Primary and secondary hydroxyl group content of polypropylene glycols

Abstract

When propylene oxide is polymerized or when it is added onto an alcohol or phenol, the terminal hydroxyl groups can be of primary or secondary types, depending on how the epoxide ring opens. The nature of the terminal hydroxyl group becomes important if the polyglycol ether is reacted further, as in the case of polyurethane foams. The primary hydroxyl group reacts much more rapidly with isocyanates than the secondary hydroxyl group, and hence the performance of the polyglycol varies with the ratio of primary to secondary hydroxyl group content. An analytical method has been developed to differentiate the primary from the secondary hydroxyl groups on polypropylene glycol, and a study was made of the variation in the ratios of the two hydroxyl types versus molecular weight of the polyglycol and versus other chemical treatments to which the polyglycol was exposed.

Primary Hydroxyl Content of Soybean Polyols

“…The reactions of hydroxyl groups with isocyanates and with organic anhydrides (acetic anhydride, phthalic anhydride, among others) are typical second order reactions [8,13,15]. The reaction of hydroxyl groups with isocyanates has a very simple stoichiometry: one hydroxyl group (compound A) reacts with one isocyanate group (compound B) and generates one urethane group (P = product of reaction).…”

“…The primary hydroxyl content is determined graphically from a second order kinetics plot of ln[(b -x)/(a -x)] as a function of time t, where a is the initial concentration of hydroxyl groups (a = 4.6 mmol/50 mL); b is the initial concentration of PI (b = 5 mmol/50 mL); x is the concentration of OH groups, in millimoles (equal to the concentration of PI groups) reacted at time t. The procedure for graphical determination of primary hydroxyl is described in detail in the literature [13,15,16]. The modifications to the method, as applied here for the first time to soybean polyols, consist in the use of DABCO as the catalyst instead of stannous octoate (stannous octoate loses the catalytic activity with time [15] while the catalytic activity of DABCO does not change with time) and the use of different concentrations of reagents.…”

“…If the water content is higher than 0.1%, the soy polyol has to be heated for 1-2 h at 100-110°C in a vacuum (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Water reacts with isocyanates at a higher rate than secondary hydroxyl [8] and leads to an artificial increase of primary hydroxyl content.…”

“…In order to correctly evaluate the primary hydroxyl of soybean polyols, we have applied a kinetic method, based on the difference in reactivity of primary and secondary hydroxyl of soybean polyols with a common reagent, phenyl isocyanate (PI), and evaluated the method precision. The determination of primary hydroxyl content in alcohol mixtures or of polyether polyols by kinetic methods has been described in several papers [13][14][15][16][17][18][19][20]. All of these methods include second order kinetics of the reaction of polyols with acetic anhydride [13], phthalic anhydride [14] or phenyl isocyanate [15,16] and pseudo-first order kinetics using a high excess of hydroxyl groups [15] or an excess of phenyl isocyanate or p-methyl-phenyl isocyanate [16,17], or the large difference in reactivity of primary and secondary hydroxyl with triphenylchloromethane [18] or 3-nitrophthalic anhydride [19].…”

Kinetic Methods of Analysis

“…For example, Clibbens and Francis (15) and Francis and Geake (32) found the decomposition of nitrosotriacetonamine into nitrogen and phorone t o be a function of the catalytic activity of hydroxyl ion. The original concentration of nitrosotriacetonamine was known and the rate of decomposition found by measuring the nitrogen produced as a function of time.…”