Dynamic Light-Scattering Characterization of the Molecular Weight Distribution of Unfractionated Polyimide MOHAMMAD SIDDIQ, 1 CHI WU 2 1 Department of Chemistry, Gomal University. D.I. Khan, North-West Frontier Province, Pakistan 2 Department of Chemistry, The Chinese University of Hong Kong, New Territories Shatin, Hong Kong, China Received 3 June 2000; accepted 29 September 2000 Published online 30 May 2001 ABSTRACT: Using a developed laser light-scattering (LLS) procedure, we accomplished the characterization of an unfractionated polyimide (UPI) in CHCl 3 at 25°C. The Laplace inversion of precisely measured intensity–intensity time correlation function from dynamic LLS leads us first to an estimate of the characteristic line-width distri- bution G(), and then to the translational diffusion coefficient distribution G(D). By using a previously established calibration of D (cm 2 /s) = 3.53  10 -4 M -0.579 , we were able to convert G(D) into a molecular weight distribution. The weight-average molec- ular weight M w , calculated from the molecular weight distribution, agrees well with that directly measured in static LLS. Our results indicate that both the calibration and LLS procedure used in this study are ready to be applied as a routine method for the characterization of the molecular weight distribution of polyimide. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1670 –1674, 2001 Key words: dynamic laser light scattering; unfractionated polyimide; poly- (BCPOBDA/DMMDA); Rayleigh ratio; intensity–intensity time correlation INTRODUCTION Polyimides, in particular those derived from fully aromatic monomers, represent a very important class of high-performance synthetic polymers be- cause of their excellent mechanical, optical, and chemical properties. 1 It is well known that a fully thermoimidized polyimide is normally insoluble in common organic solvents. On the one hand, this insolubility leads to chemical resistance; on the other hand, this insolubility becomes a major obstacle in studying the solution properties, such as the chain flexibility and conformation. In the past, the solution properties and molecular pa- rameters of these insoluble polyimides had to be estimated from their precursor, for example, poly- amic acid formed by the first-stage reaction of aromatic diamines with an anhydride. This ap- proach has some intrinsic and serious problems, including effects of polyelectrolytes and the differ- ences in chain rigidity between a poly(amic acid) and its corresponding polyimide chain. 2–4 More- over, information obtained from the study of those soluble poly(amic acids) can be strongly influ- enced by both the nature of imidization and the reversible reaction. 5 To tailor a polyimide to satisfy specific require- ments in various industries, a careful examina- tion and control of its chain conformation are of great importance. Practically, a correlation be- tween the chain flexibility and bulk properties is still missing. Recently, a soluble high-perfor- mance polyimide was synthesized: poly[1,4'- bis(3,4-carboxyphenoxy) benzene dianhydride/ 2,2'-dimethyl-4,4'-methylene dianiline], termed Correspondence to: M. Siddiq (m_sidiq12@ yahoo.com). Journal of Applied Polymer Science, Vol. 81, 1670 –1674 (2001) © 2001 John Wiley & Sons, Inc. 1670