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Relaxation in Poly(alkyl methacrylate)s: Crossover Region and Nanophase Separation
Author(s) -
Beiner Mario
Publication year - 2001
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/1521-3927(20010801)22:12<869::aid-marc869>3.0.co;2-r
Subject(s) - glass transition , relaxation (psychology) , alkyl , materials science , methacrylate , copolymer , crossover , polymer chemistry , thermodynamics , polymer , chemistry , organic chemistry , physics , composite material , computer science , psychology , social psychology , artificial intelligence
Relaxations in a poly(alkyl methacrylate) series are systematically influenced by chemical modifications like the variation of side‐chain length, random copolymerization, or molecular weight. Recent results concerning the influence of chemical modifications on special parts of the relaxation chart are reviewed. The discussion is focused on two points: (i) The influence of chemical modifications on the crossover region of dynamic glass transition, where the relaxation times of α relaxation and Johari Goldstein mode β approach each other, is discussed. A general crossover scenario with a separate onset of cooperative α relaxation is observed for all lower members of this series. High temperature process a above and cooperative α relaxation below the crossover are shown to be distinct processes. Chemical modifications related to an increase in free volume shift this scenario mainly to lower frequency and temperature. Further details depend on the specific modification. (ii) The nanophase separation of incompatible main‐ and side‐chain parts in all higher members of the poly(alkyl methacrylate) series is discussed. This effect is concluded from the coexistence of two dynamic glass transitions in these homopolymers, the conventional a (or α ) process and an additional low temperature glass transition α PE . It is shown that the low T g process is related to cooperative motions in the polyethylene‐like side‐chain parts. The existence of static nanodomains in the range 0.5 to 1.5 nm is confirmed by means of wide and small angle X‐ray scattering data. The estimated nanodomain size is compared with the size of dynamic heterogeneities estimated independently from calorimetric data for the polyethylene‐like glass transition using the fluctuation approach.