Stringent control of formaldehyde emission standards the world over has intensified research and development effort to explore several paths for reducing formaldehyde release. A new generation of low odour resins is currently being developed and some resin manufacturers are now programming formaldehyde and urea additions at two or more stages in the overall reaction. This article reports on the studies conducted on a four-stage condensation process consisting of the first stage involving a high acid environment followed by an alkaline condensation, a condensation under a pH 6, and finally neutralization to pH 7. A programmed variation consisting of changing "the number of additions" and "the duration between additions" of urea to formaldehyde was considered as an effective method to control the molecular weight, molecular weight distribution, and the oligomeric structures. Response surface methodology was employed to optimize the above conditions to produce particle boards with minimum formaldehyde emission and maximum internal bond strength. The studies showed that sequential addition of urea ["the duration between additions" and the "number of additions"] improved the internal bond strength and reduced formaldehyde emission of the particleboards. Detailed resin characterization in terms of the number and weight average molecular weights, molecular weight distribution, polydispersity, percentages of reactive moieties, and interlinking units present in the oligomer could be stipulated. (c) 2006 Wiley Periodicals, Inc.