New p-methyl- and p-oxymethyl- phenylcyclopropyl methacrylates (MePhCMA and OMePhCMA) have been synthesized and studied their radical copolymerization with glycidyl methacrylate (GMA). New cyclopropane and epo-xy-containing photosensitive copolymers have been obtained. The relative activity of mo no mers and the parameters of Q and e have been determined by Alfrey-Price method. The copolymerization constants of the specified compound (MePhCMA and OMePhCMA) (r1) with glyci dyl methacrylate (r2), calculated by the Fineman-Ross method, are: r1 = 0.63, r2 = 0.60 (–CH3); r1 = 0.62, r2 = 0.70 (–OCH3), respectively; the values of the parameters Q and e: Q1 = 1.37, e1 = –0.90 (–CH3); Q1 = 1.35, e1 = –0.94 (–OCH3), respectively. The composition and structure of this copolymer have been established. Photochemical studies of the synthesized copolymer have been carried out. It was found that structuring proceeds due to the opening of the cyclopropane ring and epoxy groups, as well as the carbonyl group.
microstructure, monomers, copolymerization, phenylcyclopropyl methacrylates, photosensitivity
INTRODUCTION
Rapid increasing of information requires new type of materials to record, storage and reproduce data. The polymers and copolymers containing various reactive groups possess valuable properties and possibility of crosslinking under action of radiation which allows to prepare various materials used in microelectronics [1-3]. This is one of the main reasons for interesting of the researchers for the preparation of new types of the photosensitive polymers [4-8].
Polymerization of functionally substituted cyclopropyl styrene [9-11] is a well-known way of preparing such materials, and polymers made of cycloprapane compounds with functional groups are subjected to UV radiation cross-linking processes to form negative photoresists with high light sensitivity [12, 13]. Copolymerization of the cyclopropanes containing vinyl groups with other reactive monomers results polymers containing cyclopropane groups located in side part of macrochain is also well known [14, 15].
This work has been devoted to synthesis and investigate the copolymerization of phenylcyclopropyl methacrylates (MePhCMA and OMePhCMA)with glycidylmethacrylate (GMA) and study of lithography properties of the copolymers prepared on their basis with the aim of creation of new photosensitive copolymers. The choice of this monomer has been stipulated with large number and chemical nature of double bonds and presence of cyclopropane ring in combination with carbonyl group in the monomer which has influence on such important photolithographic parameters of resists as photosensitivity, adhesion, film-forming exc [16, 17].
The choice of this compound to copolymerize it with GMA has been stipulated by the presence of light absorbing carbonyl, cyclopropane and epoxide groups or double bond in the molecule. In the copolymerization of the studied GMAp-PhCMA system is an important task is choosing the conditions when the polymerization is proceeded only by participation of vinyl group and the reactive fragments would be remained in the side chain without changes.
EXPERIMENT
The copolymerization of MePhCMA and OMePhCMA with GMA was carried out in benzene solution in the presence of 0.5 % azobisisobutyronitrile (AIBN) (from total mass of monomers) at 70°C. The total concentration of the initial monomers was 1.0 mol/l, and a ratio of the initial monomers was changed as it is given in table 1. The copolymers of various composition have been isolated after 10-20 min by addition excess of MeOH to the reaction mixture. The resulting copolymers were re-precipitated twice from theirs benzene solution with methanol and sulphuric acid and dried in vacuum (15-20 Hg.mm) at 30°С until constant weight. The copolymers formed were white solids which are well soluble in aromatic and chlorinated hydrocarbons. Elemental analysis for С22Н28O5: Calculated: С, 70.96 %, Н, 7.52% . Found: С, 70.42%, Н, 7.83%; for С22Н28O6׃ С, 68.04 %, Н, 7.21%. Found: С, 68.27%, Н, 7.04%.
The IR-spectra of the copolymers were registered on spectrometer “AgilentCary 630 FTIR”, NMR-spectra – on spectrometer “BrukerAFR-300 (80 MHz)” in solution of euterated chloroform.
The photosensitivity of co-polymers was determined at various concentrations (4-13% solutions) with making a layer on the glass substrate in a dust-free medium with centrifuging at 2500·min-1. The photoresists were kept for less than 20 min for increasing of adhesion to the substrate before cutting on contour on contour of the procurement preventing the film detachment.
Thickness of the prepared film-resists was measured by microinterferometer „LINNIKA”, which was proved to be 0.20-0.25 mkm after drying for 10 and 20 min at room temperature and 30-35°С/10 Hgmm, respectively. The exposure of the procurements was carried out on a device with light point source through photomask with a DPT-220 mercury lamp (current intensity was 2.2 А, distance from source of radiation was 15 cm, mobile shutter rate of exponometer was – 720 mm·h-1, exposure time was 5-20 s).
The development was carried out in a jet installation. As a developer dioxane and sopropyl alcohol was used at ratio 1׃2 at temperature of 18-25 °С. The photosensitivity is valuated on the basis of the completeness of photochemical polymerization (crosslinking). The photosensitivity – the inverse of the dose of UV-light absorbed means an UV dose necessary for transformation of photoresist to crosslinked (insoluble) state. Where
H –exposure (or dose of irradiation with UV light), J·cm
E – intensity, Wt·cm-2
t – irradiation duration, s
RESULTS AND DISCUSSION
During radical copolymerization of polyfunctional MePhCMA and OMePhCMA with GMA formation of reactive polyfunctional co-polymer showed in Formula 1 could be expected. Comparing of the IR-spectra of the copolymers formed with the spectra of the initial monomer (MePhCMA and OMePhCMA) showed that the deformation and valence vibrations of the vinyl group in the initial monomer at 990 and 1640 cm-1 are disappeared.
The absorption bands characteristic for benzene and cyclopropane rings (1410-1460 and 1500-1600 cm-1) and the absorption bands at 1720, 1030 and 1110 cm-1, referring to the carbonyl vibrations of the cyclopropyl ester fragment are remained unaffected. Availability of the characteristic absorption bands of epoxide groups in structure of the copolymers is confirmed by the absorption band at 830, 920 and 1260 cm-1.
The IR-spectrum of MePhCMA and OMePhCMA copolymer with GMA is presented in fig 1.
In the NMR spectrum (fig.2) of copolymer the resonance signals referring to protons of benzene nucleus (δ = 6.80-6.95 ppm) and cyclopropane ring (δ = 1.50-2.60 ppm) are clearly appeared. The protons of epoxide ring are characterized with signals at 2.10-2.20 ppm(–CH2–) and at 2.40 ppm (–CH–). As r1 and r2 is less than 1, in this system there is a tendency to alternation of links. According to the data of spectroscopy the copolymerization of MePhCMA and OMePhCMA with GMA proceeds only due to opening of double bonds of the vinyl groups with maintenance of the other reactive functional fragments of the both monomers. Thus, on the basis of the analysis of IR and NMR-spectra of the copolymers prepared by copolymerization of MePhCMA and OMePhCMA with GMA, the structure of copolymers is assumed as it is given in formula 1.
Formula 1.
The copolymerization was carried out at various ratios of the initial monomers. It has been revealed that the composition of forming copolymers depends on the composition of the initial monomer mixture. For estimation of polymerization activity of MePhCMA and OMePhCMA there have been calculated the values of relative activity constants of monomers by Fineman-Ross method [18] and the parameters Q-e by Alfrey and Praice method. The microstructure parameters of the copolymers were calculated by using the copolymerization constants on formulas [19]. The obtained data are presented in Table 1. The values of the relative activity constants (Table 1) evidence about greater reactivity of MePhCMA and OMePhCMA in comparison with GMA. The conjugation of the ester group causing redistribution of electron density both in the monomer and in the radical formed from it, thus the energy necessary for appearance of transition state is decreased leading to the increase of reactivity of monomer.
The calculated values of parameters Q1 and e1 during copolymerization with GMA indicate increased conjugation in monomer (MePhCMA and OMePhCMA) connected with influence of substituent – CH3, –OCH3 stipulating relatively high reactivity of monomer and more low reactivity of the radicals. In calculation of factor е1 it was chosen the negative mark based on the fact that the electron density of double bond of vinyl group in MePhCMA and OMePhCMA should be less than in GMA, since the influence of substituent of MePhCMA and OMePhCMA leads to redistribute of density of double bond in the vinyl group changing polarity of the radical.
An availability of the synthesized copolymer of the reactive groups of various chemical nature in links of macromolecule arouses interest for investigation of photochemical structuring of this copolymer, i.e. to crosslinking under action of UV-irradiation and such polymers showing as negative type photoresists. These polymers with properties of high light sensitivity, film-forming ability, good solubility before irradiation, resistance to solvents, plasma and etchants after cross-linking and good thermal stability, which are very important for photoresist. Due to availability of strongly absorbing light energy of groups (cyclopropane, glycidyl, >С=О etc.) the synthesized copolymers are photosensitive and under the influence of UV-irradiation are subjected to the photochemical conversions leading to formation of crosslinked structures.
The influence of irradiation on photosensitive polymers has been investigated by measurement in UV-spectrum. The photoreactive fragments have been considered with various concentrations 15-150 mg in thin films. The absorption bands in the UV spectrum of polymers at 296 and 300 nm, respectively, are referred to π→π transitions. The intensities of absorption through various intervals of irradiation were changed in the UV-spectrum of the copolymer with ratio 50.25:49.75 (p-MePhCMA-co-GMA) and 48.72:51.28 (p-OMePhCMA-co-GMA) (fig.3)
During irradiation decrease or disappearance of photoactive fragments could be observed. The irradiation led to fast decrease of the absorption intensity at 296 and 300 nm and to disappearance of the bands almost completely after 5 min irradiation. It has been revealed that an increase of concentration of polymers raises a photocrosslinking rate due to large quantity of photosentive units.
In films of copolymer, a conversion rate of the photosensitive fragments depends on composition of the light-sensitive links in the copolymer chain. The crosslinking rate grows with increase of cyclopropane and epoxy rings in the polymer (fig.4). It could be concluded that after 40-80 sec. irradiation (transformation is 50-70 %), the polymer films become insoluble in organic solvents in which they were dissolved at room temperature to do irradiation experiments. Such behaviour is caused by formation of hard three-dimensional network due to intermolecular photoinduced cycloaddition of hanging units.
The three-dimensional structure during irradiation has a form of a loose net with large cells, which swells strongly during development and is compressed drying of the polymer layer, causing folds and wrinkles. The good results have been prepared in work with films of thickness 0.2-0.3 mkm.
The process of 3D-structure evolution during irradtiation of the prepared cyclopropane-ring containing copolymers has been followed by IR spectroscopy as well (fig.1). The intensity of the absorption bands characteristic for cyclopropane ring (1030-1035 cm-1), carbonyl group (1720-1725 cm-1), and epoxide ring (830, 920, 1260 cm-1) were decreased with increasing of irradiation time and were completely disappeared ~ 5 min irradiation due to 3D-structure evolution with opening of double bonds and cyclopropane rings.
The availability of cyclopropane ring, glycidyl, carbonyl groups in macromolecules of the prepared copolymer allowed to create a material with high photosensitivity. These copolymers have high photochemical crosslinking ability to create solid elastic layers with good adhesion to substrates and to prepare polymer films with low microdeficiency.
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