Photocrosslinked norbornene–thiol copolymers: Synthesis, mechanical properties, and cure studies

Abstract

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.

Synthesis and Ring‐Opening Metathesis Polymerization (ROMP) Reactivity of endo‐and exo‐Norbornenylazlactone Using Ruthenium Catalysts

“…Although the synthesis of NBAz was already reported, [25,26] as far as we know, ROMP of this monomer has never been investigated.…”

Investigation of thiol-ene and thiol-ene–methacrylate based resins as dental restorative materials

“…However, the achievable glass transition temperature, flexural strength, and flexural modulus were significantly less than values for BisGMA/TEGDMA. Though not commercially available, norbornene monomers have been synthesized in an effort to achieve a wider selection of thiol-ene materials with improved mechanical properties [28]. These thiol-norbornene materials provided relatively high glass transition temperatures ranging from 41 to 94 °C [29].…”

Ultraviolet curing kinetics of cycloaliphatic epoxide with real‐time fourier transform infrared spectroscopy

“…Therefore, it is difficult to find a facile method to quantify the rate of polymerization. Several discrete and time-resolved methods have been used for the study of UV-curable systems, including dilatometry, 9,10 Fourier transform infrared (FTIR) spectroscopy, 11,12 time-resolved Raman spectroscopy, 13 and differential photocalorimetry (or photo-differential scanning calorimetry). 14,15 A relatively new technique, real-time FTIR spectroscopy, was proposed by Decker and Moussa.…”