Some aspects of the reactivity of photo‐dimerizable esters grafted onto silicone main chain polymers

Abstract

The reactivity under UV light and at room temperature of two series of photo-crosslinkable silicone polymers containing pendant cinnamic or a-cyano-8-styrylacrylic a) (CSA) esters was examined by means of UV spectroscopy. Two types of behaviour were evidenced on the basis of qualitative spectrum observation and quantitative measurements of reaction rates. Polymers with trans-cinnamic pendant groups were found to undergo during the first moments of 280 nm irradiation a fast photo-isomerization, preceding the dimerization process which takes place with a smaller rate. The mobility of the reactive cinnamic chromophores attached to the highly flexible silicone main chain leads to a collision-controlled process contrasting with the behaviour of the polymers containing more polar CSA esters. In this case, a clean dimerization with high reversibility suggests a matrix-controlled process. This is supported by kinetic data indicating a levelled reactivity for several polymers containing different amounts of CSA esters.

Photoreactivity of polymers with dimerizable side-groups: Kinetic analysis for probing morphology and molecular organization

“…At room temperature the polymers of the first series are amorphous solids 35) , whereas the second ones are viscous liquids 36) . In the functionalized polysiloxanes, the spacer is produced in the form of two isomeric structures as a consequence of the epoxy-carboxy reaction involved in the synthetic route 37) . The mole fraction of functional units having the secondary acetoxy group is typically 0.15, as indicated by NMR analysis of model polymers 38) .…”

“…This leveled reactivity with (U Dim ) 2s almost independent of the chromophore content is the expected indication that the loss of mobility upon gelation rapidly becomes more influent than the chromophore content in the photopolymers. The practical sensitivity defined as the reciprocal gel dose 37) and measured under well defined experimental conditions for the PVAm-Cin films irradiated in their neutral basic form was shown to be dependent on the square of the weight content in chromophore (Fig. 7), thus following Tsuda's model 11) .…”

Facile route to synthesis of functionalised poly(methylalkoxy)siloxane under mild and aerobic conditions in the presence of platinum catalysts

“…Moreover, organic functionalization of the polymer chain can lead to fine-tuning of physical and chemical properties of the resulting siloxanes. For example, appropriate substitution on the polysiloxane backbone can lead to diverse materials such as liquid crystals [4][5][6], cross-linking agents [7], conductive [8] and electroluminescent polymers [9], non-linear optical materials [10], and bactericides [11].…”

Photopolymers: Synthesis and Characterization of Poly(3-methacryloyloxystyryl-2-naphthyl ketone)

“…Thus, polymer 3 responded to irradiation similarly as found for cinnamic acid and its derivatives. [19,20] The photosensitivity of polymer 3 was measured in terms of the rate of disappearance of the cC2CC group with irradiation time. In chloroform solution, polymer 3 showed photoconversions of 11%, 30% and 43% after 5, 20 and 60 s of irradiation, respectively, and about 60% conversion occurred within 3 min of irradiation (Figure 5).…”