TY - JOUR
T1 - Michael-type addition reactions in NIPAAm-cysteamine copolymers follow second order rate laws with steric hindrance
AU - McLemore, Ryan
AU - Robb, Stephanie A.
AU - Lee, Bae Hoon
AU - Caplan, Michael
AU - Vernon, Brent
N1 - Funding Information:
The authors acknowledge funding from the Arizona Biomedical Research Committee, Grant # 0810, and the Reach for the Stars Fellowship from Arizona State University. Michael R. Caplan is funded by a National Institute of Dental and Craniofacial Research Career Development and Faculty Transition Award (K22DE014846).
PY - 2009/11
Y1 - 2009/11
N2 - This work investigates the differential reaction rates seen among several Michael-Type acceptors when reacted with poly(NIPAAm-co-cysteamine). This work differs from many of the previous studies upon mercaptans in that it examines systems used for network and gel formation. We find that the reaction rates of poly(NIPAAm-co-cysteamine) cross-linked with Michael type acceptors follow traditional second order rate laws. In addition, we further confirm that these reactions are pH sensitive, reliant upon the pK a of the conjugated thiols, and on local chain chemistry. Additionally, this work determines that the reaction of difunctional acrylates with the macromolecular NIPAAm molecules leads to an apparent, but not significant, increase in the rate of reaction. The low magnitude of this increase is likely indicative of increased steric hindrance arising from network formation, or reduced diffusion in the NIPAAm polymer chains. Statistical analysis shows pH and ratio of thiol to acrylates significantly affect reaction rates (p < 0.05). The type of acrylate (PEGDA, PEGMA, or HEA) does not return as significant globally or within a pH range. Since localizing charge on a chain raises the effective pK a of nearby acids, gains in reaction rate from increasing chain functionality are shown to increase much less than would be expected from the increased concentration.
AB - This work investigates the differential reaction rates seen among several Michael-Type acceptors when reacted with poly(NIPAAm-co-cysteamine). This work differs from many of the previous studies upon mercaptans in that it examines systems used for network and gel formation. We find that the reaction rates of poly(NIPAAm-co-cysteamine) cross-linked with Michael type acceptors follow traditional second order rate laws. In addition, we further confirm that these reactions are pH sensitive, reliant upon the pK a of the conjugated thiols, and on local chain chemistry. Additionally, this work determines that the reaction of difunctional acrylates with the macromolecular NIPAAm molecules leads to an apparent, but not significant, increase in the rate of reaction. The low magnitude of this increase is likely indicative of increased steric hindrance arising from network formation, or reduced diffusion in the NIPAAm polymer chains. Statistical analysis shows pH and ratio of thiol to acrylates significantly affect reaction rates (p < 0.05). The type of acrylate (PEGDA, PEGMA, or HEA) does not return as significant globally or within a pH range. Since localizing charge on a chain raises the effective pK a of nearby acids, gains in reaction rate from increasing chain functionality are shown to increase much less than would be expected from the increased concentration.
KW - Hydroxy ethyl acrylate
KW - Poly(ethylene glycol) acrylate
KW - Poly(ethylene glycol) diacrylate
KW - Polymer rate kinetics
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U2 - 10.1007/s10439-009-9776-0
DO - 10.1007/s10439-009-9776-0
M3 - Article
C2 - 19669882
AN - SCOPUS:70349661690
SN - 0090-6964
VL - 37
SP - 2416
EP - 2425
JO - Annals of Biomedical Engineering
JF - Annals of Biomedical Engineering
IS - 11
ER -