For random copolymers it is found that (15,17)... 

Methyl a-chloro acrylate-methylmethacrylate Measurement of diad configurations and mean sequence length [95]... 

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