Evolution of Structure and Properties of a Liquid Crystalline Epoxy during Curing QINGHUANG LIN, 1 ALBERT F. YEE, 1 H.-J. SUE, 2 * J. D. EARLS, 2 R. E. HEFNER, JR. 2 1 Department of Materials Science and Engineering, The University of Michigan, Ann Arbor, Michigan 48109-2136 2 The Dow Chemical Company, Organic Product Research, B-1215, Freeport, Texas 77541 Received 30 December 1996; revised 24 March 1997; accepted 25 March 1997 ABSTRACT: The evolution of structure, and thermal and dynamic mechanical properties of a liquid crystalline epoxy during curing has been studied with differential scanning calorimetry ( DSC ) , polarized optical microscopy, x-ray scattering, and dynamic me- chanical analysis. The liquid crystalline epoxy was the diglycidyl ether of 4,4 -dihy- droxy-a-methylstilbene ( DGEDHMS ) . Two curing agents were used in this study: a di- functional amine, the aniline adduct of DGEDHMS, and a tetra-functional sulfonamido amine, sulfanilamide. The effects of curing agent, cure time, and cure temperature have been investigated. Isothermal curing of the liquid crystalline epoxy with the di- functional amine and the tetra-functional sulfonamido amine causes an increase in the mesophase stability of the liquid crystalline epoxy resin. The curing also leads to various liquid crystalline textures, depending on the curing agent and cure temperature. These textures coarsen during the isothermal curing. Moreover, curing with both curing agents results in a layered structure with mesogenic units aligned perpendicular to the layer surfaces. The layer thickness decreases with cure temperature for the systems cured with the tetra-functional curing agent. The glass transition temperature of the cured networks rises with increasing cure temperature due to the increased crosslink density. The shear modulus of the cured networks shows a strong temperature depen- dence. However, it does not change appreciably with cure temperature.  1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2363 – 2378, 1997 Keywords: liquid crystalline thermoset; epoxy; curing; structural evolution; thermal and mechanical properties INTRODUCTION into the networks through thermal or photocross- linking of the functional groups of the LC precur- sors. Thus LC networks offer many potential ad- Liquid crystalline ( LC ) polymer networks com- vantages over conventional isotropic networks bine the unique properties of a liquid crystal and and liquid crystalline thermoplastics. These ad- a polymer network. Ideally the LC networks are vantages include better processability, tuned prepared such that the molecular orientational thermal expansion coefficients, and improved lat- order of the LC polymers or oligomers is locked eral strength and axial compression strength. 1,2 Furthermore, incorporation of liquid crystalline * Present address: Polymer Technology Center, Depart- order into a polymer network generates some un- ment of Mechanical Engineering, Texas A&M University, Col- usual phenomena of theoretical interest. For ex- lege Station, TX 77843-3123 Correspondence to: Q. Lin, IBM Semiconductor Research ample, a nematic network, which combines the and Development Center, Hudson Valley Research Park, 1580 effects of long-chain elasticity and nematic order, Route 52, B300-40E, Hopewell Junction, NY 12533 exhibits unusual phenomena such as spontaneous Journal of Polymer Science: Part B: Polymer Physics, Vol. 35, 2363 – 2378, 1997  1997 John Wiley & Sons, Inc. CCC 0887-6266/97 / 142363-16 shape changes, discontinuous stress-strain rela- 2363 8Q31 9612024 / 8q31$$2024 08-14-97 21:48:03 polpa W: Poly Physics