chemical diff between different viscosity celluloses

Factual Questions
1

Yet another chemistry question

I can get methyl cellulose or other cellulosic derivatives at various viscosities. Right now I have 3 containers of methyl cellulose (15cP; 400cP; and 1500cP) What chemically makes them different. Is it the degree of -OH or methyl substitution? is it the MW?

Does anyone here know for sure?

2

It’s the molecular weight.
From the info sheet available from Aldrich for Methocel A (a.k.a. methyl cellulose): The degree of substitution for all are the same at 1.5-1.9

cPs … Molecular weight
15…14,000
25…17,000
400…41,000
1500…63,000
4000…88,000