Photo-initial crosslinking

Figure 5.23 SAND can be used to modify amine-containing molecules, and then photo-initiate crosslinking to another amine-containing molecule via a ring-expansion process. The conjugates may be disrupted by reduction of the cross-bridge disulfide with DTT.

Zhuo and co-workers have synthesized PPE linkage-containing hydrogels based on PEG by photo-initial crosslinking polymerization of the... 

To study this possibility, a thin film (ca. 200 nm) of Co-PFS on Si substrate was exposed to near UV radiation (k = 350-400 nm, 450 W) for 5 min. The exposed film was developed in THF before characterization. Co-PFS was found to be a negative-tone photoresist. This appears to be consistent with photo-initiated crosslinking mechanism of acetylenes in the presence of metal carbonyls. However, it is also possible to have crossUnking in Co-PFS as a result of decarbonylation of the Co-cluster. The thickness of the film before and after UV treatment was determined by eUip-sometry. A 200-nm-thick film of Co-PFS had a thickness of ca. 170 nm after expo-sme to UV radiation and solvent development. The decrease in thickness is probably a reflection of the decreased volmne of the polymer upon crosslinking. 

Jacobine AF, Glasser DM, Nakos ST. Photo-initiated crosslinking of norbomene resins with multifunctional thiols. In Hoyle CE, Kinstle JF, eds. Radiation Curing of Polymeric Materials. ACS Series 417. Washington DC American Chemical Society 1990 160—175. 

In order for maleimide/vinyl ether photoinitiator free photopolymerization to be useful, it is important that the cured films have good thermal/UV stability. Since there are no small molecule photoinitiators added to the uncured mixture initially, there is no residual small molecule photo initiator present in the final crosslinked film. This accounts for the enhanced UV stability we have observed for cured maleimide/vinyl ether films. In addition, TGA thermograms of photocured films of the MPBM/CHVE mixture (Figure 8) exhibit excellent thermal stability, with decomposition occurring at higher temperatures than for a simple UV cured HDDA film with 3 weight percent DMAP photoinitiator. (Such thermal stability would be... 

Yang H, Lazos D, Ulbricht M. Thin, highly crosslinked polymer layer synthesized via photo-initiated graft copolymerization on a self-assembled-monolayer-coated gold surface. J Appl Polym Sci 2005 97 158-164. 

Photo-initiated polymerization of pendant vinyl ether groups attached to a polystyrene backbone has been used as a convenient method of crosslinking. However, the potential commerical importance of this is marred by the fact that a slow thermal initiation involving the acceptor is also possible and occurs, for example, during processing of the carrier polymer. ... 

To determine if either of these answers were correct, the properties of a series of polyurethane networks which contained photo labile disulfide bonds were studied (7). The creep curve of the s imple in the initial crosslink density state (comparable to Vq) was determined in the usual way. Then, after complete recovery, another creep experiment was started but, at time t during this run, the sample was subjected to ultraviolet irradiation which photochemlcally broke some of the network chains. 

AI BN absorbs and decomposes +o radicals with a quantum yield of 0.43 (0.86 radicals per proton) (28K No photocross I inking occurred. This seemed to show that the crosslinking in this system is not radical-initiated. (It might be mentioned that the only possibility left open by this experiment for a radical process is that direct photo-initiation produces a radical of much greater reactivity than (CH3>2C-CN which is able to initiate cross I inking in the presence of the acceptor.)... 

The crosslinking process is specially extensive in the solid state in the presence of external initiators, photo-initiators and sensitizers [Refs. 40, 362, 393, 489, 503, 505, 632]. For example the decomposition of di-tert-butylperoxalate in polypropylene in the absence of oxygen gives a tightly crosslinked polymer. When the decomposition is carried out in the presence of oxygen, the polymer instead softens [405]. Benzophenone and its derivatives induce the crosslinking of solid polyethylene on exposure to UV light [Refs. 138, 469, 470, 665]. Table 4 shows the influence of various photosensitizers on the amounts of the gel fraction produced in solid polyethylene exposed to UV radiation. 

Keywords Acrylates Crosslinking Dual cure Epoxides Glass laminates Interpenetrating polymer networks Isocyanates Photo initiated cationic polymerisation Photoinitiators Photopolymerisation Pressure sensitive adhesives Release coatings Structural adhesives Thiol/polyene UV radiation curing Vinyl ethers. 

Network properties. The UV-cured materials obtained by crosslinking polymerization of mixed donor-acceptor monomers or by crosslinking copolymerization of multifunctional allyl monomer with an acceptor comonomer in presence of 1 wt-% of TPO (diphenyl-(2,4,6)-tri-methylbenzoyl)phoshine oxide) as photo-initiator were placed between glass lids allowing for the formation of 1 mm-thick samples after... 

Mixed donor-acceptor monomers. The glass transition temperature of FAIR polymerized with 1 wt-% of TPO as photo-initiator gradually increases with irradiation time (Fig. 7) and conversion (Fig. 8). Furthermore, the glass transition broadens as the crosslinking proceeds due to increasing heterogeneity within the material. For a final conversion of... 

A new and elegant solvent-free approach to main chain LCEs was found by Yang et al. [39] who, based on the work on linear LC polymers by Lub et al. [40 2], made use of the photo-induced addition of thiols and olefins (click-chemistry) to synthesize nematic polymer networks. Starting from a mixture of the mesogen, a tetrafunctional crosslinker and a photo-initiator networks with a around 170 °C were obtained by UV crossUnking (Scheme 8). 

Another important molecule which is very largely used in several applications of hybrids is 3-methacryloxypropyltrimethoxy silane (MPTMS). This organically modified aUcoxide is characterized by a C=C double bond that can be opened to form an organic network the crosslinking reactions are generally thermally induced or catalyzed by a photo-initiator. FT-Raman can be used, in combination with FTIR, to follow the polymerization. The assignments of the most important modes in MPTMS are reported in Table 7-2. 

The crosslinking of acrylic acid esters in the presence of photo-initiators... 

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