  A grand challenge in designing polymeric materials is to tune their
properties by macromolecular engineering. In this context, one of the drawbacks
that often limits broader applications under high temperature conditions is
their poor thermal conductivity $\kappa$. Using molecular dynamics simulations,
we establish a structure-property relationship in hydrogen bonded polymer
blends for possible improvement of $\kappa$. For this purpose, we investigate
two experimentally relevant hydrogen bonded systems -- one system consists of
short poly({N}-acryloyl piperidine) (PAP) blended with longer chains of
poly(acrylic acid) (PAA) and the second system is a mixture of PAA and short
poly(acrylamide) (PAM) chains. Simulation results show that PAA-PAP blends are
at the onset of phase separation over the full range of PAP monomer mole
fraction $\phi_{PAP}$, which intensifies even more for $\phi_{PAP} > 0.3$.
While PAA and PAP interact with preferential hydrogen bonding, phase separation
is triggered by the dominant van der Waals attraction between the hydrophobic
side groups of PAP. However, if PAP is replaced with PAM, which has a similar
chemical structure as PAP without the hydrophobic side group, PAA-PAM blends
show much improved solubility. Better solubility is due to the preferential
hydrogen bonding between PAA and PAM. As a result, PAM oligomers act as
cross-linking bridges between PAA chains resulting in a three dimensional
highly cross-linked network. While $\kappa$ for PAA-PAP blends remain almost
invariant with $\phi_{PAP}$, PAA-PAM systems show improved $\kappa$ with
increasing PAM concentration and also with respect to PAA-PAP blends.
Consistent with the theoretical prediction for the thermal transport of
amorphous polymers, we show that $\kappa$ is proportional to the materials
stiffness, i.e., the bulk modulus K and sound velocity v of PAA-PAM blends.
