Synthesis and thermal crosslinking of carbosiloxane and oligo(oxyethylene) polymers

Abstract

Acyclic diene metathesis (ADMET) polymerization has been used in the synthesis of telechelic materials using alkoxyfunctionalized carbosiloxane or oligo(oxyethylene)-based polymers, varying from internal to terminal cured materials or the combination of them. Previous investigations demonstrated that introduction of chain-end crosslinking improves the stress-strain behavior of such materials. A series of saturated and unsaturated carbosiloxane and oligo(oxyethylene)-based polymers were synthesized by ADMET polymerization using silacyclobutane as chain-end, thermally induced crosslinker. The carbosiloxane derivatives presented pure amorphous behavior, whereas the oligo(oxyethylene) polymers were semicrystalline. The thermal curing process was monitored by differential scanning calorimetry via the exotherm between 160 and 210 C. Mechanical properties on thermoset polymers were measured, where cured polymers showed moduli from 0.6 to 9.3 MPa, tensile strengths from 0.3 to 1.0 MPa, and elongations from 12 to 76%.

Strategies to improve micelle stability for drug delivery

“…The reversible boronate ester has been used to crosslink micelles to enhance stability and improve the release kinetics with external stimuli. For example, boronic acid containing polymers and catechol containing polymers were reported to form crosslinked micelles as drug delivery carriers [91, 92]. Using FRET technology to evaluate micelle integrity, such crosslinked micelles showed prolonged blood circulation.…”

“…When triggered by the low pH in a typical tumor environment, the resulting micelles could quickly release their drug payload. The preferential accumulation of the drug in tumors was observed by imaging of harvested organs [91]. Nevertheless, the sensitivity of the boronate system to oxidative conditions, such as hydroxyl peroxide [93], is a concern with respect to toxicity because hydroxyl peroxide is necessary in the redox signaling pathway of normally-functioning cells [94].…”

“…Furthermore, using a dendrimer as the core of the micelle system also enables the combination with covalently crosslinking to facilitate the drug release at the targeted site. For example, the cross-linkable telodendrimer pair, PEG-catechol-cholic acid were prepared and crosslinked via formation of a boronate ester [91]. This ester might hydrolyze in response to the acidic pH of the tumor environment, leading to a burst release of the encapsulated drugs.…”

Carboxy-Telechelic Polyolefins in Cross-Linked Elastomers

“…Although the tensile strength of cross-linked elastomers depends on several factors, the overall tensile strength of these materials are higher than the average tensile strength of filler free silicone elastomers (0.35 MPa) 31 or related end-crosslinked poly(carbosiloxane) reported by Delgado et al (0.4 MPa). 32 Tensile hysteresis of cured elastomers (ASTM D1708 microtensile bars, Table 4, Figures S18−S21) showed less than 12% and 9% energy loss for the first and second cycles, respectively. The small loss in storage energy denotes minimal loss of mechanical integrity, which is highly desirable for an elastomeric material.…”

Thermoset Elastomers Derived from Carvomenthide

“…In contrast, the tensile strengths (σ b ) of all XL-PCM samples were similar (1.14–1.24 MPa) regardless of the increased chain extender content or the PCM chain length . The mechanical strengths are comparable or superior to those of previous reported elastomers. , …”