P-Acetoxystyrene

The p-acetoxystyrene monomer, precursor of polymer III, is prepared from p-hydroxyacetophenone using the procedure of Corson et al. (14) which involves acetylation of the phenolic group followed by catalytic hydrogenation of the ketone and dehydration of the resulting benzylic alcohol as shown in Scheme 3. 

This reaction sequence is satisfactory although the overall yield is approximately 50%. A different route for the preparation of poly(p-acetoxystyrene) involves the direct acetylation of poly (p-hydroxystyrene) with acetic anhydride. The main problem with this approach is the lack of commercial availability of high purity poly(p-hydroxystyrene). 

Reactive Pendant Groups on Styrene Backbones. The photolysis of p-acetoxystyrene (III) in acetonitrile solution gives results which are similar to those obtained in a comparable study in the solid-state using 1 /tm thick films in both cases the expected rearrangement is taking place as shown on Scheme 7. 

Fries rearrangement of aromatic formate esters suggests that phenols are the major products (.24) obtained in the reaction. As poly(p-hydroxystyrene) is remarkably clear in the deep UV, it is likely that poly(p-formyloxystyrene) will not suffer from the same problem of photostabilization upon exposure as was the case with poly (p-acetoxystyrene). This expectation was confirmed by our study of the photo-Fries reaction of p-cresyl formate no ortho rearranged product was isolated after reaction while p-cresol and a small amount of starting material were obtained. 

Preparation of p-Acetoxystyrene This compound was prepared by a modification of the procedure of Corson et al. (14), using p-hydroxyacetophenone as a starting material. Fractional distillation of the crude material gave a 46% yield of p-acetoxystyrene with b.p. 69-72 °C/0.5 mm Hg (lit. 73-75°C/0.6 mm Hg14). 

Preparation of Poly(p-Acetoxystyrene) (III) A 9.95 g aliquot of p-acetoxystyrene and 0.0997 g AIBN were added to 60 ml of toluene in a 100 ml 2-necked round-bottomed flask equipped with a water-cooled condenser, nitrogen inlet and outlet. The mixture was heated to 70-75"C under nitrogen for 24 hours. Precipitation of the polymeric solution in methanol and subsequent filtering and washing with additional methanol gave a white powder. Drying in the vacuum oven overnight at room temperature, afforded 5.46 g (55%) of poly(p-acetoxystyrene) (III). (Mn = 1.17 x 104, Mz = 2.06 x 104, polydispersity — 1.76 (gpc), Mn — 1.85 x 4). 

Solution Photolysis of Poly(p-acetoxystyrene) A 2.576 g sample of III was dissolved in 350 ml of acetonitrile and placed in a 500 ml Hanovia reactor equipped with a water-cooled quartz finger and 500 watt mercury arc lamp, condenser, nitrogen inlet and bubbler. The solution was irradiated for a total of... 

The precipitate was filtered, washed with additional methanol and dried overnight in the vacuum oven at 40°C to give 1.82 g of polymer (71% recovery). H-NMR spectral analysis of the product confirmed that it contained both p-acetoxystyrene and 2-hydroxy-5-vinylacetophenone repeating units in a molar ratio of 0.52 0.48. The polymer had M = 4.50 x 10, Mz — 3.62 x 5, polydispersity = 8.06 (gpc). The spectral data which is listed below corresponds to the product after 39.5 hrs. of irradiation. 

Aberration, spherical, 7 Acetaldehyde, in Novolak resins, 346 p-Acetamidostyrene, preparation, 286 Acetophenone derivatives, 457 p-Acetoxystyrene, preparation, 271 Acrylate systems, UV-laser initiation, 222 Acrylic backbones, pendant groups, 277-80... 

I. Preparation of Poly(2-Ethyl-2-Adamantyl Methacrylate-co-p-Acetoxystyrene)... 

A reaction flask was charged with 2-ethyl-2-adamantyl methacrylate (0.24 mol), p-acetoxystyrene (0.56 mol), and isopropanol (279 g) and then heated to 75°C. This mixture was next treated with dimethyl-2,2 -azobis(2-methylpropionate) (0.048 mol) dissolved in isopropanol (22.11 g), stirred 20 minutes, and finally refluxed for... 

Block copolymers with hydroxyl segments were prepared by various ways An example utilizes the copper-catalyzed sequential copolymerizations of nBA and 2-[(trimethylsilyl)oxy]ethyl acrylate by the macroinitiator method into B-31 to B-33. The copolymers were then hydrolyzed into amphiphilic forms by deprotection of the silyl groups.313 A direct chain-extension reaction of polystyrene and PMMA with HEMA also afforded similar block copolymers with hydroxyl segments (B-34 and B-35).241-243 In block polymer B-36, a hydroxy-functionalized acrylamide provides a hydrophilic segment.117 Block copolymers of styrene and p-acetoxystyrene (B-37 to B-39), prepared by iron... 

There have been several other well-defined random copolymers based on styrene derivatives prepared with trimethylsilylstyrene [123], p-acetoxystyrene [124], p-methoxymethylstyrene, and p-acetoxymethylstyrene [125]. The resulting copolymers served as precursors to functional materials with Si, phenol, or hydroxybenzyl moieties, or for subsequent crosslinking or grafting processes. 

Scheme 7.17 Photo-Friess rearrangement reaction of poiy(p-acetoxystyrene) resuiting in the formation of functionaiized poiy(vinyi phenoi).

A cationic to ATRP transformation was also used in the synthesis of triblock copolymers with polyisobutylene (PIB) as the middle sequence. These materials are particularly useful as thermoplastic elastomers. In this case, a few units of styrene were added to living difunctional PIB after the isobutylene had reacted. The isolated PIBs could act as bifunctional macroinitiators for ATRP [86]. A similar strategy was used by Batsberg et al. [87] for the synthesis of block copolymers of isobutylene with p-acetoxystyrene (PlB-fo-PAcSt) or styrene (PlB-b-PSt). 

NMRP has been used for the preparation of diblock copolymers of St, other styrenic derivatives, and various different monomers such as PAcOSt-l -PSt (AcOSt 4-acetoxystyrene), PVBCl-li-PSt (VBCl vinylbenzylchloride), PBA-b-PSt, PSi-b-P2VP, PMMA-li-PSt, and rod-coil block copolymers consisting of p-acetoxystyrene as the coil segment and... 

Moreover, ABA triblock copolymers with PIB as the middle sequence were synthesized by cationic-to-ATRP transformation. In this case, a few units of St were added to living difanctional PIB after the IB had reacted. The isolated PIBs could act as bifnnctional macroinitiators for ATRP of St, MA, MMA, and isobornyl acrylate (iBoA). Likewise, Chen employed 1-chloro-l-phenyl ethyl-telechelic PIB obtained by cationic living polymerization for the preparation of triblock copolymers of IB with p-acetoxystyrene (PAcOSt-I -PIB-l7-PAcOSt) or St (PSt-l -PIB-l7-PSt) (Scheme 52). 

A second possibility to attach the chromophores to the polymer backbone is the polymer analogue modification with the appropriate electron or hole transporting unit. Complete substitution of poly(p-acetoxystyrene) was achieved through Williamson condensation with chloromethylstilbene resulting in a polymer with Mn = 22,000 Da, Mw/Mn = 2.1 and rg = 71 °C (Scheme 35 [96]). 

Abbreviations AS, p-acetoxystyrene S, styrene AN, acrylonitrile MA, methyl acrylate VC, vinyl chloride VA, vinyl acetate, MMA, methyl methacrylate MAA, methacryhc add. 

Figure 7 Synthesis of poly(vmylpyrrolidone-co-isobutylstyryl-POSS) and poly-(p-acetoxystyrene-co-isobutylstyryl-POSS).

Dele 1995 Deleuze, H. and Sherrington, D.C., Poly(p-acetoxystyrene) Resin A Prospective New Support for Combinatorial Synthesis, J. Chem. Soc., Perkin Trans. 2, (1995) 2217-2221. 

In order to synthesize ot,ct)-diacetoxy-PDVB, DVB and p-acetoxystyrene were copolymerized by ACCIO4 in benzene at 70 °C (Scheme 43). ... 

Another field of application is the design of polymeric imaging systems. The lithographic potential of a photochemical reaction is based on the possibility of dissolving selectively either the exposed or the unexposed areas of a polymer film. Because aU the photo-Fries products are phenols, the irradiated polyester should be easily dissolved in aqueous base, while the unchanged starting material should remain undissolved. The key photochemical step of this sequence is shown above for the conversion of poly(p-acetoxystyrene) (34) into (35) (Scheme 9). ... 

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