I hope you'll get better answers from more knowledgeable people here.
Macromolecules use to bend easily. Preventing it is difficult; this is one trick that makes para-aramide stiff and strong, that the bond pairs prevent rotations all the way and that the repeated pattern is straight.
Already alkanes of moderate length bend statistically at several C-C bonds at room temperature. My (correct?) understanding is that polysiloxanes do it much more, because the bigger silicon atom and the naked oxygen atom ease the rotations, and this explains why silicone oils have a wide temperature range. Representations of Pdms often put all methyls at the same side, but twisting much every second Si-O suppresses the hindrance by methyls and makes the chain bendable. I attach an estimation of Pdms by Pm3, for whatever credibility software has. You can see that the methyls are nicely separated.
So my prophecy would be that attaching both ends of a polysiloxane is no more difficult than a single one, because the chain twists at random permanently. A longer chain eases this.
Will you make exotic materials for me, please? When I'm a mechanical engineer, I need unusual properties more than extreme stiffness and resistance. For instance big volume compressibility, slow sound propagation, very high or very low elastic rebound, and more.
So if your material doesn't have the property you sought, don't give it up! Search instead for other exotic attributes. It may let some gasses pass selectively, or get hugely birefringent under uniaxial pressure, cool a lot when elongated, reduce its length or volume at higher temperature, bloat in solvents, have shape memory erased by heat... Any such property would be precious in some use.