You can try to add neutral salting-out compounds -  electrolyte (NaCl, for instance) or hydrophilic solvent ( EtOH, PEG). It is media modification.

Cross-linking with silanes is not stable ( in common), citric acid esters are much more suitable and biocompartable (food grade).

Hi Andrei,

I am making a polymer (carbohydrate) film that swells up a lot in water. I want to reduce its swelling. I did not get how adding a hydrophilic solvent would reduce the swelling percentage? 

Swelling is result of solvation of carbohydrate hydroxyls by water, competition with add-on compounds lead to decreasing of  swelling. Additives should not dissolve polymer carbohydrate, PEG seems to be very convenient for this application.

Cross-linking is demand for permanent effect in pure water, maybe hydrobophobic treatment cause some temporary shielding effect.

Ph2SiCl2 or (tert-Bu)2Si(OSO2CF3)2 cross-linkers will promote both effects, problem is suitable solvent (for carbohydrate), maybe pyridine or some ionic liquids will work

Hi Andrei,

I need a permanent solution to water swelling. I am trying to use DMSO as a solvent and ATPS as a crosslinker, but no use. Will read literature on (tert-Bu)2Si(OSO2CF3)2 and see if it works.

Thanks.

I am not a specialist for carbohydrates, but maybe making a solvent mixture will lead to a cononsolvency, which then would dramatically reduce the swelling.

Hello Sankalp,

I agree with Andrei; The silane chemistry is not the most suited for what you try to achieve. Keep it simple with esterification for functionalisation and/or for crosslinking.

Maybe your were not successful with the previous attemps because your procedures  were not proper.

Best wishes and Happy New Year

A different approach is to make a W/O emulsion of the polymer using water-immiscible solvents like diethyl ether or vegetable/mineral oil. Suspend the polymer in the organic phase and then add the selected amount of water with high impact stirring. In doing so the degree of swelling is entirely governed by the water/polymer ratio.

When looking for a permanent solution, cross-linking is a logical approach, although the native polymer functionality may become irreversibly lost. There is a vast literature on cross-linking of carbohydrate polymers, notably cellulose and starch. There is no need to dissolve these polymers for doing cross-linking reactions. Suitable cross-linking agents include epichlorohydrin, phosphorus oxychloride, sodium trimetaphosphate, and acetic anhydride/adipic acid. The latter 2 are food grade. Although water is generally used as a suspending medium, these reactions can also be carried out in water-poor non-swelling systems, for example acetone.

As described in US Patent 3,135,739 by E.T. Hjermstad and L.C. Martin, 40 % polysaccharide (starch) powder was suspended in acetone, and 15 % aqueous NaOH was added to achieve 2.5 % NaOH based on starch. Then the required amount of reagent was added stepwise and reacted overnight at 25-45 C. Please note that

Thank you for the suggestions.

@Florian - Thank you for the suggestion. I am trying a solvent mixture.

@Guy - I have tried esterification, but the presence of acid (either as a reactant or as a by-product) degrades the matrix. (I cant escape the high temperature step in my process and the acid would degrade the matrix at high temperature).

@Peter - I am trying to prepare a co-solvent mixture. The other reactions bring acid into the system which degrades my matrix at high processing step.

I am trying with HMDS, adding silane to the free -OH groups and making the matrix hydrophilic. It helped me reduce the water absorption but the amount of HMDS required, is huge (1.5 moles per mole of -OH present!)

The cross-linking reactions proposed by me proceed at alkaline, not acidic conditions. Optimum reaction pH is typically 11-12 when using epichlorohydrin, phosphorous oxychloride or sodium trimetaphosphate. Reaction temperatures are quite moderate (< 45 C). So, no acid and high temperature are involved, except for neutralization afterwards.

It is also possible to achieve water insolubility by acetylation to a high degree of substitution with acetic anhydride in pyridine.  

Thank you Peter,

I am not sure if I can use pyridine in my lab. However, I will look into the acetylation protocols.

Hi Sankalp,

I searched for some literature and protocols that might be useful for you, all of these pretty old.

1. A.M. Mark, C.L. Mehltretter. Staerke 24 (1972) 73-76, describe the preparation of starch triacetates in aqueous NaOH without degradation (attached).

2. D. Horton, J. Lehmann. Carbohydr. Res. 61 (1978) 553-556, describe the manufacture of per-(trimethylsilyl) amylose. I could not retrieve this paper, but I have the protocol used by us in the early 80's. Amylose (10 g) is stirred in pyridine (500 ml) in a three-necked flask with mechanical stirrer and reflux condenser (24 h, 100 C). After cooling a mixture of hexamethyldisilazan (100 ml) and chloro-trimethylsilan (50 ml) is added with rapid stirring and then continuously stirred (24 h, 60-70 C). The mixture is cooled and oured into cold methanol (2 l). After stirring (1 h) distilled water (500 ml) is added and stirring is continued for 30 min. The product is filtered and washed several times with methanol and water, and then vacuum-dried at 40 C. All operations in a fume hood because of toxic solvents and reagents. Yield of 2,3,6-O-tri (trimethylsilyl) amylose was only 43 % in our hands.

3. E. Husemann, M. Reinhardt, M. Kafka. Makromol. Chem. 41 (1960) 184-207, describe several methods for the preparation of polysaccharide-acetates (pyridine-acetic anhydride and formamide/pyridine-acetic anhydride). Unfortunately, I could not retrieve the paper which is also in German.

Good luck,

Peter  

Thank you Peter. Will go through the papers and see if I can work on similar lines. :)