Modification and cross-linking of saturated elastomers using functionalized azides Agata Zieliñska, Auke G. Talma, Jacques W.M. Noordermeer
Introduction
3. Reactions 1. The azide group Only the singlet state of nitrene readily inserts + N N N into saturated carbon-hydrogen bonds. AKnown to exist for over 100 years. ALittle or no interest until 1950’s. O . O N 3 AUsed as a source of nitrenes. . H ROCN + H N N + . . H O R N N N CO2R The azide group can decompose photo-chemically or thermally, releasing a The triplet state of nitrene can abstract hydrogen nitrogen molecule and yielding a highly reactive nitrene species. atoms to give free radicals. O O . hv/DT . . . ROC N + H ROC N H + C R N3 R N. + N2 . . Both, singlet and triplet state of nitrenes can react with 2. Decomposition of azides double bonds. R R Initially a nitrene is formed as a singlet, with paired electrons (the H preferred state). It may, however, progress to the more stable triplet state. N H CH H H N 3 R N + + H CH3 O O O CH3 H CH CH CH3 3 3 N AJ_130_2,25 ROCN3 ROC ROC N cis product trans product Pulse Sequence: s2pul Singlet Triplet Alkyl nitrenes can undergo rearrangement, with state state 1,2-H shift. R CH N RCH NH Cross-linking H
The problem with cross-linking of saturated elastomers is their low reactivity: Cross-linking of EPM saturated chains react only under very specific conditions and by a very limited number of reactions. The common way to overcome the lack of reactivity is by 10 pursuing free-radical reactions with peroxide. Azide reactions could be an 9 8 180ºC A-Ph
alternative with much higher cross-linking efficiency and reduction of polymer ) 7 180ºC DSA m 170ºC DCP degradation. N 6 d 150ºC DAF (
e 5 ADA u
Cross-linking Different types of azide functionality can be q 4 r
o 3 of polymer distinguished: T 2 chains by a N3 N Aliphatic azide (ADA) 8 7 6 5 substance 3 1 O O containing at 0 N3 S S N3 0 5 10 15 20 25 30 35 least two azide O O Sulfonyl azide (DSA) groups can be Time (min) CH achieved as a N O 3 O N Rheogram of samples containing different azides 3 3 Azidoformate (DAF) result of the and dicumyl peroxide (DCP) O CH O reaction of two 3 azide groups O with different Different azide types are reacting in a different Azido phenyl (A-Ph) manner and also at various temperatures. Only two polymer chains. N3 N 3 of them can be applied as curing agent for saturated CH3 elastomer. Polymer modification
Solubility of modified EPM Azide amount (phr) temp. (ºC) Hexane THF Azide amount Reaction temp. (ºC) Hexane THF The azide can be synthesized so as to (phr) time (days) (days) contain a functional group which will affect <5h <24h <5h <24h 2.25 10min 150 7 6 17 10 the properties of the treated polymer. The 0.75 150 + + 10min 160 6 3 8 3 modification process can be carried out by 160 + + 3min 170 3 3 1 2 170 + + reactive mixing at a temperature above the 1.5 150 + + azide decomposition temperature. 160 + + H1 NMR spectra 170 + +
Example: Grafting efficiency EPM was modified with different amounts of benzyl Azide amount Start temp. Before After azidoformate (BAF). (phr) (ºC) purification purification (%) (%) T .. .. 0.75 150 52 52 CH2 O N3 CH O N CH O N. 160 52 52 Pure EPM C -N 2 C .. 2 . 2 C 170 68 51 O O O 1.5 150 43 43 singlet state nitrene triplet state nitrene 160 43 43 170 60 34 CH2 2.25 150 52 46 C-H-insertion H-abstraction 160 53 46 170 58 47 Conclusions EPM after modification
! Curing of EPM using di-azidoformate, disulfonyl azides and di-azidophenyl does University of Twente, occur. Faculty of EngineeringTechnology ! Modification of EPM with substances containing azidoformate group is possible. By using azido compounds with a second functional group a reactive moiety can be Elastomer Technology and Engineering attached to the polymer. e-mail: [email protected] ! The azidoformate group has the lowest decomposition temperature. DPI project nr. #580