Synthesis of well-defined, surface-initiated
was demonstrated using
a new “grafting from” chain growth technique. A solution-based
chain growth polycondensation technique was adopted from literature
and modified to form a polyaramid brush by taking advantage of the
differences in substituent effects between the activated surface-grafted
initiator (methyl 4-(methyl(3-(trimethoxysilyl)propyl)carbamoyl)benzoate)
and the deactivated deprotonated monomer (methyl 4-(octylamino)benzoate).
The surface-immobilized polymer brushes on silicon wafers were characterized
using ellipsometry, goniometry, grazing-angle attenuated total reflectance–Fourier
transform infrared spectroscopy, and X-ray photoelectron spectroscopy.
In addition, polyaramid brushes were grown from high surface area
Stöber silica and studied using thermogravimetric analysis,
and the degrafted polymers were characterized using gel permeation
chromatography and nuclear magnetic resonance spectroscopy. This is
believed to be the first report of polyaramid brushes prepared by
the surface-initiated chain growth polymerization technique, and the
overall method allows for the preparation of novel aromatic polymer
brush structures that could not be previously synthesized.
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.
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