Crosslinked PDMS Elastomers and Coatings from the Thermal Curing of Vinyl-Functionalized PDMS and a Diazide Aliphatic Crosslinker Denis Damiron, 1 Nidhal Okhay, 1 Samer Al Akhrass, 1 Philippe Cassagnau, 1 Eric Drockenmuller 1,2 1 Universite ´ Claude Bernard Lyon 1, Inge ´ nierie des Mate ´ riaux Polyme ` res (IMP - UMR CNRS 5223), 15 Boulevard Latarjet, 69622 Villeurbanne Cedex, France 2 Institut Universitaire de France (IUF) Correspondence to: E. Drockenmuller (E-mail: eric.drockenmuller@univ-lyon1.fr) Received 22 July 2011; accepted 3 September 2011; published online 22 September 2011 DOI: 10.1002/pola.24991 ABSTRACT: The crosslinking of poly(dimethylsiloxane) elasto- mers and coatings by the thermal curing of poly(dimethylsilox- ane-co-methylvinylsiloxane) and 1,12-diazido-dodecane was studied. This crosslinking pathway relies on the cycloaddition of azides and alkenes as well as the thermal generation of nitrene transient radicals, which react with alkenes, yielding respectively 1,2,3-triazoline and aziridine crosslinking knots. The influence of temperature and the ratio of azide and vinyl functionalities has been investigated by rheological, swelling, and insoluble fraction measurements for materials crosslinked in bulk and by comparison of the thickness before and after extraction of the soluble materials by soxhlet extraction for the crosslinked coatings. The preparation of highly crosslinked PDMS-based elastomers and coatings has been demonstrated, even if the fraction of elastically effective crosslinks in bulk remained below 160 mol/m 3 . Advantageously, this system does not require additional initiator or catalyst, is not sensitive to moisture or oxygen, and can be extended to a wide range of unsaturated polymers as well as different organic or inor- ganic solid substrates. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 98–107, 2012 KEYWORDS: PDMS; network; crosslinking; thin films; azide; elastomers; coating; aziridine; triazoline INTRODUCTION Poly(dimethylsiloxane) (PDMS) networks are elastomeric systems that exhibit high temperature and chemical resistance as well as peculiar mechanical and inter- facial properties that are suitable for applications such as adhesives, sealants, coatings and potting materials, food and biomedical industries as well as photodefinable materials for the preparation of highly complex patterned features and microfluidic systems. 1–5 Several one part (curing of chain- ends or randomly functionalized-polysiloxane by a low molar mass crosslinker) or two part (curing of chain-ends or ran- domly functionalized polysiloxane mixtures having comple- mentary reactive groups) systems have been developed using efficient and easy to process chemical pathways that afford network formation through covalent crosslinking of the polysiloxane chains. Most frequently used curing systems are the Sn-catalyzed condensation of alkoxysilane- or silanol- functionalized PDMS (sol-gel chemistry), 6–10 and the Pt-cata- lyzed hydrosylilation of SiH and vinyl-functionalized PDMS (frequently designated as Sylgard). 11–14 Whereas widely developed and very effective, these systems contain catalyst residuals that prevent their application in the biomedical field. 15,16 Free radical curing using organic initiators is a metal-free alternate for PDMS crosslinking, but the structural parameters of the resulting networks are difficult to control. 17- Other emerging alternates based on the crosslinking of ther- mally activated benzocyclobutene, 18 or diacetylene groups, 19 are more reliable chemical pathways but require chemical modifications of commercial products. Most recent develop- ments have been dedicated to the photo-patterning of polysi- loxanes containing vinyl, acrylate or styrenic groups by radical polymerization, and polysiloxanes containing epoxy groups by cationic ring opening polymerization. 20–24 In this scope the recent gain of interest for the thiol-ene click coupling has pro- vided efficient systems based on the thermal or photochemical curing of polysiloxanes bearing chain-ends or randomly dis- tributed alkene or thiol groups. 25–29 For instance, the curing of poly(methylthioethylsiloxane) by divinyl crosslinkers has been remarkably applied to soft imprint lithography. 30,31 Organic azides are increasingly popular consequently to their quantitative and specific reactivity with alkynes in the pres- ence of copper(I), which has been one of the most widely applied example of the click chemistry philosophy. 32 Besides, the noncatalyzed thermal and photochemical coupling of Additional Supporting Information may be found in the online version of this article. V C 2011 Wiley Periodicals, Inc. 98 JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 98–107 ARTICLE WWW.POLYMERCHEMISTRY.ORG