Effect of pH and Monomer Dosing Rate in the Anionic Polymerization of Ethyl Cyanoacrylate in Semicontinuous Operation

Hened Saade,Yolanda Garza,Julieta Sánchez,Suleidi Torres,Raúl G López,Cynthia Barrera

doi:10.1155/2015/827059

Abstract

Nanoparticles of poly(ethyl cyanoacrylate) with more than 10% solids content were prepared by semicontinuous heterophase polymerization at monomer-starved conditions varying the initial pH in the interval of 1–1.75 and at two monomer dosing rates. Measurements by scanning-transmission electron microscopy allowed us to identify an inverse dependence of particle size on pH. Furthermore, all the polymerizations conducted at the slower monomer dosing rate rendered two particle populations, with the larger one formed from the aggregation of a fraction of the smaller particles. It was believed that the so slow addition of the monomer caused the formation of very small but instable particles, thereby a fraction of which aggregated to reduce the total interface particles-aqueous phase, increasing the latex stability. An increase in the monomer dosing rate led to larger and more stable particles in such way that only one population of nanoparticles with around 40 nm in average diameter was obtained.

Highlights

Poly(alkyl cyanoacrylate), PACA, nanoparticles are a very interesting material for the design of drug delivery nanosystems [1, 2] due to their well-known biocompatibility and biodegradability [3, 4]
A revision of the quoted reports indicates that average diameters as large as 400 nm were obtained by Behan et al [13] who used Dextran 70 in emulsion polymerization of butyl cyanoacrylate (BCA) at different pH between 2 and 3
Polymerizations carried out at pH 1, 1.5, and 1.75 attained final conversions of 99.4, 99.5, and 98.6%, respectively, which correspond to 10.4, 10.6, and 10.3% solids content, respectively. This looks interesting because in accordance with the specialized literature solid contents no higher than 5-6% are common in the PACA latexes obtained by emulsion polymerization [6,7,8,9,10,11,12, 15]

Summary

Introduction

Poly(alkyl cyanoacrylate), PACA, nanoparticles are a very interesting material for the design of drug delivery nanosystems [1, 2] due to their well-known biocompatibility and biodegradability [3, 4]. The report of Yang et al [9] draws attention due to the very small particle sizes of PBCA they said have obtained These authors documented the results of emulsion polymerization of BCA, showing micrographs with two particles populations, one displaying diameters smaller than 50 nm and another with much larger sizes. This monomer adding policy has been used successfully by our group under the name of semicontinuous heterophase polymerization at monomerstarved conditions to obtain polymeric nanoparticles with average diameters substantially less than 50 nm [18,19,20] Despite those polymerizations proceeded via free radical mechanism, it was expected that this technique would lead to very small particles, taking into account that the ECA anionic polymerization would take place in surfactant stabilized compartments. Such small nanoparticles would be an excellent candidate for preparing high-efficacy drug delivery nanosystems

Experimental Section

Characterization

Results and Discussion

Conclusions