Improvement of Mechanical Properties of Anisotropic Glassy Polystyrene by Introducing Heat-Labile Reversible Bonds

Wendi Wang,Anne L Skov,Qian Huang,Jeppe Madsen

doi:10.1021/acs.macromol.9b01843

Wendi Wang, Anne L Skov + Show 2 more

Open Access

https://doi.org/10.1021/acs.macromol.9b01843

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Journal: Macromolecules	Publication Date: Nov 25, 2019
Citations: 6	License type: cc-by

Affiliation: Technical University of Denmark

Abstract

Carboxylic acid groups were introduced into polystyrene, and the effect both on melt rheology and on mechanical properties of stretched and quenched anisotropic solids below the glass-transition temperature (Tg) was investigated. First, the facile preparation of well-defined copolymers of styrene (S) and 4-vinylbenzoic acid (A) by reversible addition–fragmentation chain-transfer polymerization was demonstrated. The evaluation of monomer reactivity ratios shows that the acid polymerizes faster than styrene but shows that block formation is suppressed under the applied conditions. Addition of acid groups leads to an increase in Tg, and this is documented by the detection of acid dimers in the glassy polymers. Importantly, linear viscoelastic measurements confirm that all the tested samples have a similar number of entanglements per chain (Z), which suggests that the acid groups do not form hydrogen bonds at temperatures above Tg. These are further confirmed by nonlinear extensional rheology of the samples i...

Highlights

Polystyrene is a widely used thermoplastic polymer
Our group reported that flexible polystyrene filaments can be obtained by stretching polystyrene melts at a rate faster than the inverse Rouse time, followed by rapid quenching below Tg.[2]
Since the strength of hydrogen bonds decreases with increasing temperature,[8,9] the hypothesis is that the melt behave very similar to a non-modified polystyrene, whereas the vitrified material is reinforced by the presence of stronger inter-chain bonds

Summary

INTRODUCTION

Polystyrene is a widely used thermoplastic polymer. In its common form, it is a brittle, amorphous transparent material with a glass transition temperature of around 100 °C. One possible drawback of the previously described fibers is that the properties are highly anisotropic; the fibers are very strong in the stretch direction, but come apart perpendicular to the stretch direction This anisotropy is achieved by uniaxial stretching faster than the inverse Rouse time followed by quenching whereby a high degree of orientation of the individual polymer chains is obtained (see Scheme 1A). Since the strength of hydrogen bonds decreases with increasing temperature,[8,9] the hypothesis is that the melt behave very similar to a non-modified polystyrene, whereas the vitrified material is reinforced by the presence of stronger inter-chain bonds. We believe that this is the first time that the effect of hydrogen bonds on vitrified material below Tg has been studied. The preparation of entangled, well-defined statistical poly(styrene-co-4vinylbenzoic acid) by RAFT polymerization has not previously been the subject of detailed investigations to the best of our knowledge

B Strong

RESULTS AND DISCUSSION

B Free acid