SynopsisThe factors which can influence the availability of functional groups in polymers are considered. In particular, the importance of hydroxyl groups in the formation and film-forming reactions of alkyd resins is discussed, and evidence is presented to suggest that the number of hydroxyl groups available for chemical reaction is not necessarily equivalent to the theoretical value. Factors which influence the availability of the hydroxyl groups are considered, and some of the properties of the alkyd are related to the available hydroxyl content.

SynopsisAlkyd resins which have the same overall chemical composition and the same degree of polymerization have been prepared from synthetic mixtures of mono-, di-, and triglycendm of linoleic acid, glycerol, and phthalic anhydride. The properties of these resins difiered significantly. Microgel particles are present in all resins, but the quantity and size of the gel particles is a function of the glyceride composition. The concept of microgel is used to explain the solution and film forming properties of these resins. Examination of a range of commercially available alkyd resins has shown that microgel particles are present where the functionality is greater than two.

SynopsisAlkyds prepared from castor and hydrogenated castor oils have been prepared direct from the oil and by first subjecting the oil to a glycerolysis reaction. The molecular weight distributions of the alkyds have been measured in solvent systems designed to separate predominantly on polarity and molecular weight. The properties of the alkyds in stoving enamels have been evaluated. The results are discussed in relation to existing theories relating processing conditions to molecular weight distribution in alkyd resins. Previous suggestions regarding the reactivity of the hydroxyl groups in the oil molecules are not consistent with the results obtained in this study. INTRODUCTIONThe coatings industry uses alkyd resins (fatty acid modified polyesters) either alone or in conjunction with other film formers, for up to 50% of all paints produced.l.2 As a consequence of the commercial importance of alkyd resins a tremendous amount of technological development and modification of basic formulations has been carried out. On the other hand, fundamental studies aimed at better prediction and control of alkyd prop erties and processing are comparatively rare. In fact, some of the basic formulations and manufacturing conditions commonly used for alkyd resins are derived by extrapolation of results obtained on much simpler systems, and not verified in the more complex alkyd structures. For example, Flory's3 findings regarding the ease and rapidity with which ester interchange-type reactions occur in decamethylene adipates are often assumed to operate in alkyds of the glyceryl phthalate type, whereas Spit~e r ,~ T a~n ,~ and we6,' have shown they do not always apply. This is a most significant point when considering the preparation of alkyd resins from vegetable oils, where it is necessary to first react the oil with a polyol to ensure compatibility when the phthalic anhydride is added; in the absence of subsequent complete and rapid interchange reactions the final alkyd structure will be governed by the composition of the alcoholysis product (i.e., the amounts of mono-, di-, and triglyceride, and free polyol).* Present address: Balm Paints Ltd., Clayton, Victoria, Australia. 993 994 D. H. SOLOMON AND J. J. HOPWOODIn Part I6 of this series we have shown that with an alkyd resin based on glycerol, phthalic anhydride, and coconut oil (a predominantly saturated fatty acid triglyceride) the molecular weight distribution and film-forming properties of the polymer are related to the extent of oil-glycerol reaction as measured by a-monoglyceride analysis. As an extension of the findings of Part I to alkyds based on other oils, we now report results obtained with castor and hydrogenated castor oil. These oils are predominantly the triglycerides of 12-hydroxyoleic acid (ricinoleic acid) and 12-hydroxystearic acid, respectively. There are a number of reasons why these oils are of interest. First, the presence of a hydroxy group on the fatty acid chain renders the oil miscible with the glycerol-phthalic anhydride mixture, and thus it...