PPNCl stands for bis(triphenylphosphine)iminium chloride, is a reagent used in organic chemistry. Its primary use is as a phase transfer catalyst. PPNCl is known for its ability to enhance the efficiency and control of these polymerization reactions. In Ring-opening polymerizations, a catalyst is needed to initiate and propagate the polymerization process. PPNCl plays a vital role in activating or enhancing the activity of the main catalyst. It can do this by interacting with the catalyst to form a more reactive species or by stabilizing the active form of the catalyst. It stabilizes the reactive intermediates formed during the polymerization. PPNCl can improve the selectivity of the polymerization reaction, leading to polymers with more uniform molecular weights and structures.

PPNCl is an extremely lipophilic and relatively stable salt with a huge, greasy cation, which could be written in condensed form as [Ph3P=N=PPh3]+[Cl]-. Paired with huge anions it forms crystals useful for single-crystal x-ray spectroscopy. Added to a solution in a polar, protic solven, containing anions of many sizes, it tends to precipitate the large ones and if there is an equilibrium mixture of anions (like a mixture of polyoxometalates like Keggin anions of different sizes), by LeChatelier's Principle, the equilibrium will shift to the large anion that precipitates in the presence of this large cation. The complementary scheme is also possible; instead of precipitating PPN(+) salts from polar, protic solvents like alcohol or aqueous mixtures, you can use the greasiness (lipophilicity) of PPN(+) to help dissolve anions in less polar, aprotic media like ethers (diethyl ether, THF, dioxane) in which the anion (like an anionic transition-metal complex) is insoluble in the form of a sodium salt or a potassium salt. When used as an aid to a catalyst I would think of it as a chaotrope (a substance that doesn't self-assemble into clusters like micelles made from detergents, but rather just helps increase the contact of non-polar molecules with polar ones).

Here is a 2010 crystallography paper with useful references: Article Solvate-free bis(triphenylphosphine)iminium chloride

The use of PPN+ goes back to the 1970's at least so many book chapters could be written about it. But this should get you started.

It work as like zwitterion PTC and due to high steric hindered structure retard self polymerisation reaction of key molecule. for more literature agreed to Srinivasan Jayakumar and Louis Whaley