Bottlebrush Networks: A Primer for Advanced Architectures

Bottlebrush networks (BBNs) are an exciting new class of materials with interesting physical properties derived from their unique architecture. While great strides have been made in our fundamental understanding of bottlebrush polymers and networks, an interdisciplinary approach is necessary for the field to accelerate advancements. This review aims to act as a primer to BBN chemistry and physics for both new and current members of the community. In addition to providing an overview of contemporary BBN synthetic methods, we developed a workflow and desktop application (LengthScale), enabling bottlebrush physics to be more approachable. We conclude by addressing several topical issues and asking a series of pointed questions to stimulate conversation within the community.

Photoinduced hydrosilylation through hydrogen abstraction: an NMR and computational study of the structural effect of silane

The hydrosilylation reaction, describing the addition of Si–H bonds to unsaturated bonds, is performed in the presence of catalysts, usually highly active platinum catalysts. This work focuses on the study of a photoinduced hydrosilylation by the use of benzophenone which promotes the addition reaction of olefin on different hydrosilanes. The reactivity of silanes towards addition onto the double bond during hydrosilylation appears to depend on their structure. It was observed that the consumption of Si–H and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C functional groups increases with the irradiation time, and reaches a maximum of approx. 51% in the case of diphenylsilane. The hydrosilylation products are determined with ¹H NMR, HSQC, DEPT, COSY and ¹³C NMR. The main product corresponds to the single adduct of the silyl radical onto the double bond. Substitution of the Si–H bond by two or three phenyls groups (triphenylsilane, diphenysilane) enhances the yield of the reaction, although diphenylsilane was found to be more efficient than triphenylsilane because of its lower steric hindrance. The ketyl radical formed after hydrogen abstraction by the triplet state of benzophenone likely forms benzopinacol, a reaction which reduces the overall yield of the hydrosilylation reaction. All these experiments are in line with DFT calculations of the Gibbs free energy of the reactions involved. This sheds new light on the photoinduced hydrosilylation process and opens the way to more active combinations of photoinitiator/silane/vinylsilane systems.

Factors affecting photoinduced hydrosylilation are identified and open new opportunities.

Radiation curable polysiloxane: synthesis to applications

Among the different types of specialty polymers, polysiloxane finds its position in the pyramid's apex in terms of its performance attributes. Its unique structural features result in it having superior performance benefits over wide operational conditions. Hence, polysiloxanes are used in various industries. Like other polymers, to effectively use polysiloxanes, curing is a non-negotiable fact. Therefore, polysiloxanes are cured using different chemistries such as addition, condensation, and peroxy-mediated methods, etc. However, recently, it has been noted that there is a strong impetus towards developing radiation-curable polysiloxanes. A faster turnover time, higher yield, and marginal involvement in the release of any toxic by-products has resulted in the widespread acceptance of radiation curing techniques. This review article provides insight into the various facets of polysiloxane chemistry, the synthesis of radiation curable polysiloxane, and the curing methodology of polysiloxane using radiation sources such as ultraviolet, electron beam, and gamma radiation. We further provide an account of the various applications of such radiation-curable polysiloxanes.

Influence of the tetraalkoxysilane crosslinker on the properties of polysiloxane-based elastomers prepared by the Lewis acid-catalysed Piers-Rubinsztajn reaction

We investigate the influence of the tetrafunctional alkoxysilan R-groups, with a range of sterics and electronics. This is through a solvent free polysiloxane network formation under ambient conditions using Lewis acid catalysed Piers-Rubinsztajn (PR) reaction.

Cross-linked polydimethylsiloxane colloid as novel contrast agent for gastrointestinal magnetic resonance imaging: Transient nuclear Overhauser effect within the interface

With good contrast in T₁ and T₂ weighted imaging as well as low toxicity in 3- (4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, this work proposes the cross-linked polydimethylsiloxane colloids as a novel non-ionic contrast agent for gastrointestinal magnetic resonance imaging. The experiments of nuclear magnetic resonance spectra and relaxation show that within the interface of the colloids, there are nuclear Overhauser effect and transient nuclear Overhauser effect (cross-relaxation). Regarding the longitudinal relaxation experiments of CH₂CH₂O segments of Tween 80, a two spins system is found and modeled well by the equation IZ-I0= S0((1-X) e-tD1 -(1+X) e-tT1) which is deduced based on the transient nuclear Overhauser effect proposed by Solomon. The arbitrary constant X is additionally added with the initial conditions (I_z - I₀)_t=0 = -2XS₀ and (S_z - S₀)_t=0 = -2S₀. For the two spins system, D₁ and T₁ are corresponding to longitudinal relaxation times of the bound water and the CH₂CH₂O respectively. Concerning the transverse relaxation experiments of the CH₂CH₂O, they agree with the equation with three exponential decays, defined by three relaxation times, likely corresponding to three mechanisms. These mechanisms possibly are intramolecular and intermolecular dipole-dipole (DD) interactions and scalar coupling. Within the interface, hydrogen bonding causes the positive nuclear Overhauser effect of the CH₂CH₂O's nuclear magnetic resonance spectra, the transient nuclear Overhauser effect of the CH₂CH₂O's longitudinal relaxation experiments and the intermolecular dipole-dipole interactions of the CH₂CH₂O's transverse relaxation experiments.

Facile Functionalization of Poly(Dimethylsiloxane) Elastomer by Varying Content of Hydridosilyl Groups in a Crosslinker

Crosslinked poly(dimethylsiloxane) (PDMS) has been widely used as a dielectric elastomer for electrically driven actuators because it exhibits high elasticity, low initial modulus, and excellent moldability in spite of low dielectric constant. However, further improvement in the characteristics of the PDMS elastomer is not easy due to its chemical non-reactivity. Here, we report a simple method for functionalizing the elastomer by varying content of hydridosilyl groups in PDMS acted as a crosslinker. We synthesized poly(dimethylsiloxane-co-methylvinylsiloxane) (VPDMS) and poly(dimethylsiloxane-co-methylsiloxane) (HPDMS). Tri(ethylene glycol) divinyl ether (TEGDE) as a polar molecule was added to the mixture of VPDMS and HPDMS. TEGDE was reacted to the hydridosilyl group in HPDMS during crosslinking between VPDMS and HPDMS in the presence of platinum as a catalyst. Permittivity of the crosslinked film increased from ca. 25 to 36 pF/m at 10 kHz without a decline in other physical properties such as transparency and elasticity (T > 85%, E ~150 kPa, ɛ ~270%). It depends on the hydridosilyl group content of HPDMS. The chemical introduction of a new molecule into the hydridosilyl group in HPDMS during crosslinking would provide a facile, effective method of modifying the PDMS elastomers.

Self-crosslinkable and modifiable polysiloxanes possessing Meldrum's acid groups

Meldrum's acid functionalized poly(dimethylsiloxane)s exhibiting self-crosslinking and post-modifiable features.