Chain extension as a strategy for the development of improved reverse thermo‐responsive polymers

Abstract

The hypothesis that chain extension can be harnessed to the generation of improved reverse thermo‐responsive polymers was tested by following two basic synthetic pathways: (1) the polymerization of poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblocks using hexamethylene diisocyanate (HDI) as chain extender and (2) the covalent binding of poly(ethylene glycol) and poly(propylene glycol) chains, using phosgene as the connecting molecule. While in the former, the basic amphiphilic repeating unit is known for its own RTG behavior, the latter polymers consist of segments incapable of exhibiting a reverse thermal gelation (RTG) of their own. Dynamic light scattering (DLS) measurements revealed that the nanostructures formed by the chain extended polymers were markedly larger than those generated by PEO‐PPO‐PEO triblocks. While the size of Pluronic F127 micelles ranged from 15 to 20 nm, the higher molecular weight amphiphiles generated much larger nanostructures (20–400 nm). The chain extended polymers achieved much higher viscosities and their gels displayed enhanced long‐term stability at 37°C. Copyright © 2007 John Wiley & Sons, Ltd.

Effect of Crosslinker Length and Composition on the Hydrophobicity and Thermomechanical Response of Acrylate‐Based Shape‐Memory Polymers

“…We expect such characteristics to be required in designing materials useful in vascular stent procedures. Other groups have used information about chain length or extension and functionality of groups to modify the temperature at which these systems transition to develop a switching temperature as opposed to a glass transition temperature 41, 48, 49. Tailoring of these systems would enable finer control over material design but as demonstrated here, the relationship between chemical structures and physical properties is quite convoluted and necessitates systematic studies.…”

“…Future works may require a closer examination of cellular viability in monolayer cultures and cytotoxicity 50. Relationships should be determined between macroscopic properties and recovery times with cycling, increasing crosslinker percentage,32 and molecular weight 49. Other current steps involve determining parameters for constitutive modeling,21, 51–54 3D constitutive modeling,55 and their incorporation into models for finite element analysis 53 for compressive and tensile applications.…”

The biocompatibility of Pluronic®F127 fibrinogen-based hydrogels

“…One possible reason for this effect is that the fibrinogen functions as a chain extender in the FF127. Cohn et al showed that a solution of polymerized F127 displays RTG properties at lower concentrations with enhanced mechanical properties compared to F127 unimers; the longer chains can interact better in the solution to form a physical polymeric matrix at lower concentrations of precursor [27]. The correlation between the enzymatic degradation of the FF127 by collagenase and the resultant shear modulus (G 0 ) is another indication that fibrinogen is a chain extender in the FF127.…”

Hydrogels for Hydrophobic Drug Delivery. Classification, Synthesis and Applications

“…Several strategies have been employed to overcome these issues. The first one was the synthesis of novel temperature sensitive biomaterials or optimization of classic polymers such as PCL-PEG-PCL and Pluronic F127 [ 59 , 87 ]. Cohn et al investigated the effect of chain extension on the mechanical and rheological properties of the thermosensitive polymers and found that polymers with enhanced mechanical properties and long term stability could be produced [ 87 ].…”