Control of Intermolecular Cross-Linking Reaction in Free-Radical Cross-Linking Monovinyl/Divinyl Copolymerizations by the Aid of Amphiphilic Nature of Primary Polymer Chains and Cross-Link Units with Opposite Polarities

Abstract

The control of the intermolecular cross-linking reaction in free-radical cross-linking monovinyl/divinyl copolymerizations resulting in amphiphilic network polymers was attempted by the aid of amphiphilic nature of primary polymer chains and cross-link units with opposite polarities. First, benzyl methacrylate (BzMA)/tricosaethylene glycol dimethacrylate (PEGDMA-23) (95/5) copolymerizations in 1,4-dioxane (DO) and DO/H 2O (85/15) mixed solvent were investigated. The assembly of short primary polymer chains induced the restricted motion of propagating polymer radical, leading to a suppressed increment of molecular weight with conversion. Second, 2-hydroxyethyl methacrylate (HEMA)/henicosapropylene glycol dimethacrylate (PPGDMA-21) (95/5) copolymerizations in DO, DO/H 2O (80/20) mixture, and DO/H2O (70/30) mixture were explored. The assembly of nonpolar cross-link units led to an enhanced occurrence of intermolecular cross-linking reaction. Moreover, the assembly of polar primary polymer chains consisting of poly(HEMA) in DO suppressed the cross-linking reaction as is the case with BzMA/PEGDMA-23 (95/5) copolymerizations. Then, the solvent effect on gelation was generalized by using various solvents. Especially, our attention was focused on acetonitrile (ACN) and N,N-dimethylformamide (DMF) as solvents because the resulting gel in HEMA/PPGDMA-21 (95/5) copolymerization swelled in DMF but shrank in ACN despite almost the same solubility parameters for both solvents. Thus, both primary polymer chains and cross-link units of amphiphilic prepolymers would not assemble in DMF, whereas primary polymer chains having hydroxyl groups would assemble in ACN. The assembly of short primary polymer chains in ACN led to a suppressed increment of molecular weight with conversion as a reflection of the restricted motion of propagating polymer radical. Conclusively, the assembly of short primary polymer chains suppressed the occurrence of intermolecular cross-linking reaction, whereas the assembly of long cross-link units promoted it.

Poly(N-isopropylacrylamide) hydrogels with improved shrinking kinetics by RAFT polymerization

“…So during the time before gelation the living primary chains will further react with monomer and crosslinker to produce branched and hyperbranched structure [23,24,36]. Notably, the vinyl-type network polymers formed via highly branched prepolymer have abundant dangling chains as their characteristic feature because terminal parts of prepolymer chain would be dangling chains [31,37]. So some of the branched chains will remain in the network structure and lead to RAFT gels with a number of dangling chains when gelation occurs.…”

“…So some of the branched chains will remain in the network structure and lead to RAFT gels with a number of dangling chains when gelation occurs. However, it is difficult to obtain the amount (or density) of dangling chains quantitatively on the basis of the available data at this stage because the insoluble, infusible properties of network result in the lack of suitable analytical methods for their characterization [37]. Fig.…”

A novel shape memory polymer based on conetworks

“…It was found that the samples successfully regained their original shape in less than 15 s in hot water, with most of the recovery being accomplished within the first couple of seconds. Regretfully, only one cycle was found unless dried in air before the next cycle, which is quite different from the results in air, indicating that the water dissipated into the polymeric matrix has pronounced effect on their microstructure [5,24]. It can be explained that the PMMA/PEGDA CNs are amphiphilic to some extent.…”

Construction of Crosslink‐System‐Materials Utilizing Designed Network‐Polymer‐Precursor Modules

“…[22] This ideal NPP formation was developed to the preparation of novel amphiphilic polymers [11] and, moreover, amphiphilic CSMs. [37][38][39] As the latter case of controlling intramolecular crosslinking in the free-radical crosslinking monovinyl/divinyl copolymerization, we pursued the intramolecular crosslinking reaction to generate the net or loop structure as an origin of CSM, although the locally extensive occurrence of intramolecular crosslinking leads to microgelation. [3,[40][41][42][43][44] Eventually, we reached the preparation of novel loopstructures containing net polymers as the ultimate precursors of CSM consisting of microgel-like NPPs.…”

“…Thus, we could construct novel CSMs utilizing designed NPPs as modules, providing semi-interpenetrating polymer network (IPN) involving DAT networks and linear poly(BzMA), [46] and simultaneous-IPN between polymethacrylate and polyurethane networks, [47][48][49] novel amphiphilic CSMs [37][38][39]50,51] and patchwork-type CSMs, [52] and so on. Another example is concerned with the emulsion crosslinking (co)polymerization of multivinyl monomers, [53] especially focusing on the formation of reactive crosslinked polymer nanoparticles (CPNs) as models of microgels, with the intention of clarifying the correlation of the network structure with the reactivity of resulting CPNs which would be useful as functionalized polymeric materials.…”