Using hyperbranched oligomer functionalized glass fillers to reduce shrinkage stress.
OBJECTIVE
Fillers are widely utilized to enhance the mechanical properties of polymer resins. However, polymerization stress has the potential to increase due to the higher elastic modulus achieved upon filler addition. Here, we demonstrate a hyperbranched oligomer functionalized glass filler UV curable resin composite which is able to reduce the shrinkage stress without sacrificing mechanical properties.


METHODS
A 16-functional alkene-terminated hyperbranched oligomer is synthesized by thiol-acrylate and thiol-yne reactions and the product structure is analyzed by (1)H NMR, mass spectroscopy, and gel permeation chromatography. Surface functionalization of the glass filler is measured by thermogravimetric analysis. Reaction kinetics, mechanical properties and shrinkage stress are studied via Fourier transform infrared spectroscopy, dynamic mechanical analysis and a tensometer, respectively.


RESULTS
Silica nanoparticles are functionalized with a flexible 16-functional alkene-terminated hyperbranched oligomer which is synthesized by multistage thiol-ene/yne reactions. 93% of the particle surface was covered by this oligomer and an interfacial layer ranging from 0.7 nm to 4.5 nm thickness is generated. A composite system with these functionalized silica nanoparticles incorporated into the thiol-yne-methacrylate resin demonstrates 30% reduction of shrinkage stress (from 0.9 MPa to 0.6 MPa) without sacrificing the modulus (3100 ± 300 MPa) or glass transition temperature (62 ± 3°C). Moreover, the shrinkage stress of the composite system builds up at much later stages of the polymerization as compared to the control system.


CONCLUSIONS
Due to the capability of reducing shrinkage stress without sacrificing mechanical properties, this composite system will be a great candidate for dental composite applications.
Department of Chemical & Biological Engineering, University of Colorado, Boulder, 80309, United States. sheng.ye@colorado.edu
Sheng
S
Ye
Setareh
S
Azarnoush
Ian R
IR
Smith
Neil B
NB
Cramer
Jeffrey W
JW
Stansbury
Christopher N
CN
Bowman
D000704:Analysis of Variance; D003188:Composite Resins / Q000138:chemical synthesis*; D055119:Elastic Modulus; D005898:Glass / Q000737:chemistry*; D008689:Methacrylates / Q000737:chemistry*; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
D003188:Composite Resins; D008689:Methacrylates; D011108:Polymers; D012822:Silicon Dioxide