This report gives a description of the principal technical activities of the Polymers Division during the 1996 fiscal year. It is organized according to the program structure by which we plan our work. The report follows a concise format that was designed to make it easier for readers to understand the total range of our programs. Technologies can seldom be neatly categorized according to their technical content. Correspondingly, our industry customers rarely describe their needs in only one or two technical areas. This organization of the report also provides the reader with the management context in which we view individual projects in order to make our motivation for the work clearer. We hope this will encourage our customers to offer comments and advice on ways we can be more effective in our work.

The Polymers Division is responsible for providing standards, measurement methods, and fundamental concepts of polymer science to assist those U. S. industries that produce or use synthetic polymers in essential parts of their business. We plan our programs primarily to develop improved measurement capability for broad sectors of the industrial community. We rely heavily on advice from industrial and technical communities to set our priorities. This advice stems both from formal workshops, some of which are briefly described in this report, and from extensive informal visits to and from our customers. In all these programs, collaboration with others continues to be the most effective way to develop and transfer technology. In particular, industry collaborators who know both their business and technical needs are vital to planning and execution of the projects.

The Division has focused a majority of its resources on specific industrial sectors. This has allowed us to assess the needs of each industry group and plan a response that is appropriate to our capabilities and role. Each of the program overviews describes the industrial focus of the program even though the program outputs often have wider applicability.

There are many technical accomplishments which are described within this report under each specific program. The following is a selected list of these accomplishments which gives an overview of the output of all the Polymers Division programs.

Significant Accomplishments

ELECTRONIC PACKAGING AND INTERCONNECTION PROGRAM

Detailed analysis of transient charge response obtained from thermal pulse instrumentation now allows evaluation of the barrier to heat transmission across the interface between a dielectric polymer film and a conducting substrate.

NMR and NIR spectroscopy have detected liquid-like water as well as molecularly dispersed water in silica-filled epoxy molding compound and a polyimide when equilibrated in liquid water.

X-ray reflectivity has been used to measure the hygroscopic expansion of thin films of polyimide on silicon for a variety of film thicknesses. The results imply the existence of an interfacial region which absorbs much more water than the bulk.

POLYMER BLENDS AND PROCESSING PROGRAM

Phase separation kinetics of a model polystyrene-polybutadiene blend during shear was measured by light scattering and phase contrast microscopy in collaboration with Goodyear.

• Steady shear behavior of a solvated model polymer blend sample in the two-phase region was measured using fluorescence microscopy. In order to establish a scaling approach to understand shear mixing, phase compositions as a function of shear rate and temperature were obtained.
  
• Pressure induced shifts in the miscibility of polyolefin blends were measured via cloud point techniques in collaboration with Exxon.
  
• Phase separation kinetics in ultrathin blend films were measured to demonstrate suppression of surface induced phase separation and a transition to the behavior of a two dimensional fluid mixture. Results are in agreement with simulations of phase separation in 2-D.
  
• A patent application was filed for a temperature profile sensor based on confocal optics. The sensor, which fits the standard instrumentation port of processing machines, was used to measure temperature profiles in polyethylene resin during extrusion. The results were consistent with expected effects of shear heating in the barrel of an extrusion machine.
  
• The distribution of condensed counterions associated with the charged terminal units of polyelectrolyte dendrimer molecules in solution was characterized by small angle neutron scattering.

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POLYMER COMPOSITES PROGRAM

A micromechanical testing method developed for polymer composites was shown to be an effective tool for measuring the interfacial shear properties of dental materials. For example, using the microbond interfacial strength test, a hydrophobic silane coupling agent was demonstrated to produce more durable adhesion than the dental industry standard formula.

A traditional Lattice Boltzmann formulation was modified to model flow in heterogeneous media, where the momentum transport is expressed with a combination of the Stokes and Brinkman equations. Lattice Boltzmann techniques enable efficient computation in real materials and the inclusion of important multiphase flow physics.

A fast cure sensor was developed in cooperation with industry and demonstrated in the fabrication of epoxy, polyurethane, and polyester composite plaques. The technology is being transferred to the Ford Motor Co. laboratory where it will be used on prototype production equipment as part of a NIST/Ford/GE ATP program.

The Polymers Division and Ohio State University held a three day workshop on Liquid Composite Molding. Since the first workshop on Liquid Molding was held at NIST three years ago, a nascent liquid molding industry has emerged in the United States and a new set of technical challenges revolving around quality control has emerged.

POLYMER CHARACTERIZATION

• A general methodology was developed for comparison of the molecular weight distribution obtained from MALDI mass spectrometry with that obtained from size exclusion chromatography.
  
• The mixed phase of a metal-sulfonated poly(styrene)/methylated poly(amide) was shown by NMR to contain a near-average level of sulfonated styrenes, rather than a higher level expected from polarity arguments.
  
• Tension and compression responses of a commercial grade poly(carbonate) were shown to be predictable within 15 % based on properties obtained from torque and normal force data in torsion. This result required the development of a compressible form of Valanis-Landel Strain Energy Function.

• In collaboration with researchers from Kodak, time-temperature and time-aging time data for poly(ethylene terephthalate) and poly(ethylene naphthalate) thin films were obtained by conducting temperature jump experiments in stress relaxation.
  

DENTAL AND MEDICAL MATERIALS PROGRAM

• Low shrinkage interpenetrating polymer networks were formed by coincident free- radical methacrylate polymerization and cationic double ring-opening polymerization.
  
• The addition of urethane functional groups to fluorinated methacrylate monomers was shown to provide polymers with significantly improved strength and minimal water uptake.

• The feasibility of developing stress-bearing craniofacial implants from hydroxyapatite and bioresorbable polymers was demonstrated.
  
• Cooperative Research and Development Agreements were signed with six orthopaedic companies to evaluate the wear properties of orthopaedic joint materials.

THEORY AND MODELING PROGRAM

• A relationship was developed between the entropy of a glass-forming polymer system and its viscosity in which the viscosity is determined by the configurational free energy, rather than by the configurational entropy as expected from earlier theories.

• A new and general analytic description of transport virial coefficients of particles having general shape and arbitrary property mismatch was introduced.