Radical polymerization processes occur through a complex network of many different reactions. It is well-known that the polymerization rate is directly related to the monomer structure. The experimental polymerizability behavior is expressed as k p /k t 1/2 , where k p is the rate coefficient of propagation and k t is the rate coefficient of termination. In this study, the reactivity of a series of acrylates and methacrylates is modeled in order to understand the effect of the pendant group size, the polarity of a pendant group, and the nature of the pendant group (linear vs cyclic) on their polymerizability. The geometries and frequencies are calculated with the B3LYP/6-31+G(d) methodology whereas the energetics and kinetics of these monomers have been studied using the two-component BMK/6-311+G(3df,2p)//B3LYP/6-31+G(d) level of theory. For rotations about forming/ breaking bonds in the transition state, an uncoupled scheme for internal rotations has been applied with potentials determined at the B3LYP/6-31+G(d) level. Generally the rate constants for propagation k p mimic the qualitative polymerization trend of the monomers modeled and can be used with confidence in predicting the polymerizability behavior of acrylates. However in the case of 2-dimethylaminoethyl acrylate, chain transfer is found to play a major role in inhibiting the polymerization. On the other hand, the disproportionation reaction turns out to be too slow to be taken into consideration as a termination reaction.

Novel phosphorus-containing acrylate monomers were synthesized by two different routes. The first involved the reaction of ethyl ␣-chloromethyl acrylate and t-butyl ␣-bromomethyl acrylate with diethylphosphonoacetic acid. The monomers were bulk-and solution-polymerized at 56 -64°C with 2,2Ј-azobisisobutyronitrile. The ethyl ester monomer showed a high crosslinking tendency under these conditions. The selective hydrolysis of the ethyl ester phosphonic ester compound was carried out with trimethylsilyl bromide, producing a phosphonic acid monomer. In the second route, ethyl ␣-hydroxymethyl acrylate and t-butyl ␣-hydroxymethyl acrylate were reacted with diethylchlorophosphate. The bulk homopolymerization and copolymerization of these monomers with methyl methacrylate and 2,2Ј-azobisisobutyronitrile gave soluble polymers. The attempted hydrolysis of the monomers was unsuccessful because of the loss of the diethylphosphate group. The relative reactivities of the monomers in the photopolymerizations were also compared. The ethyl ␣-hydroxymethyl acrylate/diethylphosphonic acid monomer showed higher reactivity than the other monomers, which may explain the crosslinking during the polymerization of this monomer. The reactivities of other derivatives were similar, but the rates of polymerization were slow in comparison with those of methyl methacrylate.

Two phosphorus-containing acrylate monomers were synthesized from the reaction of ethyl ␣-chloromethyl acrylate and t-butyl ␣-bromomethyl acrylate with triethyl phosphite. The selective hydrolysis of the ethyl ester monomer with trimethylsilyl bromide (TMSBr) gave a phosphonic acid monomer. The attempted bulk polymerizations of the monomers at 57-60°C with 2,2Ј-azobisisobutyronitrile (AIBN) were unsuccessful; however, the monomers were copolymerized with methyl methacrylate (MMA) in bulk at 60°C with AIBN. The resulting copolymers produced chars on burning, showing potential as flame-retardant materials. Additionally, ␣-(chloromethyl)acryloyl chloride (CMAC) was reacted with diethyl (hydroxymethyl)phosphonate to obtain a new monomer with identical ester and ether moieties. This monomer was hydrolyzed with TMSBr, homopolymerized, and copolymerized with MMA. The thermal stabilities of the copolymers increased with increasing amounts of the phosphonate monomer in the copolymers. A new route to highly reactive phosphorus-containing acrylate monomers was developed. A new derivative of CMAC with mixed ester and ether groups was synthesized by substitution, first with diethyl (hydroxymethyl)phosphonate and then with sodium acetate. This monomer showed the highest reactivity and gave a crosslinked polymer. The incorporation of an ester group increased the rate of polymerization. The relative reactivities of the synthesized monomers in photopolymerizations were determined and compared with those of the other phosphorouscontaining acrylate monomers. Changing the monomer structure allowed control of the polymerization reactivity so that new phosphorus-containing polymers with desirable properties could be obtained.

Novel aromatic mono‐ and diphosphonate monomers based on t‐butyl α‐bromomethacrylate were prepared for use in dental composites. The synthesis of the two monomers involved three steps: the reaction of diethyl phosphite with phenol or hydroquinone, the rearrangement of the resulting phosphate derivatives into o‐hydroxyaryl phosphonates with lithium diisopropylamide, and the reaction of o‐hydroxyaryl phosphonates with t‐butyl α‐bromomethacrylate. Then, the selective hydrolysis of the t‐butyl ester groups of the monomers with trifluoroacetic acid gave the other carboxylic acid containing monomers. The photopolymerization behaviors of the synthesized monomers with glycerol dimethacrylate and triethylene glycol dimethacrylate were investigated with photodifferential scanning calorimetry at 40 °C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as the photoinitiator. The hydrolysis of the t‐butyl groups of the monomers increased the reactivity and the rates of polymerization of the monomers. The mixtures of the acid monomers showed rates of polymerizations similar to those of homopolymerizations of triethylene glycol dimethacrylate and glycerol dimethacrylate. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6775–6781, 2006

Novel phosphonate and phosphonic acid‐containing bis(methacrylamide)s were synthesized. The phosphonate‐containing monomers (1a and 1b) were synthesized by amidation of 2‐(2‐chlorocarbonyl‐allyloxymethyl)‐acryloylchloride with diethyl 2‐aminoethylphosphonate and diethyl 1‐aminomethylphosphonate. The phosphonic acid‐containing monomers (2a and 2b) were synthesized by hydrolysis of 1a and 1b with trimethylsilyl bromide (TMSBr). All monomers were liquids and dissolved in water and ethanol. Thermal homopolymerization of 1a and 1b in bulk and solution using 2,2′‐azobis(isobutyronitrile) (AIBN) at 80 °C gave crosslinked polymers indicating low cyclization tendencies of these monomers. They were also homopolymerized using photo‐DSC with 2,2′‐dimethoxy‐2‐phenyl acetophenone (DMPA) as photoinitator, and their maximum rates of polymerization were found to be higher than commercial monomers 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy propyloxy) phenyl] propane (Bis‐GMA) and 2‐hydroxyethyl methacrylate (HEMA), indicating their potential as reactive diluents or crosslinkers in dental materials. In fact, copolymerization with monomer 1a resulted in improvements in photopolymerization kinetics of both Bis‐GMA and HEMA. The acidic nature of the aqueous solutions (pH of 2a: 1.42, 2b: 1.53), stability under aqueous conditions after 1 month of study at 37 °C, interaction of 2a with hydroxyapatite (HAP) as representative of both monomers, and copolymerizability of the same with HEMA make these monomers suitable as adhesive monomers in dental adhesives, although their low observed reactivities may present a drawback. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

New methacrylate monomers containing phosphonic acid or both phosphonic and carboxylic acids were synthesized through the reaction of t-butyl a-bromomethyl acrylate with triethyl phosphite followed by the selective hydrolysis of the phosphonate or t-butyl ester groups with trimethylsilyl bromide and trifluoroacetic acid. The copolymerization of these monomers with 2-hydroxyethylmethacrylate was investigated with photodifferential scanning calorimetry at 40 8C with 2,2 0 -dimethoxy-2-phenyl acetophenone as a photoinitiator. Quantum mechanical tools were also used to understand the mechanistic behavior of the polymerization reactions of these synthesized monomers. The propagation and chain-transfer reactions were considered and rationalized. A strong effect of the monomer structure on the rate of polymerization was observed. The polymerization reactivities of the monomers increased with decreasing steric hindrance and/or increasing hydrogen-bonding capacity because of the hydrolysis of the phosphonate and the t-butyl ester groups.

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Three novel phosphonated methacrylate monomers have been synthesized and studied for use in dental applications. Two of the monomers were synthesized from the reactions of glycidyl methacrylate (GMA) with (diethoxy‐phosphoryl)‐acetic acid (monomer 1) and (2‐hydroxy‐ethyl)‐phosphonic acid dimethyl ester (monomer 2). These monomers showed high crosslinking tendencies during thermal bulk and solution polymerizations. The third monomer (monomer 3) was prepared by the reaction of bisphenol A diglycidylether (DER) with (diethoxy‐phosphoryl)‐acetic acid and subsequent conversion of the resulting diol to the methacrylate with methacryloyl chloride. The homopolymerization and copolymerization behaviors of the synthesized monomers were also investigated with glycerol dimethacrylate (GDMA), triethylene glycol dimethacrylate (TEGDMA), and 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy propyloxy) phenyl] propane (bis‐GMA) using photodifferential scanning calorimetry at 40 °C using 2,2′‐dimethoxy‐2‐phenyl acetophenone (DMPA) as photoinitiator. Monomer 1 showed polymerization rate similar or greater than dimethacrylates studied here but with higher conversion. The maximum rate of polymerizations decreased in the following order: 1∼TEGDMA>GDMA∼bis‐GMA∼3>2. A synergistic effect in the rate of polymerization was observed during copolymerizations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2290–2299, 2008