Synthesis And Characterization Of Protein Resistant Polymers

This thesis deals with the protein resistance of polymers at the solid/liquid interfaces. First, we have investigated the effect of microphase separation on the protein resistance of a polymeric surface. Second, we have studied role of hydration in protein resistance of polymers. Third, we have prepared polyurethane with zwitterionic side chains and studied their protein resistance. The main results are as follows:1. We have prepared segmented polyurethanes (PUs) containing poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) or poly(dimethylsiloxane) (PDMS) soft segments by two-step condensation polymerization. It is known that PU consisting of a hard and soft segments exhibits microphase separated structure, so we can obtain different microphase separation by altering the hard segment ratio. To obtain different surface property, we chose three different soft segments. Atom force microscopy (AFM) observation in air and solution indicates the segmented PU forms microphase separation at different levels on surface. By use of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR), we have investigated the adsorption of fibrinogen, bovine serum albumin and lysozyme on a surface constructed by such a PU in aqueous solution in real time. Our study reveal that the protein resistance of the PUs arises from the hydrated PEG segments instead of microphase separation.2. We have prepared PUs with PPG or PTMG as the soft segments. Such a polymer exhibits a microphase separation, which allows the soft segments to be anchored on a surface by the hard segments. PPG and PTMG are similar to PEG in structure, but they have one more methyl and two more methylenes in each monomeric unit, respectively. The structural difference makes a much difference in their properties. PEG exhibits a lower critical solution temperature (LCST) higher than 80°C, whereas PPG has a LCST ranging from 15 to 42°C depending on its molecular weight. PTMG is not soluble at a temperature above 0°C. Thus, in the range of temperature 15 to 30°C, PEG is always hydrated, PPG can switch from hydrated to dehydrated, and PTMG is always hydrophobic or dehydrated. Contact angle (CA) measurements indicate the PPG-PU shows a lower critical solution temperature (LCST) at ~21°C where it changes from hydrophilic to hydrophobic. The PTMG-PU is always hydrophobic at a temperature above 0°C. The adsorption of fibrinogen, bovine serum albumin or lysozyme on such a PU surface in aqueous solution has been investigated by use of QCM-D and SPR in real time. PPG-PU surface exhibits protein resistance at a temperature below the LCST of PPG, but it significantly adsorbs proteins at a temperature above the LCST. On the other hand, the hydrophobic PTMG-PU surface can adsorb the proteins at any temperatures investigated, in contrast with the hydrated PEG which has excellent protein resistance. Our study clearly reveals that the hydration is responsible for the protein resistance.3. We have prepared polyurethanes with zwitterionic side chains by combination of free radical polymerization and polyaddition. First, dihydroxy terminated poly(2-(dimethylamino)ethyl methacrylate) (PDEM(OH)2) is synthesized by free radical polymerization with 3-mercapto-1,2-propanediol as the chain transfer agent, which polyadds with diisocyanate to yield a PU with PDEM side chains. Such side chains are zwitterionized by 1,3-propane sultone. 1H NMR, FTIR and XPS show that the zwitterionic side chains are incorporated into the PU. Thermal analysis demonstrates the thermal stability is greatly affected by the content of the side chains. By use of QCM-D, we have investigated the adsorption of fibrinogen, bovine serum albumin and lysozyme on a surface constructed by such a PU. It shows that the polyurethane can effectively resist nonspecific protein adsorption when the content of zwitterionic side chains is high enough.