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The post-polymerization modification of polyglycidol is of great interest for the synthesis of functional polyether-based polymeric biomaterials. We present a degradable polyglycidol-based hydrogel system using oxime click chemistry by employing a ketone-functionalized and an amino-oxy functionalized branched polyglycidol. Ratio-controlled amino-oxy functionalized species were obtained by controlling the ratio of N-hydroxy phthalimide to the hydroxyl groups attached to the polyether backbone. A similar strategy was utilized to obtain ratio-controlled keto functionalized branched polyglycidols. This unique feature will allow for the tailoring of this branched PEG-like structural motif for the synthesis of novel biomaterials with tailored biochemical and biomechanical properties. The bio-orthogonal nature of this crosslinking reaction makes these hydrogels an attractive option for load-bearing tissue engineering. Our hydrogel synthesis methodology allows for control over the properties of the resulting polymeric network, based upon the ratio between the keto and the amino-oxy functionalities. The potential of these polyether-based networks to serve as a successful delivery platform was assessed by studying their swelling and degradation profiles. Biocompatibility and cytotoxicity of the gels were studied using NIH 3T3 cells. Our preliminary results highlighting the potential of our hydrogels platform will be discussed. 

The modification of branching in polyglycidol is of great interest for the synthesis of novel polymeric biomaterials. We present the synthesis of novel ratio-controlled amino-oxy and keto functionalized branched polyglycidols. The biocompatibility and chemospecificity of the amino-oxy functional group make it particularly well suited for applications in bioconjugation, drug delivery and tissue engineering. Amino-oxy functionalized branched polyglycidol can serve as a critical building block for the synthesis of innovative biocompatible degradable hydrogels that are injectable. Ratio-controlled amino-oxy functionalized species were obtained by controlling the ratio of N-hydroxy phthalimide to the hydroxyl groups attached to the polyether backbone. A similar strategy was utilized to obtain ratio-controlled keto functionalized branched polyglycidols. This unique feature will allow for the tailoring of this branched PEG-like structural motif for the synthesis of novel biomaterials with tailored biochemical and biomechanical properties. 

Synthetic polymers have contributed significantly to the development of advanced scaffolds for load bearing tissue engineering applications. Despite this, there is still a need to create scaffolds that can simultaneously present multiple biophysical and biochemical properties to better mimic native cellular environments. Polyglycidol has been shown to be a biocompatible polyether polyol, that forms different, sometimes complex, polymeric architectures. Furthermore, it has multiple hydroxyl groups that are capable of numerous chemical modifications. However, little is known about the biocompatibility of modified polyglycidols and their resulting 3-D network. The overarching hypothesis for this project is that changes in the mechanical, structural, and compositional cues within a polyglycidol-based network can be tailored to influence cell responses. Therefore, as a crucial first step, we investigated the biocompatibility of functionalized polyglycidols, and the swelling, degradation, and mechanical properties of polyglycidol based hydrogels. Ongoing studies aim to show that a defined subset of biophysical and biochemical cues can be incorporated simultaneously within the polyglycidol hydrogel. Such an advanced scaffold would allow us to study the synergistic effects of various chemical and physical cues on cellular behavior. 

This work probed the thermal “switchability” from ethylene coordination/insertion to controlled radical polymerization of methyl acrylate (MA) for Brookhart-type α-diimine PdII catalysts. The investigation focused on the extremely bulky 2,6-bis(3,5-dimethylphenyl)-4-methylphenyl (Xyl4Ph) α-diimine N-substituents to probe reversible PdII–C bond activation in the MA-quenched Pd-capped PE intermediate and reversible trapping during radical MA polymerization. The substituent steric effect on the relative stability of various [PE–MA–PdII(ArN═CMeCMe═NAr)]+ chain-end structures and on the bond dissociation-free energy (BDFE) for the homolytic PdII–C bond cleavage has been assessed by DFT calculations at the full quantum mechanics (QM) and QM/molecular mechanics (QM/MM) methods. The structures comprise ester-chelated forms with the Pd atom bonded to the α, β, and γ C atoms as a result of 2,1 MA insertion into the PE–Pd bond and of subsequent chain walking, as well as related monodentate (ring-opened) forms resulting from the addition of MA or acetonitrile. The opened Cα-bonded form is electronically favored for smaller N-substituents, including 2,6-diisopropylphenyl (Dipp), particularly when MeCN is added, but the open Cγ-bonded form is preferred for the extremely bulky system with Ar = Xyl4Ph. The Pdα–C bond is the weakest one to cleave, with the BDFE decreasing as the Ar steric bulk is increased (31.8, 25.8, and 12.6 kcal mol–1 for Ph, Dipp, and Xyl4Ph, respectively). However, experimental investigations on the [PE–MA–PdII(ArN═CMeCMe═NAr)]+ (Ar = Xyl4Ph) macroinitiator do not show any evidence of radical formation under thermal activation conditions, while photolytic activation produces both TEMPO-trapped (TEMPO = 2,2,6,6-tetramethylpiperidinyloxy) and unsaturated MA-containing PE chains. The DFT investigation has highlighted a low-energy pathway for termination of the PE–MA• radicals by disproportionation, promoted by β-H elimination/dissociation and H-atom abstraction from the PdII–H intermediate by a second radical. This phenomenon appears to be the main reason for the failure of this PdII system to control the radical polymerization of MA by the OMRP (OMRP = organometallic-mediated radical polymerization) mechanism. 

Despite their industrial ubiquity, polyolefin‐polyacrylate block copolymers are challenging to synthesize due to the distinct polymerization pathways necessary for respective blocks. This study utilizes MILRad, metal–organic insertion light‐initiated radical polymerization, to synthesize polyolefin‐b‐poly(methyl acrylate) copolymer by combining palladium‐catalyzed insertion–coordination polymerization and atom transfer radical polymerization (ATRP). Brookhart‐type Pd complexes used for the living polymerization of olefins are homolytically cleaved by blue‐light irradiation, generating polyolefin‐based macroradicals, which are trapped with functional nitroxide derivatives forming ATRP macroinitiators. ATRP in the presence of Cu(0), that is, supplemental activators and reducing agents , is used to polymerize methyl acrylate. An increase in the functionalization efficiency of up to 71% is demonstrated in this study by modifying the light source and optimizing the radical trapping condition. Regardless of the radical trapping efficiency, essentially quantitative chain extension of polyolefin‐Br macroinitiator with acrylates is consistently demonstrated, indicating successful second block formation.

 

The manipulation of covalent polymer networks in the bulk or in the nanoscale seeks to broaden material property variations from an existing parent structure with the possibility to make fundamental changes in nanoparticle compositions which is otherwise difficult to accomplish through bottom up approaches. In this contribution, a parent nanoparticle network prepared by an intermolecular chain cross-linking process containing trithiocarbonate photoactive cross-linking groups has been investigated in its ability to form various novel nanonetworks through a photogrowth expansion process using 10-phenylphenothiazine (PTH) as a photoredox catayst under violet light irradiation, incorporating statistical copolymers and block copolymers into the existing nanonetwork. Hydrophilic and hydrophobic homo-and statistical copolymer incorporation leads to custom designed, tailored nanonetworks and stimuli-responsive behavior. For example, particles expanded by incorporation of PNIPAAM collapse after thermoresponsive behavior above 32 °C and shrink to approximately half of their original size. Furthermore, ABA triblocks and ABABA pentablocks of MA, TFEA, NIPAAM and t BA are integrated with a high degree of control into a parent particle. In this work, we have demonstrated the feasibility of parent nanonetwork structures to expand their network architecture reaching up to the microscale range to give soluble soft matter networks, containing controlled compositions of homopolymers, statistical copolymers, or pentablock structures. The taught concept gives opportunities to further design and alter the network topology in confined structures to tailor properties and function.