  Polonium isotopes having two protons above the shell closure at $Z=82$ show a
wide variety of low-lying high-spin isomeric states across the whole chain. The
structure of neutron-deficient isotopes up to $^{210}$Po ($N=126$) is well
established as they are easily produced through various methods. However, there
is not much information available for the neutron-rich counterparts for which
only selective techniques can be used for their production. We report on the
first fast-timing measurements of yrast states up to the 8$^+$ level in
$^{214,216,218}$Po isotopes produced in the $\beta^-$ decay of
$^{214,216,218}$Bi at ISOLDE, CERN. In particular, our new half-life value of
607(14) ps for the 8$_1^+$ state in $^{214}$Po is nearly 20 times shorter than
the one available in literature and comparable with the newly measured
half-lives of 409(16) and 628(25) ps for the corresponding 8$_1^+$ states in
$^{216,218}$Po, respectively. The measured $B(E2;8_1^+ \to 6_1^+)$ transition
probability values follow an increasing trend relative to isotope mass,
reaching a maximum for $^{216}$Po. The increase contradicts the previous claims
of isomerism for the $8^+$ yrast states in neutron-rich $^{214}$Po and beyond.
Together with the other measured yrast transitions, the $B(E2)$ values provide
a crucial test of the different theoretical approaches describing the
underlying configurations of the yrast band. The new experimental results are
compared to shell-model calculations using the KHPE and H208 effective
interactions and their pairing modified versions, showing an increase in
configuration mixing when moving towards the heavier isotopes.
