carboxymethyl chitosan *

I am looking for methods to make N,O-carboxymethyl chitosan. I have
found one in an expired US patent and another in a 20 year old journal
article. Just wondering if anyone knows of more recent published
methods or could forward a copy. Thanks!

Do any patents reference the expired one?

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Hi, i'm also trying to a find a method for producing carboxymethyl chitosan. There is a more recent method that i've come across (non-specific N,O carboxylation):

Chitosan (10 g) was suspended in 50 wt% NaOH and
kept at -20 C for 16 h. The frozen alkali chitosan was
transferred to 2-propanol (100 mL), and chloroacetic acid
(10 g) was added in portions. After stirring at room temperature
for 2 h, heat was applied to bring the reaction
mixture to a temperature of 60 C for another 2 h. After
dialyzing against deionized water for 3 days, the product
was vacuum dried at room temperature.

It's from a journal by Fan et al. Preparation and properties of alginate/carboxymethyl chitosan blend fibers. [I]Carbohydrate Polymers, 65(2006) 447-452

I hope this helps!
India Sweeney