Copolymerization of 2-Hydroxyethyl Methacrylate with a Comonomer with Spiroacetal Moiety AURICA P. CHIRIAC, LOREDANA E. NITA, MANUELA T. NISTOR ‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Grigore Ghica Voda Alley No. 41-A, 700487 Iasi, Romania Received 22 December 2010; accepted 5 January 2011 DOI: 10.1002/pola.24575 Published online 3 February 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The study reports the synthesis of a copolymer based on 2-hydroxyethyl methacrylate and 3,9-divinyl-2,4,8,10-tetraoxas- piro[5.5]undecane (U) acquired through radical polymerization in the presence of 2,2 0 -azobis(2-methylpropionitrile). The attempt was to have a solid content as high as 10 wt %. The polymeriza- tion process was conducted in the presence of a classic ionic sur- factant—sodium lauryl sulfate—and comparatively using two variants of protective colloid b-cyclodextrin and poly(aspartic acid), respectively. The prepared dispersions were characterized from the viewpoint of their hydrodynamic radius, zeta potential, and conductivity evolution during syntheses. The mean particle size and size distribution and zeta potential and conductivity were also evaluated for the synthesized polymeric particles. The com- positions of the polymers were confirmed by FTIR and 1 H NMR spectra, and also, the thermal stability of the polymeric com- pounds was evaluated. SEM and AFM investigations of the poly- mer morphology are also presented. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1543–1551, 2011 KEYWORDS: b-cyclodextrin; 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5] undecane; 2-hydroxyethyl methacrylate; colloids; copolymeriza- tion; nanoparticles; poly(aspartic acid); radical polymerization INTRODUCTION The copolymerization processes between hydrophilic and hydrophobic monomers showed interest in the design and synthesis of different compounds such as hydrogels and biocompatible materials. A large number of studies were devoted to the homopolymerization and copolymerization of 2-hydroxyethyl methacrylate (HEMA) owing to the multiple application fields of the poly(HEMA) (PHEMA) and its copolymers. 1–5 Reports concerning the polymerization of HEMA described the homopolymerization in aqueous medium using redox initiators or different systems of initiation. 6,7 At the same time, the literature in the field presents the preparation of PHEMA latex with adequately high solid content not easy at all when compared with the hydrogel preparation, owing to the monomer that exhibits an extremely high aqueous solubility and the latex, which faces coagulation easily. 8,9 The incorporation of HEMA in a different content in a copolymer can yield compounds of varied properties including hydrophilic/hydrophobic balance and hemocompatibility. Its biocompatibility determines the future use for the preparation of various biomedical and pharmaceutical materials, for example, optical lenses, implants, drug delivery devices, and support for enzyme immobilization. Other studies had in view the improvement of the PHEMA properties, for example, the mechanical properties, perme- ability, temperature-responsive characteristics, and degree of hydration or extent of hydrogel network swelling, to elicit more favorable biological responses. 10,11 The degree of hydration and/or swelling is one of the impor- tant properties that allows to understand the transport of small molecule solutes through the hydrogel matrix. This property also influences mechanical properties and surface properties, for example, wettability and protein adsorption. 12 However, the mechanical properties do not fit the require- ments for many structural applications. By synthesizing amphiphilic materials, combining HEMA with hydrophobic components, one can expect the improvement of the me- chanical strength of the obtained materials. 13–16 In this con- text, the copolymerization is mainly used to improve me- chanical properties of PHEMA, the affinity for water, oxygen permeability, and so forth. The incorporation of spiroacetal groups in the structures of the polymers improves the solubility and the adhesive properties. 17 These polymers have good oxidative and thermal stabilities and are good fiber formers; films pre- pared from some of these polymers present good flexibil- ity and tensile strength. 17 These characteristics are attrib- uted to the properties inherent into the spiroacetal ring: stiffness, which is higher than cycloaliphatic rings but lower than aromatic rings and interactions on ether oxy- gen such as hydrogen bonds or coordinate bonds with other functional groups, and bulkiness. 18 Bailey et al. 19 in 1976 describe developments in synthesis of alternating poly(ester–ether)s from spiroorthoesters. These are consid- ered biodegradable and useful for biomedical applica- tions. 20 In this context, spiroacetals are key structural Correspondence to: A. P. Chiriac (E-mail: achiriac1@yahoo.com) Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 1543–1551 (2011) V C 2011 Wiley Periodicals, Inc. COPOLYMERIZATION OF 2-HYDROXYETHYL METHACRYLATE, CHIRIAC, NITA, AND NISTOR 1543