Objective:  The objective of this project is to increase the overall strength of glass-ionomer through the use of block copolymers.  The modification of polymer architecture is a novel approach to improve the properties of glass-ionomers.  In fact, this method for improving glass-ionomers is essentially absent from the literature with a few minor exceptions.  Thus, the synthesis of the block copolymer for this GI system was modeled from the reversible addition-fragmentation transfer (RAFT) synthesis conducted by Lai, Filla, and Shea.

Methods:  The RAFT catalyst, S,S'-Bis(a,a'-dimethyl-a''-acetic acid)-trithiocarbonate, was synthesized by following the procedure provided by Lai.  The catalyst was used to construct a block copolymer from acrylic acid and hydroxyethyl methacrylate.  Solutions of the synthesized block copolymers were formulated with commercially available filler.  The resulting glass-ionomer cement was then evaluated using flexural tests to determine the effect of the block copolymers on the overall strength of the material.  A tri-block copolymer (AA-HEMA-AA) and a di-block copolymer (AA-HEMA) of 2:1 acrylic acid and HEMA, a di-block copolymer of acrylic acid and ethylhexyl methacrylate, a di-block copolymer of acrylic acid and vinylphosphonic acid, as well as three controls (commercially available Fuji IX, poly-AA block, and a random block copolymer) were formulated. 

Results:

Sample	Peak Load(N)	Break Load(N)	Modulus(GP)
Fuji IX Control	14.72+/-2.84	14.55+/-3.03	4.64+/-2.26
Acrylic Acid Polymer	16.72+/-3.66	16.65+/-3.65	6.07+/-0.60
Random Copolymer (AA/HEMA)	13.48+/-1.75	13.42+/-1.76	6.31+/-0.52
Tri-Block (AA/HEMA/AA)	8.83+/-3.06	8.73+/-3.01	4.84+/-0.62
Di-Block (AA/HEMA)	10.98+/-1.72	10.78+/-1.74	5.60+/-0.55
Di-Block (AA/EHM)	8.60+/-2.96	8.60+/-2.96	2.36+/-0.40
Di-Block (AA/VPA)	4.00+/-0.48	4.00+/-0.48	2.15+/-0.29

Conclusion:  There was no significant difference in the peak load, break load, or modulus of the experimental samples when compared to the controls.  The architecture of the polymer can significantly affect the properties of the glass-ionomer and research is continuing to find structures that will improve glass-ionomer properties.

Kyle Bogan was supported by award T32DE14320 from the NIDCR.

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