Poly sensitivity, measurement

An apparatus for measuring the time dependence in the xs range of lightscattering intensity has been used to investigate the degradation of poly(phenyl vinyl ketone) (PVK) in solution.205-250 The PVK was irradiated with 25 ns pulses at 347.1 nm, and butyrophenone was also investigated in the same way. In both cases a transient absorption, identified by sensitization measurements as the PVK and butyrophenone triplet state, was shown to have a first-order decay rate-constant of 1.0 0.2 x 107 s-1. The quantum yield of triplet state formation in PVK was estimated to be between 0.1 and 0.3, whereas the quantum yield of main-chain scission was found to be 0.4—0.6, insensitive to the presence of Oa. 

There is, in fact, room for some variation of the frequencies to which the experiments are sensitive measurements of the spin-lattice relaxation time can, as a practical matter, be shifted over a range of one or two decades in frequency [iO —ii]. Moreover, variation of the radiofrequency field strength affords a range in the spectrum for Tip [4,5]. Fig. 2 shows how the spin-lattice relaxation processes are shifted to progressively higher temperatures, in poly(heptene-l), as the frequency of the measurement is increased [ii]. 

Whereas the tensile strength was not a sensitive function of the monomer structure, the tensile modulus (Young s Modulus) was clearly related to the monomer structure. This is expected since the tensile modulus is a measure of the polymer s resistance to deformation and is related to the "stiffness" of a polymeric material. The highest tensile modulus (22,000 kg/cm2,2.2 GPa) was measured for poly(BPA iminocarbonate). Replacement of BPA by Dat-Tyr-Hex reduced the tensile modulus significantly. This observation can possibly be attributed to the presence of the long hexyl ester pendent chain in Dat-Tyr-Hex. Generally, the polyiminocarbonates were somewhat "stiffer" than the corresponding polycarbonates. Thus, the tensile moduli of poly(Dat-Tyr-Hex iminocarbonate) and poly(Dat-Tyr-Hex carbonate) were 16,300 kg/cm2 (1.6 GPa) and 13,900 kg/cm2 (1.3 GPa) respectively. 

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

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