TP initiated polymerization

The use of TP initiated polymerization for 3D microfabrication has several advantages over OP initiated polymerization. A 3D resolution can be achieved with lateral and depth resolutions of 0.2 pm and 0.28 pm. This is fabrication at a... 

Figure 3.71. Optical system used for 3D microfabrication using TP initiated polymerization of a photopolymerizable composition. The numerical aperture of the objective lens is 0.85 (magnification of 40), the accuracy of the galvano-scanner set and the dc motor scanner were 0.3 and 0.5 pm, the beam power at peak in the photocrosslinkahle composition is about 3 kW, with a repetition rate of 76 MHz and a pulse width of 130 fs at a wavelength of 770 nm [76].

Figure 3.72. Dependence of lateral resolution and depth resolution on average power of a mode-locked Ti sapphire laser (wavelength 763 nm, 82MHz repetition, 130 fs pulse width) during TP initiated polymerization of a urethane acrylate resin. (From Ref. [575] with permission of SPIE—The International Society for Optical Engineering.)...

Figure 3.74. Three-dimensional microstructures (photonic band-gap structure (a), magnified top view of the photonic band-gap material (b), tapered waveguide structure (c), cantilevers (d)) obtained by TP initiated polymerization. (From Ref. [134] with permission of Macmillan Magazines.)...

Figure 3.76. Voxels manufactured by TP initiated polymerization using different focusing height level (a) and scanning electronic microscopic images of the produced voxels (b). (From Ref. [580] with permission of the American Institute of Physics.)...

Figure 3.78. Scanning electron microscope images of a coin manufactured by TP initiated polymerization of tris(2-hydroxyethyl)isocyanurate triacrylate in the presence of poly(styrene-co-acrylonitrile) as binder and 167 as TP initiator using a frequency-doubled Nd YAG microlaser (0.5-ns pulses, 6.5-kHz repetition rate, wavelength 532 nm, average power 1.2 mW, 1.8-mm focal spot) (a) overview and (b) part of the coin with larger magnification. (From Ref. [136] with permission of the Optical Society of America.)...

Figure 3.94. Waveguide structures manufactured by TP initiated polymerization of methyl methacrylate in the presence of a coumarin derivative and diphenyliodonium hexafluorophosphate as TP initiator using a 500-pW Ti sapphire femtosecond laser at 800 nm, equipped with a 0.65 NA microscope objective and a scanning speed of 40 pm/s. (a) Channel waveguide (2 pm), (b) T-shaped waveguide (signal input A signal output B probe signal C), and (c) directional coupler (coupling length is about 30 pm). (From Ref. [135] with permission of the Institute of Physics.)...

Figure 3.65. Mechanism of radical polymerization of an acrylate after excitation of a TP initiator.

Figure 3.73. Volume size of voxels assuming ellipsoid structure as a function of the inverse of the scan speed. The voxels were obtained by TP initiated crosslinking radical polymerization of acrylates in the presence of poly (styrene-co-acrylonitrile) as binder and an amino-substituted distyrylbenzene as TP active initiator using a pulsed laser (150-fs pulses at a 76-MHz repetition rate or 85-fs pulses at a repetition rate of 82 MHz). (From Ref. [133] with permission of the Technical Association of Photopolymers, Japan.)...

A photonic crystal-type stack of logs was obtained by TP initiated cross-linking radical polymerization of acrylates in the presence of poly(styrene-co-acrylonitrile) as binder and an amino substituted distyrylbenzene (58) as two-photon active initiator (Fig. 3.93) [133]. This photonic crystal-type microstructure has an average periodicity of 1 pm, a base area of 60 pm x 60 pm, and a height of 8 pm. The lines are about 200 nm wide, which is considerably smaller than the fabrication wavelength (Fig. 3.93) [133]. 

It can be seen that under the influence of sunlight, PM will initiate polymerization readily, while neither DPI nor TPS produces a cure. Under the germicidal lamp, which emits 254 nm radiation almost exclusively, the situation is reversed, with DPI and TPS which are strong absorbers of the shorter wavelength radiation, being somewhat more effective than PM. 

The ability to manipulate reactor temperature profile in the polymerization tubular reactor is very important since it directly relates to conversion and resin product properties. This is often done by using different initiators at various concentrations and at different reactor jacket temperature. The reactor temperature response in terms of the difference between the jacket temperature and the peak temperature (0=Tp-Tj) is plotted in Figure 2 as a function of the jacket temperature for various inlet initiator concentrations. The temperature response not only depends on the jacket temperature but also, for certain combinations of the variables, it is very sensitive to the jacket temperature. 

The thermoplastic-rich phase may be separated in the course of polymerization (Sec. 13.4.2) or can be incorporated as a dispersed powder in the initial formulation (Sec. 13.4.3). A strong drawback of the in situ-phase separation for processing purposes is the high viscosity of the initial solution which results from the much higher average molar mass of the TP compared with the liquid rubbers. Also, for the same reason, the critical concentration crit has a smaller value (phase inversion is observed at smaller concentrations of modifier). 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

Fig. 2.6. Conversion versus time curves for the polymerization of GMA/EDMA and MMA/ EDMA. Volume ratio monomer/inert components = 2/3, inert components dodecanol/ cydohexanol 1/9. GMA/EDMA = 17/3 (1), = 3/17 (2) MMA/EDMA = 17/3 (3), = 3/ 17 (4). Initiator AIBN, 0.5% (w/w). Polymerization temperature 50°C. K = conversion, tp = polymerization time. Reproduced from Horak et al. [20].

The whole polymerization kinetics has been followed by means of the adiabatic reactor method (3.6). which allows to simultaneously determine polymerization times and rates. In Table V data, related to the overall polymerization time, tp, as well as to the initial and maximum rates of polymerization, are given. All these parameters are, of course, very relevant to RIM technology. 

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