Since being developed over 50 years ago, aromatic polyamides have been used industrially for numerous highperformance applications due to their heat resistance, chemical stability, and high strength. Despite this extensive time span, limited applications as surface coatings have been explored due to most aromatic polyamides being insoluble in organic solvents and their extremely high melting temperatures. However, new polymerization techniques have been developed to overcome this insolubility, allowing applications such as reverse osmosis membranes and gas separation membranes to be developed. With the recent advancement of substituent effect chain-growth condensation polymerization, controlled growth aromatic polyamides have been shown to grow from flat and curved surfaces. In this study, aromatic polyamides with a protecting side chain were grown from flat and curved surfaces to allow for post polymerization deprotection and the introduction of hydrogen bonding along the backbone of the polyamide. The aromatic polyamide brushes formed were then characterized using transmission electron microscope and atomic force microscopy to explore important physical properties of the polymer brushes, including grafting density and Young's modulus. The introduction of hydrogen bonding dramatically increased the Young's modulus of the aromatic polyamide brushes from 5−6 to 22−32 GPa. Our results demonstrate the tunability of the aromatic polyamide brushes to achieve high mechanical strength and pave the way for their application in areas such as high-performance coatings.
A systematic study of the behavior of different leaving groups on a variety of ester‐based monomers was performed for the chain‐growth polycondensation synthesis of poly(N‐octyl benzamide). Linear and branched alkane esters were compared with their phenyl analogs using both computational and experimental methods. Kinetic experiments along with qualitative solubility observations were used, with the aid of nuclear magnetic resonance spectroscopy and gel‐permeation chromatography, to determine progress of the reaction, molecular weights, and molecular weight distributions. It was found that the reactivity of the monomer's ester group depends more on the stability of the leaving alkoxide than the electrophilicity of the carbonyl carbon, which contradicts previous literature. The order of reactivity increases for the alkyl esters with decreasing steric hindrance and decreasing pKa of the substituent. For the phenyl ester derivatives, the more electron withdrawing character of a para substituent increases the reactivity of the ester group, due to the higher resonance stabilization of the leaving phenoxide anion, not due to an increase in the electrophilicity of the carbonyl carbon.
A detailed investigation into the role of initiator structure, the presence of an initiator, and basicity of the non‐nucleophilic base in the chain‐growth condensation (CGC) synthesis of poly(N‐octyl benzamide) was conducted. A series of phenyl ester dimethyl amide initiators with different leaving groups were synthesized and used in the CGC preparation of poly(N‐octyl benzamide). Additional polymerizations were conducted without the presence of an initiator and with different non‐nucleophilic bases. Kinetic studies, along with nuclear magnetic resonance spectroscopy and gel‐permeation chromatography, were used to determine progress of the reaction, molecular weights, and molecular weight distributions. The experimental and computational results demonstrated that initiators containing electron‐withdrawing substituent phenyl esters, such as the p‐nitrophenyl ester, and electron‐withdrawing carbonyl character on the parent benzoate produce polymers with controllable molecular weights and narrow molecular weight distributions. Whereas, initiating species that contain electron‐donating character on the benzoate backbone, such as dimethylamino and methyl ester groups, produce polymers that resemble the results from reactions involving no initiators at all, indicating poor polymerization control.
With growing freshwater scarcity in many areas of the world, purifying alternative sources of water such as seawater, brackish water, and wastewater has become increasingly important. One of the main ways this is done is using reverse osmosis (RO) membranes composed of aromatic polyamide films synthesized using interfacial polymerization. These membranes have become the industry standard due to their excellent salt rejection. However, issues with fouling, degradation, and delamination plague current technology, which has led to renewed interest in finding innovative solutions. Polyethylene glycol (PEG) has been used extensively for its antifouling properties and has been incorporated into RO membranes with some success. In this study, oligoethylene glycol (OEG)-functionalized aromatic polyamides were covalently grown using surface initiation from silicon wafers, quartz crystal microbalance (QCM) sensors, and silica particles to form high grafting density polymer brushes. Initially, solution-based kinetic studies were used to optimize the polymerization conditions of the OEG-functionalized monomers. The optimized conditions were then used for surface-initiated substituent effect chain-growth condensation polymerization of the monomers. The use of these conditions produced uniform OEGfunctionalized aromatic polyamide brushes with well-defined molecular weight and narrow molecular weight distribution. QCM and atomic force microscopy were used to demonstrate the drastically improved antifouling characteristics of the brushes as compared to PEG monolayers and aromatic polyamides brushes without the OEG functionalization.
Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of L-lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using 1 H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of welldefined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.
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