Polymerization of methyl acrylate photoinitiated by 4‐dimethylamino‐4′‐isopropylbenzophenone

Abstract

The initial rate of the polymerization of methyl acrylate photoinitiated by Cdimethylamino-4'-isopropylbenzophenone (2) varies linearly with monomer concentration and the square-root of light intensity. For small absorbances, the initial polymerization rate, %, varies linearly with the square-root of the photoinitiator concentration. For high absorbance values, I$ is independent of the photoinitiator concentration in a well-stirred system and decreases as the photoinitiator concentration increases in an unstirred system. This marked difference between the polymerization kinetics in well-stirred and unstirred systems is discussed. The ratio of the propagation rate constant and the square-root of the termination rate constant, $,/&I/*, and the quantum yield of photoinitiation were determined and related to the results previously obtained in a study on the photoreactivity of 2.Materials: Methyl acrylate (MA) from Fluka A 0 was washed 3 times with portions of 10 v01.-% aqueous sodium hydroxide to remove the inhibitor and then 3 times with distilled water. The monomer was dried over anhydrous MgSO, and then distilled under reduce pressure before using. 4-Dirnethylamino-4'-isopropylbenzophenone (2) was prepared according to the method described in ref.'). Benzene (fluorescence grade from Carlo Erba) was used without further purification.Polymerizution procedure: The required amounts of monomer, solvents and photoinitiator were charged into a dilatometer which was degassed under vacuum by the conventional freezeand-thaw technique and sealed off under vacuum (lo-, mmHg). The dilatometer, being constructed by attaching two capillary branches (internal diameter: 0,s mm) to a cylindrical reaction vessel (internal diameter: 2 cm; volume: 13 cm'), was placed into a constant temperature bath in which the cylindrical reaction vessel fitted perfectly into the space of the metallic base of the bath, provided with two parallel quartz windows. The bath was placed on an optical bench, including a Hg-He lamp (200 W Hanovia 901B1), quartz lens, and interference 365 nm filter (International Light NB-365). A radiometer was placed immediately behind the second quartz window which allowed changes in the light intensity to be measured. Aberchrome 540 (Edward Davis Chemical Laboratories) actinometry was used to relate the digital display of the radiometer to an absolute value for the number of incident quanta per unit time'). The polymerizations were carried out to low conversion (2-4%) and invariably at 30 f 0,Ol 'C; the reaction mixture in each run was removed from the dilatometer and the polymer precipitated into cold methanol. The polymer, isolated by filtration, was washed several times with methanol and then dried at 40 "C under vacuum. The rates of all photoinitiated polymerizations were corrected to allow for the changes from run to run of the incident light intensity, assuming in all cases a square-root dependence on the intensity.Viscosity measurements: Viscosity measurements were performed in a Ubbelohde viscometer at 30°C with b...

Effects of Optical Attenuation and Consumption of a Photobleaching Initiator on Local Initiation Rates in Photopolymerizations

“…Presentation of their results in terms of position and time variables with arbitrary units, and the lack of a closed-form solution (i.e., our eq 15 for the photoinitiator concentration distribution and the analogue of (20a) for the photoinitiation rate) hinders interpretation and use. From (24), we see that for τ g ln 2 the maximum concentration occurs at y ) ln(e τ -1) and that the half-width at half of the maximum rate is (∆y) hwhm ) 2.0634. Comparison to Figure 4 of ref 23 shows that the half-width at half-maximum in that figure is about 8.41 (in "arbitrary units"), and the maximum in the volumetric photon absorption rate at each time shown (also in "arbitrary units") is at a position whose coordinate (in "arbitrary units") is numerically almost equal to the time.…”

“…The expression given for R p in eq 3-65 of Odian 26 has dimensions inconsistent with those for the same symbol used elsewhere in that work. Incorrect expressions given by Mateo et al 24 for R p are dimensionally inconsistent with each other (cf. their eqs 1 and 2 and their eqs 2 and 3).…”

“…(Note that the threshold value cited has units inconsistent with both its definition and eq 5 of ref 23. ) More generally, Mateo et al 24 discussed how nonuniformity of the photoinitiation rate can affect the molecular weight distribution, which like other quantities not predicted by simple kinetic models, can be expected to depend on whether account is taken of attenuation and initiator consumption. For "unstirred" systems (i.e., with no mass transfer), Shultz and Joshi 25 present expressions for the spatial variation of the initial photopolymerization rate.…”

“…Dimensionless photoinitiation rate profiles R ˜i ) Ri/(φI0RACA,0) as functions of z ) x/L at different degrees of photoinitiator consumption 1 -S h : s s s , S h ) 1; ;, S h ) 0.9; ‚‚‚, S h ) 0.75; -‚‚‚ -, S h ) 0.5; -‚ -, S h ) 0.25; ---, S h ) 0.1. (a) γ ) 0.1, (b) γ ) 1, (c) γ ) 2, (d) γ ) 5, (e) γ ) 10, and (f) γ ) 100.R ˜i ) R i φI 0 R A C A,0 ) -2 ∂S ∂τ )2e τ-y [1 -e -y (1 -e τ )] 2(24)…”

Photochemical Crosslinking and Enzymatic Degradation of Poly(3-hydroxyalkanoate)s for Micropatterning in Photolithography

“…The lower gel fractions of the PHU films crosslinked in the presence of 15 wt.-% of TPO might have resulted from the fact that absorption occurs only in the first layer of the film and the crosslinking rate is lower than that at lower concentrations where light absorption takes place throughout the film. [17,18] Infrared spectra of PHU irradiated for different periods of time with TPO (3 wt.-%) showed that the absorption peaks due to vinyl groups at 911 and 1640 cm -1 decreased with irradiation time indicating that the photocrosslinking of PHU proceeded at the expense of the vinyl groups. TGA traces of native PHU were virtually identical to that of crosslinked PHU while DSC analysis showed that the glass transition temperature increased from -51 to -46 8C when PHU was irradiated for 60 s with a medium pressure mercury lamp.…”