SYNOPSlSA number of norbornene-functionalized resins were prepared and their photoinitiated crosslinking reaction with a multifunctional thiol was studied. Access to these novel resins can be gained by several synthetic routes. The most general of these routes is the [ 47r + 2x1 cycloaddition reaction (the Diels-Alder reaction) of the corresponding multifunctional acrylate ester with cyclopentadiene ( CPD) monomer. The photocrosslinking reaction of these resins with multifunctional thiols such as pentaerythritol tetramercaptopropionate (PETMP) is quite rapid and sensitive to low UV dose as we11 as dose rate. FT-IR cure studies also indicated that the cure rate slows down dramatically as the conversion approaches the calculated gel points for the systems under study. Mechanical properties of cured thin films of these materials exhibited a wide range of tensile and dynamic mechanical properties, which depended on the structure of starting materials used in the preparation of the norbornene resin and the crosslinking thiol. I NTRODUCTIO NThe photoinitiated polymerization reaction between a multifunctional olefin and a multifunctional thiol (thiol-ene reaction) is a useful and versatile method for the preparation of ultraviolet (UV) curable adhesives, sealants, and coatings that find wide application in industry.' Because of the utility of this reaction, it has received a great deal of study. It is well established that the thiol-ene polymerization is a step growth process that propagates by chain transfer and that the conversion kinetics can be predicted by the Carothers e q u a t i~n .~.~ Of the many unique features of this type of photopolymerization mechanism, the feature that has set this process apart from other UV-initiated processes is the observation that thiol-ene polymerizations are not inhibited by ambient oxygen or m o i s t~r e .~.~ In fact, dissolved oxygen is actually incorporated into the polymer by a complex series of steps that have been described by Kharasch and co-workers6 and more recently by Szmant and his co-w~rkers.~-l~ This process is illustrated below.