Surface Modifying End Groups

Surface Modifying End Groups (SMEs) are surface-active oligomers covalently bonded to the base polymer during synthesis. SMEs—which include silicone (S), sulfonate (SO), fluorocarbon (F), polyethylene oxide (P), and hydrocarbon (H) groups—control surface chemistry without compromising the bulk properties of the polymer. The result is key surface properties, such as thromboresistance, biostability, and abrasion resistance, are permanently enhanced without additional post-fabrication treatments or topical coatings. This patented technology is applicable to a wide range of PTG's polymers.

SMEs provide a series of (biomedical) base polymers that can achieve a desired surface chemistry without the use of additives. Polyurethanes prepared according to PTG's development process couple endgroups to the backbone polymer during synthesis via a terminal isocyanate group, not a hard segment. The added mobility of endgroups relative to the backbone is thought to facilitate the formation of uniform overlayersby the surface-active (end) blocks. The use of the surface active endgroups leaves the original polymer backbone intact so the polymer retains strength and processability. The fact that essentially all polymer chains carry the surface- modifying moiety eliminates many of the potential problems associated with additives.

Surface modification via surface active endgroups is readily adapted to the synthesis of polymers that normally incorporate a low molecular weight monofunctional endgroups for molecular weight control. The use of dodecylamine in place of diethylamine in the synthesis of segmented polyurethaneureas is one example. Using this approach, polymers have been made with tensile strengths exceeding 5000 psi which contain 0.5 wt. % dodecyl groups. With higher molecular weight endgroups, total endgroup concentration can be much higher. Using monofunctional 2000-M polydimethylsiloxane-amine (MPSX), high-strength elastomers have been prepared with nominal 6% (wt./wt.) siloxane content. Using monofunctional polyethyleneoxide-amines or alcohols, up to 16% ethyleneoxide has been incorporated into otherwise hydrophobic polymers with good strength retention.

The SME approach also allows the incorporation of mixed endgroups into a single polymer. For example, the combination of hydrophobic and hydrophilic endgroups gives the polymer amphipathic characteristics in which the hydrophobic versus hydrophilic balance may be easily controlled.

The Polymer Technology Group, 2810 7th Street, Berkeley, CA 94710. Tel: 510-841-8800; Fax: 510-841-7800.