I have used both PEG -500 and PEG 6000 , smaller PEG is much more dispersed on particles as observed by TEM, however it depends on the nature of application and degree of polarity desired in the molecule. 

Hi Irfan,

Ideally it should react, but the reaction rate will be soo slow. Hence an catalyst will be required like stanneous chloride.

Please refer following reference to do the reaction.

Goodluck.

Li, Y.P.; Ying Pei, Y.; Zhang, X.Y.; Gu, Z.H.; Zhou, Z.H.; Yuan, W.F.;

Zhou, J.J.; Zhu, J.H.; Gao, X.J. PEGylated PLGA nanoparticles as protein

carriers: synthesis, preparation and biodistribution in rats. J. Control. Release,

2001, 71, 203-211.

What is the purpose of introducing -NH2 groups on PLGA-NHS? Direct reaction between PLGA-NHS and MAL-PEG-NH2 will result in PLGA-NH-CO-PEG-MAL. Instead of weight : weight ratio try molar ratio of reactive groups, e.g., 1:1, 1:2 etc. Since NHS groups are very labile in aqueous solutions an excess of MAL-PEG-NH2 is recommended. Good Luck! 

Hello Irfan,

PLGA is available in 2 forms. One is ester end group and another is carboxylic end group. You can directly activate COOH grp present in PLGA using EDC/NHS and add NH2-PEG-Mal. It will form PLGA-CO-NH-PEG-Mal.

To form pegylated PLGA nanoparticles, I would recommend you to perform this reaction before preparing nanoparticles. Pegylated nanoparticles can be prepared using PLGA-CO-NH-PEG-Mal in the same way in which you prepared PLGA nanoparticles.

Best Regards,

Abhinesh

Thanks Abhinesh Kumar, Pascal Bailon, Rakesh and aditya for your kind suggestions.