Degradation and stabilisation of styrene-ethylene-butadiene-styrene (SEBS)block copolymer

Citation
Ns. Allen et al., Degradation and stabilisation of styrene-ethylene-butadiene-styrene (SEBS)block copolymer, POLYM DEGR, 71(1), 2000, pp. 113-122
Citations number
9
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
POLYMER DEGRADATION AND STABILITY
ISSN journal
01413910 → ACNP
Volume
71
Issue
1
Year of publication
2000
Pages
113 - 122
Database
ISI
SICI code
0141-3910(2000)71:1<113:DASOS(>2.0.ZU;2-J
Abstract
The degradation of hydrogenated poly[styrene-b-butadiene-b-styrene] or poly [styrene-b-(ethylene-co-butylene)-b-styrene], (SEBS) has been studied using a variety of analytical and spectroscopic methods including thermal analys is, UV, luminescence and FTIR spectroscopy coupled with crosslinking and hy droperoxide analysis in order to understand the nature of the processes inv olved. High temperature oxidation of non-commercial unstabilised material r esults in chain scission and severe crosslinking giving rise to extensive d iscolouration. FTIR analysis shows complex degradation processes with disti nct features associated with each phase. There is a solvent soluble clear p hase showing oxidation due primarily to the aliphatic part with a predomina nt absorption associated with terminal carboxylic acid groups at 1713 cm(-1 ). Anhydrides and alpha,beta -unsaturated carbonyl species are also formed in this matrix. There is also a solvent insoluble phase, which is predomina ntly crosslinked aliphatic material due to the formation of hydroperoxides and peracids/peresters. Vinyl groups are also evident in this phase. Thus, end group oxidation is a predominant process with the immediate autocatalyt ic formation of high concentrations of primary hydroperoxides during the ea rly stages of oxidation. These species are unstable and breakdown rapidly l eaving a steady-state concentration of more stable hydroperoxides. The lumi nescence also shows a rapid initial disruption of the polystyrene excimers coupled with the formation of long wavelength emitting polyconjugated chrom ophores, possibly, stilbene type in nature. Colour is evident is both cross linked and uncrosslinked phases. The former shows evidence for the presence of unsaturated carbonyl products and vinyl absorption. Phosphorescence ana lysis also indicated the presence of initial acetophenone chromophores, whi ch are associated with polystyrene end groups formed by chain breakage at t he aliphatic links. These species can act as initial active sensitive sites for further breakdown, possibly via a thermally induced hydrogen atom abst raction process. The end-chain aliphatic radicals are the sites for initial rapid hydro-peroxidation. The presence of phenolic antioxidants and phosph ites appear to exhibit a powerful effect in synergistically inhibiting the discolouration and oxidation processes. This is evident through thermal ana lysis (OIT) and luminescence. In the latter case the consumption of excimer is impaired by the presence of stabilisers while the initial acetophenone end-groups in SEES are destroyed. This is in complete contrast to the effec ts observed in control unstabilised SEES material. Mechanisms are proposed and discussed for each phase oxidation. (C) 2000 Elsevier Science Ltd. All rights reserved.