Acetamide (C2)

propionamide (C3)

butyramide (C4)

isobutyramide (

i

-C4)

isovaleramide (

i

-C5) and trimethylacetamide (

t

-C5) groups each were introduced to the terminals of hyperbranched polyethylenimine (HPEI) through the amidation reaction between HPEI and the corresponding anhydride. Moreover

HPEIs terminated with two kinds of amides were also prepared. The first amide was fixed to be

i

-C4 with 52% degree of amidation (DA)

and the second amide varied from C2

C3

C4

i

-C5 to

t

-C5. All the polymers were characterized by

1

H-NMR. Turbidimetry measurements were performed for these polymers in water at different temperatures. With respect to the polymers bearing only one kind of amide group

except C2

all the other amide groups could render thermoresponsive properties to HPEI. The specific ordering of these amide groups to reduce the cloud point temperature (

T

cp

) was as follows:

i

-C5

>

t

-C5

>

C4

>

i

-C4

>

C3. Moreover

the more branched

i

-C4 and

t

-C5 were better groups than their less branched isomers C4 and

i

-C5 in the

T

cp

range of 12−51 ℃ to render the sharper phase transition to the thermoresponsive polymers. As for the polymers bearing two kinds of amide groups

the further introduction of C2

C3

C4

i

-C5 or

t

-C5 could effectively endow HPEI bearing 52% of

i

-C4 with thermoresponsive properties. The specific ordering of these second amide groups to reduce the

T

cp

was as follows:

i

-C5

>

C4

>

i

-C4

>

C3

>

C2. C4

i

-C5 and

t

-C5 were all effective second amide groups to prepare the thermoresponsive polymers with sharper phase transition.