BayMaterials

Cyclic Olefin Co-polymers (COC) are a relatively new class of polymers that have seen significant growth and penetration into the medical device and diagnostics markets. Chemically COC are generally comprised of a rigid ring structure and optionally varying amounts of ethylene and are polymerized using a metallocene catalyst. The most common ring structures are based on norbornene with various substituent groups to tailor properties. There are also commercial resins based on more complex ring structures that lead to higher Tg values.

Figure 1. Representative Structure of COC

Ticona was the highest volume COC producer but sold the business to Daicel Chemical Industries and Polyplastics Co., Ltd who markets under the original trade name TOPAS™. Injection molding and extrusion grade are also marketed as Zeonor™ by Zeon Chemicals, and Apel™ by Mitsui Chemical.

Distinguishing characteristics of COC resins are based on their amorphous character, moderate to high Tg, very high optical clarity, low birefringence and excellent moisture barrier properties. The barrier properties of COC are quite remarkable as shown in the figure below: (more…)

Medical product designers know that urethanes can be used where biocompatibility and flexibility are the key features. Electronics and packaging engineers are familiar with urethanes as conformal coatings or potting compounds where water blocking properties are important. Mechanical engineers may select the urethanes as tough, abrasion-resistant materials used for skateboard wheels, processing rollers, and adhesives.

Like the fable of the blind men and the elephant, it is common for specialists in one industry to only see the properties of Urethanes that they are familiar with and overlook others. At Bay Materials we work with clients in a broad range of industries and have specified urethanes for a wide variety of applications. This has given us many opportunities to think about the “whole elephant” with materials we are evaluating or recommending.

While many engineers are aware of low durometer urethanes used for products like catheter tips, many do not realize that transparent urethanes are commercially available with tensile modulus up to about 300,000 psi and even over 2 million with reinforcement and fillers. Bay Materials selected one of these clear, tough materials and modified it further to produce the Zendura line of orthodontic appliance materials used in dental aligners today. This took advantage of the desirable properties of biocompatibility, toughness and clarity of urethane. We have also specified urethane adhesives and coatings for use in the protection of sensing devices, taking advantage of their good adhesive and conformal properties and its strength as a water barrier.

When considering materials applications, it is important to consider all the properties of the material, or consult with someone more familiar with the subject. Don’t cross urethanes off of your list of candidates too quickly. Urethanes exist with an amazing range of properties, which can act as everything from a high-durability top-coat to a soft gasket.

A recurring theme at Bay Materials has been dealing with water. More precisely, not a problem with water itself, but keeping water out of things. Several recent projects have revolved around the difficulty of finding adhesives, encapsulants and sealants that can resist water at elevated temperatures. (more…)