材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
PMMA の最大緩和時間について
祖父江 寛村上 謙吉星野 祐幸
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1963 年 12 巻 116 号 p. 367-370

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It is widely known that the“box”type curve is depicted in the rubbery region of the relaxation spectrum of a linear amorphous polymer. Three parameters, τl, τm and E0 are defined as the minimum relaxation time, the maximum relaxation time, and the height in the “box”curve function respectively.
One of these characterizing factors, τm was shown to be the function of molecular weight and temperature in a quantitative form for polymers by Tobolsky and Andrews, and later by Tobolsky and Murakami in a more refined form. The method of obtaining the value of τm suggested previously by Tobolsky and Andrews, is less natural than those proposed by Tobolsky and Murakami, which is so-called Procedure X. In the previous papers, the possibility of measuring the molecular weights by Procedure X was briefly described for some amorphous polymers such as polyisobutylene, polyvinyl acetate, and polystyrene.
This paper deals with such a new procedure for polymethyl methacrylate with more details.
The relation among τm, a maximun relaxation time, nw, weight-average chain length, T temperature and Tg, glass transition temperature, or Ts, WLF temperature, or Td, Tobolsky's temperature is indicated as follows:
logτm(sec.)=logAi-C1T-Ti/C2+T-Ti+3.4lognw
The value of i is g, s or d, changing the values of the constants C1 and C2 in each case.
The samples of polymethyl methacrylate whose monomers were purified by means of vacuum distillation under the nitrogen currents were prepared in the presence of varying concentration of the initiator 2-azobis isobutyronitrile at 60°C, using lower conversion around 10%. The radical-initiated polymers thus obtained were found to have a heterogeneity index of 1. 9.
If the values of logτm are plotted against that of logPn, the lines consisting of two straight lines are obtained, in which the slope has a value of 3.4 in the ranges of more than logPn=3.4, or about Pn=2500, and has a value of approximately unity in the ranges of less than logPn=3.4.
It is interesting to consider that the knick point by two straight lines may have a close relation with the critical molecular weight Mc, though this point looks located at the place somewhat higher than Mc of polymethyl methacrylate.
If the value of {logτm+17.44T-Tg/51.6+T-Tg} is plotted against that of log nw beautiful straight lines are obtained for the data including polyisobutylene, polyvinyl acetate, and polystyrene.
Finally, the dependency of τm on temperatures is studied for polymethyl methacrylate whose slope is unity. For this polymer whose slope is unity, the following equation is obtained.
logτm/nw·As'+C1=C1C2/C2+T-Ts
It is found that the experimental relation between τm and temperature can be on the theoretical line shown by the above equation almost exactly.

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