EFFECT OF MOLECULAR-WEIGHT ON LATEX FILM FORMATION - PHOTON TRANSMISSION STUDY

A UV-visible (UW) technique was used to monitor the evolution of trans parency during film formation from hard latex particles. Two different latex films were prepared from particles with high and lon molecular weight (HM and LM) poly(methyl methacrylate) (PMMA) separately and ann ealed at elevated temperatures in various time intervals above the gla ss transition temperature (T-g). In both films, a continuous increase in the transmitted photon intensity (I-rf) was observed above 160 degr ees C as the annealing temperature was increased. However, the reflect ed photon intensity (I-rf) first decreased and then increased by showi ng a minimum in the same temperature range as the annealing temperatur e was increased. The increase in the transmitted photon intensity (I-t r) is attributed to increase in the ''crossing density'' at the juncti on surface. The activation energies for back-and-forth motion (Delta E -tr) were measured and found to be around 35 and 25 kcal/mol for the r eptating polymer chain across the junction surface in the LM and HM fi lms, respectively. The decrease in I-rf was explained by the void-clos ure mechanism, and the increase in the I-rf above 160 degrees C was ag ain attributed to the increase in the crossing density at thejunction surface. Back-and-forth activation energies (Delta E-rf) were measured to be around 47 and 18 kcal/mol and the void-closure constants (B) we re found to be around 24 x 10(3) and 12 x 10(3) K for the LM and HM fi lm samples, respectively. (C) 1998 John Wiley & Sons, Inc.