$(2)$ The solubility parameters of poly $($vinyl chloride$)($PVC$)$ and dibutyl seborate are $9\mathrm{.}7$ and $9\mathrm{.}2$ respectively. What amount $($in volume percent$)$ of dibutyl seberate will be required to make PVC o flexible polymes at room temp.? Assume that the $Tg$ of dibutyl sebarote is $-100C$ and that room temp. is $25C.$