Abstract
The synthesis of highly biocompatible polymers is important for modern biotechnologies and medicine. Here, we report a unique process based on a two-step high-pressure ramp (HPR) for the ultrafast and efficient bulk polymerization of 2-(hydroxyethyl)methacrylate (HEMA) at room temperature without photo- and thermal activation or addition of initiator. The HEMA monomers are first activated during the compression step but their reactivity is hindered by the dense glass-like environment. The rapid polymerization occurs in only the second step upon decompression to the liquid state. The conversion yield was found to exceed 90% in the recovered samples. The gel permeation chromatography evidences the overriding role of HEMA2•• biradicals in the polymerization mechanism. The HPR process extends the application field of HP-induced polymerization, beyond the family of crystallized monomers considered up today. It is also an appealing alternative to typical photo- or thermal activation, allowing the efficient synthesis of highly pure organic materials.
Highlights
Double or triple π -bonds which produces radical species that trigger chain reactions
We report that polymerization reactions can be efficiently induced by a new high-pressure-ramp (HPR) process without photochemical or thermal activation
We have used Raman spectroscopy to monitor the evolution of HEMA under increasing pressure (Fig. 2)
Summary
Double or triple π -bonds which produces radical species that trigger chain reactions These HP reactions occur above a pressure threshold and proceed slowly on a timescale of several hours or days. We report that polymerization reactions can be efficiently induced by a new high-pressure-ramp (HPR) process without photochemical or thermal activation. The efficiency of this new approach is demonstrated on the bulk polymerization of the 2-(hydroxyethyl)methacrylate (HEMA) monomer. The polymerization of HEMA is typically triggered by radicals produced by thermal or photoexcitation It proceeds via a classical addition reaction in three steps: initiation, propagation and termination. The first step is initiated at pressures greater than 6.5 GPa, at which radicals are formed from excited HEMA monomers.
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