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Effect of Molecular Weight on Enthalpy Relaxation in Syndiotactic Poly(Methyl‐Methacrylate)
Author(s) -
Sciucca Stefania Della,
Penco Maurizio,
Sartore Luciana
Publication year - 2007
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200750105
Subject(s) - enthalpy , tacticity , isothermal process , relaxation (psychology) , thermodynamics , activation energy , methyl methacrylate , supercooling , poly(methyl methacrylate) , glass transition , materials science , polymer chemistry , molecular mass , annealing (glass) , chemistry , polymer , organic chemistry , polymerization , psychology , social psychology , physics , enzyme
The structural relaxation behaviour of narrow fractions (M w /M n < 1.1) of syndiotactic poly(methyl methacrylate) with molecular masses ranging from 2,000 to 200,000 Daltons have been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy ( Δh *) of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (T a = T g − 10 °C). As expected, the increase of molecular weights gives rise to both a continuous increase of Δh * and a decrease of the apparent isothermal relaxation rate . More interestingly, both Δh * and the apparent isothermal relaxation rate showed abrupt changes around the syndiotactic PMMA entanglement mass ( M e ).