Water Soluble Polymers Containing Weak Links

Abstract

This thesis describes the development of a new method to confer degradability to water soluble polymers already used in the oil servicing industry. Generally, high molecular weight polymers with a C–C backbone, like vinyl polymers, tend to be resistant to hydrolysis, oxidative cleavage, enzymatic attack, etc., and therefore they are not degradable, whereas hetero-atom-containing polymer backbones like esters, carbonates, amides, anhydrides, phosphazenes, etc. confer degradability. Redox polymerisation was chosen to introduce labile links into the hydrocarbon backbone of vinyl polymers. A variety of reducing agents that could be chosen provides a platform of polymers that can degrade upon experiencing different triggers. A redox pair consisting of reducing agents such as triblock copolymer poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic aicd), polycaprolactone diol, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and L-cystine and oxidising ceric (IV) ions were used to initiate redox polymerisation of acrylamide, N,N-diamethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid. The presence of degradable groups in the polymer backbone was studied using FT-IR, NMR and DSC. The degradation behaviour of the synthesised polymers was investigated by GPC. The polymer degradation was triggered in different ways dependent on the labile group which was incorporated into the polymer backbone. Drag reduction properties were quantified using a standard rheometer equipped with a double-gap measuring geometry, by calculating percentage of drag reduction (%DR) based on apparent viscosity. From the obtained results it is clear that redox reaction between a reducing agent and oxidising metal ion can be used to initiate polymerisation of vinyl monomers, nevertheless not all the systems proved to be equally successful. It was found that using a water soluble and hydrolytically stable reducing agent containing azo functionalities gave the best results and multiple labile groups were incorporated into the polymer backbone. Polyacrylamide with azo-links in the backbone proved to be as good drag reducing agent as polyacrylamide synthesised by initiation from the poly(ethylene glycol)/Ce(IV) redox couple, however it lost its drag reduction properties once subjected to elevated temperatures. From the carried out studies it seems that triblock copolymer poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid) is not an appropriate reducing agent due to its low stability in water at low pH. H1-NMR spectra show that the reducing agent degrades during the course of the polymerisation and hence cannot be used in aqueous environment to incorporate degradable groups into the polymer. In order to use a more stable but hydrophobic polyester - polycaprolactone diol, micellar polymerisation was utilised. The results showed that using redox polymerisation amphiphilic copolymers can be obtained. It was confirmed not only by H1-NMR, FT-IR and DSC, but also by the fact that hexane/water emulsions could be stabilised by acrylamide initiated from polycaprolactone diol.