T-Butyl methacrylate

Polymerization of t-butyl methacrylate initiated by lithium compounds in toluene yields 100% isotactic polymers 64,65), and significantly, of a nearly uniform molecular-weight, while the isotactic polymethyl methacrylate formed under these conditions has a bimodal distribution. Significantly, the propagation of the lithium pairs of the t-Bu ester carbanion, is faster in toluene than in THF. In hydrocarbon solvents the monomers seem to interact strongly with the Li+ cations in the transition state of the addition, while the conventional direct monomer interaction with carbanions, that requires partial dissociation of ion-pair in the transition state of propagation, governs the addition in ethereal solvents. 

The simple and clean polymerization of t-butyl methacrylate provides an opportunity to produce well defined, poly-electrolytes of uniform size, because this poly-ester, similarly to its Si(CH3)3 analogue i9), is readily hydrolysed by acids into polymethacry-lic acid. Furthermore, as pointed out by Muller 36), it becomes possible to produce... 

Some tailor-made homopolymers can serve as starting points for chemical modifications to yield new species. Poly(hydroxyethyl methacrylate) and poly(glyceryl methacrylate) 16), already mentioned, are obtained upon hydrolysis of the OH-protecting groups that allow the anionic polymerization to proceed. Another example is the acid hydrolysis of poly(t-butyl methacrylate), a reaction which proceeds easily to completion, yielding poly(methacrylic acid) of known degree of polymerization and narrow molecular weight distribution 44 45). 

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

The alkyl methacrylate monomers were available from various sources. Isobutyl methacrylate (IBMA) (Rohm and Haas) and t-butyl methacrylate (TBMA) (Rohm Tech) may be purified first by distillation from CaH, followed by distillation from trialkyl aluminum reagents as described in detail earlier (20,21). In particular, t-butyl methacrylate (b.pt. 150°C) was successfully purified by distillation, from triethyl aluminum containing small amounts of diisobutyl aluminum hydride. The trialkyl aluminum and dialkyl aluminum hydride reagents were obtained from the Ethyl Corporation as 25 weight percent solutions in hexane. The initiator, -butyllithium, was obtained from the Lithco Division of FMC, and analyzed by the Gilman "double titration" (22). 

Hydrolysis of Poly(t Butyl Methacrylate) Containing Block... 

A TEA/DIBAH mixture can be added to cold (-78°C) monomer until the stable colored complex forms. The purification reaction is then allowed to proceed for 60 minutes at room temperature. This procedure allows for removal of impurities without reduction of the ester. Significantly narrower gel permeation chromatograms (Mw/Mn <1.25) of poly(t-butyl methacrylate) are obtained when the samples are prepared from TEA/DIBAH purified monomer. 

Various substituted styrene-alkyl methacrylate block copolymers and all-acrylic block copolymers have been synthesized in a controlled fashion demonstrating predictable molecular weight and narrow molecular weight distributions. Table I depicts various poly (t-butylstyrene)-b-poly(t-butyl methacrylate) (PTBS-PTBMA) and poly(methyl methacrylate)-b-poly(t-butyl methacrylate) (PMMA-PTBMA) samples. In addition, all-acrylic block copolymers based on poly(2-ethylhexyl methacrylate)-b-poly(t-butyl methacrylate) have been recently synthesized and offer many unique possibilities due to the low glass transition temperature of PEHMA. In most cases, a range of 5-25 wt.% of alkyl methacrylate was incorporated into the block copolymer. This composition not only facilitated solubility during subsequent hydrolysis but also limited the maximum level of derived ionic functionality. 

Figure 2. FTIR spectrum of poly(t-butyl styrene)-b-poly(t-butyl methacrylate) (10% TBMA by weight).

Although the potassium superoxide route can be universally applied to various alkyl methacrylates, it is experimentally more difficult than simple acid hydrolysis. In addition, limited yields do not permit well-defined hydrophobic-hydrophilic blocks. On the other hand, acid catalyzed hydrolysis is limited to only a few esters such as TBMA, but yields of carboxylate are quantitative. Hydrolysis attempts of poly(methyl methacrylate) (PMMA) and poly(isopropyl methacrylate) (PIPMA) do not yield an observable amount of conversion to the carboxylic acid under the established conditions for poly(t-butyl methacrylate) (PTBMA). This allows for selective hydrolysis of all-acrylic block copolymers. 

Brown and White employed this approach to prepare block copolymers of styrene and mcthacrylic acid (6). They were able to hydrolyze poly(styrene-b-methyl methacrylate) (S-b-MM) with p-toluenesulfonic acid (TsOH). Allen, et al., have recently reported acidic hydrolysis of poly(styrene-b-t-butyl methacrylate) (S-b-tBM) (7-10). These same workers have also prepared potassium methacrylate blocks directly by treating blocks of alkyl methacrylates with potassium superoxide (7-10). 

Materials. Methyl methacrylate was a product of Rohm and Haas, and t-butyl methacrylate was obtained from Polvsciences, Inc. Potassium trimethylsilanolate (PTMS) was obtained from Petrarch Systems, Inc. Anhydrous lithium iodide, trimethylsilyl iodide (TMSI), and n-butyllit.ium (in hexanes) were purchased from Aldrich Chemical Co. 

Preparation of Block Copolymers. Poly(styrene-b-methyl methacrylate) and poly(styrene-b-t-butyl methacrylate) were prepared by procedures similar to those reported for poly(styrene-b-methyl methacrylate (12,13). Poly(methyl methacrylate-b-t-butyl methacrylate) was synthesized by adaptation of the method published (14) for syndiotactic poly(methyl methacrylate) polymerization of methyl methacrylate was initiated with fluorenyllithium, and prior to termination, t-butyl methacrylate was added to give the block copolymer. Pertinent analytical data are as follows. 

We first attempted to hydrolyze S-b-tBM with TsOH under the same conditions which were unsuccessful for S-b-MM. This time, although the polymer was again incompletely soluble in the reaction milieu, the t-butyl methacrylate block appeared to be quantiatively hydrolyzed. The t-butyl bands listed above are no longer observed in the IR spectrum (Figure 2b). The carbonyl band is broadened and shifted to 1704 cm-1, and a C-O-H stretch is observed at 1280 cm-1. A weak, broad band at 2625 cm 1 and a shoulder at 1735 cm 1 can be attributed to hydrogen-bonded O-H and C=0 stretches, respectively. 

The Preparation of MM-b-MA and MM-b-MA.K. Inspired by the unexpected selectivity of the reaction of TMSI with S-b-MM and S-b-tBM, we decided to attempt the preparation of poly(methyl methacrylate-b-t-butyl methacrylate) (MM-b-tBM) and its unprecedented conversion to MM-b-MA. 

The anionic polymerization of the MM block was initiated with fluorenyllithium (14) in THF at -78°C. After several hours, t-butyl methacrylate was introduced, and the polymerization was allowed to slowly rise to room temperature. The reaction was quenched with a few drops of methanol and precipitated from ligroin. The dried polymer was analyzed by NMR, IR, and GPC. The 1H NMR spectrum displays signals at 0.85, 1.02, and 1.13 (shoulder) ppm for the... 

The results of this work are not limited to just S-b-MM and S-b-tBM, but may be extended to include styrene derivatives such as p-methylstyrene and p-t-butylstyrene 1). In addition to t-butyl methacrylate, other alkyl esters capable of stabilizing a carbonium ion, such as benzyl methacrylate and allyl methacrylate, should exhibit similar reactivity toward acidic hydrolysis and TMSI. In contrasting the hydrolysis of tBM blocks with TsOH and their reaction with TMSI, it should be noted that the hydrolysis is reportedly catalytic in nature (7-10), whereas the reaction with TMSI is stoichimetric. Therefore the latter approach may allow one to more easily "dial in" a desired level of methacrylic acid or metal methacrylate. 

The organolanthanide initiators allowed stereospecific polymerization of ethyl, isopropyl, and t-butyl methacrylates (Table 3). The rate of polymerization and the syndiotacticity decreased with increasing bulkiness of the alkyl group in... 

Preparation of a t-Butyl Methacrylate/Styrene/f-Butyl Methacrylate Acrylic Acid/Styrene/Acrylic Acid) Triblock Copolymer... 

Figure 4. Arrhenius plot of the propagation rate constants in the anionic polymerization of t-butyl methacrylate in THF using Na and Cs as the counterions...

Then the decomposition is expected to be more favorable as the number of / -hydrogen atoms is larger. This is the case for the poly(a-substituted benzyl methacrylate)s as shown in Figure 7. However, when poly(t-butyl methacrylate) containing nine / -hydrogen atoms was exposed to an electron-beam, the amount of acid group formed was smaller than that for poly (a,a-... 

Of the reported materials, the only commercially available resists are one of the MMA-MAA/MMA-MACl compositions and a t-butyl methacrylate copolymer material (13). In this work, we have chosen to examine the copolymer mixture, which crosslinks at a temperature of 160°C compared to 250 C for the single copolymer. We have carried out experiments to optimize its use for direct write electron beam lithography. 

POLYMETHYL METHACRYLATE POLY T-BUTYL METHACRYLATE POLYMETHYL ISOPROPENYL KETONE CROSSLINKED POLYMETHYL METHACRYLATE POLY OLEFIN SULFONES POLY HEXYL ISOCYANATE DIAZOQUINONE PHOTORESIST... 

Positive tone resins based on a photoacid generator and either a random copolymer of tetrahydropyranyl methacrylate and methyl methacrylate [137] or random copolymers of tetrahydropyranyl methacrylate, methyl methacrylate, and t-butyl methacrylate (180) were used for fabrication of 3D microchannel structures [264], Simple placed channels connected to cubic or prismatic trenches, which are open to the surface as well as optical grating structures, comprise a set of several parallel channels placed about 10 pm below the surface with connecting reservoirs on both ends. They were fabricated by positive TP microlithography (Fig. 3.75) [264]. 

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