The Scissors Effect in Action: The Fox-Flory Relationship between the Glass Transition Temperature of Crosslinked Poly(Methyl Methacrylate) and Mc in Nanophase Separated Poly(Methyl Methacrylate)-l-Polyisobutylene Conetworks.

Szabolcs Pásztor,Ralf Thomann,Yi Thomann,Rolf Mühlhaupt,Béla Iván,Bálint Becsei,Györgyi Szarka

doi:10.3390/ma13214822

Abstract

The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox–Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox–Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,∞ − K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5–20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.

Highlights

Revealing the correlations between material properties and their structural characteristics is the key to designing, processing, and applications of materials
As known, according to the Fox–Flory equation [66], the Tg of homopolymers is inversely proportional to their number average molecular weight: Tg = Tg,∞ − K/Mn, where Tg,∞ stands for the glass transition temperature of the polymer with infinite molecular weight, and K is a constant, as verified by experimental results for a variety of homopolymers [66,67,68,69,70,71,72,73]
We report on the synthesis of a series of poly(methyl methacrylate)-polyisobutylene (PMMA-l-PIB) conetworks by radical copolymerization of methyl methacrylate (MMA) with methacrylate-telechelic polyisobutylene (MA-PIB-MA) as a macromolecular crosslinker in order to investigate the effect of Mc on the Tg of PMMA in and the morphology of the resulting conetworks

Summary

Introduction

Revealing the correlations between material properties and their structural characteristics is the key to designing, processing, and applications of materials. As known, according to the Fox–Flory equation [66], the Tg of homopolymers is inversely proportional to their number average molecular weight: Tg = Tg,∞ − K/Mn , where Tg,∞ stands for the glass transition temperature of the polymer with infinite molecular weight, and K is a constant, as verified by experimental results for a variety of homopolymers [66,67,68,69,70,71,72,73] Because this relationship has been found between the Tg and Mc of PVIm in the PVIm-l-PTHF conetworks, it has been concluded that the PTHF macromolecular crosslinker acts like atomic scissors by “cutting” the PVIm chains at the crosslinking points strictly from the point of view of the glass transition. The question arises whether this “scissors effect” is valid exclusively only for the PVIm-l-PTHF conetworks, or this is a more general phenomenon for conetworks with immiscible polymer components

Methods

Discussion

Conclusion