ABSTRACT:The polysilsesquioxane having dithiocarbamate groups was utilized for the graftation of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAA) under thermal polymerization conditions. The controlled graft polymerization through RAFT process proceeded effectively to give several kinds of block copolymer of NIPAM and DMAA without formation of gel product, in which the sequence and the number of the monomer units were changed. The introduction of the block copolymers provided an amphiphilic property to the polysilsesquioxane. The hydrophilic property, which was shown as solubility in water and contact angle, was affected by the sequence and the number of the monomer units in the graft chain. Furthermore, as the expected property due to a hydrophobic aggregation of NIPAM units, the contact angles of the grafted polysilsesquioxanes measured at 60 C were larger than those at 23 C.[doi:10.1295/polymj.PJ2006126] KEY WORDS Amphiphilic Polysilsesquioxane / N-Isopropylacrylamide / RAFT Process / Graft Polymerization / Recently, various investigations on oligomeric and polymeric silsesquioxanes, which stress on the modifications by various organic functional groups, have been presented from the interests in a useful hybrid material. [1][2][3][4][5][6][7][8][9] As an effective procedure for the modifications of the silsesquioxanes, the graft polymerization from polysiloxane backbone is nominated. [10][11][12][13][14][15][16] This procedure enables to provide the additional functions based on the polymeric components without loosing the essential properties of inorganic polysiloxane backbone such as durability for heat and weatherability. We also have investigated on the graft polymerizations from polysilsesquioxanes, which intended to develop the new multi-functional hybrid materials. [17][18][19] As an example of such graftings, the introduction of copolymer of N,N-dimethylacrylamide (DMAA) and N-isopropylacrylamide (NIPAM) was reported in the previous work. 20 The obtained polysilsesquioxane derivative successfully showed amphiphilicity and thermoresponsive phase separation. The investigations concerning the later property caused by polymerized NIPAM (polyNIPAM) have been widely developed and various applications are proposed such as microencapsulation, biosensor, and drug delivery. [21][22][23][24][25] Such facts support the expectation that the polysilsesquioxane, combined the inorganic polysiloxane backbone with the thermoresponsive and amphiphilic graft chains, will be a candidate for high performance hybrid materials. [26][27][28] Our previous grafting was conducted through free radical polymerization by the use of mercapto groups on the polysilsesquioxane backbone. 20 In the use of the procedure, the graft chain was essentially consisted of the random copolymer of NIPAM with DMAA (polyNIPAM-ran-polyDMAA) and the number of introduced monomer units was limited because of inactivation of radical species during the polymerization. On the other hand, the investigations on such functional polymer are prog...

The adhesive force generated by a small short-term pressure, called tack, is measured by a probe tack test on pressure-sensitive adhesives (PSAs); the maximum force is evaluated by cavity growth at the interface between the PSA layer and the probe surface. As the PSA layer becomes thinner, it is more difficult to measure the tack with a cylindrical probe because of the uneven contact resulting from misalignment. A spherical probe is preferable to obtain reproducible contact on the PSA layer, but the contact area should be taken into account if the contact pressure affects the tack performance. Tack was measured on PSAs with various thicknesses in different contact areas to clarify their effect. The results showed that a larger contact area on a thinner PSA generated higher adhesive stress with larger strain. It was found that the maximum adhesive stress was not affected by the contact pressure, but it was strongly correlated to the contact radius divided by the PSA thickness. In addition, a video microscope observation showed that, in all of the experimental cases, the adhesive stress always reached the maximum when cavities were generated at the interface between the PSA and probe surface. Therefore, the criterion of cavity growth was introduced for the evaluation of the maximum adhesive stress. As a result, the experimental results, even at different release rates, were in good agreement with the estimation by considering the effect of confining a thin layer. Furthermore, the theoretical estimation indicated the ultimate value, which was not dependent upon the PSA thickness or contact area. It was defined as a material property, referred to as the "ultimate tack strength" of PSAs.

Polysilsesquioxane with phenyl and chloromethylphenyl groups (PCPSQ) was prepared readily from phenyltrimethoxysilane and [2‐(chloromethylphenyl)ethyl]trimethoxysilane under acidic conditions. Polymerization with chloromethylphenyl groups on PCPSQ with methyl methacrylate (MMA) was conducted in the presence of a catalytic amount of copper(I) bromide and (−)‐sparteine. Atom transfer radical polymerization yielded a graft polymer (PCPSQ‐g‐MMA) efficiently, and no gelation was observed. The process was also applied to the preparation of graft block copolymers on PCPSQ with several methacrylate monomers. An advantage of the graft hybrid polymers was shown in improved thermal behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4212–4221, 2004

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