Abstract
This paper summarizes the experimental results in a new class of polyolefin co- and terpolymers containing `reactive' p-methylstyrene (p-MS) groups, which includes the materials from high Tm thermoplastics to low Tg elastomers. Due to the extraordinary copolymerization capability of metallocene catalysts with constrained ligand geometry, p-MS can be effectively copolymerized with α-olefins (i.e., ethylene, propylene, 1-octene, etc.) to form co- and terpolymers having narrow molecular weight and composition distributions. Comparing with other relative styrenic comonomers, i.e., styrene, o-methylstyrene and m-methylstyrene, p-MS shows significantly higher reactivity in metallocene catalysis. In turn, the incorporated p-MS units in polyolefins are very versatile, which not only can be interconverted to various functional groups, such as -OH, -COOH, anhydride, silane and halides, but also can be conveniently transformed to `stable' anionic initiators for `living' anionic graft-from polymerization reactions. Many new functional polyolefin graft co-polymers have been prepared, containing polyolefin backbone (PE, EP, EO, etc.) and functional polymer side chains, such as PMMA, PAN, PS, etc.
Original language | English (US) |
---|---|
Pages (from-to) | 298-333 |
Number of pages | 36 |
Journal | Journal of Elastomers and Plastics |
Volume | 31 |
Issue number | 4 |
DOIs | |
State | Published - Oct 1999 |
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Materials Chemistry
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In: Journal of Elastomers and Plastics, Vol. 31, No. 4, 10.1999, p. 298-333.
Research output: Contribution to journal › Article › peer-review
TY - JOUR
T1 - Polyolefins containing reactive p-methylstyrene groups
T2 - From high Tm thermoplastics to low Tg elastomers
AU - Chung, T. C.
N1 - Funding Information: Chung T. C. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 10 1999 31 4 298 333 This paper summarizes the experimental results in a new class of polyolefin co- and terpolymers containing "reactive" p -methylstyrene (p-MS) groups, which includes the materials from high T m thermoplastics to low T g elastomers. Due to the extraordinary copolymerization capability of metallocene catalysts with constrained ligand geometry, p -MS can be effectively copolymerized with α-olefins (i.e., ethylene, propylene, 1-octene, etc.) to form co- and terpolymers having narrow molecular weight and composition distributions. Comparing with other relative styrenic comonomers, i.e., styrene, o-methylstyrene and m-methylstyrene, p -MS shows significantly higher reactivity in metallocene catalysis. In turn, the incorporated p -MS units in polyolefins are very versatile, which not only can be interconverted to various functional groups, such as -OH, -COOH, anhydride, silane and halides, but also can be conveniently transformed to "stable" anionic initiators for "living" anionic graft-from polymerization reactions. Many new functional polyolefin graft co-polymers have been prepared, containing polyolefin backbone (PE, EP, EO, etc.) and functional polymer side chains, such as PMMA, PAN, PS, etc. sagemeta-type Journal Article search-text Polyolefins Containing Reactive p-Methylstyrene Groups: From High Tm Thermoplastics to Low Tg Elastomers T. C. Chung Department of Materials Science and Engineering The Pennsylvania State University University Park, PA 16802 ABSTRACT: This paper summarizes the experimental results in a new class of polyolefin co- and terpolymers containing "reactive" p-methylstyrene (p-MS) groups, which includes the materials from high Tm thermoplastics to low Tg elastomers. Due to the extraordinary copolymerization capability of metal- locene catalysts with constrained ligand geometry, p-MS can be effectively copolymerized with a-olefins (i.e., ethylene, propylene, 1-octene, etc.) to form co- and terpolymers having narrow molecular weight and composition distribu- tions. Comparing with other relative styrenic comonomers, i.e., styrene, o-me- thylstyrene and m-methylstyrene, p-MS shows significantly higher reactivity in metallocene catalysis. In turn, the incorporated p-MS units in polyolefins are very versatile, which not only can be interconverted to various functional groups, such as -OH, -COOH, anhydride, silane and halides, but also can be conveniently transformed to "stable" anionic initiators for "living" anionic graft-from polymerization reactions. Many new functional polyolefin graft co- polymers have been prepared, containing polyolefin backbone (PE, EP, EO, etc.) and functional polymer side chains, such as PMMA, PAN, PS, etc. INTRODUCTION FOR MANY DECADES since the commercialization of PE, PP and EP: the functionalization of polyolefins [1] has been of long scientific interest and a technologically important research subject to improve 298 JOURNAL OF ELASTOMERS AND PLASTICS Vol. 31-October 1999 0095-2443/99/04 0298-36 $10.00/0 ( 1999 Technomic Publishing Co., Inc. Polyolefins Containing Reactive p-Methylstyrene Groups their adhesion to and compatibility with other materials. The lack of reactive polar groups in the polymer has limited many of their end uses, particularly where the interaction with other materials is para- mount. Unfortunately, the chemistry to prepare functional polyolefins is very limited both in the direct and post-polymerization processes, namely due to the catalyst poison [2] and the inert nature [3]. Our functionalization approach has been focusing on the reactive polyolefin intermediates, the polyolefin copolymers containingp-meth- ylstyrene [4] (I) and borane [51 (II) reactive groups, as illustrated in Scheme 1. By using metallocene technology, both "reactive" comonomers (bor- ane containing a-olefins and p-methylstyrene) can be effectively incor- porated into polyolefins. In turn, the reactive comonomer units in polyolefin can be transformed into desirable functional groups under mild reaction conditions. In addition, the reactive comonomer units in polyolefins can also be interconverted to polymeric "living" initiators [6] (free radical in borane case and carbanium in p-MS case) for graft- from polymerization reactions as illustrated in Scheme 1. The overall R CH2=CH7 CH2=)H ( IH2)n I/ Reactive -(CH x-(CH Copolymers I (I)I B Graft Copolymers -(CH2-CH),-(CH2-CH) - ( UH2)n R _(-(C2-C;H)s -(CH2-CH) - (II) |Cl-3 Graft-from Reaction -(CH2-CH) w-(CH2-CH) Y CH2 SCHEME 1. 299 T. C. CHUNG process resembles the sequential living polymerization, except involving two polymerization mechanisms. By starting with metallocene polymerization of a-olefins to prepare polyolefin seg- ments, the subsequent functional monomer polymerization is carried out by free radical or anionic mechanisms. The graft copolymers, containing polyolefin backbone and functional polymer side chains, are not only having high concentrations of func- tional groups but also preserving the original polyolefin properties, such as crystallinity, melting point, glass transition temperature, viscoelasticity, etc. These segmental polymer structures are known to be the most effective interfacial agents [7] to improve the compatibility of polyolefins with other materials, such as glass, metal, fillers and en- gineering plastics, in polymer blends and composites. RESULTS AND DISCUSSION In this section, we will focus on the p-MS containing polyolefins, in- cluding polyethylene (PE), ethylene-propylene copolymers (EP) and ethylene-1-octene copolymers (EO). Two metallocene catalysts, [C5Me4(SiMe2NtBu)]TiCl2 (III) and Et(Ind)2ZrCl2 (IV), with con- strained ligand geometry, were applied in the co- and terpolymerization reactions. (CH3)2SiTQ (TI I) TiCJ2 C(CH3)3 0 The silicon bridge in catalyst (III) pulls back both Cp and amido lig- ands from normal positions to form a highly constrained ligand geome- try, with Cp-Ti-N angle [8] of 107.60. On the other hand, ethylene bridge induces the constrained indenyl ligand geometry, with Cp-Zr-Cp angle [9] of 125.8. Based on the structure-activity relationships of the metallocene catalysts, it is logical to predict that the incorporation of p-MS in catalyst (III), with a more opened active site, will be preferable over that of catalyst (IV). Poly(ethylene-co-p-methylstyrene) Copolymers In a typical copolymerization, the reaction was started by the ad- 300 Polyolefins Containing Reactive p-Methylstyrene Groups dition of the metallocene catalyst mixture to a solution of the two monomers in solvent under an inert gas atmosphere. The slurry solu- tion with white precipitates was observed in the reaction. After ter- minating the reaction with isopropanol, the copolymer was isolated by filtering and washed completely with MeOH and dried under vac- uum at 50'C for 8 hrs. Table 1 summarizes the copolymerization re- sults [10]. The copolymerization efficiency clearly follows the sequence of [C5Me4(SiMe2NtBu)]TiCl2 > Et(Ind)2ZrCl2, which is directly relative to the spatial opening at the active site. In run p-377, about 90% of p-MS was incorporated into copolymer in 1 hour. In run p-383, the reaction produced the copolymer containing 40 mole% of p-MS, which is close to the ideal 50 mole% (the consecutive insertion of p-MS is almost impos- sible). In general, the catalyst activity systematically increases with the increase of p-MS content, which was also observed in the 1,4-hexadiene copolymerization reactions [11] and could be a physical phenomenon relative to the improvement of monomer diffusion in the lower crystalline copolymer structures. In the [C5Me4(SiMe2NtBu)]TiCl2 case, the catalyst activity attains a value of more than 2.4 x 106 g of copolymer/mole of Ti x hour in run p-380, which is about 6 times the value for the homopolymerization of ethylene in run p-270 under simi- lar reaction conditions. It is very interesting to note that a very small solvent (hexane and toluene) effect to the catalyst (II) activity was ob- served in the comparative runs (p-377/p-267) and (p-378/p-379), de- spite the significant difference in the beginning of reaction conditions (heterogeneous in hexane and homogeneous in toluene). However, the solvent effect is very significant in catalyst (I) systems; hexane solvent conditions consistently show higher p-MS incorporation. The explana- tion of solvent effect is not clear. The molecular structures of copolymers were examined by GPC and DSC measurements. Figure 1 compares GPC curves of the polymers prepared by [C5Me4(SiMe2NtBu)]TiCl2 catalyst. The uniform molecular weight distribution in all samples, with M./Mn = 2-3, implies the sin- gle-site polymerization mechanism. In fact, the GPC curves show a slight reduction of molecular weight distribution in the copolymers, from MI/Mn = 2.86 in PE to 1.68 in poly(ethylene-co-p-methylstyrene) containing 18.98 mole% of p-MS. The similar narrow molecular distri- bution results were also observed in the copolymers prepared by Et(Ind)2ZrCl2 catalyst. The better diffusibility of monomers in the co- polymer structures (due to lower crystallinity) may help to provide the ideal polymerization condition. It is very interesting to note that the average molecular weights of copolymers are very high throughout the 301 T C CHUNG CN C-. -0 C t 0 C4 CO 0) 00 C-. 00 I 0 U') C C') N C'- N - "T U) CN CN N CN C C' CN C) t '0 0 C t 0 Vo) '0 '0 0 CO , CN a- C 00 C-. C' q .C) .x) . -. CO . C' .c "0 CO . N CO to N 0 CO C' CO "0 CO - N C') N - CN C') C 00 CO CO "0 I CD -0 Cj 6 6 O 0" CO CO CO Cl. to C' CN - N C0 t CN -N CY) "T C' O C0N - CN 0 D D o o C O) C. CO -. 6 6 6 6 0 . C) 0 CO "o Vo "T 0 Lo 0 oT N 0o C t) C -- I N OU) C C-. "- tO - C - N - 0 C' 0 LOCO O- C _ N ) "t O ' _ .6 Z 6 . . . o. . . . . . . . . . C) m 6 0> a-N Co - LO N ui os c- -N N - v 5> - C14 - C - - - - - CN - 00 0 00 00 0 00 0 00 000 0 to to to to to to totC o oC) C ') C ') C') C ')0 0 C') C') e eU) LO LO U- ) LO LOU) CO m mm m CO m 0 a) ) a a) 0 a) a) a a 0 a) a) CC C C C c C c C C c C C c c c C ooo o (O ) )) O o o 0 0) 0) a , x x x xX D D DD D DXX DDD X LO CO CO tOCO F-.NI- C.N OO s No mCOtV- -." O m0 t'- t._ CN CN o C n m C o o 0 m C o T o" I o" Co Co 0 0 0 CN 0 C N 0 OO 66 6 0 7o tO tO to to tO tO tO tO LO tO to to to to tO 0 I IT IT I- -,I ' T I- I'l -lq "T llq "T " -, 'T I'l _, r-. r- r- r'-_ C- N. o 000000 -- ! Zl - - o o o- o- o- o o-1- - ---_---- "O N4 CO - - r. CN O0to 0C .ON aO "0C to NP to "0NO-. tO 0" "0 0 N . N. N. N. "0 N. CO CO C') C' C' C' C' C' C' C' C') C' N C') C') C' C') C' a a L a a a L a a a a a a a a a a 6 Oa 0 C') -a E . _4 C) u Y) 6 C - E r- c -a) 0 .E J CN C') 00 C.D " o ua, Uz) aM , I D ~ 0 a)- aE OCN Ur aD C1 C: 0, C'4 - 0 G> E -U (D C ) 0 d) 5s.c TS - 0 .. E q 302 c o Lo) * o-E QOO U (fl 0 L) US C C v) C _0 C a) C a) C I-0 -Q (U C a c U) C -0 E -0 in 0. 0 L- 0 0 E 0 I- C U 0 E -J- c 0 V) I Q n a) - C LU -O C O Z Polyolefins Containing Reactive p-Methylstyrene Groups 0 co 0a 0 cY) 0 0 CO L6 0 .4 0 co LI 0 C) (6 0 0 0 0 0) 0 0) 0) V 04 O co Co o 6 o V- o - o - o o o i C 303 o 0 O a2 U-0 C) S O8 0 00 G ) 0* - 0 t :z CD 60), very strong favorably for ethylene incorporation, and almost no possibility of p-MS consecutive insertion (r2 - 0). The less opened active site in Et(Jnd)2ZrCl2 catalyst may sterically prohibit p-MS consecutive insertion. Comparison among Styrene Derivatives It is very interesting to compare p-MS with styrene and methylstyrene isomers [13]. The consumption of comonomer during the reaction is a useful way to understand the dynamic of copolymerization reaction. Figure 3(a) shows a comparative plot of p-MS and styrene incorporation vs. reaction time in the batch copolymerization reaction of ethylene (29 psi) and comonomer (0.356 mole/L), using [C5Me4(SiMe2NtBu)]TiCl2 catalyst at 60TC. The significantly better p-MS incorporation starts at the beginning of copolymerization reaction. After 30 minutes, the difference was rela- tively'~ constant due to the depletion of p-MS. After 1 hour, more than 80% of p-MS and only less than 60% of styrene were incorporated in the ethylene copolymers. Figure 3(b) compares the incorporated comonomer concentration (mole%) in copolymer vs. comonomer ratio. Each copolymerization reaction was carried out at 40TC for 15 minutes by using [C5Me4(SiMe2NtBu)]TiCl2 catalyst. In every monomer feed ra- tio, p-MS consistently shows more than 30% higher incorporation than the corresponding styrene. Table 2 compares two sets of copolymerization reactions of ethylene and styrenic comonomers, i.e., p-MS, o-MS, m-MS and styrene, with catalysts (I) and (II), respectively. In both reaction sets, p-MS consistently shows higher incorporation than the corresponding styrenic comonomers, which is due to favor- able electronic and steric effects in p-MS comonomer. The electronic donation of p-methyl group is favorable in the "cationic" polymeriza- tion mechanism [14]. On the other hand, the methyl group at para-substitution doesn't affect the monomer insertion. Styrene doesn't have electronic benefits and both isomers (o-MS and m-MS) do not receive the full benefits of the combined electronic and steric effects. 306 Polyolefins Containing Reactive p-Methylstyrene Groups 8 8 8 8 8 8 Q 06 Cd ' N o N _ - _ _ _~~I- V. 8 8 8 8 0 0 D IV 4 %PW sewApodoo 41 ul uoqWU.K uoo waASJ So d .4 4 .4 d.4 o0 4~~ ~~ + I . I . I . I . I . 5 CD CO o- Co I) Co aw co r- co UO) sAt % 'uoISJOAUOO o 0 0 (V) (% ~~0* ~ Co CD . a E CU cu 0 L S S 0~~~ o (0 cd b CD0 o N -O .cp *n CUE (0 O X 0g 307 0 0: 0 E 0 C 0 7- 4.. to C) 0 0. E 0 0 0 E 0 0. 0 0 0~~ E * -5 a)0 0 C ._ C 3 a) E o Pu 0 .o U a) S T C Cb a C 0 0 --------r------ ;-- -- -- BBX wrr wr wr T. C. CHUNG Table 2. The comparison of copolymerization reactions between ethylene (MI) and styrene derivatives (M2). Reaction Condition0 Copolymer Product M2 M2 Run Temp. Cat.b M2C Yield Conc. Conv. Tm No. (OC) (umol) (mmol) (g) (mole%) (%) (OC) 1 30 (I) 10 none 4.27 0 0 133.7 2 30 (I) 10 p-MS (46.6) 13.0 11.0 84.3 76.0 3 30 (I) 10 o-MS (46.6) 12.9 4.52 38.7 98.3 4 30 (I) 10 rn-MS (46.6) 5.43 2.36 9.53 119.1 5 30 (I) 10 styrene (46.6) 13.6 5.35 48.6 98.7 6 53 (11) 17 p-MS (33.9) 24.7 3.30 81.5 114.3 7 53 (II) 17 o-MS (33.9) 23.0 2.54 63.5 118.6 8 53 (II) 17 m-MS (33.9) 19.0 2.35 43.2 118.1 9 53 (11) 17 styrene (33.9) 17.5 1.87 31.7 127.4 'Reaction time = 1 hour, ethylene pressure = 45 psi. b[C5Me4(SiMe2N'Bu)ITiCI2 (1) and Et(lnd)2ZrCI2 (II). cp-MS: p-methylstyrene; o-MS: o-methylstyrene; m-MS: m-methylstyrene. Copolymer Microstructures The other way to study the copolymerization reaction is to examine the copolymer molecular structure. Figure 4 compares DSC curves of poly(ethylene-co-p-methylstyrene) and poly(ethylene-co-styrene) copol- ymers containing 3 mole% of comonomers; both are prepared by the same [C5Me4(SiMe2NtBu)]TiCl2 catalyst at 50'C in hexane. The significant differences of Tm (111.9 vs. 117.20C) imply that p-MS comonomers more effectively prevent the crystallization of polyethyl- ene sequences, possibly more uniformly incorporated in copolymer than styrene comonomers. Similar results were also revealed by 13C NMR measurement. Figure 5 compares the 13C NMR spectrum (with the expanded aliphatic re- gion) of poly(ethylene-co-p-methylstyrene) and poly(ethylene-co-sty- rene) copolymers containing 10 mole% of comonomers. It is logical to expect that the methyl group substitution at the para-position will have very little effect on the chemical shifts of meth- ylene and methine carbons in the polymer backbone. In general, fewer chemical shifts shown in the poly(ethylene-co-p-methylstyrene) sample imply more homogeneous copolymer microstructure, and every chemi- cal shift can be easily assigned to polyethylene and the isolated p-MS unit. In addition to the two chemical shifts (21.01 and 29.80 ppm), cor- responding to the methyl carbon from p-methylstyrene and methylene carbons from ethylene, respectively, there are three well-resolved 308 Polyolefins Containing Reactive p-Methylstyrene Groups (0 1 1. 4 (6/A) AOU 100H 0 a L Qe L a 309 0 CD C) 0 a) 0 C) . 4 Cd 0 C) a) C) aC C) C) 0S C) .O 0 C0 > OC) EzU U de 310 T. C. CHUNG 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 \a) ppm 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 ppm 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 (b) ppm 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 ppm FIGURE 5. 13C NMR spectra of (a) poly(ethylene-co-p-methylstyrene) with 10.9 mole%p- methylstyrene and (b) poly(ethylene-co-styrene) with 9.5 mole% styrene. Polyolefins Containing Reactive p-Methylstyrene Groups peaks (27.74, 37.04 and 45.77 ppm) corresponding to methylene and methine carbons from p-methylstyrene units which are separated by multiple ethylene units along the polymer chain. On the other hand, the spectrum of poly(ethylene-co-styrene) shows much more compli- cated methylene and methine carbon species. Many tail-to-tail styrene sequences [8] clearly exist in the polymer chain. The reason for the better separation of p-methylstyrene units, with no detectable tail-to-tail sequences, may be due to the better regioselectivity of 2,1-insertion of p-MS, with electron donating p-methyl group favorable for "cationic" catalytic site. After the insertion of an ethylene unit (no consective p-MS insertion allowed), the electronic donation of p-methyl group may increase the interaction of the aromatic group with the "cationic" catalytic site to further reduce the space opening around it. p-MS Containing Polyolefin Elastomers As discussed in poly(ethylene-co-p-methylstyrene) copolymers, de- spite the completely amorphous structure the lowest Tg observed in this type copolymer was about -5TC, which is too high to be useful in most elastomer applications. For many commercial applications, elas- tomers with low Tg T M 0C C) CN CD LO 6o aco rlCyl co c CD 1 -m s a CD N0 0 C _) _ .m ~~~~~~~~O -- O0 O- O a e O C) m Q3 E 0 U O - C4 W - - os - "T C CDG s0 00 co 0l co o coc CD 10: ._ 0?o ~ N00 eOrt 'O~0 t ) ) O~~~~~~~Cn Q1 - - -00 CN - CN 04 oT " LO co - N, osz o s N o Oo i a) U o i 6 6 a 0 D N LO LO kn inC? n nnnc c o _ 0 C- I) o) Co C) L o0 o o o 'o o O E e e CD CD E~~~~~C C 0 C4~~~~~~~ CL~~~~~~~~~~~~~~~~~~~~~~~~ o ? - N c C O L O o o o o o (U .O E Q LOO 0 cO LO LO IT O LO O- OOO C 0Q 0 C) CL C) CO 04 C) Cn O 4 M ', 'T IT - 03 ur~ Iz O> CD NoOooo NC OC CI) 0 ?E uf .66666 6 ,o CL 0 ( O D CD C) C) 0 C) 0 0 0 0 o 0I o 0 C~~#.- 0)O -C ' I - D LO - CD T C O 8Q Q -o~~~~~~~~~~~~~~~oL 0 C -x N~~~aaaaa Polyolefins Containing Reactive p-Methylstyrene Groups c) > ~~~~~~~(b) -60.0 -40.0 -20.0 0.0 20.0 40.0 60.0 60.0 Temp 0C FIGURE 7. The comparison of DSC curves of EP-p-MS terpolymers from (a) run p-112, (b) run p-118 and (c) run p-120. Each curve only has a sharp Tg transition in a flat baseline, without any detectable melting point. The combination implies a homogeneous terpolymer microstructure with completely amorphous morphology. The same clean DSC curves were observed in all samples shown in Ta- ble 2, even the sample with >87 mole% of propylene content, which may have most atactic propylene sequences incapable of crystalliza- tion. The Tg is clearly a function of the propylene and p-methylstyrene contents. Comparing the ethylene-propylene copolymers (without p-MS units) (runs p-116, p-117, p-107 and p-115), the Tg transitions are linearly proportional to the propylene contents and level off at --50'C with the composition -50% of propylene content (similar re- sults were reported for the EPDM case [16]). The Tg transition signifi- cantly increases with the incorporation of p-MS in ethylene/propylene copolymers. Comparing runs p-117 and p-118, both having -42 mole% of ethylene content and p-MS/propylene mole ratios of 0/58 and 10/48, respectively, the Tg increases from -43 to -20C. A similar result was observed in the pair of runs p-107 and p-110, with 37 mole% ethylene and smaller difference in p-MS/propylene mole ratios of 0/63 and 4.5/58, respectively, the Tg change is smaller from -35 to -20C. It is 315 T. C. CHUNG very interesting to compare runs p-116 and p-120, both with ideal -54 mole% ethylene content and only very small difference in p-MS/propylene mole ratios (0/46 vs. 1.8/44), the Tg's are -50 and -450C, respectively. The same Tg trend holds, although much smaller. Overall, the composition of EP-p-MS material with low Tg -40'C. Obviously, the high Tg 's of both propylene (Tg of PP -0TC) and p-MS [Tg of poly(p-MS) -110TC] components preclude EP-p-MS from achieving some desir- able elastomers containing both high content of "reactive" p-MS and low Tg (1-octene>p-MS. In fact, the ratio is quite consistent with all results (runs p-470, p-471, p-472, p-473, p-474, p-475 and p-476), despite very different comonomer feed ratios. The thermal transition temperature of PO-p-MS terpolymer was ex- amined by DSC studies. Figure 9 shows the DSC curves of two PO-p-MS terpolymers (runs p-472 and p-478) and one poly(ethyl- ene-co-p-methylstyrene) copolymer (run p-383). Comparing the curves of runs 472 and 383, both having the same ethylene (+60 mole%) con- tent but different 1-octene/p-MS ratios, the Tg changes from >30C in run 383 (with no 1-octene) to 0 ^ N 0 s 00 0 > ~~~~~~~~0 - e O 0 0s C- 0 CO ur C o oN }c E aO 0 oo cc) oo- cso 0 cs' O4 ccu)IDU E~~~~~~C Q0 ', O r- 0f~ 10 C LOo N E s NNe LO , N- LO CD O LO "T C) 'O oq OU C co C 5 - LOMN NO M~ CN CDl NCl_ D _ R O I I I I I ~~~~~~~I - I U t E -,- M O ' N w r t , N LO 'O _ t z 0 n M 0 N 0 0 'I CN 0 C v2 Q~~~~~~~~~~~~~~ Q4 N 4 - O C O0 O 0N rl - CY) M CN t t- 00 _O S~~~~~~~~~ oo Lr 6 O- 6 6 O O C O~~~~~~- LO LO LO LO LOML I T OC C C - N -cs 0 0 V: r- Cl CD Lo o uJ -o 1 O Lo o -. o M o -I rs c E} 10 ,I U O -0 Lo C) t) CD c)o - M - LO uM u- 6 a)o O t. E O~~~~~~~I CD 4 O-- M l CNl 'st CN M r CD CD 04 X m E rc ~ ~ ~~~~ . . . . . . . . . . . . _ ) csc ^ ~~~~~~~~'-LO 10 1 ' M -0 O C, 10 O NO E C ~~~~~~~~~~~~~~~~~~~~~0 -:- CD O . ,ooo a) go~~~~0 w~~~~~~~~~~~~~~~~~~~~ Oc ~~~~~~~r' . 0 C 6 s6 Cs 1S 1, 1\ - vi E\ oso A>D U 0 '~ o8 t tnc 0 Zs L O L.) s 320 T. C. CHUNG (a) E C-) twf) =___ ~~~~~~~~~~~~(b) Cf)~~~~~~~~~~~~~~~~C -80 -60 -40 -20 0 20 40 60 80 Temperature, deg. C FIGURE 9. DSC curves of two poly(ethylene-ter-1-octene-ter-p-methylstyrene) terpoly- mers prepared from (a) run p-472, (b) poly(ethylene-co-p-methylstyrene) (run p-383), and (c) run p-478. Polyolefins Containing Reactive p-Methylstyrene Groups R -(CH2-CHHM CH2-CHt COOH R R (CH2-CH)CH2-CH) NBS/BPO i --(CH .-Clit-tCH Mo. -tuC2-CH)(Hm-CH~- n-BuLifFMEDA CH3 2 Br --(CH2-CHImCH2yH)n tH2 Li SCHEME 2. FUNCTIONALIZATION REACTIONS Our major research interest of incorporatingp-MS into polyolefins is due to its versatility to access a broad range of functional groups. The benzylic protons are ready for many chemical reactions, such as halogenation, oxidation and metallation as shown in Scheme 2. Oxidation of poly(ethylene-co-p-MS) copolymer was carried out by bubbling oxygen through the polymer solution containing a solvent mixture of chlorobenzene and acetic acid (3/1 in volume) and catalyst system of cobalt (II) acetate tetrahydrate (CoAc2 4H20) and sodium bromide (NaBr) at 105TC for 3 hours. The resulting polymer was pre- cipitated by methanol. The oxidation product is soluble in xylene or 1,1,2,2-tetrachloroethane at elevated temperature. Figure 10(a) shows 1H NMR spectrum of the product. In addition to the peak at 7.0-7.1 ppm, corresponding to the aro- matic protons in p-MS unit, there are several new peaks appearing in the range of 7.2-8.0 ppm, which are correspondent to aromatic protons of p-COOH and/or p-CHO substituted styrene units in the copolymer. Apparently, the oxidation reaction of p-CH3 groups in poly(ethyl- ene-co-p-MS) by Co(III)Ac2Br is consistent with the results shown in the literature [19]. 321 322 T. C. CHUNG (a) 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 PPM (b) 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4. 5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 ppm FIGURE 10. IH NMR spectra of (a) carboxylated poly(ethylene-co-p-methylstyrene) and (b) brominated poly(ethylene-co-p-methylstyrene). Polyolefins Containing Reactive p-Methylstyrene Groups Bromination reaction was carried out in CCl4 using benzoyl peroxide (BPO) as a free radical initiator and N-bromosuccinimide (NBS) as a bromination reagent. The reaction was performed at refluxing temper- ature under nitrogen atmosphere in dark environment and 1.5/1 of NBS to p-CH3 was used. A light brown polymer powder was obtained. Figure 10(b) shows 1H NMR spectrum of the brominated polymer. Compared to the starting poly(ethylene-co-p-MS) copolymer, two major new peaks at 4.54 ppm and 7.34 ppm are observed, which are corre- spondent to the protons in benzylbromide (PhCH2Br) and aromatic protons in p-bromomethylstyrene unit. It is clearly shown that the bromination reaction predominantly takes place at p-CH3 position. The degree of bromination estimated from the integrated peak areas between p-bromomethyl protons at 4.54 ppm and aromatic protons at 7.0-7.4 ppm is 56.8%. The lithiation reaction was carried out by mixing poly(ethyl- ene-co-p-MS) powder with excess alkyllithium, such as sec-BuLi and n-BuLi, in the presence of TMEDA at 60'C for a few hours. TMEDA functioned as dissociation reagent of butyllithium. The unreacted re- agents can be easily removed by filtration and washing the lithiated PE powders with hydrocarbon solvent, such as cyclohexane or hexane. To study the efficiency of lithiation reaction, some of the lithiated poly- mer was converted to organosilane containing polymer by reacting with chlorotrimethylsilane. Figure 11 compares the 1H NMR spectra of the starting P[E-co-(p-MS)], containing 0.9 mole% of p-MS, and the re- sulting trimethylsilane containing PE copolymers, which had been metallated by either s- or n-BuLi/TMEDA, respectively, under the same reaction conditions. In Figure 11(a), in addition to the major chemical shift at 1.35 ppm, corresponding to CH2, there are three minor chemical shifts around 2.35, 2.5 and 7.0-7.3 ppm, corresponding to CH3, CH and aromatic protons in p-MS units, respectively. After the functionalization reac- tion, Figures 11(b) and (c) show the reduction of peak intensity at 2.35 ppm and no detectable intensity change at both 2.5 and 7.0-7.3 ppm chemical shifts. In addition, two new peaks at 0.05 and 2.1 ppm, corre- sponding to Si-(CH3)3 and f-CH2-Si, are observed. Overall, the results indicate a "clean" and selective metallation reaction atp-methyl group. The integrated intensity ratio between the chemical shift at 0.05 ppm and the chemical shifts between 7.0 and 7.3 ppm and the number of protons both chemical shifts represent determines the efficiency of metallation reaction. The n-butyllithium/TMEDA converted only 24 mole% of p-methylstyrene to benzyllithium. On the other hand, the s-butyllithium/TMEDA was much more effective, achieving 67 mole% 323 324 T. C. CHUNG (C) (a) 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 PPMt FIGURE 11. The comparison of 'H NMR spectra of (a) poly(ethylene-co-p-methylstyrene) with 0.9 mole% of p-methylstyrene and two corresponding trimethylsilyl derivatives pre- pared via lithiation reactions using (b) n-BuLi/TMEDA and (c) s-BuLi/TMEDA reagents. Polyolefins Containing Reactive p-Methylstyrene Groups conversion. Apparently, the metallation reaction was not inhibited by the insolubility of polyethylene, most p-MS units must be located in the amorphous phases which are swellable by the appropriate solvent during the reaction. Figure 12 compares DSC and GPC curves of copolymer samples, eth- ylene/p-MS copolymer and the corresponding silane-containing copoly- mer. Before and after functionalization, the molecular weight and molecu- lar weight distribution of the copolymer are identical within the exper- imental error and only very slight differences in both Tm and crystallinity. Apparently, the lithiation and the subsequent transforma- tion reactions exclusively take place at p-CH3 groups of p-MS units in the copolymer without attacking polymer backbone. Anionic Graft-from Reactions Most of the lithiated PE powder was suspended in cyclohexane be- fore addition of styrene or p-methylstyrene monomers. The living an- ionic polymerization took place at room temperature, similar to the well-known solution anionic polymerization [20]. To assure sufficient time for monomer diffusion in the heterogeneous condition, the reac- tion continued for an hour before terminating by the addition of meth- anol. The conversion of monomers (estimated from the yield of graft copolymer) was almost quantitative (>90%) in one hour. The reaction mixture was usually subjected to a vigorous extraction process, by refluxing THF through the sample in a Soxhlet extractor for 24 hours, to remove any polystyrene or poly(p-methylstyrene) homopolymers. In all cases, only a small amount ( t = * > S. _ > i t wt ata . * ' >; ': is ; >f t - -~ , 4 ., , AS 4 ; i > i P X gdgSb**ti '- - * - o~~~~~~~4 4 "t ;' ; > - ~4 \t 3 ,54 >0a^3i3 - fb _ _ ,, , . _ * , t3,_* , X >_* ; * , t J v t A 4 $ 4 . 4 P * g ' 44. ~ ~ ~ ~~~~~~V FIGURE 14. Polarized optical micrographs of polymer blends, (a) two hompolymer blend with PE/PS = 50/50 (10O x), (b) two homopolymers and PE-g-PS copolymer blend with PE/PE-g-PS/PS = 45/10/45 (100x). 329 (a) (b) T. C. CHUNG The PS phases vary widely in both size and shape due to the lack of in- teraction with the PE matrix. On the other hand, the continuous crys- talline phase in Figure 14(b) shows the compatibilized blend. The large phase separated PS domains are now dispersed into the inter-spherulite regions and cannot be resolved by the resolution of the optical microscope. The graft copolymer behaving as a polymeric emul- sifier increases the interfacial interaction between the PE crystalline and the PS amorphous regions to reduce the domain sizes. Figure 15 shows the SEM micrographs, operating with secondary electron imaging, which show the surface topography of cold fractured film edges. The films were cryo-fractured in liquid N2 to obtain an un- distorted view representative of the bulk material. In the homopolymer blend, the polymers are grossly phase sepa- rated as can be seen by the PS component which exhibits non-uniform, poorly dispersed domains and voids at the fracture sur- face as shown in Figure 15(a). This "ball and socket" topography is indicative of poor interfacial adhesion between the PE and PS do- mains and represents PS domains that are pulled out of the PE ma- trix. Such pull out indicates that limited stress transfer takes place between phases during fracture. The similar blend containing graft copolymer shows a totally different morphology in Figure 15(b). The material exhibits flat mesa-like regions similar to pure PE. No dis- ~~~ 0 -~ ,:m w -* a / at + ;i (a) FIGURE 15. SEM micrographs of the cross-section of two polymer blends (a) two homo- polymers with PE/PS = 50/50 (1,000 x), (b) two homopolymers and PE-g-PS copolymer blend with PE/PE-g-PS/PS = 45/10/45 (4,000 x). 330 Polyolefins Containing Reactive p-Methylstyrene Groups c: : ,ni;'v r tA9 r -- > -; . >1. 5 5 ;+ w Ss 9 8l, E Le . - ;f nt j v .:. ! X A . w . + > > \ tN > > s >NA fa," -.',<* ,,'. k ,42F., ', ,.'ga-^ ' * - , ^ -v r ' ,- * i o.' (b) FIGURE 15 (continued). SEM micrographs of the cross-section of two polymer blends (a) two homopolymers with PETPS = 50/50 (1,OOOx), (b) two homopolymers and PE-g-PS copolymer blend with PE/PE-g-PS/PS = 45/10/45 (4,000x). tinct PS phases are observable indicating that fracture occurred through both phases or that the PS phase domains are too small to be observed. The PE-g-PS is clearly proven to be an effective compatibilizer in PE/PS blends. CONCLUSION A new class of reactive polyolefin co- and terpolymers containing p-methylstyrene groups has been prepared by metallocene catalysts with constrained ligand geometry. The combination of spatially opened cata- lytic site and cationic coordination mechanism in metallocene catalyst provides a very favorable reaction condition forp-methylstyrene incorpo- ration to obtain high polyolefin co- and terpolymers with narrow mo- lecular weight and composition distributions. The experimental results clearly show that p-methylstyrene performs distinctively better than styrene, o-methylstyrene and m-methylstyrene, in the ethylene copolymerization reaction. In turn, the copolymers are very useful in- termediates in the preparation of functional polyolefins and graft co- polymers which can serve as the effective compatibilizers in polyolefin blends. 331 I-- -- T. C. CHUNG ACKNOWLEDGMENT The authors would like to thank the Polymer Program of the Na- tional Science Foundation for financial support. REFERENCES 1. (a) Baijal, M. D. Plastics Polymer Science and Technology, John Wiley & Sons: New York, 1982; (b) Boor Jr., J. Ziegler-Natta Catalysts and Polymer- izations, Academic Press: New York, 1979; (c) Pinazzi, C., Guillaume, P and Reyx, D. J. Eur. Polym., 13:711 (1977). 2. (a) Giannini, U., Bruckner, G., Pellino, E. and Cassata, A. J. Polym. Sci., Part C, 22:157 (1968); (b) Purgett, M. D and Vogl, 0. J. Polym. Sci., Part A, Polym. Chem., 27:2051, 1989; (c) Sivak, A. J. U. S. Patent 5,373,061 (1994); (d) Kesti, M. R., Coates, G. W and Waymouth, R. M. J. Am. Chem. Soc., 114:9679 (1992). 3. (a) Gaylord, N. G. and Maiti, S. J. Polym. Sci., B11:253 (1973); (b) Ruggeri, G., Aglietto, M., Petragnani, A. and Ciardelli, F. Eur. Polymer J, 19:863 (1983); (c) Michel, A. and Monnet, C. Eur. Polym. J., 17:1145 (1981). 4. Chung, T. C. and Lu, H. L. U. S. Patent 5,543,484 (1996). 5. (a) Chung, T. C., Jiang, G. J. and Rhubright, D. U. S. Patent 5,286,800 (1994); (b) Chung, T. C., Jiang, G. J. and Rhubright, R. U. S. Patent 5,401,805 (1995); (c) Chung, T. C. and Rhubright, D. Macromolecules, 26:3019 (1993); (d) Chung, T. C., Lu, H. L. and Li, C. L. Polymer Interna- tional, 37:197 (1995). 6. (a) Chung, T. C., Lu, H. L. and Janvikul, W J. Am. Chem. Soc., 118:705 (1996); (b) Chung, T. C. and Jiang, G. J. Macromolecules, 25:4816 (1992); (c) Chung, T. C., Rhubright, D. and Jiang, G. J. Macromolecules, 26:3467 (1993); (d) Chung, T. C. and Rhubright, D. Macromolecules, 27:1313 (1994); (e) Chung, T. C., Janvikul, W, Bernard, R. and Jiang, G. J. Macromolecules, 27:26 (1994); (f) Chung, T. C., Janvikul, W, Bernard, R., Hu, R., Li, R. C., Liu, S. L. and Jiang, G. J. Polymer, 36:3565 (1995). 7. (a) Riess, G., Periard, J., and Bonderet, A. Colloidal and Morphological Be- havior of Block and Graft Copolymers, Plenum: New York, 1971; (b) Ep- stein, B. U. S. Patent 4,174,358 (1979); (c) Lohse, D., Datta, S., and Kresge, E. Macromolecules, 24:561 (1991). 8. Stevens, J. C. Stud. Surf Sci. Catal., 89:277 (1994). 9. Ewen, J. A., Jones, R. L., Razavi, A. and Ferrara, J. L. J. Am. Chem. Soc., 110:6255 (1988). 10. Chung, T. C. and Lu, H. L. J. of Polym. Sci. A, Polym. Chem. Ed., 35:575 (1997). 11. Chung, T. C., Lu, H. L. and Li, C. L. Macromolecules, 27:7533 (1994). 12. Kelen, T. and Tiidos, F. React. Kinet. Catal. Lett., 1:487 (1974). 13. Chung, T. C. and Lu, H. L. J of Polym. Sci. A, Polym. Chem. Ed., 36:1017 (1998). 332 Polyolefins Containing Reactive p-Methylstyrene Groups 333 14. (a) Jordan, R. F. J Chem. Edu., 65:285 (1988); (b) Eshuis, J. J., Tan, Y Y, Meetsma, A. and Teuben, J. H. Organometallics, 11:362 (1992); (c) Yang, X., Stern, C. L. and Marks, T. J. J Am. Chem. Soc., 116:10015 (1994). 15. Lu, H., Hong, S., and Chung, T. C. Macromolecules, 31:2028 (1998). 16. Ver Strate, G. Encycl. of Polym. Sci. and Eng., 6:522 (1986). 17. Canich, J. M. U.S. Patent 5,026,798 (1991). 18. Plate, N. A. and Shibaev, V P J. Polym. Sci.: Macromol. Rev., 8:117 (1974). 19. Ferrari, L. P and Stover, H. D. H. Macromolecules, 24:6340 (1991). 20. Szwarc, M. Adv. Polym. Sci., 47:1 (1982). 21. Chung, T. C., Lu, H. L. and Ding, R. D. Macromolecules, 30:1272 (1997). 1. (a) Baijal, M. D. Plastics Polymer Science and Technology , John Wiley & Sons : New York , 1982 ; (b) Boor Jr., J. Ziegler-Natta Catalysts and Polymerizations , Academic Press : New York , 1979 ; (c) Pinazzi, C. , Guillaume, P. and Reyx, D. J. Eur. Polym. , 13 : 711 ( 1977 ). 2. (a) Giannini, U. , Bruckner, G. , Pellino, E. and Cassata, A. J. Polym. Sci., Part C , 22 : 157 ( 1968 ); (b) Purgett, M. D. and Vogl, O. J. Polym. Sci., Part A, Polym. Chem. , 27 : 2051 , 1989 ; (c) Sivak, A. J. U. S. Patent 5,373,061 (1994); (d) Kesti, M. R. , Coates, G. W. and Waymouth, R. M. J. Am. Chem. Soc. , 114 : 9679 ( 1992 ). 3. (a) Gaylord, N. G. and Maiti, S. J. Polym. Sci. , B11 : 253 ( 1973 ); (b) Ruggeri, G. , Aglietto, M. , Petragnani, A. and Ciardelli, F. Eur. Polymer J. , 19 : 863 ( 1983 ); (c) Michel, A. and Monnet, C. Eur. Polym. J. , 17 : 1145 ( 1981 ). 4. Chung, T. C. and Lu, H. L. U. S. Patent 5,543,484 (1996). 5. (a) Chung, T. C., Jiang, G. J. and Rhubright, D. U. S. Patent 5,286,800 (1994); (b) Chung, T. C., Jiang, G. J. and Rhubright, R. U. S. Patent 5,401,805 (1995); (c) Chung, T. C. and Rhubright, D. Macromolecules , 26 : 3019 ( 1993 ); (d) Chung, T. C. , Lu, H. L. and Li, C. L. Polymer International , 37 : 197 ( 1995 ). 6. (a) Chung, T. C. , Lu, H. L. and Janvikul, W. J. Am. Chem. Soc. , 118 : 705 ( 1996 ); (b) Chung, T. C. and Jiang, G. J. Macromolecules , 25 : 4816 ( 1992 ); (c) Chung, T. C. , Rhubright, D. and Jiang, G. J. Macromolecules , 26 : 3467 ( 1993 ); (d) Chung, T. C. and Rhubright, D. Macromolecules , 27 : 1313 ( 1994 ); (e) Chung, T. C. , Janvikul, W. , Bernard, R. and Jiang, G. J. Macromolecules , 27 : 26 ( 1994 ); (f) Chung, T. C. , Janvikul, W. , Bernard, R. , Hu, R. , Li, R. C. , Liu, S. L. and Jiang, G. J. Polymer , 36 : 3565 ( 1995 ). 7. (a) Riess, G. , Periard, J. , and Bonderet, A. Colloidal and Morphological Behavior of Block and Graft Copolymers , Plenum : New York , 1971 ; (b) Epstein, B. U. S. Patent 4,174,358 (1979); (c) Lohse, D. , Datta, S. , and Kresge, E. Macromolecules , 24 : 561 ( 1991 ). 8. Stevens, J. C. Stud. Surf Sci. Catal. , 89 : 277 ( 1994 ). 9. Ewen, J. A. , Jones, R. L. , Razavi, A. and Ferrara, J. L. J. Am. Chem. Soc. , 110 : 6255 ( 1988 ). 10. Chung, T. C. and Lu, H. L. J. of Polym. Sci. A, Polym. Chem. Ed. , 35 : 575 ( 1997 ). 11. Chung, T. C. , Lu, H. L. and Li, C. L. Macromolecules , 27 : 7533 ( 1994 ). 12. Kelen, T. and Tüdos, F. React. Kinet. Catal. Lett. , 1 : 487 ( 1974 ). 13. Chung, T. C. and Lu, H. L. J. of Polym. Sci. A, Polym. Chem. Ed. , 36 : 1017 ( 1998 ). 14. (a) Jordan, R. F. J. Chem. Edu. , 65 : 285 ( 1988 ); (b) Eshuis, J. J. , Tan, Y. Y. , Meetsma, A. and Teuben, J. H. Organometallics , 11 : 362 ( 1992 ); (c) Yang, X. , Stern, C. L. and Marks, T. J. J. Am. Chem. Soc. , 116 : 10015 ( 1994 ). 15. Lu, H. , Hong, S. , and Chung, T. C. Macromolecules , 31 : 2028 ( 1998 ). 16. Ver Strate, G. Encycl. of Polym. Sci. and Eng. , 6 : 522 ( 1986 ). 17. Canich, J. M. U.S. Patent 5,026,798 (1991). 18. Plate, N. A. and Shibaev, V. P. J. Polym. Sci.: Macromol. Rev. , 8 : 117 ( 1974 ). 19. Ferrari, L. P. and Stover, H. D. H. Macromolecules , 24 : 6340 ( 1991 ). 20. Szwarc, M. Adv. Polym. Sci. , 47 : 1 ( 1982 ). 21. Chung, T. C. , Lu, H. L. and Ding, R. D. Macromolecules , 30 : 1272 ( 1997 ).
PY - 1999/10
Y1 - 1999/10
N2 - This paper summarizes the experimental results in a new class of polyolefin co- and terpolymers containing `reactive' p-methylstyrene (p-MS) groups, which includes the materials from high Tm thermoplastics to low Tg elastomers. Due to the extraordinary copolymerization capability of metallocene catalysts with constrained ligand geometry, p-MS can be effectively copolymerized with α-olefins (i.e., ethylene, propylene, 1-octene, etc.) to form co- and terpolymers having narrow molecular weight and composition distributions. Comparing with other relative styrenic comonomers, i.e., styrene, o-methylstyrene and m-methylstyrene, p-MS shows significantly higher reactivity in metallocene catalysis. In turn, the incorporated p-MS units in polyolefins are very versatile, which not only can be interconverted to various functional groups, such as -OH, -COOH, anhydride, silane and halides, but also can be conveniently transformed to `stable' anionic initiators for `living' anionic graft-from polymerization reactions. Many new functional polyolefin graft co-polymers have been prepared, containing polyolefin backbone (PE, EP, EO, etc.) and functional polymer side chains, such as PMMA, PAN, PS, etc.
AB - This paper summarizes the experimental results in a new class of polyolefin co- and terpolymers containing `reactive' p-methylstyrene (p-MS) groups, which includes the materials from high Tm thermoplastics to low Tg elastomers. Due to the extraordinary copolymerization capability of metallocene catalysts with constrained ligand geometry, p-MS can be effectively copolymerized with α-olefins (i.e., ethylene, propylene, 1-octene, etc.) to form co- and terpolymers having narrow molecular weight and composition distributions. Comparing with other relative styrenic comonomers, i.e., styrene, o-methylstyrene and m-methylstyrene, p-MS shows significantly higher reactivity in metallocene catalysis. In turn, the incorporated p-MS units in polyolefins are very versatile, which not only can be interconverted to various functional groups, such as -OH, -COOH, anhydride, silane and halides, but also can be conveniently transformed to `stable' anionic initiators for `living' anionic graft-from polymerization reactions. Many new functional polyolefin graft co-polymers have been prepared, containing polyolefin backbone (PE, EP, EO, etc.) and functional polymer side chains, such as PMMA, PAN, PS, etc.
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U2 - 10.1177/009524439903100402
DO - 10.1177/009524439903100402
M3 - Article
AN - SCOPUS:0033365273
SN - 0095-2443
VL - 31
SP - 298
EP - 333
JO - Journal of Elastomers and Plastics
JF - Journal of Elastomers and Plastics
IS - 4
ER -