Question

In the chloromethylation reaction of polysulfone (PSU), I am required to use paraformaldehyde and trimethylchlorosilane as the chloromethylating agent while stannic chloride as the catalyst. I followed the same protocol of many papers such as this one.

During the experiment, PSU was first dissolved separately in solvent (e.g dichloromethane and chloroform) then paraformaldehyde (PFA) was added in form of solid. For both solvent and at two different dissolution temperatures (25 and 60 °C), the PFA was not fully dissolved.

I tried to dissolve PFA separately in solvent than add it to the dissolved PSU, this slightly improved the degree of chlore in the produced chloromethylated PSU (C-PSU), however gelation and non-homogeneity was obtained.

Moreover, the obtained C-PSU was not soluble in many solvents (e.g. NMP, DMAc, DMSO, Toluene, DMF), which can be caused by the low degree of functionalization and the precipitation of insoluble cross-linked polymer.

I am aware that PFA is

slightly soluble in alcohol

soluble via depolymerization by heating PFA in distilled water at 60°C followed by a titration with NaOH

Which I already tried the water and it was successful in terms of PFA dissolution. The problem is that I don’t want water in my reaction due to the future application of the system.

I would appreciate if you could help me to improve my system by providing some suggestions on how to achieve a good homogeneous PFA/solvent solution. Any ideas on how to increase the degree of chloromethylation of PSU are very welcomed.

Answer 1

To achieve a good homogeneous PFA/solvent solution, you can try dissolving PFA separately in the solvent and then adding it to the dissolved PSU. However, be cautious of potential gelation and non-homogeneity issues. To increase the degree of chloromethylation of PSU, you can adjust reaction conditions and explore alternative chloromethylating agents or catalysts.

Step-by-step explanation:

Chloromethylation reactions of polysulfone (PSU) typically use paraformaldehyde (PFA) and trimethylchlorosilane as the chloromethylating agent, with stannic chloride as the catalyst. However, you have encountered issues with PFA not fully dissolving in the solvent, which leads to gelation and non-homogeneity in the chloromethylated PSU. To improve the system, you can try dissolving PFA separately in the solvent and then adding it to the dissolved PSU. This may improve the degree of chloromethylation, but be cautious of potential gelation and non-homogeneity issues. Another option is to dissolve PFA in water, but since you do not want water in your reaction, this may not be suitable for your future application.

Additionally, the low degree of functionalization and the precipitation of insoluble cross-linked polymer may contribute to the obtained C-PSU being insoluble in many solvents. To increase the degree of chloromethylation of PSU, you can consider adjusting reaction conditions such as temperature, catalyst concentration, and reaction time. You can also explore alternative chloromethylating agents or catalysts that may yield higher degrees of functionalization.