Effect of the synthetic methodology on molecular architecture: from statistical to gradient copolymers

Abstract

Styrene-butyl acrylate (S-BuA) copolymers were synthesized by nitroxide-mediated controlled radical polymerization using an alkoxyamine as an initiator. Using different synthetic methodologies, statistical copolymers were be obtained by batch nitroxide mediated polymerization while the gradient composition was a forced gradient by continuous addition of S during BuA polymerization (semi-batch process). These gradient copolymers have been studied by 1 H NMR and size exclusion chromatography to characterize the gradient composition molecular structure. The evolution of the composition was correlated with the glass transition temperature (T g ) of the copolymers. The gradient copolymers exhibit one T g with a value in between the T g of polystyrene and poly(butyl acrylate), indicating that the materials did not present well defined microphase separation. Specific organization at the air-polymer interface of such copolymers has also been demonstrated by comparison between classical and attenuated total reflection (ATR) Fourier transform infra-red spectra. This bulk soft matter assembly was confirmed by AFM analysis, which showed a different morphology at the surface and in the bulk following removal of the top layer. Moreover, for the most well defined gradient composition, a specific nano-structuring was demonstrated by small angle neutron scattering. The preliminary rheological properties of these gradient copolymers were studied and are discussed in relation with their molecular structure.

Semicrystalline Macromolecular Design by Nitroxide‐Mediated Polymerization

“…A typical ''S'' curve is obtained as described by Karaky for styrene/butylacrylate and butylacrylate/dimethylacrylamide systems. [28,29] In the present study, we observe in the first segment rich in ODA units (%90%) up to 0.3 of the apparent normalized chain length. This block is rapidly followed by a strong increase of MA, characteristic of a gradient-shape composition, which tends to a plateau, characteristic of a blocky structure, for apparent normalized chain lengths from 0.7.…”

“…In fact, semi-batch nitroxide-mediated polymerization provides a facile route to synthesize gradient copolymers as demonstrated by Karaky et al [28,29] In this work, ODA and MA were selected as monomers for synthesizing gradient copolymers. To form gradient copolymers it is also necessary that the relative incorporation of the monomers into polymer chains gradually changes throughout the polymerization process.…”

“…[26] Recently, our group was interested in synthesizing gradient copolymers by batch and semi-batch nitroxidemediated radical polymerization, demonstrating the effect of the synthetic methodology on the molecular architecture. [27][28][29] In this paper, the synthesis of PODA homopolymers, diblock, triblock and gradient copolymers composed of the crystallizable ODA monomer (T f % 34 8C) and methyl acrylate (MA) units by NMP is shown for the first time. These gradient copolymers synthesized by the semi-batch process were obtained by continuous addition of MA during the ODA-polymerization reaction in solution.…”

“…[27] A pseudo-instantaneous composition is used to describe the profile of the gradient copolymer, as we recently described. [28,29] It was calculated by monitoring the conversion of each component as the copolymerization progressed. The experimental data were estimated using 1 H NMR spectroscopy from the relationship between the relative areas of the proton signals of the OCH 2 group of ODA and the OCH 3 group of MA, which appeared at d ¼ 4.05 ppm and d ¼ 3.7 ppm, respectively.…”

“…Nevertheless, these AFM images confirm that a semicrystalline gradient copolymer is also able to organize when the gradient-shape profile and composition is well designed. [28,29] …”