Temperature dependence of ESR spectra of methyl methacrylate radicals from 77 K to 300 K

Abstract

SynopsisThe radicals formed in poly(methy1 methacrylate) (PMMA) under vacuum by UV irradiation a t room temperature were carefully examined from 77 K to 300 K by electron spin resonance (ESR). The conventional nine-line spectrum was observed with significant overall intensity changes in contrast to previous reports. The intensity decreases greatly as the temperature increases from 77 K to 100 K. The intensity of the ESR spectrum increases as the temperature increases gradually from 100 K to 260 K. The spectral changes were reversible at all temperatures. Three different models are considered to interpret the temperature dependence of the intensity of the ESR spectrum. The results indicate that the ESR spectrum depends on (1) the steady-state concentration of the propagating radical in the polymer, (2) the conformational distributions of the radicals, and (3) the environmental structures of the polymer matrix.

Reactive Conjugated Polymers: Synthesis, Modification, and Electrochemical Properties of Polypentafluorophenylacetylene (Co)Polymers

“…The interest in polyPA is due, in part, to its solubility in a range of organic The preparation of functional polyPAs typically requires the initial synthesis of the desired functional monomer. [6][7][8][9][10]12,13,15] This is due, in part, to the limited number of commercially available functional monosubstituted PAs but also highlights the high functional group tolerance exhibited by this polymerization process. Alternatively, functional (co)polymers can be accessed via post-polymerization modification, with one commonly adopted approach involving the use of activated esters that can be readily and quantitatively modified via nucleophilic acyl substitution reactions typically with small molecule 1° amines.…”

“…These include multi-component transition metal systems based on W, [1,2] Mo, [2] Pt, [3] Pd, [4] and Rh. [3,5] Within this group, Rh-based complexes have emerged as the most common and effective with the rhodium (I) norbornadiene chloride dimer, [Rh(nbd)Cl] 2 , [6][7][8][9][10][11][12] and rhodium (I) cyclooctadiene chloride dimer, [Rh(cod)Cl] 2 , [13][14][15] proving particularly popular although alternative Rh-based species are also well documented. [16][17][18][19] It should be noted that while such catalytic systems are generally highly robust and efficient the polymerizations are not controlled and as such the preparation of copolymers with complex architectures, such as block copolymers, or materials with predetermined molecular weights and narrow molecular weight distributions are not accessible with such catalysts.…”

Photochemical Study of the Transport Properties of Gases in Polymer Films

“…This mechanism has been shown by many electron spin resonance studies on the precursors of the room temperature vacuum photodegradation of PMMA where, based on the nine-line spectrum obtained, the only radical detected was the one labeled A in the reaction scheme given in Figure 1. [19][20][21][22] It originated mostly from a β-cleavage of radical B (Figure 1, reaction 3) but also from a homolytic main-chain scission of the polymer. The radicals • COOCH 3 and • CH 3 (in addition to radical A) were detected only when irradiation was carried out at liquid N 2 temperature (77 K).…”

Structural Transformation of Acrylic Resin upon Controlled Electron-Beam Exposure Yields Positive and Negative Resists

“…[12,13] Evidence for these processes includes reduced molecular weight, [6] evolution of gaseous products, [14,15] and results from electron spin resonance spectroscopy. [12,16] Low-molecularweight linear PMMA, which can be converted into a crosslinked zwitter polymer, is suitable for use as a negative resist in the semiconductor industry. [1] Electron-beam processing has been used for many years to make the masks needed for optical lithography because of the high-resolution capability of electron-beam tools.…”