  The weak commutativity group $\chi(G)$ is generated by two isomorphic groups
$G$ and $G^{\varphi }$ subject to the relations $[g,g^{\varphi}]=1$ for all $g
\in G$. The group $\chi(G)$ is an extension of $D(G) = [G,G^{\varphi}]$ by $G
\times G$. We prove that if $G$ is a finite solvable group of derived length
$d$, then $\exp(D(G))$ divides $\exp(G)^{d}$ if $|G|$ is odd and $\exp(D(G))$
divides $2^{d-1}\cdot \exp(G)^{d}$ if $|G|$ is even. Further, if $p$ is a prime
and $G$ is a $p$-group of class $p-1$, then $\exp(D(G))$ divides $\exp(G)$.
Moreover, if $G$ is a finite $p$-group of class $c\geq 2$, then $\exp(D(G))$
divides $\exp(G)^{\lceil \log_{p-1}(c+1)\rceil}$ ($p\geq 3$) and $\exp(D(G))$
divides $2^{\lfloor \log_2(c)\rfloor} \cdot \exp(G)^{\lfloor
\log_2(c)\rfloor+1}$ ($p=2$).
