The use of vegetable oil macromonomers (VOMMs) as comonomers in emulsion polymerization enables good film coalescence without the use of solvents that constitute volatile organic compounds (VOCs). VOMMs are derived from renewable resources and offer the potential of post-application crosslinking via auto-oxidation. However, chain transfer reactions of VOMMs with initiator and/or polymer radicals during emulsion polymerization reduce the amount of allylic hydrogen atoms available for primary auto-oxidation during drying. Vegetable oils and derivatives were reacted with butyl acrylate and methyl methacrylate via solution polymerization, and the polymerization was monitored using in situ infrared spectroscopy to determine the extent of chain transfer.1 H NMR spectroscopy was used to determine the loci of chain transfer and the molecular weight characteristics of the polymers were characterized by SEC. Solution polymerization was utilized because this limited temperature fluctuations and insolubility of the polymer.
Highly crosslinked networks were produced through a series of diacids and tetrakis pyridyls. These materials displayed complex crystallization behaviors over multiple heat/cool cycles. The shifting of crystallization behaviors with time in the melt phase seems to indicate that the materials move toward thermodynamically ideal structures. This behavior is suggestive of a type of memory in which the networks remember the morphological structure previous to the melt and improve upon that structure in the next cooling cycle. The network/memory phenomena observed in small molecule diacid/tetrapyridyl systems also appeared to exist when poly(ethylene terephthalate) (PET) polymer was used as the source of carboxylic acid functionalities. The same time-dependent behaviors, suggestive of sequential steps toward thermodynamically optimum states, were observed when the PET/tetrapyridyl systems were thermally cycled. It was also observed that complexation of tetrapyridyl with PET brought about a significant change in oxygen gas barrier properties; these changes were opposite to those obtained when covalent crosslinks were introduced into PET.
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