Relaxations of Poly(methyl methacrylate) Probed by Covalently Attached Anthryl Groups

Abstract

The molecular relaxations of poly(methyl methacrylate) (PMMA) were studied using three different techniques: DSC, DMTA, which are sensitive to bulk properties, and the variation of fluorescence emission with temperature, a molecular sensitive method. Because this is a nonfluorescent polymer, we synthesized copolymers of methyl methacrylate with several contents of 9-methylanthryl methacrylate. The increase in the spacing between each anthryl group brought about a gradual decrease in T g of the copolymers, leveling out at about 30−40 PMMA mers, indicating that the minimum spacing to attain the PMMA glass transition was situated in this length range. The fluorescence emission of a copolymer with 98 MMA units interspersed between each chromophoric unit was proved to be mechanically equivalent to PMMA homopolymer and was used to probe macromolecular motions involving shorter segments: apart from the main transitions commonly found for PMMA (α and β), the other two were detected at lower temperatures (γ and δ). Apparent activation energies for all relaxations using both techniques are also reported and discussed.

Polyfluorene based blends for white light emission

“…Therefore, taking this set of individual polymers, the absorption bands range from 325 to 550 nm, and the photoluminescence bands in solution that appears in the 400-600 nm range, cover almost the entire visible region. structure in the range of 300-420 nm, characteristic of the anthracenyl moieties, with the 0-0 band centered at k abs(0-0) = 390.2 nm [22,34,35]. This spectrum is broader and redshifted by 2.5 nm compared to the dilute solution.…”

“…2 presents the absorption and emission spectra of each polymer separately, recorded from the respective chloroform solutions (10 À5 mol L À1 ). Absorption of the P(MMA-co-MMAnt) is composed by a well defined vibronic structure in the range from 300 to 398 nm, characteristic of the anthracenyl moieties with the 0-0 band centered at k abs(0-0) = 387.8 nm, and emission with the 0-0 band centered at k em(0-0) = 393 nm [22,34,35]. Considering the 0-0 band for both absorption and emission, the Stokes shift is 341 cm À1 .…”

“…Generally, the presence of broad emission bands can be attributed to conformational disorders of the polymer chains where differences of microenvironment around every lumophore modifies their state densities [34]. Due to the large distance between two anthracenyl groups bonded to the main chain (35 MMA units) no excimer or aggregate emissions were observed in diluted solutions, and thus we ascribed the red-edge emission tail to aggregation of the lumophores in the solid state [34]. Emission of anthracenyl aggregates has been described and their formation requires very specific orientation of the polymer chains [37].…”

Dispositivos poliméricos eletroluminescentes

“…Quando o espectro de emissão de polímeros emissores é comparado com o espectro de emissão de moléculas pequenas similares, esses são sempre mais alargados [19][20][21][119][120][121][122] . Esse problema aparece, também, em polímeros conjugados [18][19][20][21] . No caso dos poli(fluorenos), a desordem conformacional ocorre pelo fato de que quando substituintes na posição 9 modificam a cadeia do polímero (Figuras 1, 2) esses segmentos podem se orientar de vári-as maneiras em relação à cadeia principal, produzindo pequenas modificações espectrais.…”

“…Entretanto, a possibilidade de mistura física entre componentes permitindo a obtenção de sistemas com diferentes propriedades é, sem dúvida, uma forma atraente e de custo reduzido de preparação de novos materiais. Essa flexibilidade nas formas de preparação de sistemas é particularmente interessante no caso de polímeros eletroluminescentes para os quais pequenas alterações nas rotas de síntese podem levar a materiais com diferentes estruturas e, o fato de apresentarem diferentes estruturas químicas, leva a que os materiais passem a emitir em diferentes regiões do espectro [18][19][20][21] . As diferenças nos processos sintéticos podem, também, envolver reações de copolimerização, permitindo a geração de materiais com propriedades projetadas para fornecer dispositivos mais eficientes 11,[13][14][15][16] .…”