''Bioinspired'' copolymers based on vinylbenzyl thymine (VBT) and an ionically-charged monomer, such as vinylbenzyl triethylammonium chloride (VBA), were synthesized and theoretically investigated. These watersoluble copolymers are polystyrene-(PS) based, and their structure mimics DNA. In the presence of shortwavelength UV light, the thymine groups dimerize into non-toxic, environmentally benign, and biodegradable photo-resistant materials. Copolymerizations with different comonomer ratios were carried out at 658C. Samples were taken along the reactions to determine monomer conversion, chemical composition, and molecular weight distribution. While average molecular weights fall along the reaction, the average composition remains almost constant and coincident with the initial comonomer ratios, thus indicating a similar reactivity of all the comonomer radicals. A mathematical model was developed that simulates the synthesis of the base biopolymer, in the sense of predicting the evolution of the global reaction variables and molecular structure of the polymer. The termination and propagation kinetic constants were adjusted to the experimental data. The resulting values are quite different to those of a normal styrene homopolymerization, thus suggesting a noticeable effect of the solvent and the comonomer pending groups.Keywords: Biopolymer; thymine polymer; crosslinking; biomimicry IntroductionThe increasing attention directed to the environmental and toxicological implications associated with commercial materials, together with the high energy inputs required for most existing processes, suggest that environmentally-benign alternatives must be explored (1). A smart way to do this is to mimic ''mother nature'' (2). In this context, the synthetic monomer (4-vinyl benzyl) thymine (VBT) was investigated (3Á16,20). It is especially interesting for its ability to photo-crosslink upon irradiation of short UV wavelength (Â280 nm), which is present in sunlight (17,18). ''Bioinspired'' polymers containing thymine are similar to polystyrene (PS), except that thymine and charged functional groups are chemically bonded onto the base PS structure. The chemistry of crosslinking and immobilization of these bioinspired polymers has been derived from a simple photochemical transformation that occurs in nature: the 2p'2p photo-dimerization of thymine base units within DNA when exposed to UV radiation (Figure 1) (17,18).To produce water-soluble polymers, VBT can be copolymerized in a free-radical process with ionicallycharged comonomers, such as vinyl benzyl triethyl ammonium chloride (VBA), yielding (random and cationic) linear copolymers of controlled composition (Figure 2).The adaptability of VBT makes it an attractive monomer, since the balance between photoreactivity, solubility, and non-covalent interactions can be finetuned for a wide variety of applications. In addition, the existence of natural mechanisms to reverse the photo-dimerization reaction and to restore the polymers to their original state provides exciting oppor...