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.

A number of novel organic norbornene and norbornene siloxane polymer precursors have been synthesized as part of an on-going research project to produce a non-acrylate, UV-curable adhesive system. These precursors (monomers or oligomers) are di-, tri-and tetra-functional. The crosslinking agent is a multifunctional thiol.The organic norbornene systems, formulated to stoichiometry, have been characterized using thermal, static and dynamic mechanical analysis. We have found that norbornene ester systems have a range of physical properties, with tensile moduli ranging from 820-2300 MPa (1 18-350 kpsi), tensile strengths of 17-61 MPa (2.5-8.8 kpsi) and elongations of 4-100%. Glass transition temperatures range from 30-71°C for samples cured at room temperature with a dose of 620 mJ/cm2. Norbornene siloxanes crosslinked with thiol siloxanes have been formulated with increasing levels of a high surface area reinforcing agent. Tensile properties of filled films show that filler loading to 30 wt% significantly increases peak stress and elongation to break above that of 25 wt% filler. The addition of filler did not appear to increase the T, of the films in this series monotonically. Increased levels of filler were found to produce films with a broadened cold crystallization range and an increased melting temperature.

SynopsisFibers spun from anisotropic solutions of a lyotropic rigid-rod polymer, poly ( para-phenylene benzobisthiazole) [ PBZT] , were coagulated into homogeneous nonsolvents including a solution of 18% iodine/82% ethanol, ethanol, and water. The effect of these coagulants on the structure and mechanical properties of the PBZT fibers was studied. Structural and mechanical studies were performed on as-spun fibers. Wide-angle X-ray diffraction techniques have shown that fibers coagulated in the presence of iodine anions had d-spacings that were unique, as well as d-spacings that were characteristic of PBZT or iodine anions. Tensile and shear properties were highest in a fiber having a spin/draw ratio of 3 which contained 19.5% iodine species by weight. For these fibers, an average tensile strength of 2.2 GPa and a torsional modulus of 1.14 GPa was recorded. For fibers having this spin/draw ratio, and undergoing no post-processing heat treatment or tension drying, these values are much higher than would be expected.

Poly(p-phenylene terephthalamide) [PPTA] was the first commercially successful lyotropic liquid crystalline polymer to be spun into fibers having excetonally high tensile properties [1,2]. Fibers of PPTA are commonly referred to as Kevlar®, and are a product of the du Pont de Nemours Company, Inc. These fibers are stronger than steel, and have found many applications, including use in sporting goods such as canoes, tires, bullet-proof vests, cables and pressure vessels.