[Cadwallon]

I’m a bit confused.  I thought all the bonds in diamond were carbon-carbon single bonds (each carbon bound to four others in a tetrahedral arrangement).  It was graphite, I thought that had alternating single and double bonds, with one carbon attached to three others in a planar hexagonal pattern, making graphite fairly strong in one direction (perpendicular to the plane), but easily cleaver between planes.

BC

You're quite right.  I was looking at the title graphene and simultaneously thinking diamond and conflated the two in my increasingly feeble mind.  Diamonds have all sigmatropic (single) bonding, otherwise pure diamond wouldn't be clear.  Thinking more about this, if you had very extensive sheets of graphene in each macromolecule (if that is the correct word on that scale), you might end up with quite a strong material.  While I haven't worked personally with graphene, people working next to me in the lab were.  I got the impression that the individual macromolecules are not that extensive.  If that is the case shear down through the material perpendicular to the graphene planes might cause them to sllde apart.  Graphite is quite a good lubricant, I suspect because of the this sort of reaction to shear.  The reason that a similar thing doesn't occur in high molecular weight polyethylene materials like Spectra is that the individual molecular strands are entangled with each other and cannot slide past each other.  Because the planar graphene macromolecules are very flat, they do not entangle and while there will be some interaction between planes, it will be a lot less strong than in the entangled polyethylene strands.
At any rate that's where I was trying to go in my poorly written previous post.  Also, I'm a liquid crystal guy (1-D molecules not 2-D molecules) and this whole thing is pretty rank supposition on my part.  I apologize for the confusion.

[Cadwallon]

I’m a bit confused.  I thought all the bonds in diamond were carbon-carbon single bonds (each carbon bound to four others in a tetrahedral arrangement).  It was graphite, I thought that had alternating single and double bonds, with one carbon attached to three others in a planar hexagonal pattern, making graphite fairly strong in one direction (perpendicular to the plane), but easily cleaver between planes.

BC

You're quite right.  I was looking at the title graphene and simultaneously thinking diamond and conflated the two in my increasingly feeble mind.  Diamonds have all sigmatropic (single) bonding, otherwise pure diamond wouldn't be clear.  Thinking more about this, if you had very extensive sheets of graphene in each macromolecule (if that is the correct word on that scale), you might end up with quite a strong material.  While I haven't worked personally with graphene, people working next to me in the lab were.  I got the impression that the individual macromolecules are not that extensive.  If that is the case shear down through the material perpendicular to the graphene planes might cause them to sllde apart.  Graphite is quite a good lubricant, I suspect because of the this sort of reaction to shear.  The reason that a similar thing doesn't occur in high molecular weight polyethylene materials like Spectra is that the individual molecular strands are entangled with each other and cannot slide past each other.  Because the planar graphene macromolecules are very flat, they do not entangle and while there will be some interaction between planes, it will be a lot less strong than in the entangled polyethylene strands.
At any rate that's where I was trying to go in my poorly written previous post.  Also, I'm a liquid crystal guy (1-D molecules not 2-D molecules) and this whole thing is pretty rank supposition on my part.  I apologize for the confusion.