key: cord-0010189-q5f4kezv
authors: Cai, Gangfeng; Litt, Morton H.
title: Poly(N‐acylethylenimine) copolymers containing pendant pentamethyldisiloxanyl groups. I. Synthesis
date: 2003-03-10
journal: J Polym Sci A Polym Chem
DOI: 10.1002/pola.1992.080300417
sha: c760a9f2d0add5f1a0fb0a3279c3366847d2bbb6
doc_id: 10189
cord_uid: q5f4kezv

10‐(Pentamethyl disiloxanyl) decyl oxazoline (Si) was synthesized. It was copolymerized with either undecyl (U) or nonyl (N) oxazolines using methyl 4‐nitrobenzenesulfonate as initiator. Two series of random poly(N‐acylethylenimine) copolymers, U/Si and N/Si, were synthesized over the whole composition range of Si monomer with a total degree of polymerization of about 100. Narrow molecular weight distributions were obtained. At a monomer to initator ratio of about 1060, the final degree of polymerization was 374 with a polydispersity index of 1.93. This shows the effect of chain transfer in this system.

Polymers containing siloxane groups offer a wide range of specialty applications in many diverse fields because of their unique combination of properties such as surface activity, physiological inertness (biocompatibility ) , high oxygen permeability, hydrophobicity, low temperature flexibility, etc.' Most siloxane containing polymers studied have been those with siloxane in the polymer backbones. We were interested in the synthesis and study of polymers with siloxane groups in side chains. In earlier studies, a series of undecyl oxazoline homopolymers [also called poly (N-dodecanyl ethyleneimine) s] and phenyl/undecyl oxazoline block copolymers, which were characterized as abhesive materials, were de-~eloped.'-~ In these polymers, the undecyl block is highly ~rystalline.~.~ When the undecyl homopolymers were coated on substrates, the films had the polymer backbones parallel to the surface with the undecyl tails oriented toward the ~u r f a c e .~

The addition of bulky siloxane groups at the tails of the highly crystallizable oxazoline polymers with long alkyl side chain might generate a new class of siloxane-containing polymers with interesting properties such as low critical surface energy, high oxygen permeability, etc. Since the siloxane groups are flexible and should not be able to crystallize, they could possibly form amorphous domains between the highly crystalline amide backbone / hydrocarbon tail regions and generate a sandwich-like crystalline structure.

We therefore decided to synthesize poly ( N-acylethylenimine ) s with pentamethyldisiloxanyl pendant groups attached to the terminal methylene of the alkyl side chain. We chose 10-(pentamethyl disiloxanyl) decyl oxazoline (Si) which can polymerize to generate a polymer with a highly crystallizable -( CH2)loattached to its backbone, followed by a bulky, flexible -Si ( CH3)2 -0 -Si ( CH3)3 tail.

In order to study the effect of varying the concentration of the pendant siloxane groups on the polymer surface properties, thermal and crystallization behaviors, etc., we made a series of random copolymers (U/Si) by copolymerizing Si with undecyl oxazoline ( U ) over the whole composition range. Because the U monomer unit has one more methylene group in its side chain than the Si monomer unit, the pentamethyl disiloxane group may interfere with the crystallization of the polymethylene tails. To avoid this possible interference, we made a second series of random copolymers (N/ Si) by copolymerizing Si with nonyl oxazoline ( N ) which has one less methylene group in its side chain than Si. The synthesis of the two series of random copolymers is given in this paper. Their thermal behaviors, wide angle X-ray diffraction study, and polymer crystalline structures are given in Part 116 of this series, and their surface properties are given in Part III.7

Methyl 4-nitrobenzenesulfonate ( MeONs, Aldrich, 99% ) was purified by recrystallization from acetone/ hexane. Toluene was refluxed with CaH2 for 4 h before distillation. o-Dichlorobenzene ( ODCB ) was purified by drying over Pz05 for 24 h with stirring, distilled under vacuum using a spinning band column, and stored under N2. Undecyl cyanide (Aldrich, 99%), undecylenic acid (Aldrich, 99%), decanoic acid (Aldrich, 99% ) , ethanolamine ( Aldrich, 99% ) , pentamethyldisiloxane (Petrach Systems), hydrogen hexachloroplatinate (IV) ( Alfa, H2PtC16 6Hz0, 39.12% P t ) , ferrous chloride ( FeC12 -4H20, Fisher), and basic alumina (Fisher, Brocknan Activity I, 80-200 Mesh) were used as received.

The reaction extent and the purity of the compounds were checked by GC, a Perkin-Elmer 8500 Gas Chromatograph equipped with a OV-17 phenyl silicone type column, usually running from 100 to 320°C at 3O"C/min heating rate. The molecular weight distribution was measured by gel permeation chromatography ( GPC ) ; and the polymerization progress was also followed by GPC, as described in a previous paper.' The uncorrected number and weight average molecular weights were calculated usingM-= Z H i / ( Z H i / M , ) andM,,, = ZHiMilZHi, where Hi is the height of ARI trace, measured at every 0.1 ml interval, and M i is the molecular weight obtained from the polystyrene calibration curve. Infrared spectra were recorded on a Michelson 110 FT-IR spectrophotometer from KBr pellet samples. Proton NMR spectra were taken in CDC13 solutions on an XL-200, 200 MHz FT-NMR spectrometer. TMS or CHC13 (6 7.24 ppm, for siloxane-containing monomer and polymers ) was used as internal standard. 

Undecyl oxazoline was synthesized from undecyl cyanide (Scheme 1) :

Into a 1000 mL three-necked round bottom flask were added cadmium acetate (Cd( OAc )', 10.0 g, 0.045 mol) and undecyl cyanide (400 g, 2.21 mol). The solution was heated to 132-135°C. Ethanolamine (201.6 g, 3.30 mol) was added with stirring. A mole ratio ( 1.5 : 1.0) of ethanolamine to undecyl cyanide was used to get high conversion of the cyanide to the oxazoline. The reaction mixture was refluxed under N, at 135-140°C for 24 h. GC analysis showed that more than 95% of undecyl cyanide was transformed to undecyl oxazoline after 24 h while very little ethanolamine was left. The reaction mixture was poured into cyclohexane; a phase containing the unreacted ethanolamine and other colored impurities separated. A clear cyclohexane solution was obtained after decanting from the colored ethanolamine phase. More monomer was extracted from the ethanolamine phase by cyclohexane (2 X 100 mL) . After combining the cyclohexane solutions, the cyclohexane was removed by a rotary evaporator and the crude oxazoline was purified by spinning band distillation at 128"C/O.9 T, lit., lo bp = 114"c/0.5 T. The oxazoline was distilled into a flask with stopcock. After the distillation, the receiving flask was filled with dry Nz and sealed by closing the stopcock. 344.0 g of undecyl oxazoline was obtained, yield 70.5%. GC analysis indicated that the purity of the monomer was greater than 99.5%; the main impurity was unreacted undecyl cyanide. 

The general procedure of References 11 and 12 was followed for the synthesis of decenyl oxazoline (Scheme 2). 91.62 g ( 1.5 mol) of ethanolamine was mixed with 92.2 g (0.5 mol) of undecylenic acid in a flask connected to a spinning band distillation column. The mixture was refluxed for 6 h at a pot temperature at about 180°C. 9.17 g water (theory: 9.00 g) and 61.57 g of excess ethanolamine (theory: 61.08 

g) were distilled through the spinning band column. To the resulting yellowish hydroxy amide melt, 4.01 g (3.5 wt % ) of ferrous chloride hydrate was added. The mixture was heated under reduced pressure (about 10 mm Hg) . The reaction mixture temperature was raised to -2OO"C, and the distillate, which is a mixture of water and D, was collected as rapidly as possible.

The distillate was extracted five times with 100 mL portions of cyclohexane. The cyclohexane solution was stirred with anhydrous Na2C03 and the cyclohexane was removed by rotary evaporator. 52.3 g (yield, 50.0%) of clear and colorless D with 99.0% purity (checked by GC ) was obtained. To the above product, 3 g anhydrous Na2C03 was added. Decenyl oxazoline was distilled at 100-101"C/0.25 7, lit., lo bp = 89"C/0.1 r through a spinning band distillation column. 

Since all the polymerizations were carried out using the same procedure, only the copolymerization of U decyl oxazoline (Si) .

Synthesis of 10-(pentamethyl disiloxanyl)

and Si is described here as an example. The copolymerization was carried out in o-dichlorobenzene (ODCB) at 120°C with methyl p-nitrobenzenesulfonate (MeONs) as initiator ( The copolymers of N and Si and homopolymers of U, N, and Si were synthesized similarly. In the preparation of USi( 543/521), which has the same composition as USi (59/57) but higher monomer to initiator ratio, much more dilute initiator solution (3.612 X mol/g ODCB) was used; the polymerization was complete at 120-130°C after 7 h. All the purified polymers obtained were characterized by GPC, FT-IR, and 'H-NMR. 

In the preparation of undecyl oxazoline, if a mole ratio of ethanolamine to undecyl cyanide was 1.1 : 1.0, after 1 day's refluxing all the ethanolamine was consumed or removed in the nitrogen gas stream, while more than 15% of undecyl cyanide remained unreacted. When the mole ratio was increased to 1.5 : 1.0, almost all the cyanide was transformed to undecyl oxazoline.

In the preparation of decenyl and nonyl oxazolines from the amides, ferrous chloride was used as the cyclodehydration catalyst.",'2 Temperatures above 180°C were needed to make the reaction go. Under such conditions, the oxazolines formed are not stable. Therefore, it is important to remove them as quickly as possible. When the pot temperature was higher than 230°C, the reaction was too fast for the resulting oxazoline to be removed because the evaporation of the water increased the system pressure. Over 70% yield of the oxazoline could be obtained when the temperature was kept below 200°C.

In order to study the effect of composition on the copolymer properties, we synthesized two series of copolymers over the whole composition range: ( 1 ) U and Si and ( 2 ) N and Si, with a total degree of polymerization of about 100. We did not use high vacuum technique^'^,'^ to run the polymerization.

Instead, we prepared the reaction mixtures in a dry box filled with dry nitrogen and carefully kept the monomers, initiator, and the solvent away from air and moisture. The resulting polymers had quite narrow molecular weight distributions as demonstrated by their GPC traces (Fig. 1 for U/Si series of copolymers) and their polydispersities (Table 11) calculated from the GPC traces. Their half widths ranged between 0.58 and 0.69 mL compared with 0.30 mL of ODCB. As we expected, the molecular weight of the copolymers calculated from polystyrene calibration curve were linearly proportional to the mole fraction of Si monomer (Table I1 and Fig. 2 ) .

We also prepared a U JSi copolymer, USi (543/ 521), with total monomer to initiator ratio, M/I, of 1064. The resulting polymer had a quite broad molecular weight distribution (Fig. 3 ) ; its polydispersity index was 1.93. When its peak position is compared with that of USi(59/57), which has nearly the same composition, this polymer has an estimated degree of polymerization of only 374, much lower than the M / I ratio (1064). The reason for the low molecular weight and broad molecular weight distribution is that chain transfer to monomer occurs at high M / I ratio^.'^,'^ As we can see from Figure 1 , all GPC traces have a small peak at twice the molecular weight of the main peak. We believe that the high molecular weight polymer was generated from the coupling of two lower molecular weight polymers. The mechanism of the coupling reaction is not clear. In fact, there was almost no coupled polymer after a short polymerization time with a monomer conversion of about 80% (curve 1 in Fig. 4 ) . As the polymerization uble in most organic solvents. At low temperature, they precipitated as oils from methanol. It was difficult to remove all the ODCB by washing them with methanol. They were dried at 100-115°C under vacuum (0.1 7). They are soft and transparent gel-like solids at room temperature. Heating them at 140-150°C for 24 h under vacuum resulted in their crosslinking; they could no longer be dissolved in any solvent. While we are not certain, a possible explanation of the crosslinking could be silyloxy exchange reactions, with the loss of hexamethyldisiloxane and the formation of a -Si -0 -Sicrosslink. Monomer Si and monomers U and N are all oxazolines with long alkyl tails attached to the 2-carbon of the oxazoline ring. Si, however, has a pentamethyl disiloxanyl group at the far end of the polymethylene tail. These monomers should have the same reactivity since their structural differences are ten atoms or more away from the reactive site. The copolymerization of U with Si or N with Si should be random. This hypothesis is confirmed by the fact that both monomers were consumed a t the same rate during the copolymerization of U and Si (Fig. 3 ) . The ratio of the two monomer peaks on GPC traces, Asi/Au, was 1.57 after 4 h polymerization at 120-130°C, and 1.64 after 7 h. Since the concentration ratio of the two monomers was constant, the polymerization rates of the two monomers were the same, which results in random copolymers. The relative peak areas of the methyl (i, 6 = 0.85) in the undecyl group and the methylenyl (e, 6 = 0.50) or methyl (f + g, 6 = 0.07, 0.04) in the 'H-NMR spectra were used to calculate the copolymer compositions. The monomer ratios calculated from the NMR spectra were in reasonably good agreement with the monomer ratios given in Table I (Table 111 ).

The homopolymer of Si, Si(92), was analyzed by element analysis, which also confirms the correct element composition of the Si monomer.

Calcd. for (C18H39N02Si2)92: C 60.5%, H 10.9%, N 3.9%, 0 9.0%, Si 15.7%. Found C 60.3%, H 10.9%, N 3.8%, Si 16.2%. FT-IR spectrum of USi(59/57) copolymer 

Contemporary Topics in Polymer Science, B. M. Culbertson

NSi (8/ Table I . The number of monomer units of the alkyl monomer, U or N, was assumed to be the calculated value.

10-(Pentamethyl disiloxanyl) decyl oxazoline (Si) was synthesized from decenyl oxazoline and pentamethyldisiloxane. Si copolymerizes randomly with either undecyl ( U ) or nonyl ( N ) oxazolines. Two series of random copolymers, U/Si and N/Si, were made with a total degree of polymerization of 100 and narrow molecular weight distribution.The authors gratefully acknowledge the financial support from the Center for Adhesives, Sealants and Coatings, Case Western Reserve University.