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Molecular motions in bisphenol a polycarbonates as measured by pulsed NMR techniques. I. Homopolymers and copolymers
Author(s) -
Stefan Davor,
Williams H. Leverne
Publication year - 1974
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1974.070180502
Subject(s) - polycarbonate , glass transition , bisphenol a , tetrabromobisphenol a , polymer , materials science , copolymer , amorphous solid , bisphenol , relaxation (psychology) , polymer chemistry , chemistry , composite material , organic chemistry , epoxy , psychology , social psychology , fire retardant
Molecular motions in homopolymers and copolymers based on bisphenol A polycarbonate (BAP) were investigated over a wide temperature range by means of two pulsed nuclear magnetic resonance methods: the spin‐lattice relaxation time T 1 and the spin‐lattice relaxation time in rotating frame, T 1ρ . Nuclear magnetic relaxation measurements of bisphenol A polycarbonate indicated the existence of four transitions in the solid amorphous state. This included the glass transition T α , two transitions associated with localized motions of the main chain, T β and T γ , and a transition due to side‐group motion, T δ . The results offer new evidence for the transition T β , which is ascribed to localized segmental motions of the polycarbonate chain. The physical properties of the polymer (high impact strength and a large fractional free volume in the glassy state) can be explained by the presence of the two secondary transitions T β and T γ , which are both associated with main‐chain motions. The presence of the bulky bromine on a bisphenol A unit of a polymer chain in a position ortho to the carbonate groups restricts all motions of the main chain, thus increasing T α , T β , and T γ . As a result of an increase in the secondary transition temperatures, impact strength is reduced at least 20‐fold as compared with the unsubstituted material. The results for tetrabromobisphenol A polycarbonate and copolymers of bisphenol A with tetrabromobisphenol A and bisphenol A with tetrachlorobisphenol A polycarbonate confirm the idea that the impact strength of the polymer is related to the secondary transitions ( T < T g ) arising from the main‐chain motions. Copolymers of bisphenol A polycarbonate with tetrabromobisphenol A polycarbonate showed a single glass transition temperature whose value lay between those of the homopolymers. The results indicated multiple secondary transitions which corresponded to the transitions of the homopolymers with magnitudes proportional to the comonomer content.