Synthesis of “bioinspired” copolymers: experimental and theoretical investigation on poly(vinyl benzyl thymine-co-triethyl ammonium chloride)

Abstract

''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...

Evaluation of photo-induced crosslinking of thymine polymers using FT-IR spectroscopy and chemometric analysis

“…In Casis et al the synthesis of VBT-VBA polymers in solution at low temperatures (65ºC) was theoretically and experimentally studied [18]. A mathematical model for the free radical copolymerization of VBT-VBA was developed, that allows the prediction of global variables (conversion, composition) and the molecular structure (molecular weight distribution and chemical composition) of the copolymers along the reaction.…”

Experimental studies and mathematical modeling of the curing reaction of bioinspired copolymers

“…For the SM, in the beginning, it was considered that the Flory-Stockmayer assumptions for the formation of crosslinked networks were met (26), namely: (1) all functional groups are equally reactive, (2) all functional groups react independently and (3) intra-chain or intramolecular reactions do not exist. Additionally, from the measurements of the composition during the synthesis reaction it was determined that the monomers were randomized (32). Therefore, a random distribution of reactive sites (i.e.…”

A highly sensitive and stable glucose biosensor using thymine-based polycations into laponite hydrogel films

“…Due to the poor conductivity of the anionic clay, the incorporation of polycation molecules into the hydrogel film improves both the mechanical stability and the electrical conductivity of the interface, besides retaining the active enzyme [11][12][13]. Therefore, the design of innovative polycation molecules [14] becomes a relevant issue in the development of efficient and robust bioelectrodes.…”