The refractive index increment

dynamic and static laser light scattering

intrinsic viscosity[η]and Huggins constant（K

H

）of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃.The intrinsic viscosity

R

H

R

g

A

2

and（

<

S

>

2

）

1/2

（calculated from viscosity data）and"a"values of nylon 12 are found to be higher in m-cresol than in sulphuric acid.All these parameters decrease with the increase in water contents in sulphuric acid.The refractive index increment

K

H

and activation energy show an opposite trend to that of[η].The intrinsic viscosity

R

H

R

g

A

2

and（

<

S

>

2

）

1/2

have maximum values around 30-40℃in sulphuric acid/water system

whereas in m-cresol they fall at about 20℃.It has been concluded that the variation in size

interaction parameter（second virial coefficient）

[η]and K

H

of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents

selective adsorption

hydrogen bonding and conformational transitions.It has also been concluded that the increase in temperature first enhances the quality of the solvent

encourages hydrogen bonding and specific adsorption

and then deteriorates

bringing conformational transitions in the polymer molecules.However

the addition of water to sulphuric acid continuously deteriorates the solvent quality.This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.