[JungJW]

We often use PDMS or OH-polymer.
Could it be possible to make it single- OH or - CH3 only, as shown in the picture below?


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                                 l                             l                 
 OH-PDMS-OH  +  OH-SI-Me     --->   Me-(SI-O)n-OH
                                 l                             l             
                                Me                          Me
( PDMS IS POLYDIMETHYLSILOXANE)
On condition of the above reaction

1. What kind of catalyst can a catalyst use?
2. What are the reaction conditions (hours, temperatures)?
3.It would not be a 100 % one-end polymer. So what's the percent?
   ( For example OH-PDMS-OH (20%) : PDMS (20%) : OH-PDMS-Me (60%)

[pgk]

Whatever the reaction conditions, mixtures of mono- and di- PMDS silanols with PMDS will always be obtained.
Pure PMDS monosilanol can be prepared by co-polymerization of trimethylsilanole with dimethylsilanediol, according to the usual methods (see the corresponding patents in the Google).
Molecular weight and molecular weight distribution mainly depend on the trimethylsilanole/ dimethylsilanediol ratio, as well as on the trimethylsilanol addition rate.

[JungJW]

Thank you for your comment.
However, they couldn't find any reaction(usual method) data on Google.

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              l                                   l                               l                 
      OH-(SI-O)n-H        +      OH-SI-Me        --->   Me-(SI-O)n-OH
              l                                   l                               l             
             Me                                Me                            Me
 (MW:45,000 g·mol−1)       (MW:90.20 g·mol−1)

The molar ratio was about 2: 1.
The temperature condition was only 10 to 30 minutes at 80 ° C, and The reaction went ahead, but does not seem to have increased viscosity,
close to oil or the reaction was corrected.

Ask again.
1. I want to use KOH. Since the original KOH is a solid, it is desired to dissolve it in a solvent which is not reactive. What non-reactive solvents are possible?
2. I am curious about the reaction conditions. I searched for Google patent, but it did not come out well. If the content is long, I will send it by e-mail. Or a search keyword.
3. I want to let you know the approximate reaction conditions. It would be nice to try it many times, but we do not have much money and no raw materials. I can not do many experiments and I would like to ask for your help.

[pgk]

1). Please, take a look at the following US patents, in order to get ideas. Also, search for the prior patents that are cited therein. 
Process for producing polysiloxanes and use of the same, US 20130165615
Siloxane elastomers, US 2541137
Process for making silarylenesilanediol, silarylenesiloxanediol and silarylenesiloxane-polydiorganosiloxane block copolymers, US 3959403
2). Your PDMS may not be –OH terminated but it may also be Cl- or AcO- terminated. If so, try to hydrolyze them by boiling with a little amount of aqueous HCl, like being a polymerization starting from dichlodimethylsilane.
“Synthesis of Silicone Bouncing Putty.”
https://www.wou.edu/las/physci/ch462/BouncingPutty.htm
And then, you continue by either HCl or basic catalysis.
If you choose acid catalysis, you have to add a little aqueous HCl from time to time, in order to replace the evaporated HCl during polymerization because in your case, HCl is not generated in situ, as during the procedure that is described in the above link.
3). If you can find an organotin(IV) compound from somewhere, you can use as a catalyst that works at lower temperature. But take care because organotin compounds are toxic.
4). Remember: either PDMS and Me3SIOH must be very well mixed, before polymerization, in order to ensure a homogeneous and adequate dilution; or diluted Me3SiOH is slowly added during polymerization.
5). Good luck.

[JungJW]

Thank you for your reply.

But there is a simple problem.
I already have the silicone polymer (viscosity :  4,000cP  ) and the trimethylsilanol.
Silicon polymers are - OH at both ends.

             Me                                Me                            Me
              l                                   l                               l                 
      OH-(SI-O)n-H        +      OH-SI-Me        --->   Me-(SI-O)n-OH
              l                                   l                               l             
             Me                                Me                            Me
 (MW:45,000 g·mol−1)       (MW:90.20 g·mol−1)  [ "n" is Repetition unit ]
Ask again.
1. I want to use KOH. Since the original KOH is a solid, it is desired to dissolve it in a solvent which is not reactive. What non-reactive solvents are possible?
2. I am curious about the reaction conditions.(Equivalent Ratio, Response Ratio, Response Time, Response Temperature, etc.)

[wildfyr]

Solvents that can both dissolve and not degrade with KOH are few. DMF, DMSO, and NMP just about round it out unless you really want to take a walk on a wild (and expensive) side. The problem I see is that silicones may have crappy solubility in these solvents because of how polar the solvents are. DMSO is the least likely to work. Is there a reason you can't do it neat?

Since youre just endcapping with TMS, I guess the ratio is just 1:1. You should be able to monitor is by looking for the loss of TMS by GC or GC/MS.

This reaction is going to be rather water sensitive in my view. It also creates water, so you will need a setup to continuously remove it from the system. Unfortunately KOH and DMF are just about some of the most hygroscopic compounds to work with. Water+KOH will also cause hydrolysis midchain, which will broaden your molecular weights and give undesired oligomers.

I think KOH is a bad choice for a base, because (as noted in US 20130165615) its gonna damage the polymers. That patent uses other hydroxides. It still seems messy, and that patent isnt even trying to do something as precise as endcapping.

Why not just slowly drip in 1 eq of trimethylchlorosilane in the presence of a 1 eq amine proton scavenger in hexane in a dry system? Way easier.

[pgk]

Forget the KOH because you need temperatures as high as 150-165oC (US Patent 2541137).
Start from trimethylchlorosilane, as Wildfyr indicates.