Poly(methacrylic acid) Grafted with Poly(ethylene glycol) and n-Dodecane as pH-Sensitive Surfactants for Water-in-Oil Fermentations

Abstract

pH-sensitive surfactants are potentially beneficial to water-in-oil fermentations. Ideally, the surfactants promote emulsification at fermentation pH (typically ∼7) but, upon pH adjustment, lose surface activity to allow easy phase separation for product recovery. In this study, poly-(methacrylic acid) (PMAA) grafted with poly(ethylene glycol) (PEG) and n-dodecane was synthesized with an initial MAA/EG molar ratio of 1:1 or 20:1 and a MAA/LMA (lauryl methacrylate) ratio of 1:0.16, 1:0.47, or 1:0.78. The polymers' pH sensitivity comes from the complexation between PMAA and PEG at low pH, which turns hydrophilic PMAA and PEG into a hydrophobic complex. The surface activity was confirmed to decrease markedly as pH dropped below ∼6.0. For polymers with 20:1 MAA/EG, the residual surface activity at low pH was still enough to inhibit the desired phase separation. However, the polymers with MAA/ EG/LMA ratios of 1:1:0.47 and 1:1:0.78 showed good emulsification at neutral pH and fast phase separation at pH 4. The polymer with 78% LMA produced the finest droplets, desirable for supporting higher cell concentrations in the fermentation.

Synthesis, preparation, and conformation of stimulus-responsive end-grafted poly(methacrylic acid-g-ethylene glycol) layers

“…The synthesis of poly(MAA-g-EG) without end-functionalization has been reported previously by free radical polymerication [12][13][14] and by ATRP. 15 To our knowledge the synthesis of thiol(end)-functionalized poly(MAA-g-EG) has never been reported before.…”

“…1 Schematic of a conformational transition of a chemically end-grafted stimulus-responsive side-chain graft copolymer (insets show molecular interactions for poly(MAA-g-EG)). [12][13][14] performed as described previously. 20 In a typical polymerization (Fig.…”

“…cartilage aggrecan 10 and epithelial mucins. 11 The synthesis and stimulus responsive nature of poly(MAA-g-EG) without end-functionalization has been reported previously by free radical polymerization [12][13][14] and by atom transfer radical polymerization (ATRP). 15 High molecular weight systems (y700-800 K) free in solution show a dramatic conformational transition in aqueous solution from a collapsed hydrophobic intrapolymer complex at low pH to an expanded hydrophilic coil at high pH that is essentially completed for pH > 6.0 and is amplified compared to the poly(methacrylic acid) or PMAA homopolymer.…”