Fluoroscent Probe for Cure Monitoring of Hydrosilation-Curable Silicone
Y Hotta, K Komatsu, Francis W. Wang
This study aimed to evaluate a fluorescent probe, 9,10-bis-(phenylethynyl) anthracene (BPEA), for cure monitoring of hydrosilation-curable silicone (HCS). The HCS consisted of 74.9 % mass fraction of vinyl terminated polydimethylsiloxane (DV-PDMS), methylhydrosiloxane-dimethylsiloxane copolymer (25.0 %, 2,000 g/mol molecular mass) and an inhibitor 1,3-divinyltetramethyldisiloxane (0.1 %). The catalyst consisted of the same DV-PDMS (99.7 %) used to make the HCS, DV-PDMS (0.3 %) containing 3.5 % of a platinum catalyst, and a trace amount of the probe BPEA. Three DV-PDMS polymers with molecular mass of (9,400, 28,000, 49,500) g/mol, repectively, were investigated. The HCS and the catalyst were mixed at the mass ratio of 1:1 and the mixture was placed in a mold made of a silicone o-ring (10x1) mm sandwiched between glass slides. As the mixture cured at 22 [degrees] C, its fluorescence spectrum was measured every three minutes at an excitation wavelength of 360 nm. Initially, the spectrum showed two bands at (466 and 494) nm, characteristic of BPEA, but their intensities subsequently decreased due to the hydrosilation of BPEA. Furthermore, bands characteristic of vinyl anthracene and methyl anthracene appeared at (422, 432 and 444) nm. The intensity of the band at 444 nm initially increased because of the hydrosilation of BPEA to form vinyl anthracene moieties, but subsequently decreased because of the hydrosilation of the vinyl anthracene moieties. The decreases in the intensities of the band at 444 nm relative to their peak values were different for DV-PDMS polymers of different molecular masses (p < 0.05). The fractional decreases were (38.6 ± 1.6, 35.6 ± 1.4, and 26.5 ± 3.0) %, where ± denotes standard deviation, for molecular masses of (9,400, 28,000, and 49,500) g/mol, repectively. Thus, the change in the fluorescence spectrum of BPEA due to hydrosilation can be reproducibly measured and, with calibration, can be related to the degree of curve of the HCS.