The Polymers

Porous Polymer Technology

A full description of this technology is available in a monograph written by Dr. Benson ("Highly Porous Polymers"). A summary follows:

Types of Polymer Supports

There are commonly considered four types of polymer supports that have been used in enzyme immobilization applications:

1. Non-porous polymers

2. Microporous (“gel”) polymers

3. Macroporous polymers

4. High internal phase emulsions

Non-porous Polymers

Non-porous polymers are highly cross-linked copolymers that contain pores sufficiently small that they are impenetrable by most molecules. Binding of enzymes occur only on sphere surfaces. This results in good mass transfer characteristics but mass loading is very limited due to rather small surface area. See Figure 1A.

Microporous Polymers

These “gels” are copolymers wherein pores are found in the interstices created by low cross-linking. Pores are large enough that many biomolecules can penetrate and interact with surface moieties. However, pore sizes sufficiently large to accommodate macromolecules require very low cross-linking. This renders such polymers physically unstable. They swell in solvents and change porosity in gradients. See Figure 1B.


*Figure 1A. Non-porous polymers* are created by preparing a highly cross-linked copolymer. The resulting pores are too small for most molecules to penetrate. Enzymes may be bound only on sphere surfaces. Mass loading capacity is small.	*Figure 1B. Microporous polymers* are created by preparing a low cross-linked copolymer. These materials are often called “gels”. By lowering cross-linkage, pores can be made sufficiently large to accommodate macromolecules, but the polymers are physically unstable and swell in solvents.

Macroporous Polymers

These highly cross-linked materials have large irregular pores that terminate within the copolymer matrix. Biomolecules can enter these pores, but penetrate only a few angstroms due to the irregularity of the pores and their termination within the matrix. These polymers do not swell in solvents. See Figure 2A.

High Internal Phase Emulsions

High internal phase emulsions are polymers containing high degrees of porosity and other unique features. They are highly cross-linked and therefore rigid. They do not swell in solvents. They are further characterized by having extremely large cavities of micrometer dimensions that are interconnected by a series of smaller pores. These interconnections permit full penetration into interior surfaces even of very large molecules. “Cavilink^TM “is the trade name for these highly porous materials. They differ substantially from macroporous polymers that are characterized by the presence of irregular pores of Angstrom dimensions that terminate within the polymer matrix. Features of these two structures are illustrated in Figure 2.

Fig. 2A. Conventional “macroporous” polymers are characterized by irregular pores that terminate inside matrix. Pores are of Angstrom dimensions and are generally not interconnected. Total porosity is generally in the 50% range.

Fig. 2B. Cavilink^TM polymers are “high internal phase emulsions” characterized by uniform cavities of micrometer dimensions that are interconnected by a series of smaller pores. These materials can also have very high porosity, sometimes exceeding 90%.

SEM Photos

Differences in polymer appearance are illustrated in SEM photos shown in Figures 3A and 3B.


Fig. 3A. SEM photo of conventional macroporous polymer.	*Fig. 3B. SEM photo of Cavilink^TM* polymer.** The very high porosity is evident.

These materials are shown at higher magnification in Figure 4.


Fig. 4A. High magnification SEM of typical macroporous polymer. Note “cottage cheese” appearance and irregularity of pores.	*Fig. 4B. High magnification SEM of Cavilink^TM* polymer.** Note large uniform cavities having interconnected pores.

Competitive Advantages

The figures above illustrate distinctions between Cavilink^TM polymers and conventional porous polymers. Some competitive advantages are summarized below.

Micrometer size cavities enable loading of large entities, such as macromolecules, viruses or even whole cells. Thus, it is relatively easy to attach enzymes or other macromolecules to walls of the large cavities. Large cavity volumes permit easy access to epitopes and are ideal structures for enzyme reactions.

The interconnected structure enables liquids to flow through polymers. This minimizes diffusion effects normally found in conventional porous polymers and permits very high eluent flow rates when the polymers are used as chromatographic media. Resistance to flow is extremely low and mass transfer is extremely fast.

Large pore volumes enable greater holding capacity. Cavilink^TM polymers can have porosities in excess of 90%. This means that loading cavities with large molecules such as enzymes can be easily accomplished.

Physical Properties

Some physical properties of Cavilink^TM polymers are summarized in the table below. It is important to recognize that Sunstorm’s patents cover morphology of the microspheres and are independent of polymer composition. Thus, Cavilink^TM polymers can be made into a variety of materials including polystyrene, polyvinyl alcohol, polymethylmethacrylate, polyvinylpyrrolidone and others.

*Property of Cavilink^TM polymers*	*Measurement/Description*
Density (typical)	0.1 g/cm³
Range of internal void volume	70% to > 90%
Cavity diameter	< 1 µm to > 30 µm
Interconnect pore diameter	Can be varied
Composition	Many polymer formulations possible

A list of patents covering Sunstorm's technology is found at Patents.

Return to top of page

Home