TY - JOUR
T1 - Bulk physical aging behavior of cross-linked polystyrene compared to its linear precursor
T2 - Effects of cross-linking and aging temperature
AU - Jin, Kailong
AU - Li, Lingqiao
AU - Torkelson, John M.
N1 - Publisher Copyright:
© 2017 Elsevier Ltd
PY - 2017/4/21
Y1 - 2017/4/21
N2 - The bulk physical aging behavior of cross-linked polystyrene (PS) is directly compared to that of its linear precursor polystyrene-co-vinylbenzocyclobutene (PS-VBCB) with 8.5 or 12.5 mol% VBCB content. The VBCB units incorporated into a linear PS precursor cross-link with one another upon annealing at 250 °C. Physical aging rates of bulk PS-VBCB films before and after cross-linking are characterized using ellipsometry by monitoring the decrease in thickness during isothermal annealing at a specific aging temperature (Ta) below the glass transition temperature (Tg). Physical aging rates show strong dependences on Ta values, with neat PS, linear PS-VBCB precursors with 8.5 or 12.5 mol% VBCB, and cross-linked PS with 8.5 mol% VBCB exhibiting maxima at Ta - Tg = −40 to −30 °C. In contrast, cross-linked PS with 12.5 mol% VBCB exhibits a maximum aging rate at Ta - Tg = −65 to −45 °C. The distribution of Ta-dependent aging rates broadens in cross-linked PS samples compared to linear precursors, which is correlated with increased Tg breadth or heterogeneity after cross-linking. Comparisons of aging rates of cross-linked PS with linear precursors demonstrate that cross-linking can lead to an increased, decreased, or unchanged aging rate depending on the values of Ta and Ta - Tg: e.g., when Ta - Tg > −60 °C, both cross-linked PS samples have a lower aging rate compared to their linear precursors at the same Ta - Tg whereas the cross-linked PS exhibits a similar or even greater aging rate compared to the linear precursor when Ta - Tg < −60 °C. These results help to reconcile previous seemingly contradictory observations regarding effects of cross-linking on physical aging rates. To the best of our knowledge, cross-linking induced enhancement of physical aging rates of cross-linked polymers relative to their linear precursors at the same Ta - Tg value is being reported for the first time here.
AB - The bulk physical aging behavior of cross-linked polystyrene (PS) is directly compared to that of its linear precursor polystyrene-co-vinylbenzocyclobutene (PS-VBCB) with 8.5 or 12.5 mol% VBCB content. The VBCB units incorporated into a linear PS precursor cross-link with one another upon annealing at 250 °C. Physical aging rates of bulk PS-VBCB films before and after cross-linking are characterized using ellipsometry by monitoring the decrease in thickness during isothermal annealing at a specific aging temperature (Ta) below the glass transition temperature (Tg). Physical aging rates show strong dependences on Ta values, with neat PS, linear PS-VBCB precursors with 8.5 or 12.5 mol% VBCB, and cross-linked PS with 8.5 mol% VBCB exhibiting maxima at Ta - Tg = −40 to −30 °C. In contrast, cross-linked PS with 12.5 mol% VBCB exhibits a maximum aging rate at Ta - Tg = −65 to −45 °C. The distribution of Ta-dependent aging rates broadens in cross-linked PS samples compared to linear precursors, which is correlated with increased Tg breadth or heterogeneity after cross-linking. Comparisons of aging rates of cross-linked PS with linear precursors demonstrate that cross-linking can lead to an increased, decreased, or unchanged aging rate depending on the values of Ta and Ta - Tg: e.g., when Ta - Tg > −60 °C, both cross-linked PS samples have a lower aging rate compared to their linear precursors at the same Ta - Tg whereas the cross-linked PS exhibits a similar or even greater aging rate compared to the linear precursor when Ta - Tg < −60 °C. These results help to reconcile previous seemingly contradictory observations regarding effects of cross-linking on physical aging rates. To the best of our knowledge, cross-linking induced enhancement of physical aging rates of cross-linked polymers relative to their linear precursors at the same Ta - Tg value is being reported for the first time here.
KW - Cross-linking
KW - Ellipsometry
KW - Heterogeneity
KW - Physical aging
KW - Polymer network
UR - http://www.scopus.com/inward/record.url?scp=85015984236&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85015984236&partnerID=8YFLogxK
U2 - 10.1016/j.polymer.2017.03.045
DO - 10.1016/j.polymer.2017.03.045
M3 - Article
AN - SCOPUS:85015984236
SN - 0032-3861
VL - 115
SP - 197
EP - 203
JO - Polymer
JF - Polymer
ER -