Novel Biodegradable Polymer based on Low Molecular Weight Hydrolyzing Units

Abstract

Polymer scaffolds can be used to restore, maintain, or improve tissues and organs. Poly(2-hydroxyethyl methacrylate), also known as pHEMA, is a commonly used polymer in tissue engineering due to its versatility in application. A major problem is that pHEMA is non-degradable. pHEMA can be made degradable by crosslinkers and a degradable initiator. A previous study from the Ratner lab found that degradation products of pHEMA that are <5kDa are soluble in the environment of the body and can be cleared from the body. Building upon that study, we wanted to synthesize pHEMA with an even lower molecular weight. This paper focuses on synthesizing 2-bromoethyl 3-bromopropanoate to use as a bi-functional initiator for atom transfer radical polymerization (ATRP) because it has an ester group between two organocarbon units and symmetric bromine leaving groups; the initiator was then used to synthesize symmetric, low molecular weight (<2kDa each) pHEMA chains growing from each Br with ATRP synthesis. Steglich esterification reaction with anhydrous dichloromethane (DCM) as the solvent had the highest yield at 14.6%. Copper bromide was used as the catalyst and the ATRP reaction was ran for 24 hours. Various combinations of ligands, solvents, and temperatures were used to increase the conversion of HEMA monomer to pHEMA. There was 100% conversion for the condition where 1,1,4,7,10,10-hexamethyl-triethylenetetramine (HMTETA) was the ligand, methanol/water (50:50, v/v) was the solvent, and at both room temperature and 50°C. pHEMA was crosslinked with 5% EDGMA using various solvents, temperatures, and stir bar conditions. 2-bromoethyl 3-bromopropanoate is a promising initiator to synthesize degradable, low molecular weight pHEMA hydrogels for cardiac tissue engineering applications.