Synthesis and Characterization of ω-Unsaturated Poly(styrene-b-n-butyl methacrylate) Block Copolymers Using TEMPO-Mediated Controlled Radical Polymerization

Abstract

n-Butyl methacrylate has been polymerized in bulk at 130 °C in the presence of given amounts of a nitroxide stable free radical (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) using either a low molar mass alkoxyamine initiator (2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine) or a TEMPO-capped polystyrene macroinitiator. Complete consumption of both initiators was always observed. In contrast, very low final monomer conversions were found. Proton NMR spectroscopy and MALDI-TOF mass spectrometry were used for investigation of the polymer structure. They showed that the formed poly(n-butyl methacrylate) had the attached initiator at one end and that a block copolymer was synthesized when the polystyrene macroinitiator was used. The other terminal functionality of the polymer was not a TEMPO-based alkoxyamine but a methylene unsaturation exclusively. Particularly, no saturated polymer which would also be formed by conventional disproportionation reaction between two propagating radicals could be detected. From this result, it was concluded that the main chain-breaking event is the β-hydrogen transfer from a propagating radical to TEMPO (also called disproportionation reaction). The initial concentration of added TEMPO was shown to directly influence the poly(n-butyl methacrylate) block length independently of the initial concentration of alkoxyamine: the larger the concentration of TEMPO, the shorter the block length. The rate constant of disproportionation was calculated to be k dis = 1.4 × 106 L mol-1 s-1 at 130 °C.

Synthesis of Stimuli-responsive, Water-soluble Poly[2-(dimethylamino)ethyl methacrylate/styrene] Statistical Copolymers by Nitroxide Mediated Polymerization

“…However, conversion stopped increasing after 2 h of reaction and the final copolymer contained only about 40 mol% DMAEMA. Low conversion and early termination can be results of the slow initiation of poly(styrene) macroinitiator [29,42] and/or β-hydrogen transfer from the propagating radical to the initiator [43,44].…”

Síntese de copolímeros em bloco com propriedades líquido cristalinas

“…Os copolímeros em bloco de monômeros ordinários obtidos via radicais livres mediados por nitróxidos estáveis têm sido anunciados na literatura desde 1994 [39][40][41][42][43][44][45][46][47][48][49][50] . A obtenção de um copolímero em bloco LC contendo um segmento amorfo e um segmento LC empregando essa técnica de polimerização foi um trabalho pioneiro do IMA.…”

“…A potencialidade de síntese de copolímeros em bloco LC empregando o mecanismo de polimerização via radicais livres por transferência atômica catalisada por cobre foi também investigada [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . Essa técnica começou a ser mundialmente explorada para obtenção de copolímeros em bloco não-LC, a partir de 1995, na polimerização de monômeros estirênicos e acrílicos com bom controle estrutural.…”

Synthesis and quaternization of nitroxide-terminated poly(4-vinylpyridine-co-acrylonitrile) macroinitiators and related diblock copolymers

“…Polymers of welldefined structure and properties can be obtained using the advanced synthetic techniques, such as nitroxide-mediated radical polymerization (NMRP) [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. A quasiliving polymerization takes place at elevated temperatures (usually above 100 o C) in mixtures containing monomer, a thermal initiator [(dibenzoyl peroxide, 2,2΄-azobis(isobutyronitrile)] and a nitroxide stable radical.…”