Study of polymer dynamics and conformation using solid state NMR advanced techniques (exchange and double quantum). / Estudo da dinâmica e conformação de polímeros utilizando-se técnicas avançadas de RMN no estado sólido (exchange e double quantum).

AUTOR(ES)

Fábio Becker Guedes

DATA DE PUBLICAÇÃO

2001

RESUMO

This work is based on the study of dynamics and conformation of solid-state polymers, using NMR modern techniques. For the quantitative study of slow sidegroup dynamics in a series of poly(alkyl methacrylate)s and other of poly(α-substituted acrylate)s with varying sidegroup sizes two new 13C exchange techniques were used: centerband-only detection of exchange (CODEX) and pure exchange (PUREX). Flips and small-angle motions of the ester groups associated with the p-relaxation are observed distinctly, and the fraction of slowly flipping groups has been measured with 3% precision. A decreasing in these values occurs growing the sidegroup size. In PMMA, 34% of sidegroups flip, while the fraction is c.a. 10% in PcHMA around room temperature. In PMAA, no slow sidegroup flips are detected. In PMMA, the flipping fraction is temperature-independent between 25°C and 96°C, while in PEMA, PiBMA, and PcHMA it increases continuously between room temperature and Tg (from 31 to 80% for PEMA). Backbone CH2 CODEX data confirm the results obtained for the main chain movements. Flip-independent small amplitude motions (< 5°) are also observed. Besides, it is noticed that in some poly(α -substituted acrylate)s the a sidegroup size has influence in the fraction of slowly flipping ester groups at 25°C. For the study of polymers conformation Double Quantum NMR experiments were used, for torsion angles determination between 13C-13C pairs through the polymer chain. Experiments for two standards 13C labeled samples: poly(ethy1ene oxide) - (PEO) and poly(ethy1ene teraftalate) - (PET) were performed, with and without homonuclear decoupling (13C-13C), in a Varian Inova 400 spectrometer.

ASSUNTO(S)

double quantum double quantum polymers rmn do estado sólido exchange polímeros solid state nmr exchange

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