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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. 

This work develops the Polyolefin Active‐Ester Exchange (PACE) process to afford well‐defined polyolefin–polyvinyl block copolymers. α‐Diimine Pd^II‐catalyzed olefin polymerizations were investigated through in‐depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro‐mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and photoiniferter reversible addition–fragmentation chain transfer (PI‐RAFT). The significant difference in the properties of polyolefin–polyacrylamide block copolymers was harnessed to carry out polymerization‐induced self‐assembly (PISA) and study the nanostructure behaviors.

 

This work develops the Polyolefin Active‐Ester Exchange (PACE) process to afford well‐defined polyolefin–polyvinyl block copolymers. α‐Diimine Pd^II‐catalyzed olefin polymerizations were investigated through in‐depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro‐mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and photoiniferter reversible addition–fragmentation chain transfer (PI‐RAFT). The significant difference in the properties of polyolefin–polyacrylamide block copolymers was harnessed to carry out polymerization‐induced self‐assembly (PISA) and study the nanostructure behaviors.

 

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. 

Practical synthesis of polyolefin–polyvinyl block copolymers remains a challenge for transition‐metal catalyzed polymerizations. Common approaches functionalize polyolefins for post‐radical polymerization via insertion methods, yet sacrifice the livingness of the olefin polymerization. This work identifies an orthogonal radical/spin coupling technique which affords tandem living insertion and controlled radical polymerization. The broad tolerance of this coupling technique has been demonstrated for diverse radical/spin traps such as 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide (TIPNO), 1‐oxyl‐(2,2,6,6‐tetramethylpiperidine) ‐4‐yl‐α‐bromoisobutyrate (TEMPO‐Br), andN‐tert‐butyl‐α‐phenylnitrone (PBN). Subsequent controlled radical polymerization is demonstrated with nitroxide‐mediated polymerization (NMP) and atom transfer radical polymerization (ATRP), yielding polyolefin–polyvinyl di‐ and triblock copolymers (Đ<1.3) with acrylic, vinylic and styrenic segments. These findings highlight radical trapping as an approach to expand the scope of polyolefin‐functionalization techniques to access polyolefin macroinitiators.

 

Practical synthesis of polyolefin–polyvinyl block copolymers remains a challenge for transition‐metal catalyzed polymerizations. Common approaches functionalize polyolefins for post‐radical polymerization via insertion methods, yet sacrifice the livingness of the olefin polymerization. This work identifies an orthogonal radical/spin coupling technique which affords tandem living insertion and controlled radical polymerization. The broad tolerance of this coupling technique has been demonstrated for diverse radical/spin traps such as 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide (TIPNO), 1‐oxyl‐(2,2,6,6‐tetramethylpiperidine) ‐4‐yl‐α‐bromoisobutyrate (TEMPO‐Br), andN‐tert‐butyl‐α‐phenylnitrone (PBN). Subsequent controlled radical polymerization is demonstrated with nitroxide‐mediated polymerization (NMP) and atom transfer radical polymerization (ATRP), yielding polyolefin–polyvinyl di‐ and triblock copolymers (Đ<1.3) with acrylic, vinylic and styrenic segments. These findings highlight radical trapping as an approach to expand the scope of polyolefin‐functionalization techniques to access polyolefin macroinitiators.