On the kinetics of polymer degradation in solution—IV: Laser flash photolysis studies on copolymers containing phenylvinylketone using the light scattering detection method

Copolymers of methylmethacrylate (MMA) with phenylvinylketone (PVK) and of styrene (St) with PVK were degraded in solution by irradiation with 25 nsec flashes of 347.1 nm light from a ruby laser. The time dependence of the change of light-scattering intensity (LSI) (due to the decrease of molecular weight) was measured. It was found that the half-life $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) decreases with increasing polymer concentration according to ($\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(LSI)}\text{]}{}^{\mathrm{?1}}\text{∝ C}{}_{\mathrm{<mtext>Polymer</mtext>}}$ and that $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) is proportional to the microviscosity (viscosity of the solvent). This was taken as evidence that $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) corresponds to a diffusion process. $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) decreased with increasing scattering angle, explained by the fact that at low scattering angles the diffusion of long fragments was predominantly monitored.Upon addition of naphthalene to an acetone solution of a copolymer of MMA and PVK, $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (LSI) increased with increasing naphthalene concentration and approached a limiting value. This effect was attributed to preferential solvation of the copolymer by naphthalene. From intrinsic viscosity measurements, it could be confirmed that MMA base units are preferentially solvated by an acetone/naphthalene mixture.