The polycarbonate polyols(PCD) obtained by ring-opening polymerization of a general cyclic monomer is mostly a linear flexible structure. which is used as a raw material to synthesize polyurethanes. and it is difficult to simultaneously ensure good thermal-mechanical properties and weather resistance due to insufficient rigidity of the main chain. However. https://www.markbroyard.com/special-deal-ornamental-onion-allium-summer-beauty-for-cheap-flash-choice/